# Ohrndorf 5 Cylinder Radial



## petertha (Jan 20, 2021)

Intro
I’ve been working on this radial engine on & off for <ahem> more than a few years now. You may have seen some of my prior questions or random posts scattered elsewhere on the forum. Progress has been pretty slow with the usual factors - time constraints, distractions & learn-as-you go snail’s pace. I also had a few unwelcome interruptions with my machines. The drive train on my ’97 Taiwan 14x40 lathe developed problems which took some time to source parts & repair. Then shortly thereafter my same vintage RF-45 mill gearbox decided it wasn’t happy with the world. Ultimately I decided to upgrade the mill but that required some shop shuffling & electrical work.

Anyway, rolling time forward to present day, I might actually be on the home stretch. So I figure it’s a good time to post my prior construction journey and transition into present day work so it will appear as a normal, continuous construction exercise. Actually, looking back at some of my pictures & notes leaves me wondering what I actually did myself, so this documentation exercise will benefit me as well. 

I really wanted to build a radial and avoid castings to mess up, so 5 cylinders is kind of the minimum order, at least of the more common radial plans available. The Ohrndorf seemed well designed from my amateur comparisons to other 5-cyl radials. Nothing stood out as radical or unconventional. There is a YouTube video of it running. Hard to tell, but possibly it is an early prototype. I liked the overall proportions & some aesthetic features. Anyways, it ticked most of the boxes for me at the time. 

Experience wise, this is my first engine. I’d made a few prior metalworking gadgets, but nothing remotely close to this level. I decided to attempt a single cylinder assembly prototype and if that turned out OK, then I’d carry on with the rest of the engine. The engine has yet to run, so we’ll ultimately see if that path was the right decision. Wish me luck!


----------



## petertha (Jan 20, 2021)

Design
The engine is designed by Martin Ohrndorf of Modellbau & Technik (Germany). On his web site he offers various other plans if you are so inclined (no personal affiliation). There are also some YouTube videos of his engines running.








						Martin Ohrndorf Modellbau & Technik | Martin Ohrndorf Modellbau & Technik
					

Motorbaupläne von Martin Ohrndorf Ausführliche Stücklisten Verständliche Bauanleitungen Übersichtliche Zeichnungen Die Baupläne enthalten Darstellungen der Einzelteile sowie Ansichten und Schnitte…




					www.engineman.de
				











						Bauplan: 5 Zylinder Sternmotor | Martin Ohrndorf Modellbau & Technik
					

Bauplan des 5 Zylinder Sternmotors von Martin Ohrndorf.  Für den Nachbau ist der Bauplan des 9 Zylinder Sternmotors zwingend erforderlich!




					www.engineman.de
				




Engine Specs
Methanol fuel, glow plug ignition
Bore = 24 mm
Stroke = 22 mm
Displacement = 50 cc (10 cc per cylinder)
Weight ~ 1900 g
RPM ~ 950 – 5,500
Outer diameter ~ 225 mm
Length ~ 165 mm
Propeller size 18x14 to 22x12 inch


----------



## petertha (Jan 20, 2021)

Plans
The 2D hardcopy plans are most certainly derived from a 3D CAD model. They are metric dimensions, corresponding to metric components & tooling. The instructions are in German & quite brief, however I was able to occasionally communicate with Martin by email to answer the odd question.

Once I had the plans, I set about re-drawing parts into my own CAD model. This isn’t a necessity but it certainly helped me on multiple fronts. I was better able to understand the assembly details, make my (imperial dimensioned) shop drawings, design jigs & fixtures etc. Ultimately I made a few changes here & there which I’ll detail, but for the most part stuck to the original design.

I’ll use the abbreviations O5 & O9 for the (Ohrndorf) 5 & 9 cylinder engines respectively. The 05 shares about half its parts with the 09. Unfortunately you need to purchase both O5 & O9 plan sets in order to build the 05. I suspect the O9 came first & the O5 later. The O5 plans have a pseudo assembly sheet that specifies whether to use a stock O9 part, or modify an O9 part, or make a new O5 part. This involves a bit of juggling to keep straight. A single set of O5 plans would certainly have been more convenient, but it is what it is. Who knows, maybe I’ll build the O9 one day.


----------



## petertha (Jan 20, 2021)

Plans overview


----------



## petertha (Jan 20, 2021)

Link of video circa 2010. I have not come across any others myself.


----------



## petertha (Jan 20, 2021)

My reconstructed CAD pics. Missing pushrods, carb, inlet/exhaust accessories & some other bits...


----------



## petertha (Jan 20, 2021)

Construction & Design
The engine is bar stock, no castings. Hardening is required on some specific parts. Remaining commercial components include metric fasteners, bearings, spur gears, ring gear, O-rings, circlips & such. I planned on cutting the spur gears for the learning experience, but ended up purchasing them along with the internal (ring) gear because all the gears require modification. Apparently ring gears are a bit involved to (properly) cut teeth profiles in the home shop. I found all the gears readily available at MÄDLER - your expert for power transmission elements | MÄDLER Webshop

RC glow plug ignition was my preference on a first build because it seemed simpler than spark in some respects. I have some RC experience so maybe it was more the devil you know, albeit no prior involvement with multi-cylinder engines or radials. I’ll have to figure out an igniter system when the time comes.

Lubrication is somewhat similar to other glow engines, oil is premixed with the methanol fuel. Specific to the O5, intake charge enters from the rear mounted carb into the crankcase where it mists over the moving master/link rod assembly, then flows backwards out through the induction tubes into the heads. One unique feature of the O5 is that the nose case is compartmentally sealed from the crankcase & partially filled with oil bath for the planetary gear train & cam plates to splash in. I liked this concept because it mitigates an oil pump system. But I’m also wondering what keeps oil from seeping out past the lower, submerged tappets (cam followers). He uses the same bath philosophy on the larger O9, although there seem to be seal differences between engines. Alternately, other glow radials allow the intake mist to continue further forward, flowing into the nose case via openings in the front gear plate. This option is still available to me with some modifications. So I’m still mulling this issue over in terms of how to proceed. I assume the rocker assembly gets lubricated by occasional maintenance oiling & fuel residue working its way between the valve stem & guide. At least that’s how commercial RC 4S engines seem to work.

The pistons have a single compression ring. My plan all along was to use commercial RC rings, specifically from an OS-56-4S engine because the nominal bore dimensions are very close to the O5. I thought this might provide some insurance against making inferior rings & experiencing running problems. I just assumed by matching the O5 bore & piston geometry to the OS-56, I would be good to go. What I didn’t appreciate at the time is that this construction path actually requires more exacting work on multiple fronts, but I’ll save that for later. I still intend to make my own rings because that’s part of model engine building. Whether it’s worth swapping them into this engine to see the difference remains to be determined. Because the liners are also cast iron, I assume they will run in together with the rings, as opposed to commercial RC liners which are typically hard chromed. I’m not sure I will ever fly the engine so I doubt I’ll wear them out between the test stand & trophy shelf.


----------



## petertha (Jan 20, 2021)

Pics of the prototype. If only I knew what was ahead of me LOL.


----------



## The_reach (Jan 20, 2021)

Looks to like its going to be an interesting build, look forward to following it


----------



## ddmckee54 (Jan 20, 2021)

I've wondered for some time if it might be possible to make a kind of a cross between a glow-plug and a spark ignition.  It should be possible to turn on the glow plug during the compression/power stroke and turn it off the rest of the time.  That way you'd only have the load on the battery for one glow-plug at a time, not all of them.  Your battery could be a lot smaller and your plug driver would only have to carry a fraction of the load.  At least compared to keeping all the plugs hot all the time it would be a fraction of the load.

I think it would be possible to either run a mechanical points/distributor configuration, or an electronic distributor-less configuration that would just require a crankshaft position sensor.

Don


----------



## petertha (Jan 20, 2021)

Don, I think this same hybrid glow plug / spark hybrid issue was already discussed in post #11 & possibly elsewhere?


			https://www.homemodelenginemachinist.com/threads/running-1-4-scale-v-8.32541/#post-346879
		


As mentioned, my own guess is you will never get a glow plug wire element to pulse on & off with sufficiently short duration to match the timing required of an engine. They are fundamentally different systems. In a spark plug the arc will jump the open gap when high voltage is applied. Its over with in a nanosecond? Glow is an inline resistor so once lit, it will have some defined thermal cool down period. At least that's how I visualize it.

The closest thing I've heard is glow plug igniter modules that deliver different current level modes like: high for start mode, med/low for low rpm mode, zero for running mode. I've heard the Seidel radial engine glow module works this way but haven't delved into to myself. I suspect throttle would be programmed to power glow power output maybe like a commanding a speed control to a motor. But I have never seen a timed on/off glow ignition configuration like you are wondering about. I think when you hear 'switching' or similar words its referring to electrical engineer speak - pulses on the voltage regulator side. But the end result is essentially steady power to the glow plug filament. Hope this helps.


----------



## petertha (Jan 20, 2021)

Crankcase 1. The crankcase is made from 2024 aluminum. My notes show that I started the first one in 2017, but there were a few binners along the way.

The turning operations went well, but I ran into issues cutting the cylinder facets. Possibly the setup shifted slightly. But I suspect it was my poor choice gripping the fixture OD with a 3J chuck and/or not properly confirming things where it mattered. Near the end of cutting depth, I noticed the facets were not breaking through quite equally to the internal master rod clearance groove. Not a good sign. Since the internal groove was turned in the same lathe operation as the OD, it could only mean one thing – radial runout. Therefore the facets were not equal distance relative to the CC centerline. Therefore each cylinder assembly would end up slightly up or down & a domino effect of bad things thereafter; piston geometry, compression ratio…. That that would never do. Lesson learned. Aluminum Gods = 1 point, Apprentice = Zero.

