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Alternator belt

dawgs

Regular Contributor
86 merc 170..4 cyl......my bel

86 merc 170..4 cyl......my belt keeps popping off the pulley at high RPMs...i cant understand why....what should i look for?
 
"Try tightening it but only as

"Try tightening it but only as per specs in the manual. Centrifical force may be throwing it up and off the pully.

Otherwise look for a bad belt, the wrong belt, or pully mis-alignments."
 
"Check for rust or any belt dr

"Check for rust or any belt dressing build up on the pulleys. Had the same problem with a 4.3 about about a year ago. Rusted pulley from sitting around not getting used. Ground the areas back down and sanded smooth, then repainted. Haven't lost a belt since! Was going through belts about 2 a weekend!"
 
when i loosen the bolts slight

when i loosen the bolts slightly on the pulley it rattles....it seems the bolts diameters are too skinny for the holes...when i tighten them it stays tight but like i said ...slightly loose and the pulley rattles...so when i do tighten them i have to center the pulley by eye then tighten.....should the bolts go in snug before they are even tightened?
 
The pulleys should all be held

The pulleys should all be held on center by the shaft diameter protruding through the pulley. Sounds like you have the wrong pulley.
 
"As long as it's centered

"As long as it's centered by the shaft, there may be rotational play. I wouldn't worry about that as long as you are using a good lock washer and flat washer to give the bolt enough bite on the pulley. When you spin the pulley by hand make sure there is no wobble in the pulley rotation, nor from side to side."
 
jack you lost me...."shaft

jack you lost me...."shaft diameter protruding through the pulley?"...my pulley bolts to the front of engine...theres no shaft
 
"From what I can remember, You

"From what I can remember, You should have a Crankshaft pulley (usually held on by three or four bolts at the bottom of the engine), Water pump pulley (usually four bolts and center hole with water pump shaft protruding slightly), alternator (held on by alternator nut, centered by the shaft) and power steering (generally same attatchment as alternator) The crankshaft pulley turns them all by way of the belts. Are you referring to the crankshaft pulley?"
 
ok on front of the engine on b

ok on front of the engine on bottom there is a large round drum looking thing that spins...i believe its the harmonic balance...inside was the magnetic "stator" that acted like an alternator...it no longer is used..now i have the converted alternator that is an exterior alternator attached to the lower left on the engine...the pulley in question is aftermarket bolted to that harmonic balance which spins the alternator itself...get it?
 
"I see what you are saying now

"I see what you are saying now, you made no reference to anything aftermarket in original post. If the pulley isn't being centered by something then it would be impossible to keep it running true. Sorry I was unable to help, maybe someone else has an idea for you. I am not familiar with this application. Good luck"
 
"SG:

All the pulleys have t


"SG:

All the pulleys have to align with the one it attaches to by belt. The plane of alignment has to be near perfect vertically and horizontally, or the belts will jump off. You can eyeball it or use a large carpenters square off of the engine block to check alignment.

I have a Craftsman 4-way laser level that would work perfectly. Just set the trajectory angle to 180 degrees and it will tell you right now. You may have to shim the alternator bracket with washers. Guy"
 
"SG
From my experiance genera


"SG
From my experiance generaly belts will handle slight miss alignment of the pulleys but do not particularly like pulleys that are not centred properly on the shaft that they are fixed to, or pulleys that are bent.
If it is the same belt coming off all the time the belt may have snapped a cord internaly and that will cause the belt to run off the pulleys all the time.

Regards
Peter C"
 
its not the same belt...its di

its not the same belt...its different belts.....i just discovered a crack in the alternator bracket...its cracked where it bolts to the block...but it doesnt seem like its loose or anything...there are 2 bolts ..the other one is tight also...think thats it?
 
"That bracket must have cracke

"That bracket must have cracked for a reason. It's trying to tell you something. Something is out of alignment or out of balance, and vibrating at some point in the RPM band. That is likely causing the belts to jump and also likely caused the cracked bracket. Just my opinion.
Rod"
 
"SG:
Rod has hit on a good


"SG:
Rod has hit on a good point. Some alternators have sleeves pressed into the mounting holes or spacers between the front and rear mounting holes. The short sleeves protrude out of the hole to some extent and may be there for alignment purposes. The spacer sleeves are there to prevent distortion of the case when it is tightened and also prevent cracking the case.

When the alternator belt tension is adjusted correctly, there should be no more than 1/2" deflection when you push downward on the middle of the belt. If there is more than 1/2" deflection, loosen the alt. bolts and slide the alt. along the adjusting bracket to get the proper tension and tighten the bolts per specs.
It should not jump off of the pulley. If you cannot adjust the belt due to reaching the alt. adj. limit, the belt is too long. Use a notched belt instead of a smooth one. (It looks like a sawtooth pattern) They tend to wrap around the pulleys better since they are designed to close up the gaps as they turn on the pulleys vs. standard belts. Guy"
 
ok i know what sleeve youre ta

ok i know what sleeve youre talking about...that sleeve actually loosened up and is not in there snug...i bought a new bracket and the sleev is in there tight...hopefully that is the problem
 
"If you still have belt jumpin

"If you still have belt jumping problems after the new bracket, I suggest you sit close to the engine where you can watch the belts and have someone drive the boat thru its normal operating RPM range. This will tell you for sure if you have a vibration problem at any point.
Rod"
 
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