Homebrew boxer twin prototype

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Well-Known Member
Aug 22, 2009
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Redford, MI
Boxxer twin prototype

Having finally worked up the courage to start a build thread, and finding the spare time, I offer this up to our community. I cant promise any great contributions to the art, only the hope that some might find some things here useful. We learn from our mistakes, and I have made many so far, with no reason to believe that will change, as I hopefully complete this project. If your capable of learning from the mistakes of others, I should be able to teach you a whole lot! Some folks have spoke of having a preference for showing a build warts and all. I can say this build has been mostly warts. My hope for this first prototype is simply to make noise, not necessarily look pretty. It should be a rather simple build, we can work the warts out on the next one with experiance.

This engine design started approx 14 months ago, mostly as an exercise in CAD drawing. Unfortunate circumstances forced me to put it away, and almost a full year later I was able to work on it again. It is almost entirely of my own design. Some of you may recognise the cylinder head resembles the Edwards radial engine. The reason behind that is in my research to eventually build the Edwards, I was not entirely satisfied with the cylinder head drawings. This engine is partially the result of my desire to test my design on a simpler engine. Of course, one opportunity seems to breed another. In that respect, I utilized this opportunity to add a few "firsts" to my list, gearcutting, alloy steel crankshaft, pressurized oiling system, oil pump, and bronze bearings. The drawings are still slightly unfinished, mostly just I's to be dotted and such, but I am confident enough in its viability to forge ahead.

Bogs recently commented in another thread about patience. I fully admit that is a quality I lack, and hope to improve upon in this hobby. Many things conspire against me in this respect, leaving me precious little time to devote to my projects. The addiction to the good feelings that come from making progress, keep pushing me to do more in less time. Often this leads to disaster, and the proverbial scrap bin, or going back to "change the prints to match". Occasionally, it leads to efficiency. For the benefit of our impressionable readers, do not emulate my faults, just try to learn from them. I am guilty of starting a way more complicated project then this, and not finishing it. As such, with a few types of parts, this is not my first rodeo as they say, but the spectre of an unfinished project in my past has become a haunting one. I am hoping that this forum could provide a service to me by kicking me in the rear if I begin to slack off. I have a full time job, house, and a family, so my goal would be to get some kind of updates done each week.


There is somewhat of a prequal, and you can read the thread in the casting forum here http://www.homemodelenginemachinist.com/index.php?topic=10845.0
The actual sequence of events does not start with the castings, but it fits along as a seperate side project if you will. For those of you who are turned off at the prospect of doing your own casting work, you do not need to worry. This engine can easily be built from barstock, and the maximum thickness of the case is only 1". I am sure some people would even consider barstock easier then the casting route. There have been times I would be inclined to agree with that sentiment, but I would like to make several of these, so the form work should pay off.


The first order of the feasibility study would be cutting the gears. Revisiting the drawings a year after I first drew the engine basics, I had to reverse engineer the dimensions to determine what the gears specifications were. There is good news and bad news here. The good news is I picked simple tooth counts to index, 18 and 36 tooth. This ensured even my lowly enco cheapie 5c spindex would work. The bad news, aside from my mislaying the pictures, is to obtain the required .94 inch spacing it required 29dp gears. Good luck finding them commercially. That may have been a subtle nudge to myself to force my hand at the hob method of gear generation. Whatever the forgotten reasoning, the hob and gears were quite simple to make. Once I had the gears, I knew I had to build the engine.
I will include a write-up on the gears and hob once the pictures have been found. Edit Pics found, a few of them at least, down a few posts.


Our story now picks up in early September. The most trying part of any engine build to me is the crankshaft, so I start with that first. We begin by chopping off a length of 1" 4140 steel from McMaster-Carr.

Chucked into the 3 jaw, I used a dial indicator and plastic hammer to center it as best as possible before attacking it with the center drill. The part was flipped over and centering was repeated on the other side. I always seem to have great patience at the beginning of the project. I suppose it helps when you havent made your first mistake yet. :)

Once the centers are picked up we move over to layout and scribe lines parallel on each end of the bar.

