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Thu May 08, 2008 7:47 pm

I'm finally nearing the end of my 25hp rebuild. This afternoon I went to rig up the fan belt and generator pulley, and ran into two issues...

1) the 13x850 belt is too small. The belt that came with the engine fits fine, of course, but I can't discern any markings other than a faint VW logo. I have no idea what size it is, but it is significantly longer than the 13x850. I remember trying a 900mm 'normal' belt when I first got the car, and that didn't fit, either...

2) the shop that rebuilt my generator left out the little spacers that go between the pulley and the bearing, thus when you tighten up the nut, it binds and freezes the whole assembly. Does anyone have a source for these spacers? The last time this happened (with a Bosch rebuilt generator, no less!) I scavenged one from a core generator, and ruined the unit in the process. The first pic is my generator, the 2nd is a core with said spacer.

Thu May 08, 2008 9:09 pm

Your "toothed" belt is not correct. Normal 13x850 mm belt without teeth fits fine.

Fri May 09, 2008 4:51 am

I probably have that spacer Thom, drop me an e-mail with your address and I'll send it out tomorrow. zarwerks@charter.net

As for the belt sizing, it has always been perplexing to me. I have seen VW docs that say the correct size is 850x13, but I have had one (not toothed) and there is NO WAY it wold fit. I have used 900s, 930s and even 950s. This with stock pulleys. I think the bottom line is as long as the width is correct (13mm on the widest part) use what you can find fits. There is a Gates belt that works perfectly somewhere.

Fri May 09, 2008 8:35 am

virtanen wrote: Your "toothed" belt is not correct. Normal 13x850 mm belt without teeth fits fine.

That doesn't make sense: 850mm is 850mm - the size difference between the belt that fits and the 13x850 is significant. Are Finnish mm bigger than US mm? :)

I've used 900mm and 905m toothed and non-toothed belts on later motors and there was no fit or function difference between them.

Yes, I know it's not correct, but it's $10 belt I can get locally and get things going while I look for the 'correct' belt.

Fri May 09, 2008 9:35 am

13x850LI (focus on LI) is correct. LI means the inside diameter. Some belts are marked with outside diam (LA). I recall the correct is 930 but I´ll have to check that. I have correct belts with both markings somewhere. Profile A is 13mm outside width and 8mm inside.

Fri May 09, 2008 10:56 am

HeSa wrote: 13x850LI (focus on LI) is correct. LI means the inside diameter. Some belts are marked with outside diam (LA). I recall the correct is 930 but I´ll have to check that. I have correct belts with both markings somewhere. Profile A is 13mm outside width and 8mm inside.

Now we're getting somehere - I didn't know about LI's and LA's...

So what would the outside diameter be?

I found a site to calculate the inside/outside lengths http://www.durabelt.com/beltlengthcalculator.php

Using a 5/16" (0.3125") cross section and an inside length of 33.465" (850mm) I get an OD of 34.09". Looks like a trade size of A32. $5.98 from McMaster-Carr

Fri May 09, 2008 11:50 am

Thom,

Post back here if you try that McMaster (6186K131) belt and it seems to fit.

Less than $6 solution.....I love McMaster...

Fri May 09, 2008 11:56 am

Sorry I could not find my LA belts. But I found this one. Interesting enough it is a bit shorter than the new 850x13 in Mika's picture. But those fit as well.

Fri May 23, 2008 4:46 pm

The A32 was too small - it was about the same size as the 'incorrect' 13x850 I already had. I bought an A33, and it's closer. I have an A34 on the way.

Fri May 23, 2008 8:42 pm

Crap, I just bought an A32. Let us know what finally works....

Fri May 23, 2008 9:40 pm

You weren't supposed to buy anything until I vetted it first!

Sat May 24, 2008 7:08 am

thom wrote: You weren't supposed to buy anything until I vetted it first!

I was actually ordering a belt for my plate compactor (the second time, the first one was too small... see a pattern here?) and remembered, "Hey, there was that $6 belt for the VW engines.."

My '50 engine isn't built up yet, so I can see if it is small on mine yet.....

Wed Jun 11, 2008 2:34 pm

I finally found the LA belt. 12,5x925 should work.

Wed Jun 11, 2008 5:36 pm

Interesting that it's an A34. The A34 that I bought seemed too big, but the A33 seemed to small. I've driven the car with the A33 with no apparent issues so far.

Tue Aug 12, 2008 12:57 pm

thom wrote: Interesting that it's an A34. The A34 that I bought seemed too big, but the A33 seemed to small. I've driven the car with the A33 with no apparent issues so far.

So Thom, the A33 belt is still working on the 25hp???

Tue Aug 12, 2008 1:55 pm

Well, I'm still stuck trying to get a D regulator. It did work while I drove it around for a couple of days just running off of the battery.

Thu Nov 20, 2008 9:02 pm

So guys... Ive run into the same problem.. my belt is shot and nothing I put on it seems to work. The 13 x 850.. forget it... that thing is TINY.. and just doesnt work. So.... do I go A33 or... A34. Whats the verdict.. Hep a brotha out!! :)

Thu Nov 20, 2008 10:15 pm

52HoffmanSplit wrote: So guys... Ive run into the same problem.. my belt is shot and nothing I put on it seems to work. The 13 x 850.. forget it... that thing is TINY.. and just doesnt work. So.... do I go A33 or... A34. Whats the verdict.. Hep a brotha out!! :)

All of us have the same problem it seems. :wink:

Yesterday 7:48 am

I think I ended up putting an A33 from McMaster on mine and it has worked since i got the car back on the road in August. I am not sure though and the car is tucked away for the winter already...

Yesterday 8:35 am

I'm also using an A33, although it's a bit on the small side. The A34 was too big. I bought a couple of 13x850s from Argentina, but they didn't work either - IIRC they were too small.

I've been running the A33 with no problems.