gtbjbell(at)gmail.com
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 Posted: Sun Jul 02, 2006 6:07 pm Post subject: Re Sprag Clutch |
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Thanks Duncan for reply.
Problem started about twenty hours ago with an increasing vibration winding back to 5000 revs down to 4000. We are talking a vibration that would travel up the back of the seat and down through my legs. But only at those revs. It was becoming worse so first step ( after checking prop balance and replacing the engine mounts) was dismantling gearbox. Found one of the disk spring (part no 2 in Heavy Maintenance Manual Page 95 fig 146)) had been installed the wrong way. That has been so for about 400 hours. There was also a lot of metal bits in the oil tank (912 uls). We suspected that this was a washer. Reinstalled the gearbox and the vibration was dramatically reduced, but still there. I suspected paranoia or perhaps that the gearbox problem had been amplifying a vibration somewhere else!
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15 hours down the track and without warning engine would not start.
Symptoms seemed to be as soon as there was a kick in the cylinders of the slightest nature the starter would let go, allowing the engine to “Kick Back”. The only way I could get it started was to reduce the choke to nil, and advance throttle to about half way. Totally contrary to how I have been starting it which was as recommended ie full choke throttle just cracked.
Hooking up another battery made no difference.
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Scanning Matronics site struck on sprag clutch problems, which seemed logical on research. The clutch was letting go on the slightest kick which was just before tdc allowing the engine to kick back in a very unpleasant way. By using half throttle and no choke the engine wasn’t firing so readily allowing the revs to build up a little and then starting.
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I removed the engine and sent it to dealer in Australia and they found the circlip on the sprag clutch has come off and been broken into pieces.
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There is a directive for the circlip to be replaced at 1200 hours but I suspect this could be an issue before this in some circumstances.
What I don’t know is whether the springs in the gearbox being incorrectly fitted are a primary cause or whether they are unrelated.
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As far as I can gather the springs would mean that the amount of travel would be reduced when the dog gears start to engage. The correct tension was there but there is no way to check the travel? I can’t logically see how that may affect the sprag clutch except to perhaps kick back a little more violently because the tension on the dog clutch would build up fairly quickly with less travel.
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So now we go looking for more bits of circlip and hopefully finding the source of vibration.
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Expensive!
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Any comments greatly appreciated
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Regards
Geoff Bell
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Slepcev Storch
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