Yanmar 3GM30F burning up Alternator Belts

[SV Windrush II]

Ok here is a strange one. I have a 55 amp alternator on my Yanmar 3 cyl and it goes through a belt about every 12 hours. Just turns it to black rubbery powder!

So before we jump to the easy answers I have already done the following.

1. Alternator is rebuilt and puts out good voltage, Will charge my batteries to about 14v+

2. Checked All the pulleys and everything is lined up. the pulley also runs the water pump which turns freely and is working fine.

3. Each time I tighten the belt so there is about 1/8" flex when pushing on the belt with my fingers.

4. I have tried different belts and different tension but does not make much difference.

I have 4 Group 31 Deep cycle lead acid batteries, 1 for the start battery and all seam to be charging fine, The whole system was new 2 years ago.

Any Ideas?

[undercutter]

Go back to the alignment as this is the critical factor. Using a straight edge laid against the face of the bully on the crankshaft measure the distance from the straight edge to the face of the alternator pulley on opposite sides. These measurements must be exactly the same to avoid wear of the belt(s). Misalignment will be obvious on the belts due to side wear.

Another possibility is that the belts are the wrong thickness and do not fit the pulley on the alternator, crankshaft pulley or water pump pulley properly. Any one of these will result in failure of the belt. If your alignment is ok then this would be the next obvious thing to look at.

Finally check the bearing in the alternator pulley for resistance to turning although this problem would also present as high heat at the bearing and likely failure within a short time frame so not likely.

Good Luck.

[lockie]

Try next size down (ie in length) belt. I've had a couple of instances where
OEM-spec sized belts slipped too easily and fitting next size down fixed things right up.


Hard to explain why - everything was fine: pulley condition, alignment etc, but no doubt it worked.


Cheers, Graeme

[SV Windrush II]

Thanks guys, I will double check all those things tomorrow and see if I can find anything

[ur2slo]

Windy,

sounds like you have the obvious ones going.

its strange its eating the belts , so look for an interference at power. someone said smaller belt, that may be it. Sometimes at power the belts can stretch and dia increase, maybe cheap manuf?

Also, 2 other things, whats condition of the belt pulley inner surface on all the drive pulleys?.if you have some pitting corrosion, it would act like a grinding compound when belt stretched.

Belts are also made to fit , I believe 3 , might be wrong, v cross sections,.
I had an ole car I had same prob with and it turned out it was that .


Anywho.........

hope you get er and as always don't bust a knuckle!

[GordMay]

Here ➥ Belt & Pulley - Cruisers & Sailing Photo Gallery

[Crew of Turning]

We use Gates Green Stripe belts. The current one installed runs from crank pulley to alternator. Engine is a 2QM20 with a 90 ah alternator. We have not needed to do a change out in 3 sailing summers so, about 250 engine hours.

[rognvald]

"Also, 2 other things, whats condition of the belt pulley inner surface on all the drive pulleys?.if you have some pitting corrosion, it would act like a grinding compound when belt stretched." Ur2slo


UR has a good idea. If alignment, belt size, shaft bearings and tension are correct, there is something causing the excessive dust. It usually is the result of a cheap belt or over-tightening, but there could be corrosion in your inner pulley surface. Take a cue-tip and run it through the pulley channel. If there is cotton left on the inner surface, sand with emery paper and recheck. Hope this helps.

[four winds]

An eighth inch? Could that be a bit too tight?

Pic below from the manual.

[the_alpine]

I had the exact same issue on my 2ym15. Basically new motor, no alignment issues. Can't even tell you how many belts I dusted. Switched to the gates green stripe from napa. Never had another belt issue again.

[DeepFrz]

Check to make sure you are using the correct belt type.

Notes on Pulleys and Belts

[svJasmine]

I solved it with an expensive serpentine belt kit. Same engine. rebuilt the engine and I painted the engine room. I use a 100 amp alternator.

One thing you can do is use an external regulator and tune down the output of the alternator. I think that you will still charge faster than the internal regulator (since the bulk cycle will be hotter) but keep the amperage down.

If your batteries are cruiser discharged, you will most likely be putting in the most the alt will do ALL THE TIME.

good luck

fixed.

[rognvald]

Originally Posted by svJasmine

I solved it with an expensive serpentine belt kit. Same engine. rebuilt the engine and I painted the engine room. I use a 100 amp alternator.

One thing you can do is use an external regulator and tune down the output of the alternator. I think that you will still charge faster than the internal regulator (since the bulk cycle will be hotter) but keep the amperage down.

If your batteries are cruiser discharged, you will most likely be putting in the most the alt will do ALL THE TIME.

good luck

fixed.

Any pix?

[drruss]

Be sure you aren't putting a vee belt through a flat pulley. Generates a lot of heat a the belt desentigrates. Been there before.

[Sailorman Ed]

We had the same problem until I did 3 things:

1. switched to the Gates green stripe from NAPA
2. added 4 thin washers under the water pump pulley ( top pulley) to correct a slight offset
3. be sure the inner surfaces of all 3 pulleys are clean and smooth

I also drilled out the hole for the alternator pivot and used a larger bolt as the holes had become elongated.


Strange that my Kubota tractors NEVER have a belt issue and the Yanmar engines seem to eat belts at a much faster rate.