Over to the mill, the line was picked up with the wiggler and adjusted parallel to the vise jaws. Center was found, two more centers added for the crankpins. At this point I had a change of plans. I milled a 5/16x5/16 slot parallel to the centers to assist in keeping the alignment when I flipped the bar over for the other side centers. A 5/16 square toolbit worked admirably in this function.

Second verse was pretty much same as the first, flipped over, we had centers in each end of the bar in the appropriate places.

Time to move back to the lathe, centers in place, we began making mistakes I mean learning right away. Mistake one was thinking regular steel tooling would cut this alloy crank. Look at this horrible finish.

Once I switched to carbide tooling things got noticibly better, when I started using coolant/lube I was achieving good finishes again. I got lazy with cutting brass and aluminum, this was some tough stuff. 4140 comes in a leaded version, 4140L, which may make this part easier. With carbide and coolant/lube (astrocut2000) it was a good exercise.
The journals were .25 wide. I found the best way to attack this was with a .25 square soldered bit head on. There was some wandering of the bit at first, but as I progressively tightened and retightened every part of the holder, tailstock, and crossslide this eventually went away. If you have ever done this, you know the tedium involved in hearing the thunk of the bit taking its offset cut, and gently moving the bit forward in time to the revolution. I spun it up rather fast and took approx .003 cuts with each thunk, developing a rythum with the machine. This shot is the first journal finished, you can see the layout lines for the remainder of the cuts. All measuring was done with a dial indicator, the layout was for a visual doublecheck.

Second journal went much smoother and quicker. Plunge straight in, no real stopping. Lathe speed was kept higher as the diameter decreased. Look at all the .003x.250 shavings in the first pic.

Now is the point where 4140 really started to pay off. Under tight load between centers, I only measured about .oo4 spring in the journal gaps, and that was reefed down much tighter then it needed to be. This stuff is strong! Here is a left hand positive rake soldered carbide bit taking out the center marks.

Starting to look like a crankshaft, the nose gets a taper down to a 1/4-28 thread.

Thats about a good place to stop for now, more coming soon, lotta pics to rearrange and find. In a few more days, given the time, we will be caught up in real time.

Looking good!
I`ve found 4140 a pain to machine, my lathe lacks rigidity for that stuff.
Lots of cutting fluid helps a lot.
For the next engine i`m thinking of give silver solder a try.

Hi Jeff, that looks good. I had to go back and scan through your series of pics in the photobucket and realized that you had what I assume to be a spacer taped into the gap of that first journal to keep the part from flexing too much, however I did not see any such steps being taken in the later shots while you were cutting the end shafts. I'd be scared to not have some such support in there for fear of having the thingie flex just once and ruin the piece, knowing my luck it would surely, as I'm sitting here, happen. I'm looking forward to see your prototype progress into a workable model.

nfk said:
Looking good!
I`ve found 4140 a pain to machine, my lathe lacks rigidity for that stuff.
Lots of cutting fluid helps a lot.
For the next engine i`m thinking of give silver solder a try.


Thanks Norberto. I stuck with it and kept retightening everything to help the rigidity, but the cutting fluid did wonders as well.

bearcar1 said:
Hi Jeff, that looks good. I had to go back and scan through your series of pics in the photobucket and realized that you had what I assume to be a spacer taped into the gap of that first journal to keep the part from flexing too much, however I did not see any such steps being taken in the later shots while you were cutting the end shafts. I'd be scared to not have some such support in there for fear of having the thingie flex just once and ruin the piece, knowing my luck it would surely, as I'm sitting here, happen. I'm looking forward to see your prototype progress into a workable model.


