Another Radial - this time 18 Cylinders

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Wow!
That is truly beautiful. A sight to behold. Your attention to detail and perseverance is a testament to be jealous of.
Thank you so much for taking the time to document all of this build. I am sure many of us would not have the patience to be so thorough.

Scott
 
To save some steps I tried cleaning (Scotch-Brite'ng) all the parts at one time, but I then found the solder didn't seem to wet as well as when the parts were cleaned immediately before the fluxing/soldering. Evidently, the surface oxide on stainless reforms pretty quickly after machining.- Terry

Well you are light years ahead of what probably amounted to my ~hour of 'learning' silver soldering on stainless coupons so passing on FWIW. But I recall Kent was adamant about using isopropyl alcohol + fresh stainless wire brushing + alcohol wipe again for nearly all pre-soldering joint prep (& incidentally same procedure for aluminum brazing). The Scotch-brite seemed to be reserved for post-cleanup, maybe this is why? I noticed my shiny fillets I was so proud of developed a slight, whitish chalky streak on them by the time I got them home so yes, must be something in the flux.

Maybe if you got some ~1"dia mini stainless wire wheels on a variable Dremel tool, that could make the tubing pre-solder prep go quicker? I've found the jewelry supply places sell them very reasonably by the bags vs. typical hobby suppliers. Hope this helps & thanks again for sharing.
-Peter
 
Peter,
You're probably right about the stainless wheels speeding up the cleaning. It didn't occur to me to try them. I forgot to mention it in my post, but I actually was doing a swab with a paper towel dipped in rubbing alcohol just after pre-cleaning with the ScotchBrite pad. There was always a dark reddish smudge left on the towel which was probably the alcohol cleaning off debris left behind by the pad. -Terry

Also, thanks Scott...
 
After doing some more research I came up with a solution to my intake tube splice that I'm reasonably happy with. Earlier I found that clear heat shrink tubing gave what I thought was the least conspicuous solution of all the connections I was able to mock up. But, when I checked the fuel resistance of the tubing I had on hand I found that it was quickly attacked by unleaded gas. What I didn't know at the time was that specialty heat shrink tubing is available in a wide variety of materials.
I located a variety made from a gasoline resistant material from Buyheatshrink.com. It's Kynar which is a chemical resistant material designed for hot and nasty areas. It's standardly available in clear and just happened to be the only product available from them in small quantities at about a dollar per foot. The tubing I bought is semi-rigid and comes in four foot lengths. After cutting the long intake tube in my assembly with a thin slitting saw and installing the two assembly halves into the heads, the ends should align perfectly when mounted in the engine. A short length of this tubing can be then be slid over the tiny gap and shrunk in place. If the engine has to be unassembled the splice is easily cut off and replaced with a new one during reassembly.
I cut a few test pieces and put them in a beaker of unleaded gas for several days to verify their fuel resistance. I also leak checked a few test splices with my MityVac to make sure there would be no issues with intake leaks. The worst-case measured leakage was less than a tenth of my best measured valve leakage and probably would have been just fine. But, I elected to compress a small Viton o-ring in the space between the tubing ends in order to positively seal the connection. The job of the shrink tubing then becomes one of holding the o-ring in place while the leakage is reduced to zero. As was the case here, I often find I need an odd size o-ring that isn't quite covered by a standard AS568 size. Metric o-rings come in nice in-between sizes and TheOringStore.com stocks a wide range of sizes and materials. The shrink temperature of this tubing is quite a bit higher than the common electrical variety, and is the reason I chose a high temperature o-ring. After cooling, even when pulled off the metal tubing, the shrunk tubing is quite rigid standalone.
I was able to determine that the clearances in my current flange machining program are adequate to complete the machining on the rest of the heads. I did decide, though, to open up the bore in the plenum compression nuts to clear a slight curvature in the rear intake tube. This curvature was a result of the minimum bend radius capability of my tubing bender. With this change, the rear intake tubes appear to be sealed perfectly by the o-rings that are compressed by these nuts.
I made a fixture to support the intake tube assembly while a slitting saw cut the long front tube into two pieces. The thickness of the saw was determined by my o-ring thickness. The backsides of the flanges were scribed with matching numbers in order to keep the flange pairs together during final assembly. These numbers will also be used to key each completed tube assembly to a consistent location in the engine after its spliced fit has been verified. I did trial cuts and fits on two different assemblies using my two test heads but decided to wait until the final machining on the heads is completed before cutting any more. The tube assemblies can then be fit and keyed to their actual head pairs.
I was anxious to try out a completed tube assembly in the head positions around the oil sump. As the photos show this area is very busy, but the clearances ended up as designed; and that I have clear access to the oil drain plug at the bottom of the engine. In the last photo I also added a cosmetic stainless sleeve over the Kynar splice. I may or may not use these during final assembly depending upon whether I find the friction from the shrink tubing to be sufficiently consistent to keep them in place.
Since I'm now confident in the program used to machine the flange recesses in the two test heads, my next step is to install the valve guides and complete the final machining step on the rest of the heads. - Terry