The dud part did provide some utility value. I used it to go through the motions of boring & finishing the cylinder skirt holes to tolerance as I was kind on new to boring head operations.


----------



## petertha (Jan 20, 2021)

Crankcase 2. Turning operations went good. Repetition builds confidence. This time I reverted to an independent 4J chuck for the radial operations to ensure no runout & tight grip. I also made some improvements to the mounting plate. Radial & axial runout was confirmed, this time the facets came out good. The cylinder liner holes were bored. Then while tapping the proverbial last hole (or thereabouts) for the cylinder flanges, I experienced the dreaded broken off tap. ACK!

It was entirely my own fault. The holes were blind end M3 thread. A bit finicky but nothing onerous. After feeling quite confident with my shiny new tapping head, I decided this would be a good application. However, in hindsight, I didn’t properly factor the over-depth allowance as the instructions clearly convey. So with tap firmly stuck in hole, what now. I tried drilling on the end with a carbide, no go. I tried heat. I didn’t have access to EDM or anything like it. After some forum Q&A and very convincing YouTube testimonials, I decided to try the alum solution. It was a disaster. The process slowly turned the part into something that resembled an artifact from the Titanic. The tap was eroded slightly smaller, but still there. Rather than take up more space, I’ll just insert a few choice R.I.P. pics if you want to read the original saga & we’ll carry on with the build. Aluminum Gods 2 points, Apprentice still zero.





						broken tap in aluminum cranckase
					

Dangit! 2 holes away from completion & I broke an M3 tap. I really cant say how, the preceding ones went perfectly fine & I did all the holes & tapping operation identically. It was a brand new, good quality tap, chip ejecting style which I've had excellent good results with in the past. Lots of...




					www.homemodelenginemachinist.com


----------



## petertha (Jan 20, 2021)

Crankcase 3. After 2 warm up exercises, this was the keeper. Well… maybe. Dimensionally everything was good but as I look back on the pics of so-so thready finish, I think my lathe was trying to tell me something even at that point. Forewarning of ominous events around the corner. Anyways, pleasant thoughts for now. This is how it crankcase making SHOULD have gone.


----------



## petertha (Jan 20, 2021)

Cleaned up a bit, nearing completion.


----------



## Michael Rosenbauer (Jan 21, 2021)

Hello Peter, nice to hear and see something from your project.
Looks great!


----------



## xpylonracer (Jan 22, 2021)

Nice work there Peter, the case looks very strong.


----------



## petertha (Jan 22, 2021)

Thanks for the likes. Nice to hear from you again Michael.R.

On my current crankcase I decided to drill/tap the cylinder flange holes right through vs blind. I figure the holes will be plugged with either a threaded bolt or threaded stud plus maybe a drop of weak Loctite for good measure & should provide some degree of seal. I'm going on the assumption the crankcase can never be under much vacuum or pressure because at any stage its rear end is connected to ambient via the inlet path from carb/manifold. So just trying to make it not be liquid leaky. Every RC engine I've seen has a collective puddle of oil residue in the bottom & suspect this will be no different. In fact I'm contemplating a removable drain plug. A standing puddle of fuel residue is generally not kind to parts susceptible to corrossion.


----------



## petertha (Jan 22, 2021)

Crankcase Details
The plans call for a tiny 1mm section O-ring groove recess in the front face of crankcase. I think the purpose is to prevent nose case bath oil from exiting along that joint, possibly through some of the faster holes. The gear plate mounts to this face and then the nose section mounts over the plate, both also with O-rings.

As mentioned, I’m still deliberating this nose bath lubrication method & intend to do some simple leak tests with the engine assembled to help me decide. I can still cut this O-ring groove, but I’m dragging my heels a bit. I find them to be a bit fiddly dimensionally so you end up with the fit. If the ring is slightly too proud it will take extra bolt-up pressure to compress enough & still mate the parts. If it ends up too deep in the groove & doesn’t get squeezed enough, then the seal is compromised. Also the groove occurs dangerously close to the facet edges & bolt holes.

So the plan on my radar is to first try making a thin Teflon / PTFE gasket. I found some material samples that vary between only .002-.005” thick. I’m satisfied that I can make pretty clean gaskets just using a scalpel blade along the edge of a simple CAD/plywood cut out template. I may have to make a simple punch for the holes, but surprisingly even drilling the material came out OK as long as there was backing material. A gasket should provide more surface area be re-usable with disassembly.


----------



## petertha (Jan 22, 2021)

The O5 plans also call for an O-ring groove in the crankcase under each cylinder flange. Curiously the O9 does not have these. It kind of has the appearance of an afterthought. But if it was deemed necessary, than why wasn’t it similarly incorporated into the O9 plans? When I drew up my plans I decided to make the flanges square with no external boss & extend the liners a bit deeper into the crankcase (partially for other reasons too). The liners have a sliding snug fit so hoping this will provide additional sealing area. Also I intend to make similar Teflon sheet gaskets under each cylinder flange.


----------



## petertha (Jan 22, 2021)

Before leaving the crankcase for now, I wanted to elaborate on the oil bath lubrication details. I mentioned the O5 design calls for the nose housing to be partially filled with oil. The cam plates, planetary gears & bearings spin inside this housing so bath makes great sense from that perspective.

This view shows the approximate oil level based on recommended fill up volume. Notice how the bottom set of tappets (cam followers) would always be submerged in oil. I envision even medium viscosity oil working its way out through the annulus gap between the cylindrical tappet & the bronze bushing ID hole. The tappets are sliding fit & perpetually moving up & down. So possibly even some light pumping action. Maybe any bypass oil volume is minimal & just migrates down the pushrod tube where it ends up in the lower covers. I’m not really sure. Obviously it must work because it’s common to the larger O9


----------



## petertha (Jan 22, 2021)

Here are some other methanol radial engines for comparison. The common theme seems to be that the gear plate mounted to front side of CC has openings to allow oily fuel it’s to carry forward & lubricate the gears, cams & bearings. There is no compartmental liquid oil bath like the O5 & O9.

OS Sirius


----------



## petertha (Jan 22, 2021)

Jung 7-cylinder radial (Jung-5 is similar)


----------



## petertha (Jan 22, 2021)

The Edwards radial has an integrated oil pump actuated off the crankshaft. Oil from external tank is directed to specific areas. It drains by gravity into a lower elevation sump where it is recirculated.


----------



## petertha (Jan 22, 2021)

I like the Edwards principle. I seem to recall the recommended fuel was straight methanol/nitro and either zero or low percentage (insurance?) oil added because of the pump. It’s too late to integrate a similar mechanical pump into the O5, it would require be significant modifications.

I’ve toyed with the idea of external electric oil pump. I suppose it’s maybe kind of a cheat from vintage standpoint, but so are glow plug drivers & other modern necessities. The engine wouldn’t look out of place with external oil feed lines to the nose area. But I know nothing about what kinds of pumps would work so any thoughts welcome.

But if I trust what I think I’m seeing of the mentioned designs which includes established commercial RC engines that probably see much tougher service, then all I would have to do is cut an array of openings into the front gear plate & it might closely resemble that arrangement. Remove the bearing shields as previously mentioned & fingers crossed that rear entering intake mist sufficiently coats the important rotating bits in the nose case.


----------



## Michael Rosenbauer (Jan 23, 2021)

Keep in mind, the gasket sheets change the compression ratio.


----------



## tornitore45 (Jan 23, 2021)

A note on the Edward 5 pump.
I built it to print but added the recommended springs because I had a feeling that all this little fiddly parts would not pump much.
I was surprised to see the oil running pretty fast and consistently when I run the engine. That double pump works great.


----------



## petertha (Jan 23, 2021)

Michael Rosenbauer said:


> Keep in mind, the gasket sheets change the compression ratio.


Exactly. That's why I'm trying to select material thickness as minimal as possible. The stuff I found to try is 0.1mm (.0039"). Maybe a bit less once sandwiched. I have seen the same material as low as 0.001" but just as convenient to get (for me in Canada). Initially I thought I could skim the difference off the bottom of the flanges but the way the assembly is configured now, the liners have a slight shrink fit & the liner skirt protrudes out of the bottom so flange skimming is not a good option. So any CR adjustment will have to come from the lip of liner. I'll have to go back to my notes but I think I'm still well in the (upper) range though so hopefully OK.


----------



## petertha (Jan 23, 2021)

tornitore45 said:


> A note on the Edward 5 pump....



I think the Edwards pump system was a smart idea on his part. Oil is directed to where lubrication is most needed & properly sucked away for re-circulation. I think I will spend some effort on the next methanol engine to incorporate a pump. I think the rule of thumb in methanol engines is if its fuel wet then its getting sufficiently lubricated with the pre-mix but I'd rather have more confidence.

Now that you have had some run time on your engine, have you noticed anything of note operationally? 

- I don't recall much for gaskets or O-rings on the Edwards plans but been a while since I looked at them. Did you do anything on your own engine for flange seals? How is the assembly for oil seepage when you run it? Do the rockers look lubricated or do you do them manually before a run?

- do you notice any kind of liquid (oil or spent fuel) loading on the lower cylinders? As in important to remove the plugs & turn it over by hand so no hydraulic lock?


----------



## Michael Rosenbauer (Jan 24, 2021)

By final assembly I will take a smal amount of Hylomar blue agent, to seal any necessary parts. At the crank case housing  i made groove´s for nitril O rings but I will set it also with Hylomar .


