I published this in the Navy Carrier Society many moons ago. Some disc valves have only one hole for the crankpin. Having two is not necessary to make the engine run backwards. It just gives you two options on where you can position the carb. If you started with a new, normally assembled engine, after removing the backplate screws, you would simply rotate the backplate 90 degrees without disturbing the disc valve. Trouble is, I 'm not certain which way to rotate it. I think you rotate the backplate clockwise when looking at the back of the engine. It's correct when the intake closes somewhere around 60 degrees after top center when rotating the crankshaft in the direction you want it to run.

Drum valve rear intakes are easily identified by the drum being in the center of the back cover, like a small rear crankshaft. Disc valve intakes have the intake hole offset to one of the four corners.

If that .65VR-DF isn't quite powerful enough for a sport/nostalgia model, I came across a .91VR-DF recently. It's missing a drive hub, Woodruff key, and the 9A carb but the rest looks like it would run long enough to tear you out of your shoes....   I kinda think the .65 would have the horses to do the same?  My thought would be to upgrade everything: lines, bellcrank, controls, and put a safety cable around the case and tied to the 'crank mount. And make sure that van that Paul talked about hiding behind has interior panels, too.

Quote from: Dave Hull on June 28, 2024, 10:46:47 PM
If that .65VR-DF isn't quite powerful enough for a sport/nostalgia model, I came across a .91VR-DF recently. It's missing a drive hub, Woodruff key, and the 9A carb but the rest looks like it would run long enough to tear you out of your shoes....   I kinda think the .65 would have the horses to do the same?  My thought would be to upgrade everything: lines, bellcrank, controls, and put a safety cable around the case and tied to the 'crank mount. And make sure that van that Paul talked about hiding behind has interior panels, too.

Based on some comments I found on the RC forums from guys trying to use that same engine on some RC pylon racer or something, I should be more worried about props coming apart than anything!!

After I was given a box full of parts that allegedly was an OS .91VF, I looked around on-line for a parts list. Of course, you get sucked into looking at videos....  There are a few of those that show pretty insane speeds and flying. I wouldn't want to be anywhere on that field near one of these (on a speed plane). You'd likely need a carbon prop, or at least glass, just to keep it in one piece. Even for a .65 you might need anchor chain to fly on? Respect.....

Quote from: Dennis Holler on June 27, 2024, 05:19:37 AM
If I went that way, I might be able to set up a jig on my lathe toolpost so I could clock it correctly. BTW, the box on this one is stamped 1989, so I assume it is definitely the later drum style?...

I would lay it out with ink and scribe marks then use a stone in your dremmel tool to cut the slot. Slot should be 180 degrees from the factory slot. That drum is hardened and won't play well with end mills. Try not to over heat it.

MM

Dave,
You aren't wrong!!
I wasn't kidding early on when I said I might need the speed pole to hang on too lol

MM Good point on the hardness.  We are a ways from that though.

The slot should NOT be 180 degrees opposite the original slot!  It should be a mirror image of the existing slot. Whatever distance the crankpin slot is from the edge of the port opening, the new slot should be the same distance from the other side of the port opening. In reality is should be close to 90 degrees.

That's interesting. Any reversable drum rotor or rear disk valve I've ever seen has two slots 180 degrees from each other. You did mention turning the back plate, maybe that's the difference?

A disc valve with two opposed pin holes is so you can clock the venturi position two different ways. Upper left and lower right, for example. One always seems to fit the airplane better than the other. Having the backplate 90 degrees "out of phase" is what screws up the timing and makes it run backwards.

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