Loose Yanmar belts, constant issue.

Sep 27, 2008
52
Hunter 33 salem
No matter what I do, both belts (alternator & water pump) on my 1981 Yanmar 2GM go loose shortly
(after I tighten them). It' not lack of tighten because if I tighten them any more, I know I will break the bolts.......

I must be doing something wrong????? But I can't imagine what...

It's fairy straight forward, snug up belt, tighten all bolts????

I have tried a number of different belt manufacturers....

This is bigtime annoying.

Any insight is greatly apreciated.
 
Sep 27, 2008
52
Hunter 33 salem
I get your point, same problem two places...
but , I am very certain that these bolts cannot be tightened more before braking.
I am no rookie to mechanics but this one has got me stumped...

I must be missing something here . . .
 
Apr 8, 2011
468
Hunter 36 Deale, MD
No matter what I do, both belts (alternator & water pump) on my 1981 Yanmar 2GM go loose shortly
(after I tighten them). It' not lack of tighten because if I tighten them any more, I know I will break the bolts.......

I must be doing something wrong????? But I can't imagine what...

It's fairy straight forward, snug up belt, tighten all bolts????

I have tried a number of different belt manufacturers....

This is bigtime annoying.

Any insight is greatly apreciated.
Don't know if this will help, but Mainesail once posted this suggestion:
"You can just put a longer bolt through the alternator adjuster ear (should be 5/16" X 18 but may also be M8 depending upon the vintage of the Balmar.) then lock it down with a nut and locking washer. Also be sure the pivot bolt is sized correctly for the alternator feet. Those feet are typically a 10mm bore and some Yanmar pivot bolts are 8mm."
 
Jul 23, 2009
496
Beneteau 31 Oceanis Grand Lake, Oklahoma
Don't tighten the bolts more, tighten the belts more. Are they slipping? Are you getting belt dust? If not they are probably fine.

On my old boat the belt was difficult to tighten, was never really tight, but it was tight enough and didn't slip. I never loaded the alternator very hard so your situation may be different.
 
Oct 29, 2005
2,187
Hunter Marine 326 303 Singapore
Feel the pulleys V-slot with fingers. If rough, it's probably rust and that will wears the belt as it spin causing slack. You can sand away the rust and oil V-slot lightly.

Ken Y
 
Jun 25, 2004
288
Hunter 306 Pasadena MD
I had some pretty bad problems with my alternator belt early this season: making lots of black dust, and loosening quite quickly. After reading around, I did 3 things: I sanded down the rusty inner surface of the pulleys with emory cloth (with the engine running, actually: be careful), got a new belt since the old one was worn, and finally, I put on one of the extra thick washers that Maine Sail talks about way down toward the end of his article (see above). He sells them here: CMI Grip-It Washer. Now, you might think $12 bucks is a lot for a washer, but I was having a lot of problems before changing it out, and it's been fine since maybe early July, including on some long trips, with no adjustments needed and minimal belt dust. Good luck!