----------



## minh-thanh (Jan 24, 2021)

Hi *petertha !*
I don't understand how the engine's gears and cams work, can you or anyone explain it to me ?
The better ,if there are sketch images
Thanks !


----------



## Michael Rosenbauer (Jan 24, 2021)

The gear on the crankshaft drives the middle gear which drives the inner gear to the same direction like the crank. Inner gear and camdisk are connected.
Ratio of this gears turns a cam at the right time to the lifting lowing angels. Intake- compression - ignition- exhaust!
You find runnig scetches on GRABCAD type in RADIAL ENGINE


----------



## petertha (Jan 24, 2021)

Hi minh-thanh. As Michael says the spur gear on the crankshaft drives an identical gear on a 2 gear cluster. The smaller cluster gear then drives the internal (ring gear). The ring gear is attached to 2 identical cam plates mounted face to face, one for inlet, one for exhaust. They have an angular offset to one another to yield the correct inlet/exhaust timing. Each cylinder has a tappet (cam follower) sliding in a bushing & connected to pushrod which actuates valve rocker. I will have more pictures coming with all these parts & discuss engine timing too, but that's basically how the cams work on this style of radial engine.


----------



## josodl1953 (Jan 24, 2021)

I built my Edwards without an oil pump and kept the cam housing separate from the crankcase. I fill the cam housing with gear oil SAE 80 and it works fine. Leaks from the lower cam followers is minimal. Crankcase is lubricated by blow-by oil from the fuel . I made two vents in the crankcase rear cover  so I can flush the crankcase after running. Methanol and nitro can cause nasty corrosion if left in a confined space.

Jos


----------



## Vietti (Jan 24, 2021)

Because of the cam ring cam placement almost all radials are odd numbered so the cams don't do something unwanted at 180 degrees,see Petertha's 0024 jpg above.  I suppose most all know this but it took sometime for me to discover this.


----------



## minh-thanh (Jan 24, 2021)

*Michael Rosenbauer , petertha !*
Thanks !




petertha said:


> Hi minh-thanh. As Michael says the spur gear on the crankshaft drives an identical gear on a 2 gear cluster. The smaller cluster gear then drives the internal (ring gear). The ring gear is attached to 2 identical cam plates mounted face to face, one for inlet, one for exhaust. They have an angular offset to one another to yield the correct inlet/exhaust timing. Each cylinder has a tappet (cam follower) sliding in a bushing & connected to pushrod which actuates valve rocker. I will have more pictures coming with all these parts & discuss engine timing too, but that's basically how the cams work on this style of radial engine.



Thanks for the images, the images make it easier for me to understand !


----------



## petertha (Feb 8, 2021)

Crankshaft Intro

The O5 crankshaft was turned from a bar of 1144 SP (stress proof) steel. This is the first time I've machined this material & I don’t have much comparative experience to similar tougher alloys like 4xxx series, but I was pleased with the results. The material specs are: 83% machinability (1212 reference = 100%), 132 ksi tensile, 100 ksi yield, 27 RC hardness. It turns & finishes well with my offshore carbide inserts. But the important claim to fame by other engine modelers is that it’s less prone post machining stress relief distortion on parts like crankshafts with irregular geometry.

The crankshaft is solid, by that I mean the counterweight profile and crankpin are cut from the same stock (as opposed to a built-up crankshaft with separate components). While probably stronger, a one piece also means quite a lot of waste material removal to get down to the much smaller shaft OD area. Rough turning was relatively straightforward, I just took it easy for the most part. It was around this time that my complaining lathe threw in the towel, even with moderate DOC. The clutch started rattling (disengaging), the finish was progressively crappier & I could feel this was more serious. So, reluctantly I had no other option but to remove the stock before the critical finishing stage & deal with the lathe.

The repair was a long, drawn out process. I won’t go into details but some of the story is documented here
14x40 lathe power feed improvement

The problem likely originated on the factory floor – somewhat flakey design, skewed powerfeed rod & misaligned related driveline components. I hope I don’t have to repeat this anytime soon, but the upside is that it’s never run better & I have a deeper understanding of my machine.


----------



## petertha (Feb 8, 2021)

The rear end stock was held in 3-jaw and front end in live center. With the rough turning complete, it was critical dimensions time. There are 4 bearing races and a spur gear which are slip fit on various OD sections. In retrospect this was my first real go at having to produce OD’s within a couple tenths and simultaneously with good finish. My lapping methodology was kind of crude, & learn as you go, but eventually the job got done. It is important to let the part heat stabilize to room temp after turning because that can easily trick the OD measurement. Something I would now do when it comes to bearing fits on a CS or part with a lot of time invested is turn or utilize a dummy gage pin to establish the bearing fit beforehand, then use the same (quality) micrometer to translate that dimension to your part as you transition from turning to finishing or lapping. The last of the turning related operations were completed – groove for retaining ring and (hand) threading for the spinner nut. The part was removed from the lathe & band sawed to rough length.


----------



## petertha (Feb 8, 2021)

Crankpin Roughing
I decided to rough most of the excess material in the mill leaving a remaining square of crank pin material for finish turning in the lathe. This setup also allowed me to make a center drill mark to the exact crankpin throw radius and also drill/tap the 2 holes for the added counterweight slug fasteners.


----------



## petertha (Feb 8, 2021)

Crankpin Turning
Next I made an aluminum holding fixture that was a close sliding fit over the finished shaft OD. It has 2 through holes to match the counterweight tapped holes. It also has a milled flat on one side parallel to the bolt hole line, a reference surface for later. This fixture provided something for the chuck to grip & the bolts acted as kind of dog to transfer rotation. The crankpin center was dialed in with a DTI against a pointer rod extending from the tailstock.


----------



## petertha (Feb 8, 2021)

With the setup established, the crankpin was turned down to diameter as well as the rear face of the counterweight profile and a thin boss profile for the master rod bushing. I tried a different style of lapping tool which was kind of a squeeze clamp affair.


----------



## petertha (Feb 8, 2021)

Counterweight Profiling
Back to the mill. With the holding fixture still on reference surface & presented to the vise, the counterweight profile was cut out. Then the roundover profile was milled & hand filed away using a slip on guide bushing.


----------



## petertha (Feb 8, 2021)

Crankshaft Counterweight
The design calls for an additional counterweight mass which is bolted to the matching crankshaft profile. One of those 5 minute jobs that took 3 hours. It has a relief arc cut to accommodate the master rod, but its center occurs at a different center than the OD, so required 2nd setup in the 4 jaw. I integrated that registration point in the same fixture used to hold the crankshaft for crank pin turning. Brass face mills really nice with the sharp uncoated inserts used on aluminum.


----------



## petertha (Feb 8, 2021)

Some partial assembly pics of the crankshaft components at this point


----------



## Peter Twissell (Feb 9, 2021)

Nice work.
I'm always amazed at how spindly some of these crank designs appear, although they are clearly up to the job.
The crank for my radial is a monster by comparison.


----------



## Shopgeezer (Feb 9, 2021)

petertha said:


> The O5 crankshaft was turned from a bar of 1144 SP (stress proof) steel. This is the first time I've machined this material & I don’t have much comparative experience to similar tougher alloys like 4xxx series, but I was pleased with the results.



When I took machining classes oh so long ago the instructor told us to use stressproof whenever possible but lamented that it was getting hard to find. It seems to have all but disappeared these days. I would love to find some but all the suppliers I know don’t list it. It is even getting hard to find leaded steel. The gnarly cold rolled crap I end up with is hard to finish to any degree of accuracy. I’m sticking to aluminum brass and bronze these days.


----------



## Peter Twissell (Feb 9, 2021)

I'm not sure what is meant by "stressproof" in this context.
Proof stress is a measure of the materials yield strength.
When buying steel for anything with specific requirements for strength, workability, surface finish, hardening etc. it is worth looking up the available grades and their properties, then specifying exactly what you need.
My radials crankshaft is made from EN24T (817M40T), with counterweights made from much cheaper and easier to machine EN3B (070M20).


----------



## mu38&Bg# (Feb 9, 2021)

Stressproof is a trade name for SAE 1144 equivalent to ETG100.


----------



## Peter Twissell (Feb 9, 2021)

Thanks dieselpilot, I had wondered whether it was a trade name.


----------



## petertha (Feb 9, 2021)

I've also heard it called 'stress relieved' which is probably a better description, but 'SP' is what you commonly find it listed under.
This isn't the link I was looking for but if you scroll down has a pdf spec sheet (and some of the metrics seem to vary +/- by source I've noticed).








						1144 Stressproof Round Bars - A.E.D. Motorsport Products
					






					www.aedmotorsport.com
				




Anyways, it seemed like a good choice based on what I'd had read of others experience on more complicated crankshafts, like multi throw Vee or opposed where there was more non-symmetric material removal & they struggled with post machining distortion. I suspect this radial with simpler mostly axial layout could have just as well been made from 4140 but the price was going to be the same to me regardless. Another possible option to reduce the volume of waste material left in the swarf bin is buy rectangular bar so that the crankpin & some stub of counterweight was encompassed in the width & the thickness is just a bit more than main OD. But I think 1144-SP only comes in rounds, so it would be back to 4xxx alloy available in bars. I've also read where people have made cylinder liners from 1144-SP. I didn't myself, but thought it would be good to try with the extra slug. I think it would be good for tooling shanks & such as well.


----------



## petertha (Feb 9, 2021)

I forgot to include a cad section showing the crankshaft & various mated components.