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Finishing up the 24 heads was just a matter of installing 48 valve guides that I'd already machined, tapping 192 2-56 rocker box mounting screw holes that I'd already drilled, machining and tapping 24 intake flange recesses, drilling/reaming 48 intake/exhaust tube ports, and then finally de-burring, numbering, and scrubbing the finished parts clean. Being someone who doesn't like repetitive work, I couldn't wait to get started.
Earlier, when I machined the valve guides, I delayed cutting the seats until now just before their installation. My process was to use the Brownells seat cutter I described in an earlier post to cut a preliminary .005"- .007" wide seat and then verify it with a vacuum leak check before installing the guide in the head. It was installed only after passing my leak-down criteria, also described earlier. Later, when the valves are finally installed in the heads the seats may be widened a tad more during the final lapping process. As described earlier, this lapping will be done with a separate lapping tool and not with the actual valve.
Some 'back of the envelope' calculations I did showed that a seat width of .005" will give me a factor ten margin against any further widening due to hammering by the pressures of combustion. Unnecessary widening causes unnecessary valve lash adjustments and is something I would especially like to avoid in this engine. The microscopic machining marks (<.0005" grooves and ridges) left behind by the seat cutter that initially limit valve sealing should still be hammered out in the first several minutes of actual running.
In the past I've cut the seats dry, but this time I discovered that I could significantly improve the leak-down times if I dipped the end of the guide in WD-40 before cutting the seat. Under a microscope it was obvious that the surfaces of the wet-cut seats had better surface finishes, and an improved smoothness in the cutting action of the seat cutter was also clearly felt. I'm using 544 phosphor bronze guides - other materials may give different results.
The guides are an approximate .002" slip fit in the heads in order to avoid seat distortion during installation. As an earlier photo showed, I previously cut shallow circumferential grooves in the o.d.'s of the guides to collect excess Loctite adhesive as the guides are pushed into place through the bottom of the head using a simple installation tool I made. After cleaning the head bores and guides with acetone, both surfaces were coated with a very thin layer of Loctite 620 by swabbing them with a cylindrical wooden toothpick. The installation of the guides had to be done in a single swift action because the adhesive set up almost immediately. I held a machined-flat plastic backing plate against the top of the head with one hand and pushed the guide upward with the other hand until it bottomed on this plate. This plate set the proper installation depth. A pair of plastic coated wires were temporarily inserted into the rocker box mounting holes to keep them from being filled with excess adhesive. Within seconds the adhesive between the two parts set up,mand then Q-tips were used to thoroughly clean away excess adhesive from both ends of the guide. The Loctite was allowed to cure at room temperature for a few days before the flange recess machining was started.
With the rocker box mounting holes now threaded it was finally possible to mount a few rocker boxes on a few heads and assemble them to the crankcase for a sanity check on the fit.
The most logical next step would be to machine the valves. I've gathered up the raw material, but I'm a little burned out on high volume parts right now; and so I might start working on the carburetor mount. I've already chosen the carburetor, and so I need to design and build an adapter between it and my rear housing and then add to it a fuel bowl. -Terry

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I decided to continue on with the high volume parts in his build after all, and so My next step was the valves. Since I had so many to do, I wanted an efficient process for making them in volume. What I ended up with was a five step lathe machining process that is very similar to the one I developed for my H-9 valves. This process is most suitable for making a large batch of valves. If I were making 6 instead of 60, I would combine some of the steps and also make use of the lathe tailstock.
I started by cutting up an odd diameter 303 stainless rod that I had on hand into 30 pieces each about 4-1/2" long. This rod was salvaged from a scrapped oilfield tool some 20 years ago and had been precision ground to .433" +/-.0001" over its entire eleven foot length. I had been saving it for something special, but life is short and 'special' never showed up to claim it. My process includes machining two valves, one on either end of each of these short workpieces. The work-holding spigots between the two valves will eventually be recovered for future use.
I compiled two CNC programs for my lathe - a roughing program and a finishing program. The roughing program machined the entire profile of each valve but left .020" excess stock for the finishing operation. The roughing program was run on both ends of the entire batch of 30 workpieces before reconfiguring the set-up for the finishing program. Since there were no final dimensions machined during roughing I was able to rough out the batch of blanks relatively quickly over a period of a couple days. The workpieces were fed into the lathe collet chuck one after another without much thinking or measurement checks to slow things down.
For expediency, and counter to common practice, the tailstock wasn't used in either operation to support the workpieces even with their long stick-outs. I did this to avoid a later secondary operation to finish the valve stem tip. In my process the tip was faced to its finished surface state at the start of the roughing operation, and then it was used as the z=0 datum for all succeeding operations. Lack of outboard support, though, caused a high pitch squeal whenever the cutter removed material from the far end of the stem. It didn't seem to affect the surface finish, but it was really annoying and potentially created unnecessary wear on the cutter. To squelch it, I pinched a narrow strip of leather between the valve stem tip and a small diameter metal rod chucked in the tailstock. This damped the oscillation that was causing the squeal without creating the need for a secondary tip operation. As a bonus, it burnished and probably slightly hardened the tip surface. I couldn't resist the cheesy photo of the completed roughed valve blanks posing in front of the swarf left after chewing up what was probably once an incredibly expensive piece of metal.
Concentricity of the valve's finished dimensions was achieved by machining them all in a single setup in the finishing program. The finished diameter of the valve stem is .184", but it is necked down to .140" for a short distance behind the head. After finishing the valves and taking a second look at the valve-in-valve cage drawing I included in this post, though, I wish that I had extended the necked-down area an additional hundred thousandths.
The method I'm using for machining these valves takes advantage of the fact that only a portion of the valve stem has a diameter that is actually critical. In my case, this is a half inch section behind the necked-down area that slides back and forth in the reamed bore of the guide. My goal here was a .0005" sliding fit. To achieve this, the stem was turned to a target of .185" during the finishing step. Later, in a third lathe operation, this area was manually polished to its final dimension with 400 grit paper. The remainder of the stem is not critical and needs only sufficient clearance to pass through the guide. Because the finishing step removed minimal material it ran quickly, and so I just held the leather damper against the outboard end of the stem with my fingers while the program was running. This allowed me to 'lean on' the stem a bit while the non-critical diameter of the outboard end was being cut in order to reduce the polishing time needed on this portion. The critical diameter section was tracked on each part during its finishing operation, and the work offset was adjusted as necessary to attempt to maintain a .001" excess stock in this area on the next part. In reality, the excess stock typically came out between .001" and .002" because of variations in workpiece deflection. The extra polishing time added by this uncontrolled deflection offset some of the secondary machining time I was trying to save by not using the tailstock for outboard support.
Some additional polishing was added to the third step. The valve's seat face was polished with a piece of tightly folded 600 grit paper, and then the entire valve was polished to a mirror finish with a shop towel dabbed in metal polish. Microscopic machining marks removed from the seat face by polishing will improve valve sealing. Spare valve guides were used as gages during this third step to verify the close fit of each valve blank. For efficiency, the finishing program was run on both ends of the entire batch of parts before the polishing was done. The polished valves on each end of every blank were leak-checked using a finished head before they were sawed away from the central spigot. This kept my valve making process from quietly drifting off into oblivion. Every valve passed with essentially the same vacuum leak down time: 10 secs for 25inHg to 15inHg pressure drop in a .25 cubic inch total volume. This un-lapped time matched the final average leak down time I was able to achieve with my lapped H-9 valves. I'm making several extra valves so I can experiment with improving the sealing even further.
After the polishing and leak checks were completed, the valve blanks were taken back to the bandsaw where the semi-finished valves were cut free from their work holding spigots. A simple shouldered Delrin split collet was turned and inserted into the lathe collet chuck. This allowed each semi-finished valve to be safely and consistently located on the z-axis while the valve heads were faced to their finished length. A second shouldered fixture was turned to grip each valve in the lathe collet chuck for the final operation. This time the stem tip was available so the narrow groove for the U-clip spring retainer could be cut.
The actual machining time averaged out to about 30 minutes per valve, but the total time I actually spent working on the entire batch came out closer to 60 hours. For those interested, the lathe insert I used for roughing was a Seco DCMT21.51 MF2 TP250, and for finishing I used a Kenametal DCMT21.51UF. I was able to cut all 52 valves and 3 double laps with a single edge of each insert.
Finally, I used the parts I now had available to verify with measurements what I expect for my worst-case valve-piston clearance. Fortunately, it matched the clearance in my model. My next step will be to install the valves in the heads and finally, after six months, declare the heads finished. - Terry

