Extreme clutch

[JonMann]

Have a new extreme kit that I just completed, have about 10 flights on it now. Last flight the clutch gave out, have a couple experienced MA guys I fly with who recognized the problem right away and the first thing we checked was to see if the clutch had overheated - no signs of it, clutch bell was cool to the touch, no signs of dis-coloration on the bell. The only thing we could see wrong with the clutch in the heli was a slight wobble/movement up & down with the clutch bell, but this was very slight and we thought that maybe the o-ring had gone wrong (or I forgot to put it in). Took the clutch assembly out last night, o-ring was there and looked great, clutch shoes and liner looked great, the only thing wrong was the the clutch bell had seperated from the bearing block. The bearing seems to OK, but I beleive the clutch bell is not suppose to come off this bearing block, at least not without some force, and this will just basically fall off in your hand if you remove the starter shaft.

I have this in a box on the way back to MA, but real curious about what went wrong here, and how this could have caused an in flight clutch failure? Any ideas??

[Dr.Ben]

Jon,

Can you tell me what exactly happened when the model was in the air?

The release of the pinion from lower most bearing block bearing sometimes occurs when the parts weren't cleaned thoroughly prior to assembly and/or the primer wasn't correctly applied. The problem isn't common. It can also happen when the fan runout is excessive or the engine wasn't installed in the frames to run square to the driver base. The latter has a "whipping effect" (yes, even with the driver bearing in the system) on the entire clutch stack and can loosen any and all loctite joints.

Ben Minor

[JonMann]

Dr.Ben,

Engine went to high RPM, lost all headspeed, and basically auto'd it down.

Fan was balanced before installation. Don't have anything to check the run-out though. I had the guys I fly with who are experienced with these go thru my whole set up before I started flying it and looked good to them. Everything had worked great up to this point, no signs of excessive vibration or anything like that. It was flying great, then just all of a sudden let go.

On dis-assembly everything was tight and no un-usual signs of wear, nothing to really indicate what might have gone wrong other than the clutch bell being out of the bearing block.

I am willing to accept that I did something wrong in building this one, first Fury I've put together (give me a Raptor and I can build it blindfolded). Just trying to figure out what happened and what I can do to prevent this in the future. Drives me crazy not knowing

[Dr.Ben]

If you are DOUBLE DAMN CERTAIN the clutch liner is still firmly glued inot the bell, I would be a little suspicious that the auto hub was slipping. I've heard of very, very rare instances of that occurring. The clutch self tightens on the driver hub, as does the pinion. If the liner is intact, there is no way that clutch slipped enough to allow the engine to unload like that. That's why I wonder about the sprague. The pinion popping loose fromt he bearing isn't right, but it won't begin to cause the drivetrain to slip.

Ben Minor

[Shannon Davis]

The clearence between the clutch shoe and liner is .007" new. I think when my started to slip a few weeks ago it was at .023". Contacted MA and they said .021" is the max allowed. I think these numbers are right- but my memory is only about as long as my pecker.

[Dr.Ben]

I can see where nearly 12 thou per side would slip, esp with a big disk and big block, but his clutch assembly is so new that I don't think that is as much of a concern in this case.

New clutches are about to be beta tested, BTW. Will retrofit into current frame styles with little or no modifications to the frames. New clutch and bell, same driver and bearing blocks.

Ben Minor

[Russ McC]

Dr. Ben is right if every thing was going along fine and all the sudden the engine revved and the head slowed then either the liner came loose in the bell or the auto sprag bearing has come loose in the main gear or is slipping. Did you explain the symptoms to Min Air in a letter with the clutch? If not you better call them and let them know and you may be sending the auto unit back also. Keep us posted. [/b]

[JonMann]

I am certain the clutch liner did not fail, and it wasn't even glazed over like some I've seen. I ordered a whole new clutch set-up and installed that last nite, but going to pull the main shaft and check out the sprague before I try to fly again.

How would I know, what should I look for in the sprague?? Bench testing it last nite it seems to all be good, bolts, pins everything in place and tight.

BTW, thanks for the help/support.

[Russ McC]

Good Question JonMann,

I have never had an auto unit fail, still running some of the first ones released but I have friends that have. The one that comes to mind was hard to detect, even if you held the head on the bench and revved the engine the thing would not slip but it would cut loose in the air and down it would come. What happens is that the outer race of the sprag bearing comes loose in the unit and slips/spins. The new units like yours have set screws in the side that help to hold the bearing in place, maybe even Look Tight, don't know for sure on that one. Maybe you can disassemble it and tell

[JonMann]

Spoke to Tom at MA (finally got someone on the phone back there, been trying all week) and he was pretty sure -- based on my description of the problem -- the fan came loose on the engine. Definitely something that makes sense. Gonna pull it apart and he says if that happened it should be obvious on the collet., he said I might need to another washer to pull the fan tighter on the crankshaft. Seems to be the best explaination I've heard so far.

Will let everyone know what I find.

[Russ McC]

Good idea, I never thought of this as it happens very seldom, at one time not long ago the auto unit would be more likely but sense they have fixed that then the fan might make more sense. However I have heard of even the new auto units failing.

[JonMann]

It was the fan, spun on the collet. Alot of brass shavings in there. Need to order some new parts :?

Again, thanks for the help

[Russ McC]

Happy you found it!