----------



## petertha (Oct 10, 2021)

Sorry for the long lapse again. I will now continue on with the cam drive assembly. The O5 is similar to other radial engine layouts where the crankshaft drives a planetary gear reduction assembly, the output of which is connected to two separate cam plates. One plate is dedicated to intake, the other to exhaust where cylindrical cam lifters ride along the cam profile. As the cam lobe raises the lifter, the connected pushrod act on the rocker arms to open the valves.

The O5 planetary gear is a 4:1 reduction ratio. A 15-tooth module-1 crankshaft gear drives a 15-tooth intermediary gear which is sandwiched against a 10-tooth gear, which drives a 40-tooth internal (ring) gear. The intermediary 15/10 tooth gear cluster rotate together on an idler shaft. Because of 4:1 ratio, each cam plate has 2 identical lobes 180-deg apart for 2 complete (suck/squeeze/bang/blow) events per single cam revolution. The intake & exhaust cam plates are phased angularly to each to achieve timing relative to TDC. Both plates are attached to a cup which contains the ring gear. Here are some overview sketches. Hopefully this will make more sense as the parts & assembly are shown in real life. I will have more to say about intake/exhaust timing later on.


----------



## petertha (Oct 10, 2021)

The gear plate is made from 2024 aluminum. It houses one of the 4 crankshaft bearings on the rear side & also holds the idler gear shaft on the front, nose case side. The plate attaches flush to the crankcase front face retained with M3 screws & also snugly fits the crankcase ID with a matching boss. The plans called for 1.5mm OD O-ring seal on the internal boss & another on the lip OD to seal the nose case.

I mentioned earlier that the original O5 design called for the nose case chamber to be partially filled with oil to splash lubricate the gear & cam assembly. The O-rings are to seal this bath oil from the crankcase & the outside world. But I was becoming less comfortable with potential oil migration issues & dragged my feet on this matter for as long as possible. For example, even though the rear bearing was presumably left shielded I thought oil would eventually get in behind the shield, dilute the grease & ultimately leak into the crankcase. Then the risk becomes hydraulic lock on lower cylinders. Also, because the lower cam lifter bushings would always be submerged in oil, it seemed like another potential migration path out.

So, after a lot of deliberation, I finally decided to abandon the oil bath mode. Rather, I made a series of modifications to my existing parts & this gear plate was one of them. Therefore, you will see a mashup of old & new pictures, hopefully it’s not too confusing. I decided to subsequently drill an array of passage holes in the front plate to allow intake mist charge originating from the rear via the carb & crankcase, into the nose case & lubricate the gears & cams that way. This is actually the established lubrication method of other commercial & shop made radial methanol glow engines, so hopefully will prove to be the right decision. For added insurance I will make a threaded/capped port hole on the nose case to squirt lubrication oil in prior to running. I'll be careful during break-in runs to see how wet things are. The O-rings are already done & will still serve their intended purpose.


----------



## petertha (Oct 10, 2021)

The basic gear plate profile was turned from solid bar. The main diameters & bearing counterbore were done in one setting. The O-ring groove dimensions also need to be done at this point before removing the part. The grooves were a bit fiddly to obtain the right fit to the matching components. I’ve seen some O-ring groove formulas that get you pretty close, but in the end, it was a progressive trial & error thing. I used 70 durometer Viton O-ring cord & spliced a custom ring using CA glue. That part went amazingly well. If you ever need oddball O-ring diameters to make, I can recommend this as a cost-effective alternative.


----------



## petertha (Oct 10, 2021)

Pictures showing the stock gear plate design confirming fit to crankcase.


----------



## petertha (Oct 10, 2021)

Once the plate was machined, it was set up in rotary table for hole drilling. I trusted the CAD pitch circle calculation to drill & ream the idler shaft hole using mill DRO.


----------



## petertha (Oct 10, 2021)

Then I made an MDF fixture to hold the plate, return to lathe & counterbore the relief for idler bearing spur gear.


----------



## petertha (Oct 10, 2021)

Here are some pictures of the subsequent plate modifications to drill the array of oil mist holes. Of course, that required a new fixture to reestablish the geometry which would have been SO much easier the first go-round. I managed to get the 2 lower apertures slightly intersecting the gear cluster so hoping it will get directly misted.


----------



## petertha (Oct 11, 2021)

I purchased the steel module-1 spur gears from Maedler, the same company I got the internal gear from MÄDLER - your expert for power transmission elements
Originally, I contemplated making the spur gears myself. But these were reasonably priced, high quality & each gear requires quite a bit of modification. At my snail’s pace construction, this was probably a good decision in hindsight. 

For the crankshaft gear, I first machined a closefitting aluminum pot chuck in the lathe. Then swabbed the ID surface with acetone. Then without disturbing this setting, inserted the gear blank which was as a tight push fit on the teeth & back face. Checked the bore with a DTI, all good. Then I spotted some CA in glue among the teeth to prevent it rotating loose & a spritz of kicker. Then bored out the ID to fit the crankshaft diameter & faced/profiled to length. The steel was reasonably hard but machined well. The glue held things firm, even during interrupted tooth cuts.

Once the assembly was removed, my plan was to heat the assembly with light torch heat, expand the aluminum more, break down the glue & gear would drop out. It put up a bit more resistance than I expected but eventually parted ways with slight persuasion from a rod. The crankshaft OD was just a hair over diameter near the rear stop so a bit of lapping compound got the two parts fitting snug. The gear will be permanently bonded with Loctite retainer.


----------



## petertha (Oct 11, 2021)

The 15T idler gear blank was held in a 5C collet for opening up the bore & machining to length. The 10T gear was positioned on an axle fixture to turn down a portion of the gear which then fits inside the 15T bore. The inner gear bore rides on an idler shaft. The gear assembly will be bonded together with Loctite retainer.


----------



## petertha (Oct 11, 2021)

The gear idler shaft is made from 5mm O1 tool steel. The end has a M2.5 threaded hole for flathead screw that retains a brass end washer in position. Including some pictures of one of my (many) lapping trials. My experience with drill rod is that is always within the stated tolerance, but is often eccentric in cross section. So, the purpose of lapping here is to bring it to size with appropriate finish, but also make it circular section. Here I have a steel clamp with a thumb screw tightening nut. It holds a sacrificial aluminum lap, slit through & also some internal relief slots made with a jeweler blade in scroll saw. I have a selection of inexpensive (AliExpress/Ebay) diamond lapping compound of graduated grits. The method worked reasonably well. But I have subsequently come up with an easier, less messy tool which is now my go-to method. I’ll show that tool a bit later.

After lapping & parting off, I torch heated & oil quenched. Then into the toaster oven to tan brown. I discovered it is sufficiently hard because I discovered the countersink was a teeny bit shallow & had to grind it bit to deepen, because my HSS tool just rubbed it. All good, everything seems to run smooth.


----------



## petertha (Oct 12, 2021)

Cam Plates. I only have limited hardening experience with O1 tool steel & that was confined to relatively simple parts using a torch. I don’t have heat treating equipment, but I discovered a local fellow who does heat treating for knifemaker community. He has all the appropriate equipment & experience with the many flavors of air quench blade steels. Considering the work that would go into producing the cams & the form factor, I had visions of it distorting into a Pringle chip, or cracking across the internal holes. I figured successfully heat-treating knife blades would present a tougher challenge than my cam plates. So, I sourced the (Starrett brand) A2 from my local KBC dealer, choosing a bit thicker Imperial stock which had to be thinned to prescribed metric dimensions.

I made a simple aluminum fixture puck for the lathe with 2 threaded holes. After a facing the puck face true, the A2 stock was mounted with matching screw holes & brought to thickness. The ID was rough bored with annular cutter then finished with boring bar.


----------



## petertha (Oct 12, 2021)

The cam outline was band sawed roughly to outline but leaving 2 sacrificial ears with the original screw holes, which now served second duty to secure the part to the mill fixture. The ears correspond to where the cam lobes will occur. The lobe profiles are identical shape between intake & exhaust cams, but the four M3 mounting holes are angularly phased different to each other to achieve proper timing. One plate has M3 clearance holes, the other plate holes are threaded. Therefore, the cams don’t lend themselves to be stacked together to make both intake/exhaust plates simultaneously.

The rotary table was first zeroed to the quill center. Then the fixture assembly was positioned concentrically on the ID hole with DTI & also along an edge of rectangular jig plate. Now the M3 holes could be drilled as well as the array of larger holes. These holes were a bit of foresight on my part relating to the same possibility that mist lubrication might be in my future, because drilling these holes after the cams were hardened would be very difficult. So, I came up with a CAD pattern which I could also replicate on the ring gear cup which the plates mount to & this would allow mist lubrication to flow through from rear to front. I was a bit concerned these holes would be great places for the cam to crack during heat treating but it turned out OK. Actually, the plans called for larger holes & non-symmetric spacing so it was a bit of faith.

I used an endmill & rotary table to cut the main profile, which is the valve closed, non-action surface. Overall, it went according to plan. Just have to be careful about entering & exiting the cut accounting for RT direction & backlash. The lobe ramp profile shape was created by the radius defined by the EM diameter as per the plans.  You can see I have a small Sherline 4” RT clamped in my mill vise bolted to an intermediary plate held in my main 6” vise. I feel the RT was accurate enough but found myself doing light cuts because I could feel the cutting action on the handwheel. Next time I would use my larger RT which is a bit more solid.


----------



## petertha (Oct 12, 2021)

The cam part was released from the mill fixture & ears band sawed off. Now I could transfer to another lathe fixture, this time with a boss which fit the cam hole ID & retained with screws through the holes. Now I could turn the cam lobe OD which is the valve open segment. That just left a small radius to blend the ramp segment to the open segment which was done by hand. I didn’t take a picture but basically, I blued the part, scribed a line using a radius gage tangent to both surfaces & filed it to shape. That left finishing the outer profile with rubber abrasive in a Dremel.


