View Full Version : Rotary Valve Engine help

07-07-2008, 07:48 PM
I made the rotary valve engine from the june/july issue of machinist workshop, and it visually came out awesome, all parts were made identical to the mag. One thing i noticed about the article was that some of the diagrams and pictures didn't match at all, mainly with the crankshaft. When it was time to fire it up, it wasn't even close to running. It seemed that pin on the crankshaft was in the wrong location, i changed it and it actually ran for about 5 secs then that was it, i can't get it running again. That was with about 20 pounds of pressure. I've taken it apart to check my changes and they were just. nothing leaks. I just can't figure it out, has anyone made this engine and if so did it run? Thanks.

07-08-2008, 12:20 AM
I'm building the engine, but I'm not finished yet. I looked at drawings again, looking for an error, ( which I should have done the first time thru!), and it seems that the long flat on the pressure inlet side of the crankshaft doesn't extend far enough toward the crank disk to uncover the I/O passage. It should extend to forward edge of the passage or to at least 0.187" from the rear of the crank disk. As drawn it stops .230 form the crank disk.

Thanks for letting us know about this. I would have fallen into the same error and been just as annoyed.

George Bulliss
07-08-2008, 09:03 AM
Unfortunately when I made the drawings for the Rotary Valve Engine I made a mistake in re-working Walter Yetman’s drawings. I drew the 4-40 tapped hole on the crankshaft 180 degrees off from where Walter had it. This should have no effect on the engine other than reversing the rotation. To the best of my knowledge, this is the only item in the drawings that deviates from Walter’s design and photos. The corrected drawing of the crankshaft will be in the next issue.

The length of the flat was drawn exactly as Walter had dimensioned it, and I assume built it. The crankshaft does have .030” of play built into it, so there can be some obstruction of the inlet (not total) when the engine is run. The long inlet flat can safely be extended to take care of this.

I hope this helps you and I am sorry for any frustration this mistake caused.


07-08-2008, 11:05 AM
Thanks a million for the great replys, if i rotated that pin 180 degrees then wouldn't that just make it run backwards? Also jstinem could you tell me exactly where you put the pin? maybe post a picture of it. Im going to take a look at the flats today and see what i can do. Thanks again for the help.

07-09-2008, 01:10 PM
I extended the flat as sugested, put it back together and again it would run for a few seconds then it would stop. raising the air pressure while it was running would help it but not for long. Its like once its run it won't again unless i take it apart and rebuild it. I really am not sure what else to try. If anyone has gotten it to run could you tell me how much air pressure it took and if you had any troubles?

07-09-2008, 03:39 PM
I haven't done crank yet. I think the pin goes where the drawing shows it so that the flats are vertical and I/O passage is closed at top and bottom of the stroke.

07-09-2008, 09:28 PM
Its like once its run it won't again unless i take it apart and rebuild it.

Are there any self locking nuts on the motor? The reason I ask is I had a similar experience with the extra fat shackles I designed for the Evil Pinto. Shoulda used a shoulder bolt but I didn't have a lathe then, so I settled for a self locking nut that I tightened just enough to get the sideplay out.

During operation the leaf movement would gradually tighten the nut, bind the shackle, and we'd be riding the Always Loose Pinto once again!

It took me awhile to figure this out but eventually I realized every time I took it apart and put it back together again .... the back end would stay behind me for awhile. Sounds a bit like yer motor .....