Thanks Jim. The spacer didnt seem necessary once I measured the deflection, and I had forgotten about it quickly after. The crank pins are .312, and there was only a few thou deflection when overtightening the tailstock, well under its elastic limit. 4140 is some pretty stiff stuff, and in that respect, did make the job easier.
Gearcutting via the Hob method

I am really glad I deceided to give this a try. Taken in small steps, it is really straightforward. I reviewed a few threads from this board and some nice webpages, utilized a few of Marv Klotz's gearcutting utilities to doublecheck the math (thanks Marv!) and in the end I came out with this; 20 degree pressure angle, 29 diametrical pitch, rack form.

5 rack teeth cut into a 3/4 bar of A1 tool steel serves as the hob. This proved sufficient for the 36 tooth gear but more teeth on the hob may be necessary for higher tooth counts. I hardened the hob by heating it with a propane torch and dropping it into a bucket of used motor oil. I made a mandrel for the hob from the same tool steel so future hobs would have a place to live. :)

The crank gear blank was cut from 7075 aluminum, and mounted on a cobbled up split expanding mandrel. A small piece of brass tubing was slipped over the mandrel first to keep the cutting forces from pushing the gear off the split part. The center gap on the hob was adjusted equal to the centerline of the index and locked in place. I kissed the gear blank to zero the handwheel and dialed in the full tooth depth. Cutting the aluminum was slightly gummy so we resorted to flooding the cutter with astrocut and that helped immensely.

The coolant made a mess but the gear came out beautifully! 18 and 36 tooth were really easy to index on this cheap indexer.

Machining the case castings

The thread in the casting section shows much of the trials and tribulations of casting the actual case halves, you can review it here: http://www.homemodelenginemachinist.com/index.php?topic=10845.0

The main benefits of casting are mostly cosmetic and repeatability. This engine can be made out of barstock easily. When working on castings, the trickiest thing to do is find a good datum point to measure from. The forms were second generation castings, which tended to loose some squareness. With the associated draft angles on the 4 sides, the best point was considered the deck just below the cylinder attachment boss. Special tool #1 was made to hold the face of casting the parallel to the table.

Here is one half done, showing a minor shrinkage cavity which will be machined out later. One casting is significantly higher then the other. That one was tackled first with a standard endmill before switching back to the flycutter.

Once I had a flat surface I went back and measured the height variation, on average it was acceptable +- .007". This left the cylinder mounting boss just about .065" proud of the face, taking about .030" cut of the cast surface. It may have been more luck then skill, but those measurements were approx the design ideas. This was also the easiest cut, as the face is 1 inch, I simply lowered the cutter to a 1-2-3 block to set the depth and milled it away.

Now that I had 4 surfaces all parallel to each other I finally got to see how well each half fit together at the proper parting line. Disappointment began to sink in as the variation was worse then hoped. I actually aligned the halves by eye with a best fit mentality. What I should have done was realized the imprtance of the offcenter oil pump boss in the rear, and made everything else fit that. Hindsight, of course, is 20/20 and I went with the best fit of the 3 easy edges instead. I clamped them down and drilled the flange #20 followed by a 3/16 reamer in two places. Two spring pins installed in these holes would facilitate alignment of the halves for here on out.

Back in the vise, the front timing gear boss is trued up with a dial indicator clamped to the ram, gently persuaded into place with a few taps of a plastic mallett, then machined true. Now I had my third surface at exactly 90 degrees to the first ones, this was used to rough trim the crankshaft and oil pump bosses.

Now I scribe a few lines inboard of the edge and drill #6 holes and clearance drill down to the other half. I flipped the case over and repeated on the same hand side, leaving a pair of screws straddling the crankshaft centerline threading into the other engine half. I wanted these bolts holding the halves tight for the upcoming boring operation.

Another day or so went by as I thought about the upcoming operation. I had actually never tried boring along the parting lines of a case like this, but there did not seem to be another good way to accomplish this. I had roughed the centerline out earlier based on the bosses for the purposes of the cross bolts. I now pulled out a pointed center and wondered aloud how the hades are you supposed to use this tool? Anyway, I had my ideas how it would help me here. Adjusting the center against the side of the vise for minimum point wiggle I eyeballed the parting line and the cross lines. Then I used a center drill followed by progressively larger drill bits and finished the bore off with a 1/2" reamer. Wound the table down .940" and did the same thing to the .250 camshaft bore. The smaller bore did falter a bit in the center, probably too much pecking without clearing all the chips, but it exited and began clean. I was pleasantly suprised to find everything worked as hoped.