----------



## petertha (Oct 12, 2021)

Once the cams were finished, I shipped them to the heat treat person along with some sacrificial coupons. A few weeks later they arrived back by mail. He verified the hardness & came as you see here. There was negligible distortion. They fit the ring cup the same way. The bolt threads engaged nicely so I was happy.


----------



## petertha (Oct 12, 2021)

Some partial assembly pics.


----------



## minh-thanh (Oct 13, 2021)

Thanks for sharing !
Does your engine pump oil out of the crankcase ?


----------



## petertha (Oct 13, 2021)

Minh Thanh, no there is no physical oil pump in this engine. Oil is pre-mixed with the (methanol) fuel like a typical RC engine. Intake charge (mist) enters from the carb/intake manifold at rear of engine. The mist wets the rotating master rods & link rods within the crankcase before getting sucked into each induction pipe to the head intake port. Also some mist continues forward into the nose case through the various passage holes in the ring cup & cam plates, which is intended to lubricate those parts. There will be a drain nipple at the bottom of the crankcase to allow any pooled residual oil to be vented. At least that is what I have seen on commercial radials like the OS. The concern there is accumulation of oil or fuel residue risking hydraulic lock of lower cylinders.

You might be thinking of the Edwards radial engine which is also methanol fueled glow ignition but has a dedicated pump that circulates oil to various internal components & also drains from a lower collection sump. It is actuated off a crankshaft lobe. Personally I think that is a better system, but it is incorporated into the original design. It would not be an easy add-on to this engine. Having said that, there appear to be many successful multi-cylinder glow engines without pump. I think in the methanol pre-mix engines, wherever mist can circulate internally is likely to be oily by circulation/blowby alone. Even up to the valves. At least that's the hope! LOL


----------



## petertha (Oct 13, 2021)

The 40-tooth module-1 steel ring gear blank I purchased needed to be reduced in diameter & also in thickness. I purchased 2 gears just in case, but managed to get it completed on the first try. I first made a lathe fixture with a shoulder boss sized to tightly fit the tooth crowns. With this boss feature turned, the gear was positioned to preserve concentricity. It was held with CA glue on the fixture back face a clamp plate sandwiching the gear to the fixture with a cap screw. It held sufficiently tight & the material machined quite nicely. I was able to turn the OD to size by eventually cutting both the gear & fixture cap until there was some remnant gears to trim off. Maybe there was a better machining sequence to accomplish this, but the end result doesn’t leave much of a gear one way or another. It worked out in the end.


----------



## petertha (Oct 13, 2021)

The ring gear cup is made from 2024 aluminum. It is supported on the crankshaft with the 2 smaller intermediary bearings. Once the timing is set, the ring gear is permanently bonded to the inside cup lip with Loctite. The cup has 4 countersunk holes for the M3 flathead screws to secure the cam plates. The cup was subsequently drilled with lubrication mist passage holes that match the holes in the cam plates so that lubrication mist can frow from crankcase into nose case & hopefully wetting everything in it’s path with oil film. Aside from careful turning to match all the fit tolerances, it was pretty straightforward machining.


----------



## petertha (Oct 13, 2021)

Ring gear cup machining.


----------



## petertha (Oct 13, 2021)

Subsequent modifications to add mist passage holes.


----------



## petertha (Oct 18, 2021)

Before leaving the construction aspect of gears & cams for now, this might be a good opportunity to discuss the engine timing. The O5 plans provide all the necessary dimensional information to construct the cam drive train, but the specification sheet did not express inlet/exhaust timing in terms relative to piston TDC/BDC. I’m not sure why some engine designers omit this information, but it is what it is. The instructions are also somewhat ‘abbreviated’ in terms of how to set the timing. Translation from another language probably doesn’t help matters. So, I wanted a firmer grasp of this stuff & also understand how the O5 timing compares to other 4-stroke (methanol/glow) model engines. Not that I felt qualified to modify it, but more for the sake of interest & future projects as well.

What follows is not intended as a detailed How-To. More of an overview of how I stumbled my way through this timing aspect, which is kind of a reverse engineering process starting with the parts drawings & references. Hopefully this will be of value to others.

First, one needs to know the gear ratio between the crankshaft (CS) & cam plate. As mentioned, the O5 planetary gear ratio is 4:1 which comes as a result of each gear-to-gear tooth count in the train from CS to idler cluster to ring gear. The rotational direction is also important. The O5 cams rotate in the opposite direction of the CS as shown by the sketch looking at the engine from the front.


----------



## petertha (Oct 18, 2021)

One needs to understand the intake & exhaust cams relative to each like a sub-assembly. The exhaust cam is to the front, intake to the rear, specifically orientated to one another with index bolt holes. Each cam pushes on its own dedicated lifter & respective pushrod / valve rocker. It is also important to be aware of the lifter geometry relative to the overall assembly. The sketch shows the O5 lifter action (red lines) extending radially from the CS center. Therefore, the cam contacts are occurring at different clock positions relative to the cylinder engine datum. This is important because other radials may orient their lifters differently. For example, if the lifter axis were coincident to the cylinder center (purple line) then the inlet/exhaust timing relative to TDC/BDC would be different on the exact same cam plate, all other things equal.


----------



## petertha (Oct 18, 2021)

This sketch is a bit busy, but shows how I then superimposed the lifter reference lines on the cam assembly. Then I determined the corresponding rotation angles marking the beginning & end of each lobe event which correspond to intake open, intake close, exhaust open, exhaust close.


----------



## petertha (Oct 18, 2021)

These numerical values were input into a homebrew spreadsheet from which I could calculate timing metrics in more familiar terms relative to TDC & BDC. I also determined valve overlap, lobe separation angle & made a plot to better visualize things.


----------



## petertha (Oct 18, 2021)

I recently found this website which is an excellent resource for model engines Sceptre Flight

What is particularly useful is the library of past engine review articles from magazines & other sources back in the day. Some reviews were very detailed. They disassembled, measured & photographed parts & assemblies & bench tested engines to provide useful power & rpm information. So just for the sake of a gut check comparison to my radial, I limited the data extraction to O.S. 4-stroke engines, although other brands are also represented. O.S. are generally considered to be reliable, powerful sport engines & encompass a wide range of displacements & layout’s including multi-cylinders. Of course, many design factors influence resultant engine timing which is outside the scope of this post. I have also been adding a few engines of interest here & there so don’t read too much into the individual data points. It’s kind of a work in progress. You can see the O5 timing as it relates to other engines. The overlap is relatively narrow & (I think) the values suggest conservative timing, but I’ll leave that for you to decide.


----------



## petertha (Oct 18, 2021)

Also, because there have been a few builds of the Edwards 5-cylinder engine posted on the forum & the two engines are similar in many respects, I did a timing plot overlay for comparison. If anyone spots any errors along the way, please let me know.


----------



## awake (Oct 19, 2021)

You are doing marvelous work - thanks for the detailed discussion of how you are solving the questions and problems that emerge!


----------



## petertha (Oct 20, 2021)

The nose case was machined from a round of 6061-T6 aluminum. I can’t recall if I chose incorrectly from my intention to use 2024 or it was my subconscious saying ‘odds favor a mess up somewhere along the way’. I decided to machine the outside profile first, then flip the part around to do the inside surfaces. This seemed like a better way to grip the part for ID hogging & hopefully concentricity on internal features.

The front was first drilled for the crankshaft clearance. Then a recess feature counterbored for the front bearing, which is a light press fit. The section profile contour was defined in the plans by various blended radii. I generated a series of corresponding X,Y intercept dimensions in a shop drawing. I cut these stepover terraces with a parting tool & then blued the surface. Then finished the surface with file & sandpaper until the blue was gone & finished off with a 3M pad. I left the part this way still held in the chuck & transferred to bandsaw vise where it was lopped off.


----------



## petertha (Oct 21, 2021)

The plans had some internal pocket relief (milling) features & contouring around the lifter area which I stared at for a long time. It looked very nice & it yielded a slightly thinner case section in certain areas. But to my eye actually seemed a bit thin around the front mounting bolt head recesses. So, I opted to modify the section profile a bit so that all the internal surfaces could be done in the lathe in one setting as a series of steps. This provided a bit more meat around the bolt heads, but same annular thickness around the bushing radial holes. It cost some grams of aluminum which I didn’t really care about anyways but erred on the side of bit more strength since it was 6061 & not 2024. I also wasn’t entirely clear about how the pushrod tubes were being retained on the conical lifter bushings, but trusted the plans for now.


----------



## petertha (Oct 21, 2021)

Next step was to chuck the part for the rear side internal cavity work. A spacer was positioned between the chuck face & nose as a mechanical stop. I wrapped some tape on the OD surface to protect it from jaw bite. The DTI said my 3-jaw was accurate, but in instances where required, an extra layer of tape under a jaw allows you to micro-shim. In hindsight the 4-jaw chuck would have been a better choice on 2 counts. You can dial it in exactly & also it provides one more gripping surface. This can be an issue on thin-walled parts where high initial gronk when the part is solid can result in slight deviations when the internal surface is machined out. Another thing I have subsequently learned is that not all tape adhesives play well with cutting fluids. They can dissolve, become unglued & I suppose risk the jaw grip.

I now favor an aluminum tape for protection applications like this. It also works well in shimming applications where its preferrable to pre-attach the material. I think this tape is used for furnace duct work.

So, after some material hogging, I just had to be careful as I approached the ID lip surface which becomes quite thin & must fit the gear plate OD properly c/w with its O-ring in place. It’s important to let the part cool to room temperature & take spring passes at different feed settings.