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Wow!

Is this the correct way to interpret your seal test setup:
1 = vacuum applied to port
2 = the 'double ended' valve work piece, seat finished but prior to parting off/finishing into 2 valves
3 = some kind of rubber/plastic 'blank off' piece?

- if so, can you elaborate on 3, does it somehow snub into the valve guide hole indexed into those 4 holes on the flange?

- can you elaborate on the dimensional (volume) part in "the pressure drop in a .25 cubic inch total volume"

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Peter,
You're right on 1 and 2. Number 3 is a silicone plug that goes down over the protruding valve stem and seals against the walls of the valve guide in the area where the spring will eventually go. This is needed to seal a potential leak between the valve guide and the valve stem because I'm pulling the test vacuum at the intake/exhaust port behind the valve. This leak is only present in my test and not present in actual use.
When you measure a leak by measuring a pressure drop over time, it isn't really meaningful unless the volume of the thing being measured is also known. For example a 5 psi drop over 5 seconds indicates a much larger "hole" if you're measuring that pressure drop in a 20,000 gallon tank compared with measuring the same drop in a .5 cubic inch combustion chamber. I've always used the same MityVac and same connecting hose for doing my leak down tests on all the engines I've built and so the comparative numbers mean something to me. If someone else tried to get the same numbers on one of their engines they would need to be measuring with the same volume as I am in order to try for the same leak down numbers. In my case the total .25 cubic inch volume is mostly measuring instrument volume, i.e. meter and connecting hose volume. The volume behind my actual valve is only .067 cubic inch. By the way, the 10 Hgin pressure drop measured on my MityVac works out to be a 5 psi pressure drop which, for most, is a more intuitive unit. -Terry
 
