Ohrndorf 5 Cylinder Radial

[petertha]

I made sets of brass head shims from various stock thicknesses between just in case.

[petertha]

Hello Peter. You could try opening the exhaust valve tappet gap and ride higher up the exhaust cam lobe.
Mike

Good point Mike, I neglected to mention that option too. That essentially shortens the timing duration bars visually on my little chart & ideally misses the TDC. I reviewed the recommended O5 rocker/valve gap & then went on a bit of mission checking other engines. O.S. has had the same dimensions since the dawn of time & were actually a bit under mine. If I recall, the Jung engines have a wider gap on exhaust only, maybe suggesting elevated temperature effect? I'm kind of skipping around my timeline, but the subsequent runs with modified piston valve relief crescents fixed the issue completely. No more contact. So the head shims never went in but the 0.002" Teflon gasket under the cylinder flange did.

Also, I made my valve stems flat topped with just a tiny chamfer, another thing I didn't really think much about. The rocker pads are of course curved but it seemed to me at full deflection it could have been pushing on the crest of teh valve stem. I'm pretty sure one of the commercial 4S engines I had apart had domed valve stem tops, maybe this factors into things? Splitting hairs here but I will pay more attention to this stuff on subsequent engines.

[petertha]

A few more pictures to get caught up to present day. On subsequent running sessions, the engine continued to smoothen out & 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.

[petertha]

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.

[petertha]

I made a new shaft with an integral end flange to retain the gear cluster that way. The advantages are it eliminates the bolt & washer business which could come loose one day & runs dangerously close to the back of the ring gear plate as is. The disadvantage is that the shaft is somewhat permanently bonded into the gear plate with Loctite. A tradeoff I accepted assuming I could again use local torch heat to remove it, even though it put up a fight coming out. My plate was undamaged but I think if it comes to that I’d make a new plate out of steel with a meatier shaft, although it can’t get too large a diameter ~6mm? just based on the inner diameter of the 10T gear.

I didn’t take a good picture but I drilled two ~1mm oil holes into the 10T gear & 4 holes in the 12T gear. I also drilled two axial oil bleed holes through the gear plate on either side of the idler shaft, hoping to get lubrication from the crankcase chamber into what becomes the back face of the 12T gear. Both ends of the gear have a washer made from brass shim stock. I am happy to say this seems to have worked. Yet another run & teardown showed the shaft was nice & oily with the idler spinning freely. Lesson learned.

[Admiral_dk]

Looks good and I really hope that you have solved the Lubrication issues with this 

Per     

[Roger B]

The first run sounds good   

I like the way you are very methodically working through the various teething problems   

[Laurentic]

For some reason I have been quite erratic in reading & following this thread, and for some reason thought I was completely up to date, but today found I still had quite some pages to catch up on, so have just read to the current end.

I have to say this build has impressed me. The attention to detail in both the machining and also the thought processes and reasonings why along the way, the fixtures devised and set up displayed, have all been so enjoyable to read and see in the photos, and so informative, and the end result of a beautiful engine a joy to to behold.  Loved the video too, lovely sound running.

I have learned quite a lot and have bookmarked this thread as a reference, to help me in the building of the radial I am engaged in.  I will be reading through this thread again, for sure. 

Thank you Peter.

Chris. 

[petertha]

Thank you for the nice compliments, Chris. In all fairness my posts were pretty spotty over an extended timeframe so it would be fair to surmise at many points 'he gave up', 'no, looks like he's back again' haha.
I suspect more reasonable people would have started with a single cylinder & then progressed with a multi cylinder, but it is what it is. Eventually I got over the goal line. I'm thankful of this forum & all the talented people posting their builds & sharing of knowledge. I look forward to your build!

[bent]

What Laurentic said goes for me too.  Glad to see this one run, if maybe not perfectly yet.  The video clip sounds wonderful, you should be quite chuffed with progress to date.