Alternator position: Old vs. New Belt

[bsangs]

Happy St. Paddy's Day all. Spent mine doing boat maintenance.

Changed the belts on my Yanmar 3GM30F today. Purchased the boat last March, and I have no idea when the previous owner last changed them. They were fine last season, but I wanted new ones. Took the old ones off, cleaned rust from the pulley wheels, and put on the new belts. Neither the water pump pulley or the alternator pulley were able to be put back in the exact position they were in with the older belts, so wanted to see if this is a problem.

The water pump at least got very close to where it was under the old belt, but the alternator is nowhere near the same slot, and I cannot get it to budge any higher with the new belt attached. Could barely even get the new belt attached, but finally stretched it enough to fit. I’ve attached some photos showing what I mean. Also, the older belt set inside the pulley wheels much deeper than the newer ones, even though it is the exact same model belt. Hoping that's just what happens with normal wear and tear.

Do I have a problem here, or is this just the way it works with new belts? And if I do have a problem, how in the hell do I get that alternator to slide back up to the same position with the new belt attached? As always, thanks in advance.


Old belt attached.


Old belt alternator position



New belt attached


Alternator position with new belt attached

 

[Loren Beach]

I tried several different types of belt on our OEM Universal diesel. They all worked, but not equally.
I had quite a bit of belt dust initially until, following some good advice from owners here, changed to a certain # Gates HD belt. I also had good luck with an unusual-looking design called a "top cog".

In general, you do not want the belt to ride down i the pully groove so far that it reaches the bottom, and not so far up as to have belt visible above the side of the groove. I used to know some trivia about belts for the Universal's, so a Yanmar owner will have to check in here next. (EY used to install Yanmar engines when the customer requested one.)

Our current engine is a Betamarine which uses a flat belt (aka a "serpentine" belt), and is expected to last for many many years. It has not shed any 'dust' at all.

 

[Pete the Cat]

Sort of hard to diagnose from here. But I do not see any immediate problem, but it could be a number of things and. longer term issue. If the belt is not seating well on the pulleys--that is: that the base (not just the sides) of the V belt is in contact with all three pulleys, it may have been that the original belt was never the proper size and simply wore into the pulley over time. I am always suspicious that a lot of belt dust (actually, any significant amount) indicates a misaligned alternator or the wrong belt. Properly fitted belts can last thousands of hours. While there are generally multiple belts that "will work" on an engine, there are fewer that are properly shaped to maximize contact with all the pulley grooves. I would carefully check that the old belt was actually the right one in the first place. Often this gets complicated when folks add new alternators with different pulleys though yours looks to be original.

 

[bsangs]

Sort of hard to diagnose from here. But I do not see any immediate problem, but it could be a number of things and. longer term issue. If the belt is not seating well on the pulleys--that is: that the base (not just the sides) of the V belt is in contact with all three pulleys, it may have been that the original belt was never the proper size and simply wore into the pulley over time. I am always suspicious that a lot of belt dust (actually, any significant amount) indicates a misaligned alternator or the wrong belt. Properly fitted belts can last thousands of hours. While there are generally multiple belts that "will work" on an engine, there are fewer that are properly shaped to maximize contact with all the pulley grooves. I would carefully check that the old belt was actually the right one in the first place. Often this gets complicated when folks add new alternators with different pulleys though yours looks to be original.

According to Yanmar, it's the correct model belt. The previous owner never swapped out the alternator, and the owner prior to him replaced the original Universal engine with this 3GM30F around 2004, so I'm thinking it's the original alternator. The old belt worked, not a single issue with it last season, but I could tell it was old, and wanted to be safe and replace it before this season. The new one appears to fit in the pulleys fine, but there's no way I can get that alternator to slide up into its previous position.

 

[Pete the Cat]

Yanmar always sells an alternator with their new engines (unlike some) that has matching pulleys (again unlike some cobbled tractor engines), so maybe that is not the issue if everything looks right (hard to tell--I am sympathetic). If you are getting a lot of belt dust something is wearing and you will need to check tension regularly in the first 50 hours. A very light dust in 100 hours might not be a problem, but if it is more than that, something is wearing. I would not go anywhere without an extra belt. Is this alternator externally regulated? (especially with one of those old Auto Mac manual regulators)? That could cause the belt to wear very quickly in circumstances where you have a huge load on the alternator. It could be just normal wear and stretch. I would just watch it closely and go sailing.
The future is serpentine belts. And common rail engines with computers like our cars have that will tell us instantly where the problems are. But we are not there yet.

