Tolerances on polyvee alternator belts

[RobbieH]

I've just upgraded my alternator from 40A with V-drive to 70A with polyvee drive. Would like to check the mechnaical installation with the good people of the parish.

How fussy do I need to be about alignment, runout, etc.? Has anyone got any rules of thumb for tolerances for parallel alignment, angular alignment, etc.?

For tension I'm working on 10mm deflection at middle of longest run (pressing with thumb). Is there a more scientific way of setting up the belt than this?

Cheers,

Robbie.

 

[Avocet]

I used to have one, but gave it up. In my case, I was simply asking too much of it. At the time, I used to put a straight edge between the pulleys. It depends on how far apart they are, and how wide the belt is. My pulleys were only at about 300mm centres, with a belt that was about 20mm across, so I used to try and align them very closely (about 0.25mm or better). I'm sure you could get away with more over a longer belt run and / or with a narrower belt. All I can suggest is taking your best guess and monitoring condition and black dust carefully for the first hundred hours or so.

 

[rob2]

It has to be best effort really, doesn't it? As Avocet says, you can get away with more on a long belt run but it's worth getting it so you can't detect any misalignment. That will give you best longevity and quietest running (belts can be noisy). If you think it is a bit noisy, try rubbing a little soap onto the belt's contact surface - careful you don't get dragged in! If the noise diminishes you probably have some misalignment, so at least you know you're not running a bearing.

There are tension guages made but they're an uneccessary expense when 10-12mm deflection on the longest run will be OK.

Rob.

 

[2Tizwoz]

This Fenner pdf describes what tolerances are recommended and how to set them up.(click)

 

[RobbieH]

This Fenner pdf describes what tolerances are recommended and how to set them up.(click)

Thanks - that is the info I was looking for.

 

[macd]

RobbieH: you're clearly trying to get the set-up right and if you do you won't be disappointed. Polyvees are so superior to ordinary V-belts it's a wonder anyone fits the latter these days (certainly car manufacturers haven't for donkey's years). Mine (a standard Beta upgrade when I bought the engine) had done over 2000 hours without adjustment or problems when I changed it for no reason other than caution.