In the process of gathering up all my bagged parts related to valve installation I ran across a note I had written to remind me about a cosmetic chamfer I had decided to add to the tops of the spring caps. So, I spent a couple hours finishing up some parts that I thought were already done. If you think this was an extravagant waste of time wait till you read below about what I did next.
Before starting the valve installation, though, it might be useful to review the parts involved since their fabrication has been spread over several weeks. First, the valves are completely finished. The heads and seats were turned concentrically with the stems, and the seat faces have been brilliantly polished. The valve cages, though, are only semi-finished. The seats have been cut to a width of just under .005" using a manual piloted seat cutter which insured they are concentric with the integral guides. However, the machining marks left in the seats by the seat cutter have not yet been addressed. I have two seat cutters - one shop made and one recently purchased - and they both leave machining marks that ultimately limit sealing. The one I've been using most recently is a ten flute 45 degree muzzle cutter from Brownells. To the naked eye it produces a nice surface finish, but under magnification tiny circumferential grooves can be seen in the seat's surface similar to the ones left by my shop-made cutter. The prominence of these grooves is important and at the end of the day their depths can't seem to be limited by manipulating the cutter. With either cutter used individually, I get about the same results. The leak-down times they produce are essentially identical and remarkably consistent across a large number of seats.
What I learned through some testing, however, is that if the seats are cut using both cutters - one alternated with the other - I can always get a significantly longer (up to 2X) leak-down time compared with what I can get with either cutter used individually. I eventually discovered that with the pair of cutters I could often reach 20 seconds, and with a time this long lapping really isn't necessary. It appears each cutter is knocking down the machining marks left by the other, and the net result is a better over-all surface finish. But, I've jumped ahead.
The cages have already been installed in the heads with high temperature Loctite and are free of any distortion due to installation. Just before installation each seat was cut with the Brownells cutter and then leak-checked using a single H-9 test valve. The average leak-down time was typically 10 seconds +/- 3 seconds for a vacuum leak of 25 Hgin to 15 Hgin. The total involved volume for this measurement including the vacuum gage and connecting hose was approximately .25 cubic inches.
This leak-down time is probably only meaningful to me because it became an empirically derived target while building my previous two multi-cylinder engines. It might be more interesting to others, though, if it is converted into something a little more familiar. With just a simple units conversion this 10 second leak-down can be shown to be equal to a 5 psi pressure drop over 10 secs or, equivalently, a 0.5 psi drop per second. Through sheer coincidence the volume of my combustion chamber at TDC is also approximately .25 cubic inch. So, without having to correct for a volume difference the effect of this leak on, say, a compression measurement can be roughly estimated for my shop-made peak-reading compression gauge. This gauge has negligible internal volume compared with that of my combustion chamber. Assuming a compression ratio of something over five, the expected pressure in the combustion chamber during a compression test will be about 5X atmospheric or about 75 psi. Scaling my measured pressure drop created by a single leaking valve to the increased internal pressure during a compression measurement gives, roughly, a 5X or 2.5 psi drop per second. With a cranking speed of 120 rpm or 1/2 second per 4-stroke cycle, a cylinder with this single leaking valve will have about 1/2 second (yes, I'm making some outrageous simplifications here) to lose roughly 2.5 psi or about 3% of its actual value.
The effect of this leak on combustion pressure during worst-case running can also be roughly estimated. Assuming the maximum combustion pressure is about 5 times the compression pressure (rough rule of thumb I found on the web) the pressure loss due to this single valve during running will scale up another factor of 5 to some 12.5 psi drop per second. With a worst-case minimum running speed of, say, 600 rpm or .2 sec per 4-stroke cycle, the cylinder will lose roughly 2.5 psi of its 375 peak pressure (simplification alert again) for a loss less than 1%.
So, it seems perfectly reasonable to leave things as they are. That is, I can with good conscience install the valves and let the pressure pulses from combustion beat the final machining marks on the valve seats into submission even though with this level of sealing the leaks really aren't significant. But, I like to experiment, and I'm interested in learning more about what's involved in getting to the next level in valve sealing. I have plenty of parts to play with, and I've never been one to stop at a point of diminishing returns.
So, the goal in front of me was to remove the machining marks from the valve seats in order to obtain the best possible seal with the valves. In previous builds I've learned that lapping valves to their seats immediately after cutting them is not always a good idea because if the machining marks left on the seats are prominent, lapping will just transfer them over onto the valves and score their beautifully polished surfaces. I've also learned that the grit of the lapping compound needs to be scaled for the narrow seats typically found in a model engine. For my own lapping I now use nothing coarser than metal polish. In a model engine the effect of using typical automotive valve lapping compounds can be inconsistent, and even disastrous.
I made three double-ended metal laps for lapping my seats while I was making the valves for this engine. My intentions were to use them instead of my valves to do any needed lapping. But, I began having second thoughts about them wearing too quickly even with metal polish as a lapping compound. The hardness and narrow seat widths of my new phosphor bronze valve cages were my concern. When I made my H-9 valves I inadvertently used a softer bearing bronze for the cages and was forced to cut the seats to a width of .015" - .020" in order to clean up distortion created by pressing them into the heads. The two double-ended laps that I made for that project lasted long enough to lap all the seats in that engine plus a few spares. With the much narrower and harder seats in these cages, though, I'm afraid the laps will wear out before I finish the whole lot of 48 valves.
The first alternative I came up with was a new piloted lap turned from a wood dowel rod. Two photos show the lap and the seat in a spare valve cage after one minute of lapping with Honda (motorcycle) metal polish. The grooves in this particular seat were almost entirely polished out as evidenced by its initial 10 second leak-down time increasing to over a minute. One minute is actually close to the noise floor of my measurement set-up. Using the same lap on a second valve cage, though, improved the leak down time to only 20 seconds and then on a third there was no improvement and, in fact, minor damage to the seat. Examination of the lap under magnification showed that even with super fine metal polish the narrow seat had eroded away the surface of the lap and destroyed its profile. It would be possible to make a separate lap for each valve - something not unreasonable for a smaller engine - but I wanted to see if I could avoid making another 50 somethings for this engine. I have a note of caution to anyone who might want to try a wood lap. I found it only useful with metal polish as a lapping compound. Some testing I did showed that even fine TimeSaver lapping compound is much too aggressive for wood and can destroy the lap during its first time use.
