Alternator - scratching head

[jtorre4272]

Hi folks,

I am replacing my alternator with a Bosch reman i just received from Pelican yesterday.

https://www.pelicanparts.com/More_Info/928603011FX.htm?pn=928-603-011-FX-M14&gclid=EAIaIQobChMI5pfv1sOHgAMVYv7jBx0e_Ae1EAQY ASABEgLMOfD_BwE

Note the small pulley, which is what I want, as I don't want my voltage to drop at idle. Apparently this is supposed to be the factory setup.

I pulled my old alternator and noticed it has a larger pulley. The previous owner did tell me when he had the engine overhauled, he used an underdrive kit. This explains the pulley size I guess.

Anyway, when I went to reinstall the belt, the turnbuckle is simply too short and getting proper belt tension seems impossible. I am running a contitech 6pk1000 which seems like it should be the correct part number based on my look up. The smaller pulley is the cause.

What's going on here? The turnbuckle appears original, and the alternator pulley and belt seem like the correct designs from factory. I don't want to reinstall the under drive pulley. I hated it. Some pics: Note the amount of threaded rod exposed as a result of the smaller pulley. The alternator in the box is the core i am returning with the big pulley.

any help?

[kdjones2000]

Go to your autoparts store and order a new belt. They had to have gone to a larger belt for the underdrive pulley.

Good luck....

[zedsn]

Looks like you are using the correct belt for the stock setup and I am wondering if the PO lopped some meat off of the turnbuckle assembly is why it could be too short? Maybe you can look online to see what the correct length should be.

[zedsn]

My turnbuckle itself is 6 3/4" long and I can get a factory pulley diameter if you need it.

[kdjones2000]

Did the PO replace the drive pulley as well, the one on the crank? That is the only way I would see that you could use the stock belt with that larger alternator pulley.

Looking at LR's site, they use a smaller drive pulley with the larger alternator pulley, so that is probably what is going on here.

https://www.lindseyracing.com/LR/Porsche/LRA-944-PUL-ALT.html

[nize]

okay i have to ask, why would anyone want to under-drive their alternator? wouldn't you want as much juice as possible?

edit: i did some google searching and it seems the goal is to reduce load on the engine to make more power. now i'm curious how much HP (or torque?) gain you would get with an underdrive. is it worth it?

[kdjones2000]

It also saves the alternator/bearing during racing, as you are at high revs much more often.

[jtorre4272]

Thanks everyone for your comments. The PO did in fact install an overdrive pulley on the crank combined with underdrive on alternator, so that is exactly what happened. Since I didn't want to swap crank pulleys, i got lucky and opted for a Continental belt that is 972mm vs 1000mm and it was a perfect solution. The turnbuckle does not have excess threads exposed and i adjusted the belt to flex 1/4" at its longest point

I think the PO got a little trigger happy with LR parts. No reason for him to have done what he did with pulleys for a street application. Not worth the grief. For a high rev racing app, sure.