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At this point I will end todays installment, and bid you to join me next time for the "how things go wrong and how to adjust for them" follys. :)

Feel free to chime in if you can tell me exactly how you use those pointed centers.
Case machining continued

Right about now is when things fall apart. :( The cylinder is measured off the side of the casting along the centerline and bored through 1" diameter. Then I flip the casting over and with a roughing mill a full depth (.850") rough cut is done by eye. I switch to a long endmill and begin to check measurements against the print. I zig along the side and much to my suprise I break into the bolt threads.

I am still approximately .050" shy of desired width of the inside of the case. The attaching bolts wont allow any further width expansion, although they are still useful, owing to the 3/4" thread engagement. I am discouraged and figgure I will probably need to start over. :'(

Looking back over the various parts and drawings I find at least part of the reason for the problems. I had recreated the cad drawings to make the masters with additional draft angles, but somehow I missed a dimension somewhere and left both masters .040" too short. Adding a double shrinkage allowance might account for the remaining discrepancy, I am not sure. I will have to double check before I order the version 2 masters. Lesson learned, the hard way. I took the rest of the day off and considered how to start another set of castings. After some reflection, that path did not seem too desirable. There could be further issues and lessons to learn that may catch me in the future with this design, so I wanted to go as far as possible. The crankshaft had plenty of extra meat on the counterweights, and could be shortened easily, as well as less work to redo if I started another engine. So I ended up shortening the crankshaft, shaving a little from the crank/thrust bearings. The game was back on! We will just have to keep our eyes open for any other adjustments this will force me to make. Once I sit down to do the version 2 blueprints, I will be a whole lot wiser.

Back to the mill!

For some reason, I always considered this the fun part of the build, hogging out the crankcase. This time, its becoming a bit of a chore with some tight cuts into the threads. I am not happy about it but lets just see how it will break. :) Side A was cleaned up as best as possible. The curved section is only cut approx .430 deep to provide a bore for the cam followers to ride in. Side B was blued and the halves joined together, a bent tip scriber transferring the rough outline through the cylinder opening. The cylinder mounting flange was bored through 1" again and the roughing mill does the lions share of the stock removal.

The halves were fitted together with the newly shaved crankshaft and only required minimal fitting. Endplay was good and the case screws held ample torque. Now to make a few more things fit. With a 1/2 collet both my boring head and drill chuck interchange quickly. The block is screwed together and clamped with the forward side up for the next boring operation. I chucked up a piece of .25 round stock and used that to find center for the cam bore. Using the boring head we make clearance for the cam gear, move the table back .940 and make the smaller bore for the crank gear.

Time for a little fun, we get to test fit everything together and begin to see what it looks like.

And now, were almost caught up to real-time.
I would like to offer my apologies to everyone. Someone very kindly dropped a clue rake on my head about the image sizes and load times. I have reloaded most of the images to correct this. This will still be a very image intensive thread, but I will attempt to keep the pictures both relevent and reasonable in size for now on. Apologies again, for being so inconsiderate.
Looks good, Jeff.
I like boxers so this thread is high on my watch list. I also like the "warts and all" approach as it helps save me from making the same mistakes my self. Then I can make my own mistakes.
Gail in NM
Thanks Gail! More warts coming but I am trying.... :)

Oil pump

One of the many "firsts" I scheduled into this project would be a pressure oiling system. If this engine would be done for production for a large company, oiling would be from a gerrotor style pump driven directly off the crankshaft.


While that is undoubtably the best way to do things, it is probably difficult to reproduce in a home shop. I only say probably because I dont have the first clue on how I would produce one. It might be easy, but it is definately beyond my skills at this point. Model size gerotor's are available rather commonly, as scrap automotive electic fuel pumps here in the states, but they are still too big for my intended purposes.