As a second alternative, I made some protective covers for my metal laps. I tried several fabrics but eventually settled on strips of thin suede leather purchased from a craft store. I punched a hole in the center of the strip through which I inserted the stem of my lap. With the thin leather patch coated with metal polish and sandwiched between the lap and the seat I was again able to increase the leak-down time on a few test valves to 20-30 seconds after one minute of lapping. These leather patches need to be replaced after lapping four or five valves, but they are very simple to make. The thin suede stretches nicely over the end of the lapping tool so there is no puckering in the seat area to give an inconsistent contact patch. One of the photos shows some of the patches I used. The combination of the leather patch and metal lap is a bit awkward to deal with after the valves have been installed in the heads, but it works really well on cages that have not yet been installed. After only several seconds of lapping a bronze colored ring shows up on the patch to indicate where to add more polish.
And so, after several days of experimenting with all my spare parts and nearly a third of my finished heads, I finally settled on a process I was happy with: 1) re-cut the seats using my two manual piloted seat cutters and alternate between them for several light (to avoid unnecessary widening of the seat) cycles until reaching a 15-20 second leak-down time, and then 2) lap the seat for one minute using metal polish on a thin suede patch sandwiched between the seat and a metal lap to obtain 20-30 seconds, and then 3) lap the valve against the seat using metal polish to extend the leak-down up to 60 seconds. (Skipping step two would never be noticed in an engine's actual use.) One of the photos shows a silicone cap that I used to grip the stems of the valves in their installed cages during lapping. (Harbor Freight used to sell a nice assortment of these caps in various sizes, and I've used the one I bought to solve lots of different problems around the shop.) The ultimate goal of my process became a 60 second leak-down with mInimum damage to the valve. All but two of my seats ended up less than .007" wide, and the histogram shows the distribution of leak-down times I actually achieved. This histogram includes several valves I went back to and re-worked after learning about the dual cutter technique. I wasn't able to reach my ridiculous goal on most of my valves, frankly, because after some 60 hours I was getting weary of the project. But I kept working until every valve reached at least 20 seconds just to prove to myself I could. On about the last dozen valves the dual cutters produced 20-30 second leak-down times on their own before any lapping. I think this was because I was developing a feel for using the cutters. Even though I could have skipped their lapping steps, I chose not to because I wanted to add more valves on the right side of the histogram.
I'm still curious as to why it was so difficult to reach one minute leak-downs on some valves but not others. Any further improvements and learning will have to be left to a future project where not so many parts are involved. Again, what turned out out to be a 40 hour diversion created by a ridiculous target was totally unnecessary and done only for the sake of learning.
I ran into a few frustrating issues involving my own poor quality control that ended up taking a lot of time to sort out. For example, I had evidently damaged a couple seats while drilling and de-burring the intersection of the valve cages with the cross-drilled intake/exhaust ports. Some tiny nicks located on a difficult to see area of the installed seats were only visible only under 10X magnification. One of the seat photos is actually of one of these seats. They were probably caused by slips of the X-Acto knife I had used for de-burring. Until I deepened the seats beyond those nicks I was not able to get leak-down times better than 5 seconds no matter how much lapping I did.
On several heads I found I had left burr remnants on the top of the valve guide bore while machining the spring cavity. My process for machining the heads included manually running a reamer in the guide bore to remove these, but I had evidently skipped this step for one of my batches. Even with only .0005" valve stem clearance this burr tilted the valve enough on its seat to limit the leak-down time to 15 seconds regardless of lapping. By the time I had discovered the source of the problem in the first head that had the problem I had leather-lapped the seat so many times that when the burr was finally removed I had absolutely no measurable leakage. After this experience every valve guide was re-reamed before starting the valve seating work.
After completing four heads and then reviewing the notes I made while sealing my H-9 valves I found a note I had made to remind me in the future to clean the seat surfaces with alcohol before making a leak test. I had found the metal polish could leave some residue on the seat that wasn't being buffed away by the Q-tips I was using, and this residue was sometimes preventing an ultimate seal. I verified the benefit of the alcohol on one head that was giving me inconsistent measurement results. When I found it stabilized my measurements on this particular head to 2X the best time previously measured on it, I added an alcohol swabbing step to my t-18 valve process.
I did a lot of other experiments - several of them destructive, but too numerous to include here - on the many extra parts that I had made. The really important things I learned while seating these 48 valves and those things that I'll apply to my next engine are:
1) Cut the seats using two different piloted seat cutters so that one can mitigate the machining marks left behind by the other. Alternate using them for 3 or 4 cycles until, with very light pressure, no further cutting action is felt,
2) Keep the seat width to .005" - .007",
3) If the concentricity's were well maintained during the original machining a leak-down time of 20 seconds or more should result from using the dual cutters with no lapping needed,
3) Blowing into a closed valve using one's lung power can only tell you that you have a leak so big that it should be visually very obvious,
4) Don't use lapping compound coarser than metal polish on a model engine,
4) If, during final assembly, the valve stems are lubed with a drop of light sewing machine oil don't get too excited when you come back later to re-check the leak-down times on the completed heads. You'll likely measure infinitely long leak-down times on all of them. What has really happened is that the oil has flowed down the stems and onto the seats where it has been wicked into what's left of the machining grooves leaving the valves with a false appearance that they are perfectly sealed. Don't ask me how I know this.
I don't plan to make much progress during the next week. Some of my grand kids are coming to spend a week with us and they aren't much interested in shop stuff. - Terry

