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Sprag clutch dragging?

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tatters
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Joined: 05 Jan 2004
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PostPosted: 11:24 - 01 Oct 2012    Post subject: Sprag clutch dragging? Reply with quote

Last month l replaced the starter sprag clutch on my BMW G650XC which had failed, this incurred the replacement of the free wheel and sprag retaining ring as the failed sprag had worn theses two parts at a cost of £300 in all. Evil or Very Mad


Now that this all has been replaced the bike now starts with no grinding banging noises unlike before but when l shut the engine off l can hear a clicking noise from the sprag as the engine comes to a stop, it does,nt make this noise when the engine is running but only when the engine is turned off and it spins down. Could this be the sprag dragging? any ideas how to correct this as before the sprag failed there was no such noise.
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hmmmnz
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Joined: 22 Aug 2006
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PostPosted: 11:30 - 01 Oct 2012    Post subject: Reply with quote

its how they get worn, zip you can do about it, it a kick back froom the engine,
the old rotax motors had a de-comp lever so you could kill your engine like that, which would save the sprag, no such option on the water cooled motors im afraid,
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jjdugen
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Joined: 03 Jun 2011
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PostPosted: 11:33 - 01 Oct 2012    Post subject: Reply with quote

Sprags work on the principle of centrifugal force, basically, as the crankshaft spins, it forces the sprag bearings into a curved housing, removing them from contact with the crank. A light spring behind each bearing pushes them back into contact with the crank when the engine stops.
New springs can allow the bearings into contact with the crank at low engine revs, generally, they weaken slightly with a bit of heat and age. As long as they are not gripping it should be OK.
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