Yanmar 3GM30F burning up Alternator Belts

[Martkimwat]

Sounds like you are overtightening the belt. Here is an extract from the Seloc Yanmar Manual, Inboards 1975-98 Repair Manual, section: Maintenance and tune-up page 3-25:
'Determine the belt tension at a point halfway between the pulleys by pressing on the belt with moderate thumb pressure. If the distance between the pulleys (measured at the centre of the pulleys) is 13-16in. (330-400mm) the belt should deflect 1/2 in.(13mm) at the halfway point of its longest straight run; 1/4 in. (6mm) if the distance is 7-10 in. (178-250mm).'

1/8 in. is way too tight.

[roverhi]

Originally Posted by Sailorman Ed

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

Your Kubota tractor alternator isn't trying to put out the amperage that the typical boat alternator is tasked with. The stock alternator on your tractor is probably less than 35amps and is only trying to charge a group 24 battery if it's a small tractor. The same as in Yanmar/John Deere small tractors from which our engines derive. Even into a totally discharged battery it isn't putting out nearly the capacity of the alternator and then not for an appreciable amount of time as the voltage/amperage cuts back right quick.

The OP didn't say what amperage the alternator is. Could be high torque at start up because the alternator is trying to put out maximum amps. If you have a 100 amp alternator on a single belt drive system, the start up amps are really pushing the physics of alternator belt drive reality. Perhaps a separate voltage regulator with soft start capability could be the answer. I've got a 100 amp alternator as a spare for my 3GM30F but have hesitated to install it without a separate smart regulator.

All in all, would go for alignment as the cause of the problem, however.

[tml]

Had all sorts of similar problems for years and was constantly adjusting and replacing belts.No matter what always had black belt dust. Finally changed over to serpentine belt; did not need to adjust for 1000 hours;replaced it only because it seemed the thing to do not because it needed replacing.

[Cadence]

Originally Posted by 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?

I'd go back to alignment or maybe having a bad pulley, that has a bit if a skew?

[DeepFrz]

Originally Posted by roverhi

Your Kubota tractor alternator isn't trying to put out the amperage that the typical boat alternator is tasked with. The stock alternator on your tractor is probably less than 35amps and is only trying to charge a group 24 battery if it's a small tractor. The same as in Yanmar/John Deere small tractors from which our engines derive. Even into a totally discharged battery it isn't putting out nearly the capacity of the alternator and then not for an appreciable amount of time as the voltage/amperage cuts back right quick.

The OP didn't say what amperage the alternator is. Could be high torque at start up because the alternator is trying to put out maximum amps. If you have a 100 amp alternator on a single belt drive system, the start up amps are really pushing the physics of alternator belt drive reality. Perhaps a separate voltage regulator with soft start capability could be the answer. I've got a 100 amp alternator as a spare for my 3GM30F but have hesitated to install it without a separate smart regulator.

All in all, would go for alignment as the cause of the problem, however.

Yes he did. Read the first line of his post.

[Cadence]

Originally Posted by 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?

Just out of curiosity is there an idler in the mix? If so a bearing can be shot.

[Kita]

Another thing nobody has mentioned is about the rebuilt alternator. I have one that the bearing was not all that great they had bound it up a little bit somehow on the rebuild,you could spin it by hand & there was a slight drag,but when the engine would spin at rpm it was much harder to spin & created belt slippage,that in turn polished the pull & was also a problem. .I have seen the same thing with a water pump & idler pullys. See which one is the hardest to spin & me sure you can spin the alternator freely,check for the hot spot ,that will be where it's slipping, or maybe a Lazer temperature gun ,the heat where it's slips is the key

[jacktheflyer]

I have trouble with the alternator belts on my 3Ym30's. After consulting this forum I cleaned up the pulley surfaces with emery paper and found that one alternator pulleys took an 11mm belt instead of a 13mm for which the belts were bought. (not as easy to see unless you're looking) Since doing this the belts have gone for 100hrs before needing adjustment though I still think they should be more resilient.

I have been looking for the Gates Green Stripe belts that some respondents have mentioned but haven't been able to find them in Australia. All the Gates belts I buy seem to be a standard material and have a Red Stripe on the packaging.

Scrubby

[Captndave1]

I had the same issue with my 3GM, finally ended up with a Gates notched belt. This solved my problem, and I have not replaced a belt in the last 100 hours of running. There is a difference in the belt profile that seems to work better, the Gates belt is slightly wider and fits the groves better.

[hamburking]

First, good for you for checking the simple and obvious first.

Check the belt shape...they range from deep vee to almost flat. The wrong shape belt could be the problem. Just look closely at how it fits in the groove of ALL the pulleys...it only takes one weird pulley to burn the belt.

Also, 1/8 inch of deflection when pressed? I think thats too tight. Just saying.

And finally, where did you get the belts? Old stock? Try a different supplier.

Best of luck, and please let us know what happens. My last boat came with a Volvo 2002 and the belt looked pretty worn. I wasn't worried because I had 2 brand new spares. That belt lasted, and looked exactly the same 5 years later when I sold the boat, complete with the never used spares. It was a repower, and because of the fit in the boat it was hard to tighten the belt really tight, so it always seemed kind of slack...but was working fine.

[wsmurdoch]

On my Yanmar I am unable to check the v-belt pulley alignment with a straight edge because the distance from the center of the vee notch to the forward face of two of the pulleys are not identical and because the third pulley does not even have a flat forward face.

I can check the alignment by tightly laying a short piece of round rod in the vee of one pulley and checking that it lands directly in the middle of each of the other two then repeating the check again for each pulley.

Of course, for this method to work none of the three shafts can deflect under the tension of the installed belt.

[SV Windrush II]

WOW so much good info, I just mentioned 1/8" play in the belt as an example, Ive tried less tension with no better result. I do notice when I am running the engine with the battery selector OFF so I'm not charging anything and the engine runs about 200 RPMs faster, so the alternator is working pretty hard. But even with no load on the alternator, it still goes through belts, just not as fast.

I will be checking on the alignment and condition of the pulleys today and let you all know.

[NoTies]

+1 on the Gates Green Stripe. Yanmars eat belts and this is the only solution I have discovered.

[jimbunyard]

Originally Posted by SV Windrush II

WOW so much good info, I just mentioned 1/8" play in the belt as an example, Ive tried less tension with no better result. I do notice when I am running the engine with the battery selector OFF so I'm not charging anything and the engine runs about 200 RPMs faster, so the alternator is working pretty hard. But even with no load on the alternator, it still goes through belts, just not as fast.

I will be checking on the alignment and condition of the pulleys today and let you all know.

Which would seem to indicate misaligned or even mismatched pulleys, or an improperly sized (sectionally speaking) belt.

If all else fails, try an agricultural spec, wrapped belt. The commercial link below has a ton of information on sizes and types of available belts.

https://www.jdv-belts.com/products.htm

[01kiwijohn]

Whoa! Way too tight! At that rate you'll trash the engine coolant pump bearings pretty soon too.
As has been mentioned; check the sheave groove condition(s), the alignment, the rotating resistance of the engine coolant pump and alternator ( and any other accessories driven off it.)
Do you have a remote, regulator? If so, does it have a "soft start" feature? Or does it immediately lug the engine down when it engages?
Other than that, set the tension according to the manual. Alternatively, a quick and easy test is to see of you can roll the belt, on it's longest span, between you fingers, through 180 degrees. It's not precise, but years of experience have proven it to be a good approximation.

I have an 80 amp alternator with a Sterling regulator. 80 amps is about the max you can use on a single 3/8" belt, as is standard on those small Yanmars.