Fast wearing V belt solution?

Hi there,

A couple days ago we heard a new 'background hum' to our 100 hp Yanmar 4JH2-UTE as we were getting close to the marina, so we lowered RPM and kept a close eye on the temperature and oil gauges, which didn't budge.

Turns out it was a loose v belt that runs the alternator and cooling water pump...like really sloppy loose and about 20% had disintegrated to fine dust.

Bad us for not noticing the dust earlier, but lucky us we noticed the engine sounding a little odd. Would have been grim to fry our engine...

We checked the house and starter batteries, and all was okay. We put a new v belt on and checked that the internal regulator in the alternator was working properly, and it was.

I noticed that the manual suggests loosening the belt if the vessel wouldn't be used for a prolonged period, and it wasn't until we bought it, so we thought there might be some 'memory' bends in the belt causing it to wear excessively.

Today we went for a three hour out and back, and the new belt had become loose...not as loose as the old one, but noticeably looser than it should be.

The current theory is that on the inside edges of the pulleys (shivs?) there's some corrosion or deposits that felt 'pebbley' to my finger tips.

Do you think that is causing the fast wear in the v belt? If so, could this be the solution?

Yanmar Serpentine Pulley Conversion Kits - Electromaax

I would start with dressing the pulleys to make sure they are smooth were the belt rides, make sure the alignment of all pulleys is parallel and in line with each other, and then try a new belt. See if all pulleys are running true or if there is some wobble.

While I prefer serpentine belts, if the pulleys are out of alignment or you have a bad bearing in one of the items, a serpentine belt isn't going to cure that problem.

Ted

I agree with Ted, if you can feel rust or anything on the the pulley, clean it up as it can destroy belts quickly. I usually just use fine sandpaper. So far as your new bell loosing after one trip,it is normal for a new belt to stretch slightly after a run and should always be checked afterwards.

Check your alignment with a straight edge. You might also want to find a V-belt sheave gauge and check your sheaves for wear. Acklands-Grainger will have one. Either will make your belt wear fast.

Stock alternator?

Thanks for the tips. There wasn't any noticeable wobble when I watched after tightening things up. I'll put some more tension on today, make sure everything is aligned, clean up the area really good, take it for a spin, and see if there's anymore belt dust created.

What's the best way to use fine sandpaper or emery cloth to dress up the sheave/pulley surface?

Northern Spy said:

Stock alternator?

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Yup.

smooth the bully at with sandpaper , ;then painted with the spray bomb

You didn't mention the size of your alternator, but a single belt has trouble with more than 100 amps. You can take a piece of a stick-on sand disc, put it on your belt, and after running a few mintues, all your pulleys will be nice & clean.
If your alternator and/or pump brackets are the type than can be adjusted (other than to tension the belt) then I suggest they have been maladjusted and it doesn't take much. Overtightening the belt/s will just stress all your accessory bearings and not get to the heart of the problem.

Make certain that the belt taper angle is the exact match for the pulley. I used a cross matched belt on my Cat 3208. The taper was off slightly, and the belt slipped. Also, it may be a good idea to get an external regulator with a "soft start" feature. This brings the alternator up to full power in steps to lessen the jerk on the belt.

Moonstruck said:

Also, it may be a good idea to get an external regulator with a "soft start" feature. This brings the alternator up to full power in steps to lessen the jerk on the belt.

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Interesting! I did that a couple of months ago and really like it.

Brooksie said:

You didn't mention the size of your alternator, but a single belt has trouble with more than 100 amps.

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I believe it's original: Hitachi 12 volt 80 amp.

Brooksie said:

You can take a piece of a stick-on sand disc, put it on your belt, and after running a few mintues, all your pulleys will be nice & clean.

Click to expand...

Thanks, will give that a try for sure!

Tightened things up and went out for a couple hours today...belt was looser again when we got back. (The bottoms of all the pulleys have not been burnished, so that's a good sign).

Sorry for the rookie questions, but should the belt be loose enough to be able to spin the alternator pulley by hand by putting 'a little muscle' to it? I can also rotate the belt past 90 degrees with my index finger and thumb in the middle of the long section. Does that sound about right?

Moonstruck said:

Also, it may be a good idea to get an external regulator with a "soft start" feature. This brings the alternator up to full power in steps to lessen the jerk on the belt.

Click to expand...

Will keep that in mind

Sounds loose. That said you don't want it zinging tight either as it puts undue stress on the bearings. Most belt companies will provide tensioning guides to check deflection. All you'll need is the belt size and the distance between sheaves and sheave size. Pretty simple math. I've used gates.com for years, and before that, their catalogs. You don't need a tension measuring tool, you can be creative with a fish scale. (You need to make friends with a millwright in the marina.)

Might want to check size of sheaves and belt size. It'll usually have a number stamped on it. Yanmar is likely metric, so the number will likely represent the top width in mm (if it is imperial it will be xx/32"). Often the sheave will have a stamp on them with width too. They should match obviously. Sometimes people will put the right length on, but not understand that the come in different widths. Found that on used things I've bought before.

Are you sure both adjusting bolts on the alternator are tight once you've tensioned the belt. I mean really tight, with a lock washer.

The 4JH2-UTE manual says 10kg force to move 10mm..

Northern Spy said:

Are you sure both adjusting bolts on the alternator are tight once you've tensioned the belt. I mean really tight, with a lock washer.

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I'm not sure if the lower front and back pivot bolts have lock washers, but the upper bolt does. They were tight, for sure.

The old belt that came off was well below the top of the crankshaft sheave, and the new one was flush when I put it on.

Would these be an idea?

http://www.electromaax.com/yanmar-serpentine-pulley-conversion-kits/

That sounds good. Might just be breaking in a new belt then.

Sometimes a cogged or notched style V belt helps on alternators as the driven sheave is small and the belt will wrap easier around the small diameter. Is it supposed to be cogged?

Northern Spy said:

Sometimes a cogged or notched style V belt helps on alternators as the driven sheave is small and the belt will wrap easier around the small diameter. Is it supposed to be cogged?

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There was an old, used spare on board with the Yanmar wrapper with the part # on it, and it wasn't of the notched variety.

The only spare belt I could find in town on Saturday (only one place open) was a notched one.

Will watch the wear rate on the one that's on now, try and find the stick-on sand/emery paper do-hickey to dress up the sheaves, and keep the notched one for back up and comparison purposes.

Thanks a bunch