breaking Alternator belts

[redman2363]

I have a '89 Mercruiser 4.3v6 stern drive that keeps breaking the alternator belt. I have checked belt alignment, tension, and tried the stop squeal type products.

The normal occurrence is to squeal when the boat is being powered up for the first time. I will back down to idle the squealing will stop and all will be ok. Some time later during the day the belt will squeal and this time it will only end when the belt breaks.

There is some roughness on the pulley—rust I think.

Any thoughts on why they are breaking?

How hard would it be to convert to a serpentine belt?

[TerryKing]

If the tension is really correct, and it's the right belt, it shouldn't be squealing at startup even.

The squealing is slippage. The alternator is putting a lot of torque (rotary force) on the pulley and the belt slips.

If it's slipping bad enough to wear thru and break the belt, something else is wrong. The alternator is developing shorted wire turns, bad rectifiers, etc. would be my guess. Possibly the regulator is failing. Unless the battery has a shorted cell and the battery VOLTAGE is dropping to 11 or 12 volts or less, while being charged..

But something's wrong and it's not the belts...

[lazeyjack]

Originally Posted by redman2363

I have a '89 Mercruiser 4.3v6 stern drive that keeps breaking the alternator belt. I have checked belt alignment, tension, and tried the stop squeal type products.

The normal occurrence is to squeal when the boat is being powered up for the first time. I will back down to idle the squealing will stop and all will be ok. Some time later during the day the belt will squeal and this time it will only end when the belt breaks.

There is some roughness on the pulley—rust I think.

Any thoughts on why they are breaking?

How hard would it be to convert to a serpentine belt?

HOW FAR DOWN DOES IT SIT mATE, ARE YOU SURE YOU HAVE A TRUE A SECTION AND NOT A CONTINENTAL?

[redman2363]

Thanks TerryKing!

I am the secound owner of the boat (at least) and this is the second alternator (at least). It is a automative alternator--not the marine grade it should be. I noticed the voltage field on the GPS showing 14.4 volts--so I guess it is time to buy a marine grade alternator and replace it.

[TerryKing]

Originally Posted by redman2363

(snip).. I noticed the voltage field on the GPS showing 14.4 volts--so I guess it is time to buy a marine grade alternator and replace it.

14.4 Volts is pretty normal under charge...

Jack may be right.. maybe the 'replacement' alternator has a V pulley that's really not right for the belt ...

[Frosty]

What do you mean by 'break' You mean it just snaps clean or it wears out to a thread.

[alan white]

Straight-edge the two pulleys and tension the new belt well. Check for burrs on both pulleys. Sounds like a mechanical problem. Either misalignment or a burr, or low tension, and probably two of the three, since it's hard to destroy a brand new belt unless you really try.
Also calculate the driven pulley's ratio to engine RPM to ensure it's not running the alternator too fast. Turn the alternator by hand without the belt on. A bad ball bearing can catch, though it's rare. The alternator should turn smoothly, without a gravelly feel.

Alan

[redman2363]

It breaks completely--although it is a jagged separation.

[charmc]

Squealing followed by a break indicates either a loss of tension allowing the belt to slip (not likely to break in a short period of time) or an increased load caused by resistance to rotation by one of the driven components. If the only driven sheave on this belt is the alternator, the problem lies there. Rotate it by hand; it should turn freely. If there is any noise or feeling of dragging, the alternator needs rebuilding, as the bearings are bad. If it turns freely by hand, be sure the sheaves (pulleys) are aligned properly, i.e. in the same plane and not tilted (use a straight edge to check) and that there are no burrs, nicks, or rough spots where the belt rides. If there is an idler, do the same with that. One of these things should show a problem, as a belt drive is a simple element, with only a few parts involved.

[Frosty]

Ive never seen a belt snap like that--ever. I have to question the belts. Are they repeatedly the same ones that are snapping or have you bought different brands.

How do you measure the tension when you fit a new one? and how long does a belt last?

Are you sure nothing is falling into the belt while it is running,--A loose pipe for instance.

[redman2363]

Thanks for all the reply's.

I am trying a wider belt to bring the belt closer to the top of the v pulley. Seems to be working better.

[Frosty]

The correct belt should be infact above the pulley slightly. 2-3mm