Checking Sprag clutch operation.

by Jeremy Jordan in 912 / 914 Technical Questions 12 years ago

Hi there guys and gals, first time poster here, I hope its not too silly a question to begin with....

Here is my general discussion question for the experts.

After reading a bit on these forums about violent kick back problems and the associated sprag clutch remedies (amongst other fixes) for the 912ULS 100Hp engine, I was wondering this; can a sprag clutch be tested for serviceability whilst installed in the engine? I can't find any reference to such a procedure in the maintenance manual, and as far as I can tell the heavy maintenance manual only talsk about removing/dismantling/installing.

I guess what I am asking is can I test the sprag clutch for serviceabilty without dismantling the engine? If so, how?

Any thoughts on this discussion topic would be appreciated.

Re: Checking Sprag clutch operation.

by Roger Lee » 12 years ago

Roger Lee

125 5.12k 4.53k

Hi Jeremy,

It's rare the sprag clutch has an issue. If you have kick back it is usually something else. Such as poor carb sync, wrong idle adjustment, giving it throttle to start, poor slipper clutch friction,poor battery condition. Those are the most common and easily fixed. There are a few more, but also more rare to be the problem.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

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Re: Checking Sprag clutch operation.

by bill martin » 12 years ago

bill martin

10 757 0

Jeremy,

Not much you can do to check a sprague clutch. You can pull the starter off and stick your finger or a screwdriver in the hole and try to turn the freewheel gear. It should turn in one direction only. This still doesn't tell you much about the condition of the clutch unfortunately. Sprague clutches are simple devices. They look like a roller
bearing only the rollers aren't round. They are usually shaped like little milk bone dog biscuits and set in the races at an angle. (That's the only description i could think of) When either race is held stationary, the other race can only turn in one direction. Its a simple device and not much can go wrong with them. Sometimes they will wear and slip after many, many years of use or they will just suddenly self destruct: a very rare occurrence. Like roller bearings, they are not repairable, but are relatively easy to replace. 99% of the time, the problem will be one or more of the faults Roger mentioned.

Bill.

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Re: Checking Sprag clutch operation.

by Jeremy Jordan » 12 years ago

Jeremy Jordan

2 4 0

Thanks for the replies gents, much appreciated. I personally do not have any of these kick back problems, simply opening a topic for discussion. I hear about people having these kick back problems where changing the sprag clutch out fixes the problem (or at least the owner believes so), and the only literature I can find refers to changing it out in toto, as opposed to checking in situ...I suppose in retrospect changing the clutch out is the last thing looked at due to expense.

I understand what Bill says in relation to the construction of the clutch (having dealt with them on other aircraft types), and his thought process is logical. I kinda thought simarlarly to be honest, although I was hoping there might be a torque figure required to turn the engine that I could hang my hat on....

JJ

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Checking Sprag clutch operation.

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