New Alternator installed - but how to do a good belt tension?

I installed a new high output (105 amp) HD alternator. The old unit was not putting out so i figured why not spend a little extra and get more amps (thanks FF)

The only real challenge was to transfer the pulley from the old unit, had it done at a shop in the marina.

Now I am wondering if the belt is too loose, seems to move a little up and down when running, any rule of thuimbs of how tight or loose belts should be?

And whats a good method to get a good and tight belt?

I use a prybar, normally a large screwdriver for tension while I tighten the bolts.

I don't make it as tight as I can get it, rather just tight enough so that when you try to rotate the alternator with your hand (by grabbing the cooling fins) the pulley will not slip.

Yes there are tension tools, but I read about "my" method and it has worked for me for many years and I have never burned bearings from being too tight, and the belts don't slip or bounce.

*


-- Edited by jleonard on Tuesday 2nd of August 2011 07:44:33 PM

I have always done the same thing as jleonard does and normally works fine. *Just don't overdue it. *On the Perkins the same belt runs the water pump, to much tension will run the bearings out of it.

The old 60 amp Delco's had a automotive style bracket and there is a lot of flex in them, so a little movement isn't unusual. *Just start out with a new belt and check your pulleys for wear and proper belt depth. *Since you are going to a higher output alternator check it under heavy load for slippage. *Some higher output units may really need a dual pulley setup to keep the belt from slipping.

Larry B

All you need is enough tension to keep the belt from slipping.

THis will depend on the % of belt wrap, if its high (goes almost 1/2 war round the pully ) lowerr tendion is fine.


You are looking to keep slippage low as it causes heat in the pulley , which is passed to the font bearing .

With the batts low start the engine and after 5 or 10 min shoot the temp of the alt , and the pulley.

If the alt is hotter than the pulley , the tension is fine.

This might not be the most scientific method of doing it (or even correct), but what I have always done is to find the longest span the belt makes and twist the belt with my fingers. It should start to get hard to turn at 90 degrees. It seems simplistic, but it has always seemed to work for me.

FF wrote:
All you need is enough tension to keep the belt from slipping.

THis will depend on the % of belt wrap, if its high (goes almost 1/2 war round the pully ) lowerr tendion is fine.


You are looking to keep slippage low as it causes heat in the pulley , which is passed to the font bearing .

With the batts low start the engine and after 5 or 10 min shoot the temp of the alt , and the pulley.

If the alt is hotter than the pulley , the tension is fine.

Click to expand...

*yes, definitively need to be tested under load. if the batts are 100% charged the alternator is not under load and the belt is basically just going around..

its a dedicated alternator belt and covers a good part of the pulley, probably 1/2 way around.

thanks to everyone, i will try some of those methods.

Per wrote:FF wrote:
All you need is enough tension to keep the belt from slipping.

THis will depend on the % of belt wrap, if its high (goes almost 1/2 war round the pully ) lowerr tendion is fine.


You are looking to keep slippage low as it causes heat in the pulley , which is passed to the font bearing .

With the batts low start the engine and after 5 or 10 min shoot the temp of the alt , and the pulley.

If the alt is hotter than the pulley , the tension is fine.

Click to expand...

*yes, definitively need to be tested under load. if the batts are 100% charged the alternator is not under load and the belt is basically just going around..

its a dedicated alternator belt and covers a good part of the pulley, probably 1/2 way around.

thanks to everyone, i will try some of those methods.

*1/4" deflection down from a straight line*on the long*span*is what will work.* Plain and simple.* Don't forget to tighten after four or five hours of run time.

We have 2 alternators that we tension using SS fork/fork turnbuckles.* They're*easy to adjust for the correct*tension.

Larry M wrote:
We have 2 alternators that we tension using SS fork/fork turnbuckles.* They're*easy to adjust for the correct*tension.

Click to expand...

*** Nice!

Larry M wrote:
We have 2 alternators that we tension using SS fork/fork turnbuckles.* They're*easy to adjust for the correct*tension.

Click to expand...

Now that is an elegant solution Larry. It also avoids the horrible discovery that you have levered against a temperature or pressure sender that was hidden in the gap between alternator and engine block. Any Yanmar owners out there will likely know what I am refering to!

i checked the tension again, and it seems to be good according to the above mentioned methods.
also is similar to the tension on the other engine.

however when i run the engine i get some squeaky squealing sounds, pronounced at lower rpm, this was also occurring prior the new alternator.
the other engine does not produce this sound.. any clues?

Per, It could be you need to change the belt. Old belts get a hard glaze on the contact surfaces which make them slip and squeal. I don't recommend belt lubricant - strictly a temporary remedy.

Per wrote:
i checked the tension again, and it seems to be good according to the above mentioned methods.
also is similar to the tension on the other engine.

however when i run the engine i get some squeaky squealing sounds, pronounced at lower rpm, this was also occurring prior the new alternator.
the other engine does not produce this sound.. any clues?

Click to expand...

.

Yes and also check the belt depth, could be the belt is bottoming out in the pulley. Worn pulley are a concern too.

Take a good look at the sheaves. If the bottom of the sheave v-groove or the bottom of the belt is shiny, the belt is not riding correctly. It should contact ONLY the sheave sides, not the bottom.

The sheave sides should be smooth and the tapered sides appear straight, no dips or worn grooves or steps. Anything like that reduces the contact patch, friction, and the belt may slip even if it is screaming tight [ not good].

The belt may be worn or the wrong size, cross section. I've had this happen and it took a couple replacements before I took a hard look at why and realized the cross section was wrong. I'd just replaced the slipping belt with the same type. When I got the correct belt there were no problems after.

The sheaves may be glazed. The glaze can be removed with some sandpaper or a small wire brush and solvent. A thorough wipe down afterwards with something like acetone to completely remove any trace of oily residue should help.

Larry M wrote:
We have 2 alternators that we tension using SS fork/fork turnbuckles.* They're*easy to adjust for the correct*tension.

Click to expand...

That is so smart.* Very clever, Larry.* I am going to see if that will work for mine as well, and I don't see why not.

Per wrote:
however when i run the engine i get some squeaky squealing sounds, pronounced at lower rpm, this was also occurring prior the new alternator.
the other engine does not produce this sound.. any clues?

Click to expand...

My grandfather use to press a soap bar against a squealing alternator belt.*Works great. *