Engine crank shaft is too short.

Stuka Stunt Main Forum · 8 of 8 known posts recovered

Gary Weaver · Sep 30, 2003 09:41 AM

Engine crank shaft is too short.#0 source

I have an interesting problem. I am building a new airplane with a full fuselage. The OS Max 40 LA engine is all the way forward with the venturi up against the 1/8" plywood nose of the fuselage. The plywood nose is a 2" diameter plywood circle with a 1" hole for the engine to stick through. The engine sticks out 1/4" past the plywood. The spinner drags against the front of the fuselage. The fuselage is not finished yet. The plans call for a piece of 1/4" balsa to be glued to the front surface of the 1/8" plywood on the nose. I can use 1/16" balsa instead of 1/4" balsa to save space but the spinner is going to drag even worse. I could cut 1/8" off the front of the venturi and move the engine forward another 1/8" but that will be a lot of work. I have several other spinners and they all drag on the fuselage. I can put some flat washers on the crank shaft and make it work but there are no crips on a flat washer to keep the prop and spinner from slipping. Is there some type of extension, washer, or spacer I can buy and put on the front of the engine to make the prop and spinner stick out about another 1/4".

Gary Weaver

LNeumann · Sep 30, 2003 09:50 AM

RE: Engine crank shaft is too short.#1 source

There are 1/2 inch extensions and 3/4 inch extensions, but I don't know of 1/4 inch (maybe somebody has one??) I do have a half inch extension here (made by Fox), and if you can move the engine back a little, this should work and give you more room to get at the venturi to choke or needle to twist as well. Or just add a little larger spacer to the nose to accomodate if your engine is mounted and "stuck" in that location.

Leonard Neumann

Randy Ryan · Sep 30, 2003 10:01 AM

RE: Engine crank shaft is too short.#2 source

If you have access to a lathe or know a machinist just make a spacer up, it can be knurled to stop slippage. I've done is and even made custom prop nuts with a center pilot (spiggot) and the front end threaded to accept the spinner screw. As long as the fits are close and the part concentric you can do almost anything you want up front.

Randy Ryan
AMA 8500
SAM 36
I fly 'em all and love it!

Bigiron13 · Sep 30, 2003 10:29 AM

RE: Engine crank shaft is too short.#3 source

LAST EDITED ON Sep-30-03 AT 10:36 AM (CDT)

If he already has the engine as far forward as it will go, perhaps he can slip it rearward enough to permit the 1/2 inch extension to fit right in.. I have a large number of Fox brand 1/2 and 3/4 inch shaft extensions . Let me know if a 1/2 inch will work Gary. Slide the engine to the rear of the engine compartment as far as it will go, and measure from the face of the thrust washer to the front of the plane INCLUDING the 1/4th inch balsa front ring called for. If the space is over 1/2 inch, then a 1/2 inch spacer should work just fine.
Bigiron

Added: What part of the engine is protruding past the plywood ring?? Just the front end of the shaft, or part of the front end of the crankcase?? If it is the case, then put the thrust washer on and a short stub of a propp with the spinner backplate behind it and then the spinner and see if there is room. Seems to me that there should be more room from the front of the venturi and the front face of the thrust washer than 1/8th inch. especially on an OS. Seems as if something ain't right here.

Bigiron

Bigiron13

Heavy Stunt · Sep 30, 2003 11:03 AM

RE: Engine crank shaft is too short.#4 source

Gary,

This is a recuring adjustment issue for me, so I've worked out my own method. It also comes up when you want to change from a flat backed spinner to a plastic spinner which has 1/8 inch inset.

What I do is laminate 1/64 ply as a spacer. You can use a prop washer as a pattern. 1/64 ply can be cut out with sissors, glued with CA and attached to the back of the spinner plate to get your desired clearance. The ply compresses enough to grip the thrust washer but is hard enough to resist prop tightening.

I have also used prop washers that have been knurled with a dremel tool as a spacer.

Remember: "An average screwdriver is better than a hammer for driving screws; but if all you have is a hammer everything looks like a nail!"

Bruce Hunt
Salem, OR

Will Reeb · Sep 30, 2003 12:03 PM

RE: Engine crank shaft is too short.#5 source

One technique that is simple and effective is to cut some pieces of eighty grit sandpaper the same size as your drive washer and using a 1/4" hole punch to put a hole in the center, you can then use these to shim the spinner backplate outward until you get correct clearance.

Will Reeb

Currell · Sep 30, 2003 12:36 PM

RE: Engine crank shaft is too short.#6 source

As Bigiron said, I have a ton of them, too. Let me know which one you want. Currell

SRiese5283 · Sep 30, 2003 01:44 PM

RE: Engine crank shaft is too short.#7 source

WHY can't you cut the nose ring to make the engine fit? Can you round out a small area for the venturi?.

Scott(this is why I don't use ply nose rings) Riese

Scott Riese