Ohrndorf 5 Cylinder Radial

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congratulations on a great build and a great start. What joy it must have given you after such Alot of work. I am still trying in vain to get martins's single-cylinder engine working but to no avail while still working on his 4 cylinder boxer engine. Well done you should be very proud of your achievement.

Regards
Andy
 
I concur the above! Congratulations on a first time starter! - Those are more rare than preferred, but prove how good an engine builder you are. To get all cylinders firing first time without valve/piston leaks and low compression is a great achievement. Testimony to the build quality.
K2
 
friend of mine did a vid on it thought you might like to see it
 
I think I did about 5 runs of a couple minutes duration each. I didn’t want to push my luck any further the first outing. Mostly what you will now see is lots of oily pictures from initial teardown. The components looked acceptable, but I also discovered some near miss problems which I’ll discuss in more detail. The good news is there appeared to be a decent oil slick on all the internal parts. Oil residue was migrating sufficiently forward in the engine to lubricate the cam plates, gear train, front bearings & rod assembly either by blow-by or induction charge. I did see quite a bit of cast iron ‘dust’ entrained in the oil which would be quite abnormal for a commercial engine break-in. It doesn’t look very nice but I couldn’t feel anything one could describe as grit by just rubbing the oil residue between my fingers, more like a dark watercolor like stain. For now, I chocked this up to bedding in new rings within shop made cast iron liners. Of note, this blackness diminished more & more with every subsequent run but I stopped taking pictures.

The cam plates showed shiny skid tracks from the lifters wearing through the black heat treat coloration, more like polishing but no grooves. I could also detect some unequal contact wear thickness near the rise & fall cam fillets, but too early to comment on that.
 

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On my last runs I noticed a few cylinder flange screws loosened again after I had already tightened them the prior run. This may have been contributing to what my ear said was rougher running. One of my pushrod tubes was starting to jiggle around, probably as a result. Another good reason to stop while ahead. A floating cylinder is a bad thing. Thankfully the M3 threads were still in good shape but this issue required attention.
 

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General Parts Condition
 

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The #1 piston assembly looked pretty good overall. Lots of lubrication, no shiny wear areas or hot spots. The ring looked like it was just starting to wear in evenly enough around the periphery. A few vertical scratches on the piston here & there but nothing of consequence. However, I noticed a little divot on the piston top which I assumed maybe from particle ingestion or something, but on closer inspection looked remarkably like a crescent shape valve impression. It was on the exhaust side only. I immediately checked around the edge of the edge of the exhaust valve but could not see any deformation of feel a burr. As I proceeded to each cylinder I saw more or less the exact same impression on all piston crowns. Not good. I immediately suspected my cam timing was perhaps incorrectly set a gear tooth off, but my witness marks were correct… unless I somehow messed up the clocking from the initial get go. I also noticed considerably more valve gap on the exhaust rockers than was pre-set. I’ll return to this issue under remediation, but I think I used up one cat life. This could have been much worse.
 

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Remediation. First the easier stuff. Here is my initial makeshift drill starter. It mostly turned the engine over OK to where it would fire, but the prop engagement pegs were mangling the delicate trailing edge root despite my attempts to rubberize it with tubing, heat shrink & electrical tape to help snub the contact. I was concerned about weakening the prop to the point of it breaking.

My spinner nut fell off a few times which caused a few Keystone Kops episodes of locating parts in the grass, so I made a more robust wrench to tighten.
 

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After subsequent runs it was becoming obvious the drill starter had to go. It continued to chew the prop and had more difficulty turning it over as compression improved. I also suspect as the engine began firing, the drill’s gear drive was probably limiting it from free running until I could withdraw the peg drive, which is probably not healthy vs. a one-way clutch mechanism or freewheeling motor with power off. I searched for gear reduction drive RC starters & realized the RC world has changed. There are some big boy starters for much larger, typically 2-stroke engines. I was aware of Kavan planetary gear starters used on RC 4-strokes back in the day, but they are no longer made. Eventually I found this PGD reduction starter from Just Engines in UK. I bought a dedicated 4S (14.4v) LIPO hard shell RC battery pack & made a plywood carrier frame. So far it has worked very well. Fortunately, the silicone cone could be flipped to expose a smaller diameter hole, so I made a matching, lager spinner nut.
 

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I actually made a tester Teflon gasket for under the cylinder flange earlier but elected to omit them initially. I wasn’t too keen about using Loctite on the threads if it could be avoided. I sourced some 0.002” thick sheet so it wouldn’t affect CR very much. As it turns out, the gaskets did some good. The screws thereafter stayed intact on subsequent runs, so maybe it provided a bit of conformance to the prior metal on metal contact?
 

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The exhaust valve indentation on the piston tops was a serious issue to address. My first suspicion was that I had incorrectly placed the ring gear cam plate assembly onto the idler gear cluster off by a tooth. This would have the timing effect of lagging the exhaust valve closing beyond TDC (black bars on the timing diagram). This might explain why there was no matching intake valve indentation on the intake side of the piston. All pistons had the same exhaust only mark dent. One would think altered timing would mean rougher running, but I really had no smooth/rough reference experience yet. It seemed to idle & transition reasonably well but this was my first rodeo. I didn’t take it beyond half throttle for more than an occasional blip. But it turns out, I my cam position was indeed correct, my original witness alignment marks were correct. This engine is relatively simple to set up & verify in this regard. Exhaust valve closure & intake valve opening occurs equally either side of TDC.
 

