Prop hub help needed.
 

I have never retained a flywheel. I will for initial testing on this one. It is a Craftsman 29cc 4-stroke. I know it is a wimpy engine. Someone else used this engine in a 1/4 BUSA fokker d-7 and was real happy. I am building that exact plane. The idea of it sounding cool appeals to me. I am interested in running it with the minimal time imput, at first.

From the pics you can see I have it stripped down. The front of the flywheel is flat. If I make a bushing with a knurl to hold the prop it will spin against the prop hub. What is the most expedicious way to prevent that. I am thinking one of those nasty looking lock washers with a dozen or so radial teeth.

If if gives reasonable power I will probably set it up with electronic ignition and carve off all the un-needed bits like the other one. It was my "practice" case. Unfortunately the jug is ruined from water inside. I did not nottice that soon enough. Swapping the case is probably not an option. The bearings and seals are super tight and difficult to remove and install. I think they must have used an arbor press with depth stops.

RE: Prop hub help needed.
 

Some Craftsman trimmers used a Briggs and Stratton 4 stroke. Is this one of them?

Others will have better ideas for keeping the prop driver from slipping. I guess I would drill and tap the hub for two setscrews that tighten against flats ground on the crankshaft. Position the setscrews 90 degrees apart. However, if you plan to convert to electronic CDI, then maybe the internal or external tooth lockwasher would work for trials. The hub/prop driver as drilled for the CDI sensor magnet will need to be positively retained against rotation to keep the ignition timing fixed. Good luck

RE: Prop hub help needed.
 

" Some Craftsman trimmers used a Briggs and Stratton 4 stroke. Is this one of them? "

I am not sure. I am not feeling the joy on grub screws. I bet they would slip and mar the shaft.

My initial thought was to use a couple of pins that mate between the flywheel an the hub. It is easy to make them match up if you use shortie pins with a center punch ground on the end. You get an exact mark that way. I have some of those agressive lock washers and it looked plausable. The long shaft would help with the inevitable misalignment. I guess if it slips I can do the pins. If I were getting fancy I would mill a slot in the flywheel and a protrusiuon on the hub that mated in the slot.

RE: Prop hub help needed.
 

If you create 2 flats on the crankshaft at 90 degrees to each other, any mars that the screws make won't protrude beyond the periphery of the shaft. That would also provide a more positive method of locating the flywheel than the two screws alone. This is the same idea that spaceworm gave you. It's done in industry for the same reason. You could also put some Loctite 242 (the blue stuff) on the screws to keep them from vibrating loose.

RE: Prop hub help needed.
 

I'd use the pin method...It's easy and foolproof. I've done that exact same thing with great results.

John

RE: Prop hub help needed.
 

I really don't think a hub tightened up against the flywheel would move. I've done it many times. If you are really worried, clean the mating surfaces well and put some Loctite on them....

AV8TOR

RE: Prop hub help needed.
 

A fancy lock washer and a ryobi EI hub and there you go. Starting a new post on funny walbros with the non butterfly...........