Fan belt slipping?

[dt100]

I've just rebuilt the engine (1600 in a 1972 Devon) and put the engine back in. It started good and overall sounds fine..... the van is still on Ramps, so not road tested, just stationary with the engine running.

When accelerating the engine, the fan belt sounds fine, but when I take my foot off the gas the fan belt makes horrible screeching sound, and looks to be jumping a little. It is a brand new fanbelt from JK.... I've tried tightening it, but after moving 6 of the washes over, it doesn't seem to be much different, and I think the belt seems too tight now.

Can someone please confirm, I originally set it at half inch defection.... how much pressure do you put on the belt to get the deflection?..... or what else is there to look at? Everything original, and I've already checked that the pulleys are in line....

 

[Moseley]

Deflection should only be 10mm iirc. I've not long fitted a brand new belt, and although tight at first, it soon stretches as it beds in, so worth keeping an eye on for the grist few hundred miles.

 

[mike202]

Check you've got the right fan belt. They do stretch after the first 100 or so miles but you should only need to remove a couple of shims. Are you sure the screeching is coming from the fan belt and not the generator bearings? Maybe you've already replaced the generator though.


Sent from my iPhone

 

[dt100]

How would I know if the noise is coming from the generator, would there be any other tell tail signs. The gerator wasn't replaced, just the original cleaned of 'crud' and re-used, as there wasn't any issue previously. I've measured the output from the regulator and it seems to be around 13.5v at tickover and 14.0v at 3,000 rpm, which is where I think it should be?

I think I'll get another fan belt and see if it makes any difference.... are any makes better than others?

 

[mike202]

It was the screeching sound you mentioned. My dynamo was replaced recently due to noisy bearings that were worn, although they weren't screeching more of a grinding noise. It was just a thought- it could well be the fan belt. You need to get it to the right tension, and if its the right one it shouldn't slip unless its covered in oil!

 

[dt100]

Thank you.... I think I may have the wrong belt....

I've just been on VW Heritage, and it shows a solid belt of 9.5 x 905.... Whilst the one I've got is 10 x 905 and of ribbed design.... not sure if that will make the difference but I've ordered another belt, and I'll take it from there.... prefer it to be the £5 belt rather than the dynamo!!

 

[mike202]

yea- see how you go with a new one, I prefer the solid belts. You don't want it too tight because it will damage the generator bearings, but about 10mm deflection is right. 8)

 

[StuF]

Also when changing your belt have a good look at the top pulley - mine let go in an explosive fashion at about 3k!
Crappy repro parts!

 

[madmike]

Try a cpl. drops of transmission fluid on the belt, won't hurt and it does make them quit making noise to confirm it isn't the dynamo/Gen

 

[VeeDubMan]

Try a cpl. drops of transmission fluid on the belt, won't hurt and it does make them quit making noise to confirm it isn't the dynamo/Gen

I had an AA man tell me once to dab a bit of brake fluid on a fan belt if it's squeaking. Done this on modern cars before now and it does work!

 

[Dave.P]

Easy way to check if its the belt making a noise is take it off and run it without, but Not for long!!
Correct tension is being able to twist the belt 90 degrees half way between pulleys / push in half inch from straight.

 

[dt100]

Having purchased what I'm hoping is the correct belt, I think I've found at least part of the problem..... there was a crack in the back half of the pulley, which when I jabbed with a screwdriver broke off:



Next couple of questions:

1. Should this just pull off.... it wont, does it need a puller?
2. Where best to get a good quality replacement. My engine is fairly 1972 standard, so want to keep it this way, but cant afford to overspend.... or buy rubbish!!

Thanks for all input on this..... guess I wont be getting the engine timed up this weekend!!

 

[dt100]

I have eventually found 20mins to spend on the problem, and thought I'd update those who offered advise, as the actual problem was a little different....

Basically the wudruff key had sheared. Whilst under normal load, the belt was still working fine on the pulley, but on deceleration the additional load was causing the spinning of the whole pulley on the shaft, which in turn I believe caused the pulley itself to start to break up. It was the spinning on the shaft that was causing the screeching noise!

Another one to check for when changing the belt!!

 

[matt-me]

wow, not heard of that before. Is the slot in the alternator spindle still ok? best to check it hasn't enlarged when you get your new key