1986 Mercruiser 3.0 alternator adjustment bracket breaking

[RubberButt]

I've got a 1986 Mercruiser 3.0 140 alternator adjustment bracket that I've replaced twice in the past five years. Both times the bracket broke at the same place (right in the middle), looks like a manufacturing defect to me because there is rust (in the metal crossectional fibers) where it slowly broke until it was just a small sliver holding it together. When the engine is running there is not an unusual vibration of the belt or out of alignment of the alternator.

Is this a usual problem for this engine? Is there a work around of a stronger aftermarket stainless steel adjustment bracket? I've looked but could not find anything for the in-line 4 cylinder Mercruiser engines.

 

[grahamh]

Re: 1986 Mercruiser 3.0 alternator adjustment bracket breaking

Make sure that the alternator is aligned straight.

I'm not familiar with the exact setup off the top of my head, but does the alternator mount with rubber bushings? I've seen cases in cars where the bushings wear out, which leads to the alternator not being properly aligned, which put more stress on the bracket.

Just a wild guess though.

My grandparents have the same setup, and I know they haven't had any problems with it, but they don't use the boat too much either.

 

[RubberButt]

Re: 1986 Mercruiser 3.0 alternator adjustment bracket breaking

There are no bushings. Pretty much just a bolt it in and adjust tension. It did apprear to be in perfect alignment and belt did not shimmy when running. The belt ran smooth. I don't know if this is a case of bad luck parts or a trend.

 

[RubberButt]

Re: 1986 Mercruiser 3.0 alternator adjustment bracket breaking

I can find stronger than OEM brackets for the V6 and V8 but not for the inline 4 cylnders. Any ideas?

 

[Don S]

Re: 1986 Mercruiser 3.0 alternator adjustment bracket breaking

Install a shorter belt, so you don't have the bolt is not out near the end of it's travel.
The 3.0L's do have a tendency to shake a lot when cold, especially if out of tune. That even exagerates the problem.
When you tighten the lower alternator bolt, it should clamp down on the base of the alt. so the alternator stays tight, does it? if it's loose, you have even more room for movement.

 

[RubberButt]

Re: 1986 Mercruiser 3.0 alternator adjustment bracket breaking

Thanks for the suggestion Don, I think you are onto something by shorting the belt. When I had bought the boat six years ago the belt was missing (broken); I took a guess at the belt size. A shorter belt will reduce the stress on the bracket by focusing more of the stress near the engine side of the bracket which is solid metal.

 

[Bt Doctur]

Re: 1986 Mercruiser 3.0 alternator adjustment bracket breaking

Looks familiar, I shortened my belts and the issue never came up again. Also used a larger washer for the tension bolt.

 

[jenn2310]

Re: 1986 Mercruiser 3.0 alternator adjustment bracket breaking

mine did the same thing. a mig welder does wonders!!!

 

[Don S]

Re: 1986 Mercruiser 3.0 alternator adjustment bracket breaking

mine did the same thing. a mig welder does wonders!!!

He didn't ask how to fix it, he wants to know how to cure it from happening again. He has already replaced it a number of times.

 

[Bt Doctur]

Re: 1986 Mercruiser 3.0 alternator adjustment bracket breaking

Shame I done have the flame cutting setup, could cut him a dozen from 1/4 inch plate

 

[Wakesilver]

Re: 1986 Mercruiser 3.0 alternator adjustment bracket breaking

Shame I done have the flame cutting setup, could cut him a dozen from 1/4 inch plate

I'd take a couple while you are at it, mine's broke too.

I'd weld it right up but someone brazed it once so now I need to get it clean before welding.

The shorter belt sound like a great idea.

 

[RubberButt]

Re: 1986 Mercruiser 3.0 alternator adjustment bracket breaking

I guess the question now is how short should I go? I cross referenced the current size that I have as 40.5" inches and the suggested size is 40". I'm going to try a 39.5" belt. I'll post later if this worked for future poster's reference.

FYI, I was reading another post and thought this was a fantastic idea. When replacing a belt, install two belts for the Mercruiser 3.0 engines due to needing to remove one of the side engine mount braces. The second belt, use zip ties to strap the second one to the front engine mount out of the way. This way if your belt breaks while out on the water it is a easy swap fix.

 

[Don S]

Re: 1986 Mercruiser 3.0 alternator adjustment bracket breaking

It's not a bad idea to put on a second belt. But if you keep the pulleys free of rust, and the belt in good condition, I doubt it wil break out on the water. Those belts just don't fall apart that easily.

 

[RubberButt]

Re: 1986 Mercruiser 3.0 alternator adjustment bracket breaking

40" belt is as small as I could go. Tight fit. Thanks for your help!

 

[Oletrapper]

Re: 1986 Mercruiser 3.0 alternator adjustment bracket breaking

Hello. I know I am replying to a very old thread but thought I would give it a shot anyway. I have the same broken bracket. (just bought the boat) Alternator belt was very worn and when I went to replace it, found the adjustment bracket was broken at the engine block mounting bolt. Anybody have a part # for this bracket. I can't seem to find one. Can't mig it because of where the break is.
Thanks, Oletrapper

 

[Don S]

Re: 1986 Mercruiser 3.0 alternator adjustment bracket breaking

Welcome to iboats,
Please don't hijack old threads to ask your question on, start a new thread of your own, then people will actually see it.