Why am I shredding belts on Yanmar?

davewarburton said:
Yanmar belts are prone to this problem.
Click to expand...

I also have a 2GM20F using genuine Yanmar belts for the past 4 years without any problems. I adjust the belts to give a deflection of about 10 mm on the longest length between pulleys and have never had to adjust them for the past two years. I think the correct tension is very important to prevent stretch or slipping, both of which will shred a belt.

Cheers, Allan
 
I had a 2GM20 for 15 years, it too produced black dust and belts soon wore through and needed constant re-tightening. Some of the posts above have already put their finger on the reason to the problem that I had for many years.

An experienced German Yanmar mechanic eventually showed me the reason - the surface of the pulley wheel on the engine was pitted from years of corrosion - not really visible - eating into the metal. He took the belt off and ran the engine while holding an emery cloth in the vee of the pulley. After it was shiny and smooth he lightly greased it and advised me to reapply the grease every year to prevent further rusting.

From that day on, no more problems.
 
Last edited:
Barnac1e said:
I had a 2GM20 for 15 years, it too produced black dust and belts soon wore through and needed constant re-tightening. Some of the posts above have already put their finger on the reason to the problem that I had for many years.

An experienced German Yanmar mechanic eventually showed me the reason - the surface of the pulley wheel on the engine was pitted from years of corrosion - not really visible - eating into the metal. He took the belt off and ran the engine while holding an emery cloth in the vee of the pulley. After it was shiny and smooth he lightly greased it and advised me to reapply the grease every year to prevent further rusting.

From that day on, no more problems.
Click to expand...

Doesn't grease cause the belt to slip?
 
tim3057 said:
I'm getting through alternator belts at an alarming rate - what's the principal cause? Too tight? Too loose?
Click to expand...

If your engine is munching Yanmar belts then there is something wrong with the installtion. Too loose will cause a belt wear problem ( too tight will simple bu**er up alternator / pump bearings) but you could also have a knackered pulley. The Yanmar ones are pressed steel and I have seen the two halves separate with the result that the belt bottoms out rather than gripping on the sides and wears rapidly.

If the problem is with car spares belts then you could also have a size issue. Yanmar belts are 13mm wide whilst many car spares are half inch. Car spares belts can also be a different profile. Rather than use Halfrauds, why not go to a belt specialist like Fenner and get the right size at a good price. You can even get the little water pump belt from them.
 
tim3057 said:
Barnac1le - a mate of mine did that on his motorbike - lost his finger in the sprocket!
Click to expand...
I'm not advocating the technique, just recounting what someone who had worked around marine engines all his life did to cure my problem, which was similar to yours. I was quite shocked myself at his blasé attitude but it sure was a quick fix.

In his support though, once the belt is off the pulley has a plain hub with nothing to catch anything on. But now that you mention it, he is missing the top of one of his fingers .... Hmm, I wonder how he did that.
 
In the past when specifying belt drives I used to use Fenner Cogged Raw Edge belts which transmit considerably more power than conventional Vee or Wedge belts. Much better than Vee or Wedge belts if you are on the HP limit.
 
This thread was very helpful, so I just want to mention what I did.

I used a wire brush and emery cloth on the pulleys. Then I put two thin coats of spray paint on them. Have only run the engine a few hours, but so far, no black dust.

I have a 2YM15 and use the Gates 9380 instead of the Yanmar part.
 
Just changed my first Yanmar belt on a 12 year old engine so no complaints. However, I sailed a boat which, briefly, got through belts on a weekly basis. The cause was play in the alternator mounting bolt which allowed it to offset the belt run. Very slight but very problematical.

Edit: Oh dear, I've been zombified.
 
Last edited:
I’ve had this problem off and on with a 35hp Nanni fitted with two alternators (one for The engine battery and the other for the house bank.) The no 2 alternator has been playing up with excessive wear and slippage. It’s taken us some time to sort it out.

I would recommend ensuring no corrosion on the pulleys (a bit of rust can eat up a belt) look at the alignment of the belt as well as the tension, and check that the alternator is working properly. All of these have helped to some extent.

However, this year I took my number 2 alternator for a rebuild after I noticed it sparking internally. I told the electrical engineer about the difficulties who asked if we had an old Adverc smart charger in the system, which we have. He advised me to disconnect it, and this seems to have helped. In his experience (which is considerable) he says that some older models can go wrong, putting high loads on the alternator.

Good luck with it
 
Barnac1e said:
No, not to any noticable degree probably because it was so thinly applied that it retained its overall coefficient of friction but was enough to exclude moisture and stop the imperceptible rusting. It also probably spread along the belt so that it was always reapplied in a miniscule amount.
Click to expand...

+1 for micro- pitted pulleys due to rust. They looked nice and shiny but on closer inspection it wadn't a mirror shine as it is supposed to be. I too used v fine emery cloth in the grooves with the pulleys mounted in an electric drill. The situation was improved but not totally solved until I replaced the pulleys with non-yanmar standard items from a bely &pulley supplier.

Surely the ideal solution is to replace the antedelluvian vee belt with a toothed flat belt system - which virtually never give trouble.
 
Bilgediver said:
Too Tight..

Too Loose

Grooves too rough

Alternator set up overloading the drive

Wrong belts

Alternator axis out of line so pulleys not on the same axis


Could be one of many reasons or a combination.
Click to expand...

My favourite one that doesn't get noticed...

But could be any of the others or a combination as said.

Have you got a charge controller fitted? Sometimes the extra load doesn't add to belt life. But it doesn't usually shred them.
 
john_morris_uk said:
My favourite one that doesn't get noticed...

But could be any of the others or a combination as said.

Have you got a charge controller fitted? Sometimes the extra load doesn't add to belt life. But it doesn't usually shred them.
Click to expand...

Charge controllers ("smart" regulators) can't produce more current than the alternator was designed to produce. With a single V-belt, the effective limit is about a 90A alternator. People who fit bigger alternators driven by a single V-belt can expect problems.
 
pvb said:
Charge controllers ("smart" regulators) can't produce more current than the alternator was designed to produce. With a single V-belt, the effective limit is about a 90A alternator. People who fit bigger alternators driven by a single V-belt can expect problems.
Click to expand...

Charge controllers ("smart" regulators) can't produce more current than the alternator was designed to produce. This is certainly or self evidently true - but with a traditional regulator and a starter battery being up or near full charge most of the time, the belt doesn't have to transfer much power for very long. My point was (and I think you are agreeing with me) is that a 90 amp alternator charging a large house battery bank that is allowed to run down a long way, can be asked to produce near it's full output for a longer period. Actually, in practice, the alternator gets hot and self limits to a degree (if you'll pardon the pun).

However I suppose my supplementary question should have been, "Have you fitted a bigger alternator?"
 
Last edited:
You must log in or register to reply here.

Share this page

Top