Ohrndorf 5 Cylinder Radial

[petertha]

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]

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]

Some partial assembly pics

[Kim]

Wow!  Very nice work Pertha! The cams look beautiful!  Did they just come back the nice black color?  Or is that the color of hardened A1?  Regardless,it looks great.

Kim

[petertha]

Thanks Kim, yes that's the way they came. I'm not quite sure how far the black actually penetrates. It doesn't scratch or buff off easily. I guess we'll see after running. I know he quenches A-steel blades between slabs of ground aluminum to quench & also help prevent distortion. My memory is foggy now but he also mentioned salt bath. Would that be for the secondary tempering stage? I've been meaning to call him back because I will have some more parts to do. Unfortunately timing didn't work out for a shop tour, I would have liked to see it.

[petertha]

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 a 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]

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]

Ring gear cup machining.

[petertha]

Subsequent modifications to add mist passage holes.

[Admiral_dk]

More beuatiful parts and nice description of the proces of making them 

I got one question though - as you can't move the cams nor the rest of the gears - did you use a slow setting Loctite, so you can keep on 'turning the assembly until you are happy with the timing ?

[90LX_Notch]

Excellent work.

-Bob

[Mike R]

Nice work, I always follow along on radial builds!

[petertha]

I got one question though - as you can't move the cams nor the rest of the gears - did you use a slow setting Loctite, so you can keep on 'turning the assembly until you are happy with the timing ?

Thanks for the compliment. I haven't timed the engine yet, that part is coming, hopefully before hell freezes over LoL. The plan is to fix the crankshaft gear and also fix the idler gear cluster together face to face. That secures that relationship & leaves the remaining ring gear OD temporarily able to slide within the ring cup ID, thus cam plate pair can rotate independent of the crankshaft in this setup mode. But since the cams are bolted together through the cup, they cant vary between each other. I will make an arbitrary witness line across both ring gear & cup edge. The business end of the engine and one cylinder stack are temporarily assembled. Then an indicator probe  in the glow plug hole to identify TDC. The target cam position occurs when intake & exhaust are mid way of their 20-deg overlap relative to TDC. So comparing this actual event point (indicated by valve lift) will reveal how far out it is in CS degrees. Divide by 4 equals how much to rotationally adjust the ring gear relative to cup using the witness line as reference guide. Hopefully converge after a few iterations. Once convinced, make a suitable sacrifice to the engine Gods & glue the ring gear in this position & mark the intersecting teeth. At least this is my plan, reality may have something different to say.

I'll have more to say about timing in a few posts. I was curious to figure out what the exact resultant engine time actually was & how that compared to other engines. The plans didn't specify this. I mean intake/exhaust open/close relative to TDC, BDC etc.

[Roger B]

Looking good     

I have a similar set of Chinese diamond lapping pastes 

[petertha]

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.