Yanmar 3gm30F excessive belt ware

sebastiannr

sebastiannr

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Hi there,

I have extremely excessive belt ware (both water pump belt and alternator belt) on my Yanmar 3GM30F. The belts need tightening at least every 5-10 engine hours and the entire area in the engine room around the belts is covered in black dust from the belts. I know that my father was having this problem (I recently inherited the boat from him), but despite having worked as a marine engineer he couldn't figure out the cause of the problem. I have used both the correct 'thick' belt that rests on the sides and not the bottom of the belt and the thinner type of belt that seems to rest on the bottom of the wheels, the problem persists in both cases. I apply generous amounts of belt dressing to stop slippage, but that's obviously no solution.

If anyone has any ideas as to the cause of this problem, or even just a temporary solution, it would be much appreciated as I'm in the Ionian and am having to motor far more than I would like!

Many thanks,

Seb.
 
You should check if your pulleys are aligned properly. You need to pick a datum point and measure the distance from there to the centre of the groove on each pulley sheave. Obviously the should be the same. Or you can go hi-tech and use lasers?
 
Not much help I know but the belt must drive on the angled sides of the pulley not in the centre.
The belt tension is translated into a load perpendicular to the pulley groves to allow the belt to grip.
Does the belt angle match the pulleys ?
Has the configuration been changed so that the angle of lap (the amount of circumferential length of belt wrapped around each pulley) been reduced ?
Are you putting on enough tension?
Is the adjuster slipping and allowing the belt to slacken ?
 
Standard or oversized alternator?
Does the engine note/revs vary repeatedly at idle? The charge controller is kicking in and out a lot and the belt is repeatedly loading up as the alternator kicks in and out... maybe! Are the batteries and wiring knackered /corroded.

And check the alignment as said. Raw water pump can be very slack and still work ( better IMO-IMO ok?)- for bearing wear.
 
Check the pulleys for corrosion pits. The usual cause is alignment but if it happens on both the alternator and water pump belts the only explanation would be that the pulley is not correctly set on the shaft. Could be many explanations but the first move has to be to check. A ruler will do for a start.
 
On my 3YM30 it is really difficult to get at the tension adjuster on the raw water pump drive belt. Has anyone solved this problem ?

Not sure what belt dressing is - having run large diesel fleets for many years never heard of any of my mechanics using it either - so are you sure this is dressing is not causing the problem??
 
vyv_cox said:
Check the pulleys for corrosion pits.
Click to expand...
Miniscule pulley corrosion was indeed my problem with exactly the same symptoms when I had a Yanma 2GM20 - continuously slackening belt and black dust everywhere in the engine compartment. I asked a mechanic friend about it and he came along, started the engine without the belt, casually pushed a wad of emery paper into the groove while it was spinning to hone it to a smooth surface.

He told me it was fine rusting of the vee'd surface and to occasionally lightly oil it. I did and never had the problem again.
 
Barnac1e said:
Miniscule pulley corrosion was indeed my problem with exactly the same symptoms when I had a Yanma 2GM20 - continuously slackening belt and black dust everywhere in the engine compartment. I asked a mechanic friend about it and he came along, started the engine without the belt, casually pushed a wad of emery paper into the groove while it was spinning to hone it to a smooth surface.

He told me it was fine rusting of the vee'd surface and to occasionally lightly oil it. I did and never had the problem again.
Click to expand...

Statement of the bl**ding obvious to some but DO NOT get fingers anywhere near a working belt - they grab fingers and mangle them. I have known two "professional" mechanics to loose finger ends in this way
 
Halo said:
Statement of the bl**ding obvious to some but DO NOT get fingers anywhere near a working belt - they grab fingers and mangle them. I have known two "professional" mechanics to loose finger ends in this way
Click to expand...
You are quite right, of course. It was something I would never have done myself - poke around in a running engine. I was merely recounting his particular technique, not recommending it. Clearly one can achieve the same result by polishing the static pulley.

Edit: BTW, the corrosion before the treatment was not really visible - it just wasn't so shiny as it finished up as. However, it was enough to wear dust particles off the belt.
 
Last edited:
Fantastic advice from all, thank you. I will check the alignment of the pulleys, but I can see visible corrosion on the pulley groove so will tend to that immediately (not when engine is running). If that is the issue it would be a huge weight off my mind. I was worried that it might involve replacing pulley cranks etc

Thanks again for the excellent advice and the sudden feeling of hope that it's instilled!
 
Instead of cleaning the sheave grooves while the engine is running, take the pulley off the engine and either clean by hand or mount it in a battery drill by putting the bolt back through the pulley wheel and place the bolt in the drill chuck, then mount the drill in a vice. This will allow you clean them in a safer environment than in the engine compartment with a running engine.

Belt dressing is used to extend the life of a belt.
 
I had a lot of ware on the alternater belts for the first 5 years of owning a 3GM 30. I eventualy got an original yanmar belt that sat quite proud of the drive pully. Lasted well and little or no black dust last year.
I also polished the drive pully with emery paper using the had crank to bring the pully round. The driven altenater pully appears to be some sort of universal as the belt sits well into it.
 
Barnac1e said:
Miniscule pulley corrosion was indeed my problem with exactly the same symptoms when I had a Yanma 2GM20 - continuously slackening belt and black dust everywhere in the engine compartment. I asked a mechanic friend about it and he came along, started the engine without the belt, casually pushed a wad of emery paper into the groove while it was spinning to hone it to a smooth surface.

He told me it was fine rusting of the vee'd surface and to occasionally lightly oil it. I did and never had the problem again.
Click to expand...


Yep, that solved my problem too.......................and as previously stated keep fingers well out of the way......it hurts if you don't !!
 
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