Alternator belt length

[mike202]

Ok I have tried a few belts now. The Optibelt 11.3x 912 I had used for a fair while was looking a bit old and had one shim between the generator pulley wheel. I made a mistake in my earlier post. I said this was a new pulley wheel is in fact the one I got when I had the alternator conversion done, so came with the Bosch alternator conversion kit. It still looks new though which is why I got confused.
The crank pulley is a new billet aluminium CSP one that CSP recommend using a belt 11.3x 912.
The SPA 12.7mm belts I tried are too wide for the crank pulley.

I went on a short test drive after fitting both the 900 and the 907 which both fitted with 8 shims but I found that when back home there was black particles all over the engine bay. I surmised this was the crank pulley shredding the outer edge of the belts. The gap at the top of the crank pulley wheel is 11.5mm approx.

The SPA 907 belt after a 5 mile test.

I then tried another belt I had lying around. This is a new 11.3x912 belt

This fitted with one shim which ideally is not enough for a new belt, and I am not a big fan of the toothed belts. So I ended up back at the Optibelt 11.3x912 which I got from machine7
[emoji23]
Fitted this new belt which measures correctly width wise, and I have 6 shims so I’m a happy amateur mechanic. [emoji106][emoji3]

 

[Moseley]

Useful post Mike, thanks for sharing your results.

I’ve just gotten round to fitting the Optibelt 11.3x912 although I haven’t been able to start the bus yet to see where it settles. Currently I’ve used 7 shims, so am happy that that setup is working fine and no need to find an alternative.

It certainly seems from the measurements I’ve taken that the belt length varies from manufacturer to manufacturer. Bear in mind that the original ones I tried from JP Group are the same advertised length as the Optibelt, but are substantially longer. Hopefully Optibelt will continue manufacturing these belts for us air cooled folks.


Sent from my iPhone using Tapatalk

 

[atafonso]

These engines were designed originally with dynamos, but there are no specific dynamo or alternator bottom pulleys.
Because I'd had some many issues with currently available alternator belts, I measured the inner length between the pulleys using some wire, and then searched for a drive belt to suit.

Sparky, i also thought for a long time that the pulleys were the same, but there’s actually two sizes of stock crank pulley.
I have had both with me and could compare the size difference. With the bigger one, the 912 belt fits perfectly and does not require the removal of all the shims to make the belt tight.

Abel

OK, every day's a school day. I measured the ones I have lying around and they are all the same.
I'm running a Berg Equalizer, so out of interest what are the sizes?

Sorry Sparky to take so long to reply :shock:
I don`t have one of the bigger ones anymore, so i can`t measure it. But i did compare when i had and one was slightly bigger than the normal ones. They look exactly the same right up to the very edge of the pulley. I also had one bigger pulley from a 1962 Split Screen engine 1200cc, and they were the same size but the internal stamping was different, just the design, the 62 being with no dimples unlike the later ones.
Abel

 

[sparkywig]

That's OK Abel, just wanted to know for reference purposes.

 

[purpledog07]

Glad you got something suitable now.
To save anyone the expense and disappointment: Avoid gates belts for aircooled vw's. I found one that's the correct length but the 'V' profiles are angled differently which would cause them to wear rapidly against the pulleys.
I was trying to find something better quality than the optibelt but there doesn't seem to be anything else.
I ran 11.3 x 905 on standard pulleys and currently on Scat and CSP billet, perfect fit.
A good tip to prolong belt life when the vehicle is off the road is to turn the engine over regular, even if by hand only, and always try to leave with the join In the belt on a straight run.

 

[purpledog07]

Glad you got something suitable now.
To save anyone the expense and disappointment: Avoid gates belts for aircooled vw's. I found one that's the correct length but the 'V' profiles are angled differently which would cause them to wear rapidly against the pulleys.
I was trying to find something better quality than the optibelt but there doesn't seem to be anything else.
I ran 11.3 x 905 on standard pulleys and currently on Scat and CSP billet, perfect fit.
A good tip to prolong belt life when the vehicle is off the road is to turn the engine over regular, even if by hand only, and always try to leave with the join In the belt on a straight run.

Just checked, I was running 905, now 912mm, only a couple of shims though when new.

 

[mike202]

The belts vary between suppliers even though they say the same length of 912mm. Try to find one that fits best.