There is a way to use two spur gears to pump fluids, and that is the way I settled on doing it. Two gears meshing will carry fluid around the outside of the teeth, producing pressure just before the gears mesh again. While I dont expect to hold tolerances close enough to obtain maximum output, I hope to obtain a useable flow of oil. For gear material, I bought 12" of 20PA 32DP 12 tooth spur gear stock from Mcmaster for approx $23. These have a .375 pitch diameter, and need to be bored and cut to length.

Center was found with another probable misuse of the pointy centering tool. We bore using the existing hole .428 down to approx .1 from the inside, setting and checking the repeatability of the power downfeed stop. Boring with a power downfeed is a bit of a luxury, but avoids a lot of possible mistakes when hand feeding.

The two case halves are assymetric in the rear to allow for the oil pump idler gear offset from the centerline. This is where I should have paid more attention to the alignment of the case halves, as the offset portion is not at a right angle

to the case halves and the camshaft centerline. This was compensated for by scribing the layout dye with a 3/4 endmill, so I have the proper radius to offset the second gear in the center of the casting.

Center was picked up off the scribe mark, followed by a center drill and #20 then a 3/16 reamer. An endmill begins the hole and boring head takes over from there.

A gear cut for an earlier test pump used as a gauge.

The remaining 10" or so of pinion stock I had was then chucked up nearly flush with a homemade pot chuck, center drilled, #20 and 3/16 reamer followed in a series of short pecks with the drill to keep it as straight as possible. Plenty of coolant/lube us used.

The pot chuck is held tightly to the face of the barely loosened jaws of the 3 jaw with a wrench and the pinion is advanced by gently tapping it up with a brass drift. In theory, this should minimize the error in retightening the pot chuck. It is then skimmed to .435 od and parted off .320 deep

And sitting on the tail of the camshaft it is starting to look like an oil pump. :)

Next installment will likely bring me up to date. Its more necessary then fun but we will do keyways.
hi jeff
dont know if its my fault, but i have only been able to see parts of meny of your pics,
which is a shame, cos i recon a picture is worth a thousand words.
looking forward to your next posting, in what is starting to look like a very nice little motor
pete in australia.
metalmad said:
hi jeff
dont know if its my fault, but i have only been able to see parts of meny of your pics,
which is a shame, cos i recon a picture is worth a thousand words.

I'm having the same problem. Wonder if using a site like photobucket would help wiyh this?

Excellent work. Following along with envy.

Thanks for the comments guys. I am not sure what the problem is with imageshack. I have flushed my cache by several different methods and still dont see the problem, but imageshack has been kinda slow lately. I will keep hammering away at it.
Thanks for all the positive comments! Hopefully, imageshack has sorted out its problems, but I am investigating another source for images soon.


Not the most sexy part of any build but definately important. In the continuing tradition of using some areas to make up for deficiencies in others, we will make a cut length to fit key for the cam gear.

First, we catch up on crankshaft work. A variety of holding methods are used to whittle away the outside counterweights. The part of the crankshaft between the two connecting rod pins will be left as is in case any other changes are called for. I also ended up redrilling the oil hole from the front bearing as I flipped my angles backwards drilling down from the rod pin.

Cutting the keyway was straightforward. 1/16 carbide endmill taking .003 deep cuts for .063. Slot was started in the missed oiling hole to cover it up. A 1/8 square piece of steel was milled down to make a 1/16x1/8 key. Once back on the block the gear depth was set and I removed the excess key with a file.

Now we put two keys in the camshaft, on for the timing gear and one for the oil pump drive. The cam was made out of 3/8 4140L, and thus I did not have extra material to leave a face for the timing gear to but up against. Here we cut the keyway almost completely through and use a variable depth key to center the gear. The timing gear is also cut to less then full depth.

The tiny keyway is adjusted for length to keep the cam gear at the correct depth.