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So, I commenced measuring all the contributing dimensions (there are many). Rod throw, piston height, cylinder deck height, cam lobe rise, valve clearance… Everything was within a thou of drawings. I did deviate slightly from drawings by decreasing the valve seat width, but net effect actually increased the valve cage submergence up into the head chamber & served to provide even more valve clearance.

I did a little bit of CAD motion study & concluded there was indeed theoretical clearance but it was actually quite close which I never bothered to consider before. If I was seeing the effects of valve float or temperature increase, this might add up to several thou & that seemed to be the extent of valve strike impression.

I’m really not sure but in any event, it needed to be dealt with, so I considered my options. I could add a head shim & gain some valve clearance that way, but at the expense of compression ratio. I estimated I was nominally at or under 9:1 but CR drops to 8.6:1 with only 0.005” shim or 8.3:1 with 0.010” etc. Maybe I had sufficient CR to spare but it seemed counterproductive to chase that option if the interference represented the same 0.010” confined to a tiny, localized impression area.

I could add a shim under the cylinder flange which raises the head from the fixed piston throw. That has the same CR reduction effect, but I was already contemplating some kind of gasket under the cylinder flanges to help with metal-on-metal mating & bolts loosening.

The other option was to cut extended crescent shaped recess pockets into the piston tops aligned to the valve strike area. I couldn’t go too crazy on this depth wise, limited by the piston crown thickness, but on paper it bought me significantly more potential clearance with minimal CR change. I could always still do the shimming if required.

I still had my piston holding fixture used for milling the rod clearance pockets. The fixture has a through hole for the wristpin, so that would self-align the piston orientation. Then it was a relatively simple matter of angling the piston/fixture in the mill vise to the valve angle & dropping down an endmill to increase the pocket dimensions. I did the other (intake) side the same just as a precaution & smoothened the edges with rubber abrasive. You can see the before & after net result.
 

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I made sets of brass head shims from various stock thicknesses just in case.
Rather than planting a like on the pics (and possibly missing one - - - grin!) I will do it this way.

I like your work and your procedures - - - - well they will make it easy to follow your story
if I choose to make such a girl myself!!

Thank YOU very much!!!
 
Peter
Congratulations!!
Thank you so much for sharing this stellar build with us ! Your detailed write ups on parts and fixtures to your great photos really make it feel like I'm in your shop :) Well done and very much appreciated.
It must have been really exciting to see it come to life even if it did surprise you a bit :) A testament to your attention to detail and all the testing of components beforehand, it paid off in spades!

Please keep us posted on what else you find and I can't wait for more video, even if it is in the spring. I will continue to follow along.

Thanks again

Scott
 
A few more pictures to get caught up to present day. On subsequent running sessions, the engine continued to smoothen out & I could also reliably hand start if still warm. The cylinder flange bolts remained tight & no more valve/piston competition for the same real estate

But I had another unexpected incident that could have been much worse. Another cat life consumed. After a number of runs the engine basically quit from medium throttle. As I turned it over by hand, something was obviously very wrong. It was very stiff through the rotation. No grinding or clunking noises but lots of resistance. On the drive home I thought a seized bearing might explain this. Under teardown, everything looked heavily lubricated & much clearer, much less black soot. All the bearings seemed fine. With the ring gear cam plate assembly off I could spin the crankshaft freely.

But what became obvious is the idler gear assembly was seized on its shaft which extends off the gear plate. I’ve included an earlier build pic to show the stock configuration. On the front of the shaft is a teeny bronze washer, spot drilled to accommodate a M2 flathead screw. I could still get a feeler gage between the washer & front gear indicating the running gap was still there & the bolt was still secured with Loctite. But it took some persuasion to get the gear cluster off revealing a scored & heated shaft. That then had to be removed from the aluminum gear plate with heat & persuasion.
 

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I never really cared for this washer/screw arrangement but assumed it was necessary for disassembly, but it actually isn’t. The crankshaft can just exit from the rear with its gear still on the shaft & disengage from the idler gears axially. My temporary conclusion was that the steel gear running on (hardened/tempered O1) steel shaft was not getting sufficient lubrication axially through the shaft/bore annulus.

So, I decided to sleeve the gear cluster bore with bronze as a better material & also drill some teeny radial bleed holes through the roots of the gears to lubricate the shaft for good measure. It was a bit of crap shoot that oil would want to migrate inward to the shaft when the gear rotation would want to sling it out, but I was hoping an oily coated gear might squeeze some oil into the holes, kind of like a rudimentary oil pump mode.

The next challenge was cleaning up the badly gouged gear bore, but I had precious little material left before I encountered the axial key pin, which was in fact a HSS drill bit slug. For reference the small gear is 10-tooth & large gear is 12-tooth M1 running on 5mm shaft. I utilized my gear fixture & stopped boring when I got to the pin, turned some bronze & set it in with Loctite.
 

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