Cylinder Liners

[petertha]

Shop time has been very limited for me lately, but I managed some progress on my 5-cyl radial liner prototypes. My plan is to match the bore to a commercial engine (OS-56) as it’s very close to what the plans call for. I intend to use purchased rings. If the engine decides to run, I will have a good baseline & confidence to proceed making my own rings & all that that entails. But going down this path means I have to hit both the bore & surface finish simultaneously & that has proved to be a bit challenging (for me). Many builders get the bores established by whatever means & then make the rings to suit.

I tried 12L14 steel (not shown here). It went reasonably well, but I was under the delusion I could lap my way from 11/16” reamer bore (0.9375”) to 0.9445” finish bore. Well, trying to remove 0.007” by lapping would take a long time. The first 0.001” comes off pretty quick (lopping the tops off the hills so to speak), then progress diminishes to a crawl when in full material. I didn’t track time but I’m guessing over an hour went by lapping & cleaning & recharging for a teeny 0.001” gain. I got hold of some coarse compound (220) which cut more aggressive but wasn’t fun either. Tightening the lap expansion screw is a bit sensitive, just a bit too much & can get grabby & risk injury. Plus it consumes & scratches the (brass) lap.

Next test was to skip the reamer & target ID within 0.002-0.003” undersize with boring bar alone in order to leave something more reasonable remaining for lapping. I found that trying to creep up on the target ID thou-by-thou didn’t yield the best results. My consistency improved by planning it backwards & removing a predetermined fixed increment between the last 2 passes. For example: cut 0.010”, measure, then final cut 0.010”. This of course would be the ideal case. It could also go: 0.010 + 0.009 remaining, or 0.010 + 0.011 remaining depending on the last measurement. The general idea is try & make the tool work the same & normalize the variables as much as possible. At least that's my thinking.

I ran the tool the exact same way on both final passes, 2 runs with the carriage locked to allow the boring bar to unspring. And I decreased the leadscrew traverse pitch selection finer between each run so the tool would not thread along its same path (ie. deepen the valley but not change the crests). Temperature can play a factor if the metal is still warm from heavy preceding boring. It pays to have your dial gage all set up beforehand against some repeatable target reference. Well I think these lessons consumed another 3 slugs worth of 12L14.

Next up was trying cast iron, of which I had no prior experience. I bought a 12” chunk of Red Gray Class-40 from Speedy metals (USA). It is quite cheap, however UPS shipping cost me 5 Canadian beaver pelts, a birch bark canoe & 7 barrels of dirty oil. But it was worth it. I was pleasantly surprised how nice this stuff machines. The OD finished up with a homebrew lapping donut & 1000 paper. I was able to hit the ID bore pre-lap dimension (practice makes perfect). This pic shows the CI liner with a quick 400 grit lap, maybe 0.0003 - 0.0005” removed. It’s at the early silky satin finish look but still shows tool path valleys even though you would be hard pressed to actually feel it. The only thing is, CI is harder than 12L14 so I’m expecting longer lap times. So far I think I like CI a bit more than 12L14.

 

[petertha]

My homebrew aluminum split lap for OD sizing. I need to make a proper radial clamping tool. My fingers are now muscle locked in a permanent 'OK' sign

This is the OS-56 liner. I think typical RC chrome plated, ground & surface cross hatched. I noticed it is about 0.0008" larger bore near the bottom than the top. I'm guessing that's by design & not a quality issue. The question is, should I try & adopt this taper by working the lower portion a bit more or just go for parallel. My liner is longer so I'm not keen on extending the taper. Parallel it is!

 

[Mechanicboy]

1. Without pistonring ---> tapered cylinder, also more wide in bottom of cylinder and more tight in top of cylinder. It make easy to start engine with good compression and when engine is in working temperature then the cylinder will expanding to near parallel without loose compression.

To check clearance in lapped piston/cylinder is correct: Dry piston/cylinder ---> piston feel tight in cylinder. Oiled piston/cylinder ---> Piston is loose in bottom of cylinder and more tight in top of cylinder. The surface will be dull grey ---> a lot of oil pockets in cylinder/piston will make the engine last long time.