 

[bsangs]

Yanmar always sells an alternator with their new engines (unlike some) that has matching pulleys (again unlike some cobbled tractor engines), so maybe that is not the issue if everything looks right (hard to tell--I am sympathetic). If you are getting a lot of belt dust something is wearing and you will need to check tension regularly in the first 50 hours. A very light dust in 100 hours might not be a problem, but if it is more than that, something is wearing. I would not go anywhere without an extra belt. Is this alternator externally regulated? (especially with one of those old Auto Mac manual regulators)? That could cause the belt to wear very quickly in circumstances where you have a huge load on the alternator. It could be just normal wear and stretch. I would just watch it closely and go sailing.
The future is serpentine belts. And common rail engines with computers like our cars have that will tell us instantly where the problems are. But we are not there yet.

Oh don't worry, I have three extra belts each for the water pump and alternator on board - Yanmar OEMs and a couple Gates heavy duty belts. Mama didn't raise no dummy. Might've raised a hoarder, but that seems to come in handy for sailing. Will keep an eye out for any excessive dust once the engine starts running again. Didn't appear to be much of an issue with the old belt. There was some, but not much. Slow down on the common rail deployment please! I'm still learning the ins and outs of regular Joe Six Pack diesel.

 

[Second Star]

I am intrigued by a couple of things from your pictures. In the pic of the old belt, there is visible "wear" on the alt bracket that would indicate the alt has been moved further and further outward over time to account for the belt stretching. Does your new belt place the alt in about the inner part of the "worn" area?
The other thing that interests me is that the bolt that tightens the alt to the adjustment bracket faces aft. In the pictured arrangement this is what it must do to properly tighten the alt to the bracket. This seems odd because the bolt head is then in an awkward position, out of sight and harder to work with. Is the bracket on the wrong side if the alt lip? ie Should the bracket be on the forward side of the alternator so the bolt is easily adjustable? Any indication that the alt is misaligned?

 

[bsangs]

I am intrigued by a couple of things from your pictures. In the pic of the old belt, there is visible "wear" on the alt bracket that would indicate the alt has been moved further and further outward over time to account for the belt stretching. Does your new belt place the alt in about the inner part of the "worn" area?
The other thing that interests me is that the bolt that tightens the alt to the adjustment bracket faces aft. In the pictured arrangement this is what it must do to properly tighten the alt to the bracket. This seems odd because the bolt head is then in an awkward position, out of sight and harder to work with. Is the bracket on the wrong side if the alt lip? ie Should the bracket be on the forward side of the alternator so the bolt is easily adjustable? Any indication that the alt is misaligned?

New belt places the alt below that worn area, actually. (You can see it in the third and fourth photos.) Nothing appears to be misaligned. As for how the bolt and bracket are facing? I've no idea if it's correct, but the bolt head was not difficult to access. Couple turns with a ratcheted wrench loosened it.

 

[SurfingGuru]

I tried several different types of belt on our OEM Universal diesel. They all worked, but not equally.
I had quite a bit of belt dust initially until, following some good advice from owners here, changed to a certain # Gates HD belt. I also had good luck with an unusual-looking design called a "top cog".

In general, you do not want the belt to ride down i the pully groove so far that it reaches the bottom, and not so far up as to have belt visible above the side of the groove. I used to know some trivia about belts for the Universal's, so a Yanmar owner will have to check in here next. (EY used to install Yanmar engines when the customer requested one.)

Our current engine is a Betamarine which uses a flat belt (aka a "serpentine" belt), and is expected to last for many many years. It has not shed any 'dust' at all.

Loren, do you happen to have a belt number for the universal? My mechanic said my boat was fitted with the wrong belt. It does seem to vibrate more then I'm used to. Maybe its a sign its falling too far down into the pulley.

 

[Loren Beach]

Unfortunately I do not. My former universal has gone to a new owner, along with notes on belts. And a couple of spare belts.
Our new Betamarine uses a flat ("serpentine") type of belt.

We did get into some V belt trivia in reply 11 in this previous thread, however. https://ericsonyachts.org/ie/threads/upgrading-from-v-belts-to-serpentine.6726/#post-54624

You may want to do some searching for v belt info on this site.

 

[Christian Williams]

I think I had a Gates XL 7390 belt on the M25, with upgraded bracket. I think a 7400 also worked.

Note pivot bolt on the upgrade. Many reports of sloppy pivot bolt, caused by Universal (or Balmar, or the upgrade kit, or somebody ) supplying Imperial bolt not metric. The pivot bolt should fit firm and not wobble.

Here's a thread: https://ericsonyachts.org/ie/threads/v-belt-tension.15822/