----------



## petertha (Oct 21, 2021)

Some interim assembly testing pictures


----------



## petertha (Oct 21, 2021)

Next step was to make a fixture to hold the nose case by the ID lip so that the part could be gripped in a rotary table. It has a threaded hole for a retention stud. After some trial fit-ups that were a bit too tight & concerning moments where the parts were firmly stuck together, I put a smear of anti-seize on the surfaces for insurance.

The fixture/part assembly was gripped in a RT & 4-jaw chuck & 5 bolt holes drilled & counterbored. Now the RT was flipped upright. I used a parallel & DTI to register what is equivalent to horizontal reference off 2 bolt holes & then proceeded to drill & recess the holes for the lifter bushings. These are offset on either side of center nose case center & also offset fore & aft corresponding to the respective cam plates positions.


----------



## josodl1953 (Oct 23, 2021)

Peter,
I think cam timing isn't an issue at all. Just  put the  engine  at TDC and the  camring at the point amidst the intake and exhaust cam lobe. I did this  with my Edwards ( as stated on the drawing, see sketch) and it works fine. 





Apart from this, I think the profile of your cam lobes is rather odd compared to the Edwards ( and other radials, for that matter). The Ohrndorf cams seem to have a  flat spot on top of the cam lobes whereas  the  Edwards lobes have a more hill-shape profile, causing a more smooth opening and closing sequence. Now I assume you  fabricate the cams according to the drawings but I would like your opinion on this matter.

Jos


----------



## petertha (Oct 23, 2021)

Hi Jos. Yes, hard to know exactly what the rationale was behind designers thinking. Maybe construction simplicity was a dominating factor. All we can do is compare the lift & duration profile relative to TDC/BDC & compare engines on that rough preliminary basis. My chart only speaks to beginning & end of intake/exhaust events. But when it comes to actual valve lift, one has to carry on & figure out the rest of the motion down the line - the lift of the cam followers translated to the effective motion of pushrods, translated through the rockers assembly & finally to the valves themselves. There are 3D angles (thus 3D motion) to factor & potentially non 1:1 lever ratio of the rockers. The fact that the O5 intake & exhaust cam profiles are identical, but are pushing against lifters which occur at different fore/aft planes tells me that the resultant intake vs exhaust valve lift itself must be slightly different. Now is that by design, or doesn't really matter in grand scheme?

The Edwards, as you already know, has it's cam lifters aligned & coincident to cylinder center whereas O5 draws a direct line from crankshaft center radially outward. So the cam profiles would look even if the timing were the same. I also noticed Edwards has a cam ramp up/down & more momentary max opening whereas O5 opens & holds that max open position for sustained period. I can envision for example a differently shaped piston top + combustion bowl shape combination may limit valve stroke into the combustion chamber, so if that's a limiting factor then maybe duration is opened up to compensate? The Edwards is a 20-deg conical piston top inside a similar shaped combustion chamber. The O5 is flat top piston with hemispherical chamber. I know from some of the Jung radial plans I have, the cams look more like O5 (sustained period of valve open) than they do vs. Edwards. Yet among this group, they all have comparable compression ratio & all appear to run & idle & transition well enough, at least from videos. So maybe not as sensitive as we think or within the range of other factors? You can see in the other comparison chart of RC engines, the radials are arguably more similar to each other but can differ quite a bit to other commercial 4S engines. Another Edwards build had a neat idea where the cam plate holes were slotted so the relative timing could be altered (but you are still stuck with duration). I think I posted (what I assume to be correct) Edwards timing on another post, but attached below FWIW. Hopefully this aligns with your assessment.


----------



## Bentwings (Oct 24, 2021)

josodl1953 said:


> Peter,
> I think cam timing isn't an issue at all. Just  put the  engine  at TDC and the  camring at the point amidst the intake and exhaust cam lobe. I did this  with my Edwards ( as stated on the drawing, see sketch) and it works fine.
> View attachment 130250
> 
> ...


Actually this is how we installed hot rod cams until specialty cams with much more radical timing and lift became available


----------



## josodl1953 (Oct 26, 2021)

Hello Peter, 
I wasn't aware of the fact that your cam followers were offset ,contrary to the Edwards. Having said this, the original radial made by Forest Edwards himself did also have offset cam followers.







I suppose  Robert Sigler  put the cam followers in line on his CAD drawings to make fabrication and timing somewhat easier.

Jos


----------



## petertha (Oct 26, 2021)

Interesting Jos. I've seen those pictures before but never spotted the different lifter orientation. The pushrod angle on the current plans is relatively steep by comparison, but obviously its not a problem. They run!


----------



## petertha (Oct 26, 2021)

The lifters (or maybe they are called tappets, I’m never sure) are made from nominal 3mm O1 tool steel. The internal end is a dome shape which runs along the cam plate profile. The external end has a partial depth 2mm OD spherical socket seat which mates the ball ended pushrods. The lifters slide up & down within bronze valve guides. So, I made some test guides first so that the drilled & reamed bores could be used as guides for lapping the lifter stock OD.

The male dome profile was formed by a ball turner accessory. Then the part was flipped in the collet, trimmed to length & the female radius profile made with a ball end mill. These lifters were sent at the same time to the same heat treat guy who did the cams so I wanted to get the finish as good as possible now. The lifters would have been easy enough to heat treat with a torch to ‘some’ level of hardness but I wanted them to be a few points softer than the resultant cam plate hardness so as to preferentially wear the (easier to replicate) lifters. I didn’t trust my repurposed toaster oven to deliver accurate temperature for tempering. The male end was polished by gripping in my Dremel chuck & lightly running in a shallow well drilled in MDF wood with a smear of compound.


----------



## petertha (Oct 26, 2021)

The lifter guides are made from bronze as per plans. The turning profile is pretty straightforward. I used my 5C collet chuck & sharp, uncoated insert like I use on aluminum. The holes were drilled & reamed. Its interesting when you make a bunch of the same parts, you gain an appreciation for variation. Some lifters slid nicely in the guides as planned, others felt a bit scratchy on entry or exit. The bore looked good. Turns out my handheld hole chamfer gizmo was leaving a micro burr, so I used a small polishing point to dress the edge.

The lifter guides will eventually get bonded into counterbored holes in the crankcase with Loctite. The conical shape is intended to accommodate the ID of the pushrod cover tubes which meet the guides at a mild 3D angle relative to the lifter axis. At this point I’m not really crazy about the metal on metal contact & mitered end. I would prefer some kind of rubberized or silicone material between tube & cone or somehow making a union. The plans call for the tubes being retained in the rocker perch with a small lateral set screw. I have some hopefully better ideas to test but don’t yet have a clear game plan. So, I have deferred this for now & maybe some divine inspiration will occur closer to final assembly. If I have to re-make the guides m, it’s not a big deal.


----------



## petertha (Oct 31, 2021)

I will discuss the cylinders next. Spoiler alert – in my case it wasn’t quite a straightforward path making 5 cylinders, liners & heads as per drawings in batch mode. I first make some tester parts as per design to get an idea of what was in front of me. This highlighted a few issues where I thought some modifications might be a better way to go. But these 3 components in particular closely integrate with one another, so a design change to one part for whatever reason very likely has a direct knock-on effect to the other parts they mate. I guess we will ultimately see if my decisions were right, wrong or somewhere in between. Overall, I tried to stick to the critical dimensions.

So why the departure from the plans?  The cylinder head (to be discussed later) is really the most critical part to have nailed down first because it encompasses many features (read lots of invested machining time). The inlet & exhaust ports are comprised of a smaller diameter gas passage drilled through into the valve cage. And a larger ID counterbore segment, threaded for a steel screw-in fitting which retains the tubing into the head against the counterbore ledge. This threaded style is used in other model engines, including commercial RC engines. Because the port axis is orientated to the head at an oddball angle in top view, the threads of the retention fitting are not initially fully engaged the way they would be like a bolt enters a nut. They must first hook up to a portion of the head thread for a few turns before becoming fully engaged around the port ID. At that point, it’s only a few more turns before the fitting bottoms out, sandwiching the tubing flared end to the counterbore step. No mention was made in the plans of a seal washer at the end of the pipe which I wanted to use particularly for induction pipe, but this would further reducing the engaged thread length. In other words, the design counterbore length is kind of short IMHO. To complicate matters, the heads also have a series of radial cooling fins cut through the port area which further reduces thread contact area. I figured with heat cycles & fuel mung & vibration, it might be asking a lot of these threads. I could select a finer pitch bottoming tap, but I was trying to avoid turning oddball metric threads in my imperial lathe for the matching fittings if possible. As it turns out, some imperial threads might be better candidates. This is a very longwinded way of saying that I really wanted the head to be slightly larger diameter to get more threaded meat in port area.

I modelled the new head in CAD. Everything looked good except aesthetically the head diameter was now extending over the original cylinder top diameter, not as pretty as when they were the same diameter. I’ve seen full size radial examples of both, but I preferred the original look & it solved other issues. So, I changed the cylinder crown diameter, which then meant a different taper angle to end up the same base skirt area dimensions. I also changed the cooling fin thickness & pattern to match my grooving inserts & a more nominal inch spacing pattern. The net change helped provide a bit of cylinder meat for what were shaping up to be slightly thicker liners. More on that later.


----------



## petertha (Oct 31, 2021)

So, with a new plan in place, on with actual cylinder making. They start out as drops of 6061-T6. I rough drilled them 7/8" in a batch mode. Then each is chucked & machined with most all features to preserve the setup. A boring bar was used to open ID to ~0.005" undersize. Then a 1.0625" reamer passed through so the ID would all be consistent diameter & finish in preparation for the liners.


