Jim Elliott

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All of a sudden my OS .91 FX prop drive hub just spins on the crankshaft. What can I do? Thanks for any help! Jim

big max 1935

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you probably lost the woodruf key that goes in the crank & in the slot on the drive washer. Max

Gray Beard

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Thank you Max, I forgot the name of the key, seems I'm forgetting a lot these days. Woodruf!!! Thanks. And yes, that is what it sounds like happened, I remembered that!!!

Jim Elliott

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I looked closely at the crankshaft and it looks like the key must have sheared off. It still has metal fragments in the slot it appears. Should I order a new crankshaft and drive washer with a woodruff key ? Or is there any other way to fix it.

Lone Star Charles

Jim

The Woodruff key is made of steel - The drive hub is made of aluminum. Check the metal fragments with a magnet to determine where they might have come from. As long as the crankshaft is still straight and the drive hub keyway has not been enlarged, then all you will need is the key. I have lost these several times in the past - its easy to do.

big max 1935

My Feedback: (9)

I would take the glow plug out , put the drive washer back on with a prop , tighten it up good & see if it turns over ok . Did you have a prop strike ? Very unusal to shear the key .Maybe the metal in the crank groove is from the washer turning on the crank . One other thing is a liquid lock & it sheared when you tried cranking it . You may have more damage . Max

Jim Elliott

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I ordered a couple of keys from TH that are supposed to fit . Do you install it by putting the key flat side down in the prop hub and then slide it onto the crankshaft, then tap it in, or what?

big max 1935

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It will come with a flat top & a rounded bottom. Make sure the crank slot is cleaned out very good . The rounded part goes in the crank . I would test it & the drive washer for fit & then what I do with mine is remove the key & put it back in with some RTV ,put the drive washer back on & your ready to go. Good luck , Max

Gray Beard

My Feedback: (-1)

The keys can be found at most any hardware store or auto parts store, no reason to mail order them.

Jim Elliott

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Thanks to everyone who posted.. It was a big help. Around here it is practically impossible to find a 1/16"x1/2" woodruff key, so I ordered some from TH. I checked at all the auto parts stores, and while they all had keys they were all too big! Thanks.. Jim

big max 1935

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One last thought ! If I remember right some OS engines came with a extra key . If you have the box & are lucky one may be in the bottom of the box . NAH! If your like me ,NO LUCK! Max

dbacque

My Feedback: (3)

The RTV is really good advice. The first time you remove a prop at the field and have the drive washer slide forward, dropping the key in the grass will make a believer out of you. It only takes one ruined day of flying to start sticking them in place. I also like to keep a spare in my flight box just in case.

I've always used Lock-Tite and it has worked for me but it can cook out of a hot engine. RTV makes a lot of sense.

Dave

Jim Elliott

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really!

Jim Elliott

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Update:

Well, I ordered a Woodruff key from TH, and installed it on the crankshaft rounded side down, then slipped the prop drive hub over it and was able to rotate it so I thought OK, this is fixed. But when I put the prop on it and tightend it down, it kept slipping, so I tightnened it a little more and then the crankshaft wouldn't rotate at all! I thought maybe there was something wrong with the prop drive hub, so I ordered another one.If that doesn't work I guess I'll send the engine in and have it checked over.

big max 1935

My Feedback: (9)

You should have a spacer between the front ball bearing & the drive washer, if gone the drive washer will rub the front of the crankcasse & lock it up. you must have lost it also . May find one that will work at a good hardware store it needs to fit the crank & hit just the inner race of the bearing only. Max