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Old 07-01-2012, 14:12   #1
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Yanmar 2GM20 Squealing

I have recently been doing a lot of hours with our Yanmar 2GM20 and I seem to be having to tighten the alternator and water pump belts after 2 or 3 hours running time, or each time I start the engine. It seems to be becoming loose and I can't work out why.

I have tried replacing belts, using various sprung washers, and even Loctite on the bolts but to no avail.

I am considering chopping the slide mechanism off at the end and welding a washer to a piece of threaded bar and tightening up the alternator using a nut (similar to the system used on BMX bikes!)

Does anyone have any better ideas as this seems a bit drastic....?
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Old 07-01-2012, 14:29   #2
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Re: Yanmar 2GM20 squealing

Do you mean that the belt is stretching and wearing, causing looseness, or the alternator is moving back in ? How tight do you adjust it in the first place? Have you checked the waterpump and alternator bearings with the belt removed?
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Old 07-01-2012, 14:36   #3
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Re: Yanmar 2GM20 squealing

FYI alternator pulleys do year out, which wear the the belts extremely fast or just don't grip anymore. Especially the serpentine pulleys. Is the pulley very shinny in the grove?
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Old 07-01-2012, 15:05   #4
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Re: Yanmar 2GM20 squealing

Quote:
Originally Posted by boden36 View Post
Do you mean that the belt is stretching and wearing, causing looseness, or the alternator is moving back in ? How tight do you adjust it in the first place? Have you checked the waterpump and alternator bearings with the belt removed?
Regards,
Richard.
I'm not sure if it's the belt wearing or if the alternator is moving to be honest. Not sure how I would tell? I tighten it as much as I can each time using a large screwdriver as a lever (fairly unscientific!). I have recently replaced the impellor for the waterpump and that is now moving freely but I haven't checked the alternator (I'll do that tomorrow).

Thanks
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Old 07-01-2012, 15:08   #5
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Re: Yanmar 2GM20 squealing

Quote:
Originally Posted by delmarrey View Post
FYI alternator pulleys do year out, which wear the the belts extremely fast or just don't grip anymore. Especially the serpentine pulleys. Is the pulley very shinny in the grove?
Yes - it appears to be quite shiny. Should it be? Next question - is it a big job to change the pulley (sounds like it!)?

Thanks
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Old 07-01-2012, 15:08   #6
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Re: Yanmar 2GM20 squealing

Check for alignment as well. If it's cocked or off center, that can wear the system too.
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Old 07-01-2012, 15:11   #7
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Re: Yanmar 2GM20 squealing

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Originally Posted by vcsmithuk View Post
Yes - it appears to be quite shiny. Should it be? Next question - is it a big job to change the pulley (sounds like it!)?

Thanks
Iain
If you have an air impac wrench and a 15/16" socket the end nut will spin right off/on fairly EZ, if not rusty.

A highly polished pulley is the first indicator of excessive wear.
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Old 07-01-2012, 15:17   #8
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Re: Yanmar 2GM20 squealing

Is it a high output alternator and what is the state of charge of the battery bank it is charging?
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Old 08-01-2012, 02:25   #9
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Re: Yanmar 2GM20 squealing

Iain,to find out if the alternator is slipping in its adjustment, just make a scratch with a screwdriver across the adjusting bracket and the alternator and see if the alignment changes over time.
It is true that vee belt pulleys can wear but is is unusual. An easy check is to make sure that the sides of the vee are not scored or stepped, and that when an unworn belt is pressed hard into the pulley, it does not bottom against the base of the vee. If the pulley passes these tests and has no cracks etc. it is usable.
The belt should be tensioned to the engine's specifications, which will be probably half inch deflection with moderate thumb pressure on its longest run.
You can also buy aerosol packs of belt dressing which limit slip and wear.
Regards,
Richard.
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Old 11-01-2012, 02:49   #10
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Re: Yanmar 2GM20 squealing

Hi all - thanks for all the tips, very helpful indeed!

In the end I found the present belt to be excessively worn again, so I also checked the pulley wheel for rust as well (entirely possible as I do have a very old wooden boat!) and found there was a fair bit of rust and some shiny patches. I then ran the engine without alternator belt and ran a fine file in the pulley wheel which seems to have given me a good surface and still plenty of space for a new belt, which I have put on.

I suspect I have a standard alternator that comes with this engine, but I am fairly sure it wasn't the battery bank as they are brand new batteries (although heavily used as I only have space for two totalling 110 AH).

Using a ruler, the alternator pulley seemed to be very slightly out of alignment, maybe one or two degrees. I'm not sure how much this would have affected the wear, but I am also not sure how to correct it as the alternator bracket appears to be a casting.

I will only know if I've solved the problem in the next 4-5 running hours, but looking good early on.

Thanks again all.
Regards
Iain
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Old 11-01-2012, 04:55   #11
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Re: Yanmar 2GM20 squealing

If the pulleys are out of alignment, it will cause fairly fast wear on the belts. Once you get the pulleys aligned, try using a belt with the slots on the inside edge, they do not require as much pressure to get good traction on the pulley. You can check if your alternator is slipping by marking the bracket after you set the tension and watch if it moves.
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