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Thanks for the excellent discussion on valves and valve lapping.
 
Before I can start work on the pistons and rings I need to return briefly to the cylinders I made seven months ago. Although their machining was completed, their bores were not honed to an exact same diameter nor were they lapped to an acceptable surface finish for the rings. After finishing the machining, I sprayed each cylinder with light gun oil and individually bagged them in plastic sandwich bags because I was concerned about the 12L14 rusting from my own handling. To my surprise the exteriors of a few of the cylinders had grown some brown splotches on them from oxidized coolant that hadn't been completely removed before storing them. Fortunately, it cleaned off with WD-40 and some light scrubbing.
My preferred goal is to finish the cylinders for an eventual -0.0000"/+.0002" interference fit with the pre-gapped rings. After gapping and installing the rings, the tiny remaining high spots will quickly wear down after several minutes of 'motoring', and the rings should then fit the cylinders perfectly. If I try, instead, for a zero interference fit I'll likely miss it, and the rings will end up undersize. In that case if the clearance wasn't too great they can still wear-in to the bores, but the process will take much longer. I tried this oversize technique on my H-9 and was able to almost immediately measure a cranking cylinder pressure very close to what I was expecting from my compression ratio.
My first step was to engrave a tiny tracking number on the skirt of each cylinder and then create a set of worksheets on which I could track the measurements of each bore during the lapping process. I next made a cardboard crate to keep the cylinders organized during these final steps and also for use as a container to transport them later to a gunsmith for bluing.
I filled in the first lines of the worksheets with starting measurements taken at the top, center, and bottom of each cylinder. Since I can make my rings any diameter I choose, my goal was to finish the upper 75% of each cylinder bore to an exact same diameter as best I can. It's only this portion of the cylinder that actually comes into contact with the compression rings. I'm not as concerned with the lower 25% since this area sees little compression, and so I'll accept up to a +.001" diameter down there. Since the lathe I used to bore the cylinders cuts a slight taper, the cylinders were oriented during machining so the largest diameter ended up at their bottoms. I could lap these tapers completely away, but I think a bit of taper is of some advantage in lubricating the cylinders.
With one of my dial bore gauges, a lot of care, and some luck, I can sometimes get a measurement repeatability of just over .0001" if all the measurements are taken during a single fitting session. Of my 24 cylinders all but three started out within +/-.00025" of an arbitrary reference point I set on my dial bore gauge. The diameters of the three 'rogue' cylinders were .002" under-size and were likely the first cylinders bored after each insert change during the finish-boring step last year. These were the only cylinders to now be honed. The rest were lapped. I managed to bring two of them into the same ballpark as the rest of the batch using 180 grit brush hones, but in the process I discovered the third was also out of round by a whopping .001" at the top of its bore. My notes showed that I didn't have my boring tool properly tightened down in the tool post when I finish-bored one of the cylinders, and I suspect this particular cylinder was that one. I wore out three brush hones on these three cylinders, and so their correction was an expensive exercise. The still non-circular third cylinder was then lapped with a 180 grit barrel lap which repaired the bore circularity issue but in the process opened up its diameter to .0010" beyond the starting diameters of all the rest of the cylinders. Rather than lap the entire batch of cylinders an extra .0005" to match this one, I decided it will just become the guinea pig for the final head installation step and cylinder flange drilling program.
The 23 cylinder bores were next lapped using a 600 grit barrel lap. Rather than lap each cylinder until its particular diameter opened up to my target value, I moved from cylinder to cylinder always working with the smallest bore and lapping it a tenth or so at a time until the batch as a whole arrived at the same diameter. I like working with a batch of parts in this way since less re-work is generated by a subtle change in gauge calibration. Since lapping proceeds pretty slowly with only small amounts of material being removed at a time it isn't difficult, with care, to avoid overshooting a final dimension and adding a lot of extra work to the rest of the batch. After all 23 bores measured within .0001" of one another, I switched to a 1000 grit barrel lap and then removed a final tenth from each one. This last step left a nice finish on the bores for the rings.
Finally after some remorse I went back to my oversize cylinder and finish-lapped it. I'll likely make a special +.001" piston and ring set for it. The cylinders are now ready for hot bluing by a local gunsmith. I hate losing control of them to someone else, but I really need the corrosion protection of the bluing, and that's a process I'm not willing to get involved with for a number of reasons. - Terry

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As usual...Beautiful work Terry!

In your last picture of the lap, is that an expanding mandrel ? Or was it turned to size and hope it does not wear much with the 1000 grit?
Thank you so much for taking the time to document this impressive build for us!

Scott
 
Scott,
It's a commercial expandable brass lap available from MSC in sets or individually:


http://www.mscdirect.com/product/details/05060645

For this project I was able to set the lap and run through all 23 cylinders with the same setting. I haven't noticed any wear. I typically overload the lap with valve grinding grease and it quickly collects in the grooves of the lap while in the cylinder at low rpm. I can then adjust the rpm of the drill until the grease starts coming out of the grooves under centrifugal force and then I can feel the cutting action. The lapping compound I use is Clover valve grinding grease which I think is now owned by Loctite. The brass portion is available separately from the expanding mandrel and I use a different one for each grit. - Terry