Diameter difference in top and bottom of cylinder is about 0.001-0.005 millimetre depending on size of length and bore and material in piston and cylinder. To make tapered cylinder is done by lapping---> Put the piston into the cylinder and lap togheter with very fine lapping paste (or chrome polish paste if you not have the very fine lapping paste) and rotate piston while you are pushing the piston more and more into the cylinder. Stop work when the piston is tight in the cylinder and wash piston and cylinder clean then test piston/cylinder clearance is correct as i wrote above in this comments.

2. With pistonring ---> parallel cylinder. The aluminium piston is more "sloppy" in cylinder due expansion by heat. The piston is tapered (smaller at top of piston and wider at bottom of piston) or piston in parallel in small diameter than cylinder.

 

[mayhugh1]

Peter,
Your honing experience parallels my own. I try to bore the cylinders in my radials to withn a thousandth of one another before honing. I then hone them all together a couple tenths at a time until they're all identical. Then I make the rings to match. You're right about more than .002" being too much to hone. Both of my lathes cut tapers and so I orient the cylinders in the lathe so the larger diameter will end up at the bottom. I then try to straighten the bore during honing, but if some cylinders still end up a few tenths bigger at the bottom I accept them rather than continuing to hone the whole batch even further to match. The top of the cylinder is where the compression pressure will be highest and where the ring fit is most important. If it is a few tenths sloppier at the bottom of the cylinder, you'll have a bit less friction (more important for a single cylinder engine), but your rings will wear with a portion of the taper. Again, a few tenths shouldn't be a big deal, because modt of the ring wear will occur just after tdc of the power stroke where the compression pressure is highest.
More important is to make sure you measure the i.d.'s at two orthogonal places to make sure the bore is truly round. Especially on the cast iron, re-measure it a few days after all the lathe work is completed. I let my cast iron 'settle out' maybe a week after the machining is completed and before doing the honing so the change in internal stresses has time to settle out. I find this to be especially important with the c.i. ring blanks, and depending upon tbe wall thickness of the liners, it can be important for the liners as well. I'm going to try Stressproof for the liners for my Merlin because or their very thin wall construction and my concern for them 'moving around' during and after machining. By the way, those surface finishes are really nice. You're probably also finding out that there is technique involved in getting repeatability on tenths-level bore measurements. - Terry

 

[lohring]

It is very common for ringless pistons to have a large taper. The fit at the top of the bore has close to no clearance and the bottom of the sleeve can be as much as .007" bigger. This cylinder fit makes a huge difference in power. There are several approaches to this fit. Jim Allen's can be seen in his gallery. He discusses some of his methods in this forum as well. While these fits don't strictly apply to ringed piston fits, Jim has applied these methods to a 26 cc ringed piston engine. This and other modifications added around 2 hp to a 7 1/2 hp engine.

Lohring Miller

 

[petertha]

Terry, I helped myself to all your great posts, so thanks again for sharing.

Re measurement, I set the bore gage up in a makeshift but repeatable way, measuring at 3 or 4 spots along the liner and then perpendicular to that using a longitudinal felt pen line reference. (I'm talking the lapping stage here). Question: my gage has 0.0005" increments. It seems quite repeatable, but someone told me it should be a finer range. I doubt I'll buy a new one, but was just curious what you were measuring with?

Re lathe turning, This is the boring bar I used (largest shank). I didn't pay much attention to the CCMT insert type & nose radius because I took the same tool from 5/8 (.625) drilling to .945 finishing. In fact I used the same one between 12L14 & CI. I thought the CI might wear it a bit but so far so good. You hit some pretty close numbers, do you have any advice on this aspect?

Your 'resting period' comment is very interesting. In fact that's what I saw on the 12L14 & chocked it up to temperature which never really sat right with me. I haven't done this on CI yet, but will now. I just assumed 'cast' would distort less, but that's more naivety & wishful thinking & on my part.

