The alternator/water pump belt on my 4JH3E Yanmar diesel has failed 3 times this year. The belt is either stretching (unlikely I would guess) or the alternator is loosening up somehow on the adjustment bracket, then the belt shreads along the edges. It doesn't actually break, but gets ripped & burnt pretty badly. I have the bolts on the alternator adjustment bracket as tight as I can get them. Has anyone else had this problem?
Belt failure on Yanmar 4JH3E
- Thread starter Persy
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heres a method
Put on a new belt. Tighten everything and dab a little bit of white paint to mark all the bolts for position. Then every so often check the to see what is moving or coming undone. Also do you have to loosen things to install a new belt? I suspect you have a warped pulley or someplace things are rubbing. Is there alot of rust inside the pully groves that could cause abrasion.
Put on a new belt. Tighten everything and dab a little bit of white paint to mark all the bolts for position. Then every so often check the to see what is moving or coming undone. Also do you have to loosen things to install a new belt? I suspect you have a warped pulley or someplace things are rubbing. Is there alot of rust inside the pully groves that could cause abrasion.
A 'typical' Yanmar problem (?)
The belt drive sheeves on yanmars are prone to pitting and rusting. Such roughness once it occurs will quickly abrade a drive belt. The 'problem' sheeve is usually on the water pump. Yanmar sells a LOT of these sheeves. When I shut down my engine for a long period of inactivity, I spray on a product called "Boeshield" to prevent the rust bloom. Boeshield is a wax so the tension on the belt has to be 'perfect' or the belt may slip later on .... and I spray on belt dressing rosin to re-commission the belt/sheeves when putting the engine back into service. The rosin spray will help retard rust for short term layup (month). Ive found that if I dont do this 'maintenance', the sheeve groove faces will soon become rough/pitted. I always keep a spare water pump sheeve; and, if I wear out a belt I usually inspect the sheeve change the sheeve AND the belt. If you have a means to 'chuck-up' the sheeve in a drill press etc., you can 'dress' the face of the pitted sheeves with a file and emery cloth. Then 'blue' the faces to prevent rust during storage by using a commercial 'blueing' compound or simply boil in hot water (plus a little phosphoric acid) for about 2+ hours. Hope this helps.
The belt drive sheeves on yanmars are prone to pitting and rusting. Such roughness once it occurs will quickly abrade a drive belt. The 'problem' sheeve is usually on the water pump. Yanmar sells a LOT of these sheeves. When I shut down my engine for a long period of inactivity, I spray on a product called "Boeshield" to prevent the rust bloom. Boeshield is a wax so the tension on the belt has to be 'perfect' or the belt may slip later on .... and I spray on belt dressing rosin to re-commission the belt/sheeves when putting the engine back into service. The rosin spray will help retard rust for short term layup (month). Ive found that if I dont do this 'maintenance', the sheeve groove faces will soon become rough/pitted. I always keep a spare water pump sheeve; and, if I wear out a belt I usually inspect the sheeve change the sheeve AND the belt. If you have a means to 'chuck-up' the sheeve in a drill press etc., you can 'dress' the face of the pitted sheeves with a file and emery cloth. Then 'blue' the faces to prevent rust during storage by using a commercial 'blueing' compound or simply boil in hot water (plus a little phosphoric acid) for about 2+ hours. Hope this helps.
Check condition of pulleys
I had a nearly new water pump belt fail on my Yanmar last year. I think the belt was defective, but not sure. In investigating the possible causes, I also found that I was probably keeping belt tension too tight. Are you getting any black powder residue in the engine compartment? If so, your belts may have been too tight. Also, check the condition of your pulleys. It is not uncommon for some rust to form in the grooves. If it does, it will cause early belt wear and early failure.
I had a nearly new water pump belt fail on my Yanmar last year. I think the belt was defective, but not sure. In investigating the possible causes, I also found that I was probably keeping belt tension too tight. Are you getting any black powder residue in the engine compartment? If so, your belts may have been too tight. Also, check the condition of your pulleys. It is not uncommon for some rust to form in the grooves. If it does, it will cause early belt wear and early failure.
Check Belt Alingment
You do not say what was the experience prior to this year. Was some work done on the engine prior to these failures? Could a spacer to the alternator been placed on an incorrect position? Check alignment and leave the belt as loose as possible without having it screech or slip when the engine is running. Check the pulleys for undue rust pitting. If everything is ok I would suspect the belts, switch supplier. Bad batches, improper storage and exposure to chemicals can ruin the life of belts. Good luck and let us know what solution you may come up with.
You do not say what was the experience prior to this year. Was some work done on the engine prior to these failures? Could a spacer to the alternator been placed on an incorrect position? Check alignment and leave the belt as loose as possible without having it screech or slip when the engine is running. Check the pulleys for undue rust pitting. If everything is ok I would suspect the belts, switch supplier. Bad batches, improper storage and exposure to chemicals can ruin the life of belts. Good luck and let us know what solution you may come up with.
My experience
I have the 3jh engine which is similar. A burnt belt indicates slipping (you may also have black dust on the alternator). I found that the alternator bolt slips on the adjustment bracket. I found that the way to stop the slippage is to put an external star washer on the bolt so that it digs into the adjustment bracket. Your manual will give you the tension specs on the belt (probably 10 mm deflection of the belt with 10 kilo pressure at that point on the belt. I put a felt pencil mark on the bracket at the bolt to monitor for possible slippage. Allan
I have the 3jh engine which is similar. A burnt belt indicates slipping (you may also have black dust on the alternator). I found that the alternator bolt slips on the adjustment bracket. I found that the way to stop the slippage is to put an external star washer on the bolt so that it digs into the adjustment bracket. Your manual will give you the tension specs on the belt (probably 10 mm deflection of the belt with 10 kilo pressure at that point on the belt. I put a felt pencil mark on the bracket at the bolt to monitor for possible slippage. Allan
great tips, thanks
* belts from various vendors, so that is probably not problem * Engine is practially new with no rust, so that's probably not the issue * I just got the boat this year, so don't know history * there was black powder, but that was from slipping due to being too loose. I think the alternator is slipping in it's bracket. I will mark the bracket per ideas here and monitor to confirm. Will also add locking/star washer to prevent slipping. Thanks for the ideas!
* belts from various vendors, so that is probably not problem * Engine is practially new with no rust, so that's probably not the issue * I just got the boat this year, so don't know history * there was black powder, but that was from slipping due to being too loose. I think the alternator is slipping in it's bracket. I will mark the bracket per ideas here and monitor to confirm. Will also add locking/star washer to prevent slipping. Thanks for the ideas!
Yanmar yarns
Mates, exceptional info here. I've run many a Yanmar, had a problem with only one. A good forum; helpful folks.
Mates, exceptional info here. I've run many a Yanmar, had a problem with only one. A good forum; helpful folks.
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