The oil pump gear fits at the back of the camshaft, it is slotted 1/16 the full depth. More tiny mill work, done mostly under magnification.

Now all the turney bits turn the other bits. This is really fun! We are almost caught up, although I do have a few more pictures in the can. Next up is finishing the oil pump, and then likely we will be putting the bumps on the bumpstick.

Jeff, this is fantastic and Im thoroughly enjoying your write up! :bow:

Looking forward to the next instalment...

Rob T ;D
Thanks Artie!

We have made a bit more progress, and have some neet new toys for the next part. Been real busy but I will have some picture updates coming soon. Perhaps sometime this afternoon or tomorrow. I have already finished off the oil pump (for now) and added some lobes to the test camshaft, currently working on the first cylinder.

I am hoping this thread makes it to the second page before I post any more pictures, just to keep the loading time down. If not, I will just use thumbnails for the rest of this page.
Oil pump
Lots of work here, mostly under magnification. These are the tightest tolerances I have ever tried to work to. As most of them are outside of my measuring capability, I make it tight and had fit a lot of it. Once the keyways were installed there was, as expected, significant binding in spots. Tooth by tooth, each oil pump gear was deburred under a magnifying lens and that got rid of most of it. I blued the cavities and hand scraped some areas, and rebored the one cavity another .001 larger to make up for a slight offset in the gear center bore. An 8260? rod I had purchased for the wrist pins was used for an idler shaft for the offset gear. Then we measure and cut the oil pump cavity to give approx .002 clearance, which will later be reduced to .0003 by hand filing.

Then I take a chunk of 3/8 aluminum and ream two 3/16 holes .375 apart to a depth of .312. It is dyed up and placed over the protruding camshaft end with the idler shaft holding the idler gear in position. Held tight, it is scribed with the outline of the casting. With my template visiable in the vise I drill the inlet and outlet holes. Back at the computer, I finally draw the cover and figure out the proper angle for the outlet port, which is a drilling that intersects the camshaft bore and pump outlet, as well as allowing a flat area to tap 10-32 for a pressure relief valve. Looking at the remaining area scribed, I can get 1 4-40 screw in a fatter section of the casting, and 3 2-56 screws to hold the remainder of the cover on. They are drilled in the cover first and transferred to the block. Later, I can shape this ugly but functional cover back to the scribe marks. For now, the flat surfaces allow easy vise chucking.


This started as a rough part, and has only gotten rougher. I dont know if it will survive as a working part but it has been an experiance. Early on, right after the crankshaft, I took a piece of 3/8 4140L and turned the journals, lobes, and thrust surfaces, as well as double ended drilling through to act as the oil feed from the pump to the front main bearing. This was only mockup quality as I made the lobes slightly offset from the drawing, but we have pressed on regardless.

The part was chucked up in a Sherline 4 jaw attached to a rotary table. I dont have the proper tailstock for this so I supported it with a shimmed V block. The cam is flat sided, so the first flat was indicated and slowly nibbled down to the baseline depth. Once at depth the rotary table allowed nearly effortless cutting by rotating the cam to the next flat angle.

You can see where the lobes were offset from the drawing. In practice, it likely wont matter much because of the .375 mushroom tappets. The slight nose radius is put in with a few easy passes of a file. I went with 3 lobe design to make the pushrod angles a little bit flatter, opposed motors often use only two lobes. I may eventually scrap this part as the timing is suspect, done long ago and I had lost my notes. But for now its definately serving a useful purpose.

This essentially brings us up to date. ;D I have one cylinder complete and one block half cylinder bolt pattern drilled and tapped. Maybe another update tonight if I have them all completed
How to turn 420grams of steel into a 48 gram part​

This is one of those parts that looked great on the cad program, but making it to print would be nearly impossible. I changed the block flange width from .035 to .050, just because I wanted it a bit stronger, but 10 .020 cooling fins were a pipe dream.

To begin, we tap the part with a plastic hammer to center it for the accuracy of the center drill.

