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Discussion Starter · #1 ·
Hello everyone! I own a 91 Indy 500. Sled runs really good. I have one problem. I have an awful vibration at 3000 to 4000 rpm. Anything above and below that it is fine. I think that it is the crank bearings. I have rebuilt the clutch and that didn't seem to help. If anyone out there has had this problem, let me know. And if you have had it repaired, how much?
 

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Is the belt new? Are the clutch weights new and did you balance them?
 

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Sounds like a clutch out of balance as Offshore said, but it could also be a cracked engine mounting plate, or loose or worn mounts.
Balancing should be left to a good shop I think, too touchy for us back-yard guys.
 

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I am not ruling out crank berrings at all, that was your first guess, but a broken engine mounting plate is easier to check for than replacing berrings.
 

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Discussion Starter · #8 ·
When I move the primary clutch back and forth a little bit, I can hear a clanking noise. Does anybody know if that is a sign of anything?
 

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Your weights will flop around when the clutch isn't spinning.
 

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Discussion Starter · #10 ·
This sounds more internal. I wonder if I was to take the clutch off. And I still got the vibration, would this prove that it was the crank bearings?
 

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I have heard the 500 are bullet proof and also not so bullet proof. Kinda like the xlt's . Some go 12,000 miles with no major upkeep and some dont. I hear the probs. with the few 500 are the cylinders start to go out of round and become oblong. This is what a qualified tech. had told me. whether this or not causes vibration, don't have a clue. Just thought I would give ya another avenue to go down. TXC
 

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I'd pull the clutches and thoroughly check em out. Another cause for the vibration might be that the clutches are out of alignment.
 

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Are you saying you have play in the crank?Move the clutch side to side while watching the end of the crank,if there is play it's the bearing. Is there sign of leaking there also?
When you wiggle side to side is the outer sheave of the clutch moving and not the inner sheave? then it's clutch cover bushing, or movable sheave bushing.
Is the crank end bent?
 

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Have you tried running engine with out clutch on,may be able to eliminate a few things that could vibrate.
 

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Definatly start it up with the clutch removed...if your vibratijon is gone then you will be looking into clutching or driveline problems. Next if it is still there do you have twin carbs? If so have you sync'ed them recently? If its not still there start looking into driveline problems (clutches, bearings, belts, idler wheels, chaincase, etc.)
 
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