Yanmar Alternator Belt Tension Problem

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Thames 4 Blood

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I am having a hell of a problem keeping my alternator belt tight on my Yanmar 4JH3-TE engine.
Never mind the difficulty of pulling the alternator across to get the tension right in the 1st place.
No matter how tight I do the tensioning bolt it will not maintain the correct strain.
I have replaced the bolt.
Other than ditching it for a serpentine setup what could I try?
Thanks
 
Thames 4 Blood said:
Other than ditching it for a serpentine setup what could I try?
Click to expand...

I'm assuming you're loosening the other bolt(s) on which the alternator pivots?
If so, I once fitted a bottle screw with ball-end ('Rose') joints to allow positive determination of the distance. It's sometimes puzzled me why even high end cars use just a bolt and a slot, but I guess it works...usually.
 
Thames 4 Blood said:
I am having a hell of a problem keeping my alternator belt tight on my Yanmar 4JH3-TE engine.
Never mind the difficulty of pulling the alternator across to get the tension right in the 1st place.
No matter how tight I do the tensioning bolt it will not maintain the correct strain.
I have replaced the bolt.
Other than ditching it for a serpentine setup what could I try?
Thanks
Click to expand...

Are you sure that it is the right belt size? I often see belts which have an outside flat surface which is below the level of the outside edge of the pulleys, particularly the alternator pulley., although all the pulleys should have the same depth/width. If your belt is not flush with the outside edge of the pulleys it is the wrong size and you will be forever adjusting it. :(

Richard
 
Use a cogged type belt.
Gates are arguably the best brand.
RS sell conti these days, they will be OK.
https://uk.rs-online.com/web/c/pneu...-belts/?searchTerm=Contitech&searchType=Brand
Do you have a problem with the belt slipping, or is it just not as per manual?
Is the belt wearing and losing tension, or just never right?

If it's a wearing problem, you can give the belt an easier life by idling at higher RPM when you first start the engine and the batteries demand a lot from the alternator.
The critical thing with belt size is that the belt must not bottom out on the pulley.
 
Topcat47 said:
+1 for the "cogged belt types. The OEM Bee belts always slacken off, then wear and eventually bottom out on the pulley.
Click to expand...

Never had any tension problems with my 4JH4AE. I eventually changed the original belt after 7 years use (approx. 1,700 hours). The old belt still looks OK but I could just spot some cracking in places. Yanmar supplied original and replacement were both cogged type V-belts. Tension always remained fairly constant over the season until it was removed for winter storage.

Not a lot of black dust when using the standard 80A alternator. I believe that the cogged design will handle more extreme curvature (i.e. smaller pulley) and are also better at transmitting HP from engine to alternator with less slippage.
 
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macd said:
If so, I once fitted a bottle screw with ball-end ('Rose') joints to allow positive determination of the distance. It's sometimes puzzled me why even high end cars use just a bolt and a slot, but I guess it works...usually.
Click to expand...

My Volvo D1-30 came with a screw arrangement, similar in principle to your fix, from the factory. As you say, it's weird that many still don't.

Pete
 
Thames 4 Blood said:
I am having a hell of a problem keeping my alternator belt tight on my Yanmar 4JH3-TE engine.
Click to expand...

I have a vague recollection that Yanmars expect a rather wider belt than is normally used, so that if you use a standard one it will bottom out and cause problems. Or do they expect a narrower one? Vague recollection , as I said.
 
I had the same problem with the 4JH4-HTE fitted to our boat.

This has a Balmar 110 AMP Alternator and smart regulator. I found that fitting a longer bolt which protuded far enough to get a flanged nut on fixed the problem.

I suspect the aluminium thread in the alternator was defective, causing the adjustment to back off. I will remove the unit and helicoil the thread. While it is off I will make up a threaded adjusting mechanism.

Which is what should have been fitted by the engine maker........................................

IMHO, of course!
 
Are you sure the bolt on the alternator is slipping, or is the belt just rapidly wearing away? This also results in a lack of tension, as the belt wears on the sides and then rides deeper in the pulleys. There'll be black belt dust in evidence in this case. This was happening to on our engine due to some rust on the pulleys chewing up the belt. After polishing them and replacing the belt, the problem has gone away.

My low-tech tensioning aid is a wooden bung (as sold for plugging failed seacocks) hammered in between the alternator and the bracket. This does the job, although a turnbuckle would be much nicer.
 
You shouldn't need to be hammering anything to get the right belt tension.
The correct tension is not a huge amount of pre-load.
Too much tension will wear the bearings.
If the tension keeps reducing, check the alternator and water pump for play.
Also check the alternator is not moving on its mountings. It could be something silly like the bolt which clamps the slotted adjuster is bottoming out and not clamping properly.
Washers and spacers go awol etc.

But many of us are pushing the limits of simple vee belts. Cars with big alternators have multi-vee belts with spring tensioners for several reasons, one is they transmit more power.
 
