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How to check the Sprag Clutch?

  • Brian Mollerup Sørensen
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2 months 1 week ago - 2 months 1 week ago #15970 by Brian Mollerup Sørensen
Brian Mollerup Sørensen created the topic: How to check the Sprag Clutch?
Hello.
I have this 912ULS engine that I'm doing service and repair on ones in a while.
The engine has now 1100+ hours and have experienced starting problems lately.
Carbs, batteries ect are checked and I suspect that the Sprag Clutch is damaged.
It certainly sounds like as the starter is only engaged for a few revolutions and then disengages from the crankshaft and continues to turn and then engages again when the starter rpm reduces close to zero.
This last engagement sounds really bad.
Like the sound from a car manual gearbox when one tries to shift gears without using the clutch.

Before I take the engine apart I would like to know if any of you knows if there is a way to check if the Sprag Clutch is damaged?

Any comment is welcome at this point.

Cheers
Brian
Last Edit: 2 months 1 week ago by Brian Mollerup Sørensen.

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  • Roger Lee
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2 months 1 week ago #15972 by Roger Lee
Roger Lee replied the topic: How to check the Sprag Clutch?
Hi Brian,

Since you've checked the battery, carbs and because the starter engages and disengages by itself I would say it's the sprag. Once you turn the key the starter should stay engaged. Some experience kickback which should always be remedied immediately and not allowed to continue or it will definitely trash the sprag. Things like a weak battery, poor carb sync, poor starting technique and bad plugs can add to poor starting and eventually excessive sprag wear.
What gets my attention in your comments is that it engages and disengages on its own and the starter still spins without engaging the engine.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-574-1080 Home (TRY HOME FIRST)
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2 months 1 week ago #15974 by Brian Mollerup Sørensen
Brian Mollerup Sørensen replied the topic: How to check the Sprag Clutch?
Hi Roger.

Yes that's also what I reasoned. Thank you for your comment.

But is there no way else to check if it really is the sprag clutch other that taking the engine apart?

Cheers
Brian

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2 months 1 week ago #15976 by Rob Seaton
Rob Seaton replied the topic: How to check the Sprag Clutch?
Follow the SB-912-042 instructions: Use a amp-clamp on the starter cable to detect the unloading of the starter (amps will suddenly decrease if sprag slips).
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2 months 1 week ago #15980 by Brian Mollerup Sørensen
Brian Mollerup Sørensen replied the topic: How to check the Sprag Clutch?
Thank you Rob for the SB reference.
I will do this check and see what happens.

Cheers
Brian

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