----------



## petertha (Oct 31, 2021)

Next was the bring the crown and skirt flange to finish OD & turn the taper portion.


----------



## petertha (Oct 31, 2021)

Next was cutting the cooling fin grooves. I used a 0.043" wide Nikcole insert. They cut like a dream, just keep a bit of cutting fluid on it. Some groove depths are different. The top 3 are a bit shallower to stay clear of the threaded head bolt holes. The next 3 are limited by maximum DOC of the insert ~0.220". Then the remainder grooves are one constant base diameter which then & matches the diameter occurring above the skirt flange. All the edges were lightly chamfered using one of those HSS triangular scraper tools & cleaned up with fine 3M pad. Then parted off.


----------



## petertha (Oct 31, 2021)

I had one of those machinable expansion arbor blanks handy, so turned the main portion to match the cylinder ID with the bolt lightly engaged & also a raised step datum surface for the cylinder top to rest against. With the cylinder lightly gripped I could face the bottom flange & bring the cylinder to final length.


----------



## petertha (Oct 31, 2021)

Next, I turned a spacer collar so the chuck jaws could grip the head portion, because at this point the skirt flange is a larger diameter. Using a rotary table, drill & tap the 5 x M3 holes for the head bolts. These holes were then utilized to attach a rectangular fixture plate. The assembly was held in a vise so the flange could be drilled for clearance bolt holes & milled to the rectangular profile. I have a choice to use SHCS, or threaded studs in the crankcase with topside nuts on the flange.


----------



## petertha (Oct 31, 2021)

Partial assembly pics. BTW, the liners will extend through the cylinder bottoms and that portion is what mates the matching hole in the crankcase


----------



## petertha (Nov 13, 2021)

Next up are the liners. I should mention upfront that the path I took detoured a bit as things progressed, so the pictures might seem a bit out of sequence without some elaboration. When the CI liners were lapped to final bore & heat shrunk into the aluminum cylinders, the cylinders squeezed back under cooling. The bores reduced to the extent that they needed to be lapped all over again to return them to target dimension. I figured any shrinkage would be quite small, like within a few tenths, thus only requiring a quick lapping correction tweak. But they reduced more like 0.0005-0.0015” & also non-linearly down length of liner. Likely a function of the cylinder’s tapered shape squeezing it differently on the top vs. bottom of liner. Anyways the bottom line is my careful bore finishing work before mating into the cylinders kind of went out the window. I could have opted for something more like a slip fit, but I started to read articles suggesting some liner interference is required to achieve proper heat transfer. And as the engine warms up under running condition, a sliding fit will only get looser yet as the aluminum cylinder expands more than CI liner.

My initial workflow was to first establish the bores of the aluminum cylinders to a consistent diameter & finish, which was brought about by a reamer. It was an imperial size next closest to the nominal metric size specified on the plans. I was already modifying the cylinder barrels as mentioned earlier, so this change was incorporated. This resulted in a slightly thicker liner wall which I thought was fine, maybe even desirable. With the cylinder ID established, I would finish the liner OD to whatever dimension was required for the correct slight interference fit. The interference amount was driven by being able to place the mated liner/cylinder assembly into an oven at moderate soak temperature so that they would release from one another based on the different thermal expansion of the two materials. I’ve done this operation many times on RC engines with my small toaster oven to replace liners.

But let me back up a step. This is my first engine & I was intimidated by making good quality piston rings. This topic has been beaten to death in many other posts, so let’s just say I found myself at the same fork in the road I suspect others have arrived. I was aware of the Trimble ring method documented in Strictly IC magazine. There are also some excellent build posts on this forum where others followed Trimble’s procedures with great results. I find Terry Mayhugh’s (Mayhugh1) build posts to be particularly informative. Making the ring fixtures represents some work, but didn’t seem too onerous. But I didn’t have access to heat treating equipment or related experience which seemed pretty important to success. I wanted this engine to run & rings are crucial to success. So, to my thinking, there are 2 main paths:

(A) Bring all liner bores to ‘whatever’ diameter they arrive at, as long as each are identical to one another & appropriate final finish. Using that resultant measured bore as an input value, all of the dimensions to make the ring blanks & heat set fixtures can be determined using Trimble’s equations. The advantage here is that all the liners can proceed along together somewhat as a group. They receive the same tool setup treatment one after another, especially up to the latter stage of finishing where it counts most.

(B) Purchase commercial rings, assuming they can be reliably sourced. This solves the ring making issue. But you need to make the bores exactly the same as the liners they were intended to run in. The O5 is a nominal 24mm bore which happens to be the same as an OS-56 4 stroke engine. Therefore, it seemed like a good idea at the time in my case to purchase 5 rings, including spares for unforeseen replacement. So, I somewhat naively, went down this path. Although it seems like a good plan, in reality it’s actually more work & higher potential for mess up. At least for multi-cylinder engines where the count increases. The issue is the dimensional target – trying to stay within say 0.0001” bore target and simultaneously arriving at that target with the appropriate finish. If the bore is inadvertently exceeded for whatever reason, that’s kind of the end of the trail as it will no longer match the commercial ring. Next engine I will likely go the Trimble route.

When the rings arrived, I measured the cross section against the Trimble values & they were quite closely which is assuring. I also got a new OS-56 liner to closely examine for fit, finish & use as a dedicated glorified bore gage. And added a piston to obtaining corresponding dimensions like ring groove, crown & skirt OD’s etc. to replicate for my pistons. Thus, the shopping list expanded but I figured I could sell the piston & liner as spares one day & recoup some costs. As of today, several years later, they are still sitting in my box. :/


----------



## petertha (Nov 13, 2021)

So, onto the liners. They start out as drops of 1.25" nominal diameter Class 40 grey cast iron bought from Speedy Metal in USA. They arrive ~1.35" OD I think so you arrive at the good stuff under the skin. Previous to the real liners I also made some testers out of 12L14 & 1144 Stressproof. The 12L14 finishes beautifully but I was a bit concerned about corrosion in methanol fuel environment. The Stressproof machined well, likely a bit stronger & probably a good choice too according to others experience. But sourcing the appropriate diameter was more difficult at the time & sadly 90% of material core ends up in the swarf bin. CI seems to have a reputable track record in conjunction with CI rings. I’m sure wear will be just fine for my occasional running. CI is relatively inexpensive & available in progressive sizes for expected mess ups, so CI it was!

I took a skim cut to get through the crust, faced the end, then pilot drilled 0.375” to 0.875. On my prior testers I experienced a bit of harmonic ringing & minor chatter which I assumed was because I turned the OD to size first & then the bore work. This time I reversed & did the boring first while there was more meat on the wall. Seems to have helped but could also be CI itself vs the prior steel alloys. I found I could hold dimensions quite well as long as one account for any heat buildup. CI is a bit messy so I cover the ways.


----------



## petertha (Nov 13, 2021)

I used the thickest section boring bar with carbide insert & bored to 0.940” ID. This lands me with 0.005" left to remove for target 0.945" finish bore.


----------



## petertha (Nov 13, 2021)

I rough turned the main OD slightly oversize, then did the upper liner features. The crown is an extended lip with an undercut so the liner registers onto the cylinder top deck. Then I used some homebrew sanding sticks made from 2" wide MDF boards with wet-o-dry paper bonded with 3M spray adhesive. I found this to be an expedient way to remove the turning grooves & work the material down to size in a controlled manner. The board width spans the entire liner length which helps correct & minimize undulations that can result from traversing a narrower abrasive belt strip back & forth because the dwell time & tension can be different across the length. For reference the OS-56 liner was within a tenth OD all along the surface.


----------



## petertha (Nov 13, 2021)

The final 0.0010-0.0015" came off with a homebrew OD lapping tool of sorts. This was kind of an experimental venture driven by how much time it took me to achieve acceptable surfaces on my prior test liners. I hoped these generic lapping blanks could be utilized used for this job & future projects if they worked out. Commercial tools are available but they are expensive, especially in larger sizes.

The idea was to have some aluminum blanks cut with the radial pie segment slit pattern you see. Then they could be bored out to the requisite ID & either lap directly on the bored surface, or perhaps in conjunction with a sacrificial split lapping collar to get more utility out of the bore size, kind of like how a collet grips a part. I made a CAD drawing & send it to a waterjet outfit. They cut the slit profile including end holes leaving me to drill & tap for a cross screw for setting lap pressure. I tried different lapping compounds & settled on some cheapo oil based AliExpress diamond paste that comes in a syringe tube.

I guess I could say my lapping tool worked out OK in that any diameter undulations (hilltops) are worked down & the diameter can become quite consistent. But I find lapping to be messy business & best confined to removing small material thickness. It also requires a bit of hand technique like stroke & dwell time & re-charging the lapping goop & fiddling with the clamp tension. Then you have to clean everything spotless, measure at various spots down the length & go at it again. It all takes time. I left the last 0.0005" for 1000 & 1200 paper using my full width backing boards & in all honesty might be just as quick as lapping. Eventually I arrived there. It’s Interesting how CI can get a finish, eh?


----------



## petertha (Nov 13, 2021)

The skirt ID has a shallow chamfer to provide clearance for the rod motion. One last check of finish dimensions, lightly knock down any corner edges, then part off the liner. Then apply a single layer of protection tape, hold reversed in collet chuck & face the lip surface to final length.