Thank you all for the thoughts. It is an original Yanmar belt and the main concern is that it is wearing away quickly. Alarming ammt of black dust created. We are half way from Inverkip to Gib and have motored a lot and I am readjusting belt every 24 hrs or so. Its pretty early here and wife is asleep but I will check the pulleys for rust ( I dont think there is any ) and I may fit a new belt today. I have 2 spares both Yanmar originals and neither are toothed.
Will have another play today and will report back for interest sake.
THANK YOU FOR TAKING THE TIME!!!
Mark
 
rotrax said:
I suspect the aluminium thread in the alternator was defective, causing the adjustment to back off. I will remove the unit and helicoil the thread. While it is off I will make up a threaded adjusting mechanism.
Click to expand...

I'm sure someone of your background won't need this suggestion, rotrax, but the advantage of a bottle screw (or anything else with one left-hand and one right-hand thread), is that the adjuster can simply be wound out in situ after slackening the lock-nuts.: no need to remove anything.
 
Thames 4 Blood said:
Thank you all for the thoughts. It is an original Yanmar belt and the main concern is that it is wearing away quickly. Alarming ammt of black dust created. We are half way from Inverkip to Gib and have motored a lot and I am readjusting belt every 24 hrs or so. Its pretty early here and wife is asleep but I will check the pulleys for rust ( I dont think there is any ) and I may fit a new belt today. I have 2 spares both Yanmar originals and neither are toothed.
Click to expand...

How confident are you in the state of your alternator? My 1GM10 started eating belts on the boat's delivery trip to me. It turned out to be an faulty alternator bearing; completely free when cold but got progressively stiffer as it warmed up. Eventually it had the decency to seize, which made diagnosis easy, but until then it seemed to be turning fine.
 
When I acquired a Yanmar GM, at first it ate belts at a high rate, with lots of black dust. Eventually I realised that the flanks of the crankshaft pulley were rough due to corrosion. A session with emery-paper worked wonders. Worth checking.
 
macd said:
I'm sure someone of your background won't need this suggestion, rotrax, but the advantage of a bottle screw (or anything else with one left-hand and one right-hand thread), is that the adjuster can simply be wound out in situ after slackening the lock-nuts.: no need to remove anything.
Click to expand...

Exactly.

I use Gates toothed belts and they seem pretty durable, but the previous owner must have operated with a slack or slipping OE non toothed belt by the amount of nasty black rubber dust I cleaned off the power unit. Most of it is now in the bilge sump where it looks disgusting!

Another job for the vacuum pump.................................
 
Thames 4 Blood said:
Thank you all for the thoughts. It is an original Yanmar belt and the main concern is that it is wearing away quickly. Alarming ammt of black dust created. We are half way from Inverkip to Gib and have motored a lot and I am readjusting belt every 24 hrs or so. Its pretty early here and wife is asleep but I will check the pulleys for rust ( I dont think there is any ) and I may fit a new belt today. I have 2 spares both Yanmar originals and neither are toothed.
Will have another play today and will report back for interest sake.
THANK YOU FOR TAKING THE TIME!!!
Mark
Click to expand...

I've swapped my original Yanmar plain belt for a Gates cogged belt and they are definitely an improvement. I'll bet that your belt is not flush with outside of the pulleys and that is the source of the problem.

Richard
 
Thames 4 Blood said:
Thank you all for the thoughts. It is an original Yanmar belt and the main concern is that it is wearing away quickly. Alarming ammt of black dust created. We are half way from Inverkip to Gib and have motored a lot and I am readjusting belt every 24 hrs or so. Its pretty early here and wife is asleep but I will check the pulleys for rust ( I dont think there is any ) and I may fit a new belt today. I have 2 spares both Yanmar originals and neither are toothed.
Will have another play today and will report back for interest sake.
THANK YOU FOR TAKING THE TIME!!!
Mark
Click to expand...

Sounds like it is indeed a problem with rusty/rough pulley surfaces, as earlybird and myself suggested. Run your finger inside the pulley grooves all around all of them to check. It should be perfectly smooth on both sides. I did a round of sanding and polishing by hand until I realized I could just smear polishing paste on the pulleys, set the belt intentionally lose and then run the engine for a few minutes, then wipe the pulleys clean, which did a great job and no more issues with belt wear (or tension, as result thereof).
 
RichardS said:
I've swapped my original Yanmar plain belt for a Gates cogged belt and they are definitely an improvement. I'll bet that your belt is not flush with outside of the pulleys and that is the source of the problem.

Richard
Click to expand...

+1 I had the same problem as the OP, first suspected the pulley surfaces, then switched from Yanmar OEM to Gates cogged and the problem was instantly and completely solved. Gates advice was that a tight small-pulley alternator turn is asking for trouble with the std belt in the absence of dynamic tensioning. Go this route and one enters the trade-off zone between bearing and belt life.

So Gates every time as a first fix ;)
 
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