Once faced off and centerdrilled, we go to the layout table. One of my new toys arrived Friday from Enco. I could have borrowed one from a friend but the height layout scriber is just too important not to have. First, we dye up the lump of 1 3/8 12l40 and scribe the important lines. Sorry about the blurry pic but this operation would have not come off as well without this accessory.

The cylinder wall OD is 1", the bore will be .950. This is my first attempt at such a thinwall design. We turn the .350 deep protrusion to 1" and dive into the middle of the fins and flange, squaring it off with a square bit.

Then begins the nightmare of finning. I think I will stick to watercooled engines for now on. The .020 finning tool lasted about .035 before it broke. I went to .040 cuts and doubled the spacing. I eventually got through it, but the second shot is a rouge's gallery of failed cutters.

Boring was pretty straightforward. My largest 1/2 shank drill is 17/32, so a lot of boring had to be done. If I do any more of these, Ill spring for a big drill and a .950 reamer and save an hour for each part. Why do you only think of the easy solutions on a Sunday.... Both cylinders came out within .001 of each other, just running a ball hone in them is all the bore needs now. Again, on a Sunday, my 1" ball hone has disappeared. Time to get a new one. Once bored, it is parted off and reversed in the chuck, and lightly we take material off back to the overall height scribe line. There is not much material there and I could easily crush it with the 3 jaw.

Two days worth of work, most of the time spent boring when I should have been drilling, and grinding toolbits for finning. With the right tools, everything but the finning could be done in an hour. I am not sure how to fin any better without a whole lot more rigidity in my cheap toolpost. Now it is beginning to look like an engine. :)

Once we hone the cylinders and determine the final bore I can finalize the piston prints and we can make those. The con rod drawings are done, the cylinder head drawings are 90% finished, and we have some little things to do, like the bolt holes for the cylinders. It feels good to make some progress. :)

Thanks for the suggestion Phil. Once I get one running IC under my belt I probably wont be so anxious when I build the next one. There wasnt the normal level of forethought put into manufacturing those pieces, it was more like "it's only 3 inches of a 12 inch bar, not much lost if I screw it up". :)

Cylinder honing

Not too much to see here. My 1" ball hone has disappeared but I did have some new stones for my two stone flex hone. Not even 200 revolutions on either cylinder, and I am quite proud to claim both came out .9507 bores. I used an old quart oil container cut down to contain the mess of grinding grit and kerosene I squirted on for lube. I also used the parted off stub as a guide for the hone to keep from bellmouthing the bore.

The felines derriere

My new tool gloat now, from Enco. I did put some forethought into how I would find center for the block to cylinder mounting screws. At only ~3x the price Guy Lautard's bedside reader, which I believe has a method using regular wigglers, this tool does work, and does it with a bit of style. :) Here we drill and tap the block and drill the cylinder mounting flange. One side is 6-32, when I realized I had to cut the screws down quite a bit to clear the cylinder barrel, I did the other side in 4-40.

I spent a good part of this morning tweaking the piston drawings with the intention of making them today. This is my first dual ring design with one oil control ring and one compression. As I reread all my references I deceided that I should make the rings first. A few hours of reading, and thanks to Phil Burman's spreadsheet from Min_Int_Comb_Eng circa 2004, along with the collective works of Trimble and Walshaw, I settled on a set of .035x.035 thin rings, with the oil control ring a simple bevel top version. The piston will have many radial holes centered on the bottom land of the oil ring to flush the oil away. A bar of cast iron was turned down to .954 with .8807ID and the rings were parted off. The sharpie mark on the oil rings denotes the bevel edge.

I am pretty excited, as I have made pistons before but never rings, so there is another first I can check off my list. Once I get the pistons done, I will make the ring heat treating holder to specs, skim them down to .9507, and check the closing force to see how the wall pressure works out. If I need to adjust the holder from there we can accomodate that.

Next up? Probably the pistons. Thanksgiving is next week, and I am looking forward to getting a lot more done with two extra days in the shop while the ladies do their shopping. :)