I'll be watching for your stress-proof steel findings. Are you thinking 1144?What wall thickness will the Merlin be?
http://www.onlinemetals.com/merchant.cfm?pid=7644&step=4&showunits=inches&id=286&top_cat=0

This original liner design called for 0.039" WT but I modified things to yield 0.065". Actually I thought about 1144 too but seemed like it wasn't as popular among ME builders for whatever reason. Lots of praise for use on crankshafts but less for liners for. But I just found this 2007 link with Ron's comment. My 12L14 is showing teeny rust spots sitting on my bench. I'm concerned what will happen in the engine with methanol fuel despite some oil coating protection.

Guys: I am currently machining the eight liners for my Novi V-8. I am using 1144 Stressproof steel. This stuff is ideal. It machines so easily and with such a superior finish that I will probably never use cast iron for liners again. Leaded steel would be my second choice. Cast iron is dirty and I always end up making a trip to the eye doctor whenever I have to machine it. I get swelling in my eyelids from the dust no matter what protection I use. Some allergy I suppose. Best of luck. Ron Colonna

http://www.floridaame.org/cgi-bin/discus/discus.cgi?pg=prev&topic=6&page=260

 

[petertha]

Jim Allen's can be seen in his gallery. He discusses some of his methods in this forum as well. Lohring Miller

Hi Lohring. I follow that MEM post closely but was not aware of the boating link, thanks. Yes, incredible achievement considering the controlled taper boring, chroming & surface grinding. I missed the reference to a 26cc ringed engine. Can you direct me to that or do you mean engine was built by same person but not really a build/pics posting?

 

[petertha]

2. With pistonring ---> parallel cylinder. The aluminium piston is more "sloppy" in cylinder due expansion by heat. The piston is tapered (smaller at top of piston and wider at bottom of piston) or piston in parallel in small diameter than cylinder.

Thanks Mechanicboy. This will be for 4-stroke methanol/oil premix fuel model engine with CI ring, 7075 aluminum piston, liner material to be finalized. Regarding the taper, the top end expansion at elevated temperature makes perfect sense. But after that I kind of lose what is growing and to what degree. The aluminum piston material expands more than constrained steel liner, but its the protruding CI ring with radial expansion force that is actually contacting against liner ID providing seal. I *think* there is excess depth relief designed in the piston ring groove that it never really mates & forces the ring outward. At least that's my limited understanding. But this is a different animal yet again to ring-less pistons like typical RC 2-strokes.

I measured a commercial OS-56 liner (the one shown) and its corresponding piston & ring. For now I will just clone the dimensions assuming they did it consciously. I had a old liner from similar commercial engine which showed similar taper but I didn't trust it as it was well worn. But this one is brand new & for sure tapered. If anyone else has similar engines, I'd be interested to hear. I might be able to adjust my lapping method to achieve this taper, but its one more level of complexity. I was just wondering out loud if parallel would be so bad.

 

[mayhugh1]

Peter,
I'm using pretty much the same dial bore gage you're using but only under a different importer's name. To get the final bored i.d.'s close on the lathe before honing I do all the finish passes using a Korloy CCMT 21.51 insert normally used for machining aluminum. These inserts, available from Travers, are polished and razor sharp. I do all the final passes as a batch in the same set-up without moving the cross-feed.
The stock Merlin liners are .030" but I plan to make some modifications to increase their wall thickness to at least .060". Again, though, I don't have to hit a specific diameter since I make my rings to suit. What you're doing is more difficult. If I were using commercial rings I would want them in my hands before honing the cylinders so I could measure them with the same device I'm using to measure the bores. In my shop, I can measure to a few tenths, but they are usually different tenths than are measured by someone else. - Terry

 

[lohring]

Jim has been working on an old 26 cc Quickdraw. We set a record with a similar engine in 2004 that stood until this year. I don't have pictures of the liner but it is a ground out stock steel liner that was chromed and resized. The manufacturer now offers chrome liners, probably as a result of this work. We found as much as 1/4 hp difference from engine to engine depending on liner hone pattern and fit. Below are a couple pictures of Jim's engine. In addition to the liner he has added a custom pipe, carb, toroidal combustion chamber and a custom rod with custom big end bearing.