Terry
 
The carburetor that I ended up using on my H-9 was a Super Tigre model 12163145. This RC barrel carb had high and low speed mixture adjustments, a measured venturi diameter of about .35", and was marketed for .40"-.52" RC engines. Remarkably, this carb was probably too big for my H-9 since although the final tuning has been stable, both mixture adjustments ended up near fully closed. With an additional nine cylinders I figured it might be closer to optimum for this engine, and so when I started construction on my 18 cylinder radial I placed an order for a second one. A year later, delivery is still 'pending' since it appears last year's Fukushima tsunami has evidently disrupted it's supply to the U.S for the foreseeable future.
After some web searching, though, I came across Perry Carburetors:
http://www.perrypumps.com
which is now owned by Gary Conley, a well-known member of the model engine building community. Perry offers a large variety of model engine carbs, and the best thing about their website is the way their products are categorized. If you're trying to replace a particular manufacturer's part they have their list of direct replacements. Of more interest to me, though, was their listing of carbs by venturi size. With an intake runner i.d. of .257", I finally decided on a carb with a .312" throat. Venturi's with other i.d.'s but with the same o.d. are also available; and so, if necessary, I can later change the throat size without having to purchase a new carb or make a new engine adapter. Gary also changed the fuel mixture disk for me to improve the carb's compatibility with gasoline.
Since I plan to use a fuel pump to maintain a constant fuel level to the carb, I need an adapter between this new carb and the rear end of my engine with a fuel bowl to support the recirculating fuel system I plan to use. I previously built two of these closed loop systems for my H-9 - one for the Super Tigre carb and one for a Walbro carb that I unsuccessfully tried to use with that engine. So, I decided to save some work and re-cycle the Walbro adapter by sleeving and re-boring it to accept the Perry carb. I designed the rear end of my T-18 crankcase to match that of my H-9, and so no changes were required on the engine-side of the adapter. The fuel bowl, however, was another matter. I originally designed the Walbro fuel bowl with an internal adjustable pressure regulator to drop the 10-15 psi of my fuel pump down to the 1.5 psi that the Walbro wanted to see. I had to do some re-machining of the internals to remove the regulator and to install new inlet/outlet tubes in order to adapt it for use with the Perry. The re-design work cut into my time savings a bit. In the end, though, the combination adapter and fuel bowl fits nicely on the rear of the engine and without interference from the engine stand. I was able to try out the re-circulator using my H-9 fuel pump. The level of fuel inside the bowl is nicely regulated to a half inch below the sealed top cover, and this level is about 1/4" below the carb's spray bar. Later, I plan to swap this new carb assembly with the Super Tigre on my H-9 in order to verify the carb works and to get some starting carb settings for my new engine.
I'm getting very close to being able to start final assembly. The cylinders came back safely from my local gunsmith, and the bluing job is gorgeous. The stacks of bagged and boxed parts on my workbench are now only missing the pistons and rings. I still have several pieces of external running gear such as the firewall and the oil and fuel tanks to make, but I plan to continue on with those during final assembly. I'm also planning to design an analog tach for this engine around an old-style panel meter if I can find just the right one. -Terry

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Kvom,
Well, I can tell you how I used them. Since I'm learning as I go this might not match up with how they are supposed to be used. Others are welcome to add their expertise and experience.
The barrel, itself, is threaded onto a mandrel which I held in my drill. The barrel has four longitudinal slots which allow it to expand when a threaded tapered bolt is turned into its end. When the lap is expanded one would think that a good portion of its length expands parallel to the longitudinal axis without introducing a slight taper in the barrel. But, the fact is, unless the barrel is re-cut for a particular setting there will always be a taper when you consider you're working with tenths. A slight taper isn't an issue, though, and ends up being useful. Anyway, the barrel is made from soft brass and so when the lapping compound is smeared over it and then the lap is inserted int the cylinder, the lapping compound embeds itself into the brass and the barrel becomes a precision grinding tool. The expanding screw is turned in small increments until there is a slight drag on the lap when the drill is spinning. It's best to not use a lapping compound such as TimeSaver that breaks down easily during the lapping process so that the compound has a chance to embed and do its job. Anyway, while spinning, the lap is continually oscillated back and forth within the cylinder. I hold the drill in one hand and the cylinder in the other and allow the lap to find its own center of the cylinder as I feed the cylinder back and forth over the lap. The larger o.d. portion of the lap can easily be felt cutting on the 'tight' portions of the cylinder as you pass over them. I kept the same screw setting as I went through each of my cylinders increasing their bores a tenth at a time. I was turning the screw about 1/8 turn at a time. During the final pass I used the same setting on all 23 cylinders to open them up the the last tenth, and I noticed no wear on the lap. At the same lap setting, all 23 cylinders came out to within .0001" of one another.
I wasn't interested in taking all the taper out of my cylinders since the .0005" taper I had at the bottom wasn't important and maybe even desirable. I was interested in removing all the taper from the top 3/4 of the cylinders and so I lapped for 1 minute and then measured at three places in the cylinder to see if I was working in the right part of the cylinder. The slightly larger o.d. of the lap always turned out to be at its outer end, and so it was easy to oscillate the lap back and forth in the right portion of the cylinder. One issue I ran into was cleaning the lapping compound out of the cylinder for measurement. I used dry shop paper towels to clean out the bores and I kept cleaning until the towel came perfectly clean. What I didn't figure out until very late in the process was that some fibers from the towels were embedding into the cylinder bore even though the bore looked perfectly clean. Eventually on the third or fourth lapping session these fibers would start showing up in the lapping compound on the lap. They would slightly increase the diameter of the lap (always at the bottom of the lap for some reason) and keep the taper I had at the bottom of the bore from cleaning up. It wasn't until I started using lacquer thinner to clean the bores that this problem went away.
So, the through-laps give you the ability to lap the whole bore or only a portion of the bore if you are trying to remove a taper. They are very effective in cleaning up non-circular bores. They don't round over the ends of the cylinders as do the brush hones, and they are much cheaper. Unlike the brush hones they don't remove a lot I material, though. They seem to be more suitable for removing up to a max .0005" over a reasonable time of ten minutes or so including measurements. -Terry
 
