Yanmar 4JH4E 54 hp - SO 40.3 - Alternator Belt

[john50]

My Yanmar 4JH4E eats alternator drive belts. I have examined alignment, tension, looked for rust on pulleys etc and also use a belt lubricant but my alternator belt requires adjusment about every six hous use or slip increases.

It is subject to a great deal of wear and leaves a sticky black powder over the engine bay.

Has anyone any further useful advice or modified their systems to cope with this problem?

[Trevor]

Hi John50,

The drive belt should not require any lubrication or treatment to make them work properly.

It may be worth checking that the replacement belt is exactly the correct size. If it is too small it may touch the bottom of the pulley wedge and that would be bad.

If the alignment is correct and the sides of the pulleys are smooth and not damaged in any way, I would check to ensure that the alternator bearings do not tighten up with heat. If the alternator bearings are seizing, the stiffness in the alternator will cause premature aging of the belt and result in the sort of problems you describe.

Good luck

Trevor

[john50]

Hi Trevor,

Thanks for the reply. I have tried everything I can think of including the points you raise. I have had three Yanmar dealers examine the installation and they also can find nothing wrong. The only solution I can think of is a double drive belt but unforunately I am unable to find a supplier for the pulleys involved. I am using a Yanmar replacement belt which is meant to be the correct size. I have changed this twice since the boat was launched a year ago. My engine has the 80 amp alternator which may contribute to the problem.

Your point regarding the overheating of the alternator bearings may be valid and I will check at the next opportunity.

Kind regards,

John50

[Trevor]

John50,

My boat is the 36i and it has the 29HP engine with a 60amp alternator. So far I have seen no problem with the belt. I was going to increase the size of the alternator but your note has caused me to stop and think about that a bit longer.

I would have thought the 80 amp alternator would not cause a problem though. I think the best bet to check is the alternator bearings at this stage.

It would be a bit tragic to have to fit dual belts for an 80 amp alternator.

This is one of those seemingly simple problems that can be so painful to resolve.

Good luck with it,

Regards,

Trevor

[davideso37]

I had a little show of black dust from my alternator belt back in February. As we were at sea I phoned the service mechanic. The service mechanic advised me to tighten the belt so that when turning the nut on the alternator the belt was able to turn the engine over. Now this is very tight. Since doing this six months ago there has been no further problem. We use the boat twice a week and have motored many nautical miles since. I did put a spare belt on board just in case. Mine is the 3 cylinder version 3JH4E but the that should not affect the advice in the tension of the belt.

Regards

David

[tomina]

I have the same engine and alternator on an SO 40 (2001)with no problems. My arrangement includes an additional belt pulling downwards to drive the compressor for my fridge unit. Perhaps provides a balance against the alternator. Although we replace our belts unnually and are running the engine for about 150 hours we've never had a problem and keep the old belts because they are in the same condition as when fitted.!! sorry that does not help a great deal Tomina

[fobug62]

I have had the same problem and find that Yanmar belts should be kept in the spare parts locker. I ended up using Gates Greenstripe belts but Dayco Top Cog belts are equally good.
Part of the problem is the way the engine is designed by Yanmar to fit in the smallest cube possible. The alternator location suffers as a result of this and does not allow enough "wrap" on the pulley to prevent slippage. Using premium quality belts and tension them as stated above by davideso37. New belts should also be retensioned 5 to 6 times in the first 15-20 hours of operation as they will stretch until they take a "set". Like a good pilot, always check your belt tension when you check the oil and coolant.

[tean]

John50

I see that you are in Plymouth, have you tried Industrial Component Supplies at Saltash 01752 846517? They are your local Fenner stockists and I'm sure they would be able to help you with the drive problem, double pulleys, toothed pulleys etc. whatever it takes.

I have had the problem of rapid belt wear on a 1GM10 engine when I fitted a more powerful alternator and Sterling regulator.

John

[john50]

Additional thanks to tean and fobug62. I have now had my alternator pulley replaced by Yanmar via the local agent and will be trying out this mod once back in the water in April.

Regards, John50

[yachtwork]

Greetings-Scott here from Yachtwork, we are the worlds largest supplier of Yanmar Second Alternator kits and I have to say I have yet to come across your situation.

I read that you have had three Yanmar guys come and view to no avail. I'm still amazed.

One thing you might consider is an alternator for the house batteries and use the Yanmar alternator for the engine start. This might simply de-load the original alternator enough to solve the belt issue. Still something is wrong.

We charge about 1000 for a second alternator kit including 160 amp alternator, pulley and kit. You can do a search for Yanmar Second Alternator kit or Yachtwork and we'll come up.

Since were in the alternator business I look forward to hearing the solution to your belt issue.

Thanks for posting
Scott

[yachtwork]

Another thought is you might look at the V belt conversion that can be found here-

www.yachtwork.com/yanmar-alternator-pulley.htm





This gets rid of the original V belt and uses a serpentine belt and up to a 180 amp alternator in place of the original 80, or you can keep the original and use the alt pulley from the kit.

Just another idea of a way to help fix the V belt issues.

Scott

[dilligaf]

I have a 90amp alt. on my 100hp yanmar with no problems........I'm fustrated you are having problems. I will watch to see your relief.....
Dilligaf

[electricmonk]

the Yanmar alternator belt is hard to tension correctly and this is probably your problem. A good solution is to put a bottle screw in place of the pivoting link - your problem will be gone.

[malickson]

I have the Yanmar 3GM30F with 80 amp alternator. Does anyone know the Gates Green Stripe or Dayco Top Cog part #s for a heavy duty belt for this engine, and where "machined pulleys" can be obtained ?

[Calmseas]

I have a 2005 SO 40.3 with the 54HP Yanmar 4JH4E. I have the replacement belt from the local dealer and even after loosing the alternator I can't get it around the pulleys. The new Mitsubishi belt has a slightly wider profile than the older OEM belt and sits

higher in the three pulleys involved. That makes just enough difference in trying to get it on the last pulley. I try the water pump pulley since it is easiest to work on.

I put the old belt back on which shows very little wear and is several years old. (I have always had the black dust from the belt even when the boatyard has replaced the v-belt and tensioned it. It's not a major problem, just a little dusty when I take off the shroud.)

Anyone has a solution for getting the new belt on? The online manual says to remove the water pump pulley. Not going to even mess with that. 

Thanks,

Frank

[Mistroma]

The method in the manual is to split the water pump pulley. I had the same belt for about 7 years and it always looked perfect when removed in the winter. It wasn't difficult to pop it back on each spring. I eventually decided to switch it for one of my 2 spares even though it still appeared to be in excellent condition.

The new belt would not pull over the pulley and I did have to split the pulley as per Yanmar instructions. It was an easy job to undo the bolts to dismantle the pulley and refit using loc-tite.

I think that I had to do the same thing that winter and following spring before it stretched slightly.