Lohring Miller

 

[Mechanicboy]

This is the OS-56 liner. I think typical RC chrome plated, ground & surface cross hatched.

OS engines Ltd. manufactures no longer cylinder liner with chrome coating. You can see there is difference of color coating. The chrome coating is brighter than the coating on your cylinder liner from OS 56 at the photo. It is nickel coated cylinder liner with darker and color difference surface of nickel.
The problem with nickel coatings in cylinder liner occurring in OS engines (usually in two stroke engines): peeling of nickel caused by incorrect use of the engine to example incorrect running in or running with rich fuel due lack of expanding of the nickel coated liner since the ABL (Advanced Bimetallic Liner)/ABC (Aluminium, Brass, Composite (nickel))/ABN (Aluminium, Brass, Nickel) is produced by OS engines Ltd. The real ABC (aluminium, brass, chrome) engine has chrome coated inside and brass outside cylinder liner while the nickel coated cylinder liner is overall to preventing cracking of nickel.

Never problem with chromed cylinder liner compared with nickel coated cylinder liner. I has some engine with nickel coated cylinder engine, never had problem, but i repaired the old OS MAX 61 with peeled cylinder liner when i bought used engine in this link: http://www.rcuniverse.com/forum/everything-diesel-87/4929500-convertering-os-61-pure-diesel-engine.html

1. Picture of the real ABC cylinder liner.
2. Picture of the nickel coated ABC/ABL/ABN cylinder liner from OS Engines Ltd.
3. Picture of the peeled nickel coated ABC liner from OS engine

 

[petertha]

You are absolutely correct, Jens. My bad. I just meant 'coating' in general as opposed to native material like these home shop liners. ps - I'm a long time punisher of pattern & pylon engines... but haven't seen a liner THAT bad before

 

[lohring]

We've had chromed brass liners with ringed pistons fail as well. Gasoline engines are much harder on their liners. The CMB liner below failed due to an out of round bore just above the exhaust port, seizing the piston. For our record trials we need the maximum rpm. This 36 cc engine's wrist pin bore started to elongate at 25,000 rpm. After that we limited the rpm to 23,000.

Lohring Miller

 

[xpylonracer]

Hi Lohring
The piston shown seems to me to be damaged at the transfer port position, looks like the engine has in injested something to cause the damage.

Emgee

 

[lohring]

This is the other side of the piston. It seized and was damaged in two places. I will take some pictures of the liner that show where some of the chrome peeled off, but it was the out of round condition that caused it. The previous non ringed pistons were a complete failure. We went through at least 6 sleeves trying to get that to work. CMB changed to the ringed piston so we weren't the only ones with problems. We tested a lot of modifications on the engine. A summary of that work is here.

Lohring Miller

 

[xpylonracer]

Hi Lohring

Very interesting article, takes lots of effort and parts to achieve top performance, congratulations on the record.

Emgee

 

[lohring]

Thanks. That and our other record in the 26cc class that stood for11 years have both been broken recently. I'm working very slowly on a new engine to go after both records again. When I get farther along, I'll post the build. You might be interested in my articles in the NAMBA Propwash on two strokes; High Power Two Stroke Design part 1, High Power Two Stroke Design part 2, High Power Two Stroke Design part 3.

Lohring Miller

 

[xpylonracer]

Hi Lohring

I wanted to read the articles but whether it's my computer or the site it's on I found it the book unmanageable, couldn't expand or scroll properly so gave up, got as far as Bill Wisnewski using the tuned pipe. Tried to download but that didn't work either.

Emgee

 

[Cogsy]

I had a look at the first link and although it lagged a bit, I could scroll and zoom without a problem.

 

[lohring]

The flipping book format seems poor to me as well. I can get it to work with the latest flash and a fast internet connection, but it's troublesome even then. They put the Propwash in .pdf format previously. This always worked better forb me. I'll forward your comments to NAMBA.

Lohring Miller