Fantastic info Terry, thanks. It's like I've been there & done that when I really haven't. This thread is a treasure trove of instructions for future use by many of us.;D
 
My next step was the machining of the pistons. I used 6061 aluminum and happened to have a 23 inch long rod whose diameter was just .012" over the finished diameter of my pistons. So, there wasn't many chips associated with the lathe work.
I'm using the exact same piston that I used in my H-9 except for a slight change in diameter to accommodate my T-18 cylinder bores. The pistons' finished diameters are .0025" smaller than the cylinder bores to insure adequate clearance between the aluminum pistons and the steel cylinders over the pistons' expected operating temperature.
These pistons are essentially stock H-9 design but with modified ring groove clearances and a slight relocation of the oil ring. The compression ring grooves' axial width clearance is .001" and the radial thickness clearance is .005". The compression ring grooves' axial widths are .027" because that is a standard width grooving insert available for my particular grooving tool. This set my compression rings' axial width to .026". This width is on the low end of the usual recommendations for a one inch piston, but with 54 of them on a single crankshaft frictional losses aren't insignificant. Assuming the same 350 psi peak cylinder pressure used earlier, the top ring will end up with some 25 pounds of radial force pressing it against the cylinder wall during the power stroke. This is a nice number for ring seating, sealing, and heat transfer but not so nice for frictional losses. The downside of a narrow width compression ring is its higher thermal resistance to removing heat from the piston's crown.
These pistons have two compression rings and one oil ring, although the second compression ring provides more oil and piston temperature control than it does compression sealing. The wrist pins are full floating and my saga dealing their machining was the topic of a much earlier post.
In order to conserve material I fed the workpiece through the lathe's headstock where each piston was faced and turned, and the ring grooves were cut. The depths of the grooves were machined so the radial clearance behind the compression rings will be .005" and behind the oil scraper rings the clearance will be .010".
I used a new side-relieved grooving insert to cut the ring grooves at high rpm with a low feed rate in order to get the best possible surface finish on the side walls of the grooves. A fine surface finish is especially important on the lower wall of the compression ring groove since it is an important ring sealing surface. Previous valve sealing experience showed that narrow seats are much easier to seal than wide seats, and the sealing surfaces formed by the rings against the lower wall of the grooves are an order of magnitude greater in width than the valve seats. Fortunately, under normal operation cylinder oil is scraped into the interface (assuming the ring has a proper clearance and isn't frozen in position with cylinder deposits) to fill in minor machining grooves and help with the seal. Sometimes, in fact, a bit of oil added to the cylinders of an engine left standing for a long period of time is helpful in replacing this film when trying to measure compression.
Parting off stock at this diameter in my 9X20 lathe is usually not pretty, and so after turning the semi-finished piston the workpiece was removed from the lathe and taken to the bandsaw where it was removed before returning the workpiece to the lathe for the next part. The pistons were brought to their finished length later in the mill during the pistons' bottom and interior machining. I made a fixture to hold my H-9 pistons while their interiors were being machined, and I was able to re-use it for these pistons. The fixture was rotated 90 degrees after machining the bottom of the piston in order to spot, drill, and ream the wrist pin hole. The last thousandth of the wrist pin hole was reamed in a secondary operation in order to insure a precise fit with the wrist pin. The accuracy of the piston machining fixture is very important because the wrist pin must wind up precisely square to the longitudinal axis of the piston in order to avoid a connecting rod bind and an eventual worn taper on the rings.
The last operation on the pistons was drilling eight .050" diameter radial oil return holes in the bottom of each oil ring groove, and this was done on a horizontal rotary under the mill's spindle. The ring grooves' locations were originally referenced to the crown of the piston, and so a collet stop was a sufficient workpiece locator for the hole drilling. In total, 176 holes were drilled using a single re-sharpened carbide circuit board drill purchased on E-Bay.
I made a total of 22 pistons including one that is .001" oversize to fit the PITA over-size cylinder that I ended up with during honing. The next step will be the piston rings. - Terry

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Very nice. I'm keenly following your cylinder boring/lapping workflow & now the piston details. But now that I see it all come together, I'm re-thinking my forthcoming winter project plan of attack. Sorry for the sidestep, but would appreciate your input.

Basically I was thinking of slightly altering the original ?arbitrary?design internal dimensions by replicating a 'pretty close' bore ID & piston OD combo of existing commercial RC engine dimensions. My logic being, utilize & replicate those 'known' dimensions, utilize the commercially available rings & that's several variables less for me to mess up at my novice level. If the engine ran, great, maybe then proceed to replicate ring making in home shop & join the elite club.:) But maybe this solves one problem but creates others?

What I think I see you doing is starting with finished, identical bores to some known consistent dimension, then pistons, then rings? When I re-read your post, its almost like you had a sample sizing ring pre-made & then nailed the bore diameter to that. But I think you're saying, the rings are coming next? If so, is this to facilitate any necessary adjustment tweak to ring dimensions if anything did go south on the bores (more work invested in the cylinders?). I've pulled your excerpt for reference below, maybe I misunderstood. What would you do if you were in my shoes? Is it reasonable to hit 5 target bores/tolerances by honing/lapping knowing pistons will be made, but not the rings?

My preferred goal is to finish the cylinders for an eventual -0.0000"/+.0002" interference fit with the pre-gapped rings. After gapping and installing the rings, the tiny remaining high spots will quickly wear down after several minutes of 'motoring', and the rings should then fit the cylinders perfectly. If I try, instead, for a zero interference fit I'll likely miss it...
 

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