----------



## petertha (Nov 13, 2021)

Onto finishing the bores. A while back I acquired a Themac tool post grinder (TPG) grinder & played around with it on my previous test liners. I now have mixed feelings about TPG’s. I suppose it suites this kind of application where relatively short length work sticks out of the headstock cantilever mode. Accurate surface dimension & finish combinations can be achieved with the right technique. If the work involves hardened materials, grinding may be the only way to go, but I don’t consider CI to fall in this class. I also had hopes of using TPG for several other applications & that’s where some shortcomings & complications become apparent, especially if the project involves tailstock support. The TPG assembly just wants to occupy the same real estate as TS assembly which really is difficult to work around. I also had a tough time finding suitable wheels, meaning the right diameter & grit & composition combination. I ended up buying a surface grinder wheel from KBC & had a water jet cutter make me a bunch of wheel blanks. I was a bit apprehensive about them blowing up but so far so good. Dumore is another popular name. I can’t speak for their wheel arbors but the Themac has an oddball taper that doesn’t match any common taper, seems to be unique to them. Ultimately, I figured it out, but suffice to say making your own arbors is more work.

Most of the time you will see a TPG lathe setup where people pre-align the lathe compound at a shallow angle & finely increment cross travel depth that way. The magic trig number for convenience is 5.739 degrees compound angle (off of spindle axis) which yields the relationship of 0.001” increment on compound dial equates to 0.0001” of cross bed travel, times 2 equals 0.0002” in bore increment. Just remember the same rules of removing backlash apply. And this is not exact because unlike a cutting tool, the wheel is slowly eroding in diameter as grinding proceeds. So you have to measure & re-calibrate more so than other lathe operations.

My compound leadscrew is in pretty good shape. But when I secure the compound dovetail between each pass, the clamping action itself can drift the actual position a bit. I’ve made some improvements to the lock, but it’s still there. So, I don’t completely trust this setup on my machine although I do like the fine incremental feed aspect. Alternatively, I made a fixture to hold a tenth’s reading dial gauge to bear against the end of the cross slide itself which directly measures Y infeed displacement that way. This removes both backlash & table lock issues simultaneously. A sensitive dial gage also acts as a sober indicator of machine vibration which is flowing through to the grinding wheel. The needle fluctuates on either side of the true reading. Ideally, deflection is low & somewhat dependent on where the indicator is mounted & how things are tightened down. I think the TPG is probably approaching the limits of my lathe rigidity & spindle bearing condition. If you don’t have dovetail locks, my opinion is that TPG might be the wrong weapon of choice because once the motor winds up, the sliding surfaces can become ‘buzzy’ & prone to free floating, even with a good quality TPG. A suitable DRO can measure displacement independent of dials so long as you have the right resolution. But consider even typical 0.0005” step increment on DRO display represents 0.001” of bore gone. That’s what made me a believer in a mounted analog indicator. So, after some trials I kind of considered the TPG as a ‘truing’ tool, not a finished bore tool. At least on my lathe & limited experience. That leaves the last thou or more for lapping but TPG is still a time saver. Whether this warrants the expense & setup of TPG is probably another discussion. So, who knows, it may get traded for a TIG welder one day which costs about as much & would see a lot more use in my shop, but that’s another story. What I REALLY need is a Sunnen hone LOL.

Back to liner grinding. I plugged off the back end of my collet chuck so grinding debris would not migrate in behind. I used a single wrap of tape on the liner OD for protection & gripped it in 5C collet chuck.

The wheel was dressed in-situ with a homebrew diamond tool holder. Cover the machine & use a vacuum for this operation please. Then it was a matter of selecting a low spindle RPM, power feed the TPG on low traverse setting & start opening the bore in small ~0.0005” bore increments. It is a somewhat satisfying experience to see partial patches being removed under grinding, meaning non circular sections features you thought were quite true by a boring bar alone. The liner never got warm because of low DOC & more time measuring & futzing. I tried a fluid but t didn seem to be adding any value, the wheel looked clean at these removal rates. The bore finish was ‘ok’ not stunning. The geometry & roughness seemed acceptable but I think it exhibited skip or maybe secondary vibration. I’ve been told my grit selection was too fine, that actually coarser would be better. Grinding is a science in itself. But they popped off pretty quickly. I have been making 6 cylinders, 1 guinea pig & hopefully 5 keepers.


----------



## petertha (Nov 13, 2021)

TPG grinding examples


----------



## petertha (Nov 13, 2021)

At this point I was ready to lap the liners using a brass Acro brand lapping tool and a tenths reading bore gauge. I used my OS-56 liner as a glorified bore gage setting tool.


----------



## petertha (Nov 13, 2021)

Many hours later of mind-numbing work I had 6 liners to a nice matt finish & within a tenth. And all this was basically a warm up run.


----------



## petertha (Nov 13, 2021)

Now we arrive at the nasty bit. I put a cylinder in the oven at 450F for a set time & dropped in an ambient liner with no drama. But as mentioned previously, once the assembly cooled, the bore had reduced differentially. About +0.0015” near the top & ~ 0.0005” near the skirt. So not only a significant bore diameter change, but the barrel walls were no longer parallel either. I returned the assembly to the oven & repeated what I’d done a few times already on the tester; heat up & separate to evaluate what was going on. Well, this time even a light love tap after heating was not removing them. This always worked with my test cylinder.

When I carefully remeasured all the cylinders, I had more questions than answers. Maybe because the new cylinder design had more mass. Maybe the reaming was not quite as perfect as I imagined. Maybe the cylinders relaxed a little post-machining because I could measure as much as 0.0005” oval in spots. Or maybe there are micro undulations in the surfaces kind of acting like a screw thread where the mean distance between hill tops is correct, but the surface itself can act like a secondary grip once the shrink has occurred? I decided I wanted these parts separated to be utilized so had to resort to light torch heat. They finally let go. The liner came out a light tan color but amazingly neither seemed worse for wear. They had the same dimensions as when they started out.


----------



## petertha (Nov 13, 2021)

At this point it was time to weigh my options. I already sunk some effort making the liner OD’s nice & consistent between one another. But the interference just seemed a bit excessive now. It was obviously shrinking the bores quite a bit. Had the liner bores remained unfinished at this stage, it would be of no real consequence, I could have just carried on. I no longer saw much merit pursuing the ability to swap in a replacement liner at some later time because I had already decided to make a complete 6th cylinder assembly spare to just bolt on the crankcase if something bad happened.

I tried mounting my test liner to an offshore expanding arbor held between centers in the lathe to see how easy it would be to somehow lap off a thou in a controlled manner. I’m not sure if I received a Monday arbor but it did not turn concentrically. I put a dial on the OD & it had about 0.002” TIR. I didn’t need more bad geometry problems so abandoned that idea. Glad I didn’t buy a complete arbor set!

So, I bought another Acro brass lap barrel to slightly enlarge the cylinder ID, thus reducing the amount of liner interference & simultaneously tuning up the surface geometry & finish. Hopefully I could use the liners as they were & reduce the amount of subsequent bore correction once shrunk again. Kind of bass-akwards to the original plan but seemed like the best option. This worked quite well. I haven’t lapped aluminum like this before with brass but it yielded a nice light matt finish & the bore gage said it was consistent down the length.


----------



## petertha (Nov 13, 2021)

Some trial & error futzing, eventually I arrived at combination where the liners could be re-inserted & the bores were undersized in the 0.0005 – 0.0010” range.


----------



## petertha (Nov 13, 2021)

So once again, the liner bores were re-lapped to target ID, this time as a mated assembly. I will now call these good. I had the bright idea to submerge the assemblies in my ultrasonic cleaner again to remove trace lapping compound. But very shortly thereafter I noticed some corrosion stains starting to form on the liner surface, so I immediately pulled them out. Swabbing & rinsing with mineral spirits is a better way to go. Then a light coat of oil for storage.

Next engine I would leave the liner bores unfinished (undersized) at the boring bar stage. Some of the interference surface conditioning could probably be minimized, particularly if there was no need to pull & replace the liner. The cylinder assembly would now have to be jigged so that the grinding / lapping / honing operation could proceeded on the mated surfaces.


----------



## cwelkie (Nov 13, 2021)

You are a very patient fellow with results to prove it!
A lot of hours but you are achieving your expectations and standards.


----------



## josodl1953 (Nov 14, 2021)

Hello Peter,
I wonder what  the point  is of a heavy interference fit between cylinder barrel and liner. I think the main objective is a good heat transfer between the two parts. I gave my Edwards barrels and liners  only a light interference fit and had very little deformation issues with these parts.

Jos


----------



## petertha (Nov 14, 2021)

Hi Jos. The short answer is that I agree with you. I don't think there is an advantage to excessive interference, in fact several potential disadvantages. For example, in my case where the cylinder shape is tapered & thicker wall near the top can contribute to different shrink force on upper vs. lower liner. Pretty much every RC engine I have disassembled requires oven heat to install & remove the liner, even when brand new.

My initial heat testing was based on a separate spare test cylinder which was the original design, not my subsequent modified design. But I think either reamed ID surfaces were not as consistent, or possibly they stress relieved a bit. In this kind of application, a half thou one way or another seems to make a big difference.

My longwinded story was just to say in hindsight I would not bother grinding & lapping the liner bore until mated to cylinder & completely stabilized. Unless you have good shop methods to very tightly control both OD & ID dimensions & finishes. Jung provides these instructions in his 5-cylinder engine which is probably not far off how mine ended up after lapping the cylinder ID (0.02mm = 0.0008”).

_To ensure optimum heat transfer, the cylinder liners must be shrunk into the cylinders. The inner diameter of the cylinder is about 0.02 mm smaller than the respective outer diameter of the liners to unscrew. After uniform heating of the aluminum cylinder by means of gas burner or hot plate (to about 200 ° C), the cold liners are inserted into the cylinder._


----------

