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Old 24-04-2014, 13:51   #1
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Pulley alignment for serpentine belt

I am in the process of upgrading my Beta M35b engine from a 40 amp(?) factory alternator to a 200 amp Balmer AT alternator with a serpentine pulley system. The alternator and pulley kit came from Electromaax and was ordered specifically for my engine. Not surprisingly based on all the other issues/problems I ran into with Electromaax, the pulleys, when installed, do not align perfectly with each other. The kit had a spacer for each pulley but they still do not line up.
I am wondering how much of an alignment error is acceptable assuming a belt span of about 9 inches between pulley contacts.
I realize that perfect alignment is ideal and will allow longest belt life but I am wondering if I can get away with a 1/8 misalignment without causing a big belt wear problem. How about 1/16" misalignment?
I do not have the exact misalignment figures yet as the pulleys have different thicknesses for the edge to first groove dimension and a simple straight edge test to the side of the pulley is not conclusive. I will have to do some detailed measuring taking edge thickness into account.

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Old 24-04-2014, 14:15   #2
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Re: Pulley alignment for serpentine belt

I don't know the correct answer to your problem but my gut says to make it as accurate as possible. A couple of hours spent measuring, shimming, etc. might be cheap preventive maintenance.

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Old 24-04-2014, 16:25   #3
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Re: Pulley alignment for serpentine belt

The answer to your alignment question is on page 4 of this PDF. 1/16" offset over each foot of distance run between pulleys.

Also, this is a link to help you derive a belt part number from the dimensions of the belt.

Micro-V Heavy-Duty Belts | Gates Corporation

Remember that most successful serpentine belt systems use a spring-loaded tensioner because a belt will shorten as it heats up. If the tension is set when the belt is cold the belt will increase tension as it heats up under load. Too much tension can ruin bearings in the belt driven devices. Not enough tension will allow the belt to slip.

Some of what you might have heard may be true.
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Old 24-04-2014, 18:47   #4
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Re: Pulley alignment for serpentine belt

Thank you very much Guy! Exactly what I was trying to find out!
My engine does not have sufficient spare space to install an automatic belt tensioner but it ran fine for some 750 hrs of run time without a belt tensioner on the original V belt drive and I would think that a V belt system is more susceptible to belt tension errors and requiring more tension.
I will look into belt length vs temperature and try to keep that in mind when I set up belt tension when the system is cold. Without checking Google, I have always heard that serpentine systems require less tension so I m hoping that there will be enough room to shrink and not overload the bearings.

I will make some new spacers tomorrow and see how that will work out.

Thanks again!
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Old 12-05-2014, 20:15   #5
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Re: Pulley alignment for serpentine belt

Interested to hear serpent belts shorten when heated....find that a hard one! However I report my serpent belt is now slipping on startup or shortly after when the reg winds up the amps on the 180 Electromaax alt. Never used to but the belts been on and extensively used for 2 yrs, perhaps time to change it.
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