plumbum

I purchaced my car this spring (1986 951) with new belts and around a week ago they were checked for re tension and I was told they were within spec, last night I started the car (cold) and could hear a rattling noise which increased with engine speed.

The noise was comming from under the timing cover would increase with rpm and sounded like a can with coins in it. I removed the cover and found no sign of anything hitting or banging around (belts looked good, no wear on the plastic cover) I started the car and could still make out the noise but as the car warmed up the noise went away.

I noticed the timing and countershaft belts move around alot (up and down) there seems to be play on the timing belt and lots on the counter shaft belt. I dont have a tension tool and hope to have someone pop by with one this week to double check the tension my question is what play would I expect to see in the belts?

John_AZ

Here is the belt information on clarks www.clarks-garage.com

I do not understand if you checked the tension one week ago and the tension seemed fine, but now they are loose?? Did you adjust anything?

http://www.clarks-garage.com/shop-manual/eng-10.htm

The balance belt (counter shaft belt) will seen very loose. If you over tighten it the belt will "whine" at idle.

The cam belt has to have specific tension or you will bend valves.
Clarks mentions the 90 degree twist method.

I hope your friend is familiar with the cam belt tension. If you are not sure, take it to a garage or shop that understands the Porsche 951 tension system.

Things that can cause a belt to loose tension is a tension pully not torqued correctly.
OR a tension roller that is defective. Original rollers were defective--the plastic cracked --Were new rollers every put on the car?
OR the bolt that secures the tension roller is loose. The OEM tension roller bolt should be replaced if not done.
OR Your cam belt is defective.

GL
John

royalschwarz

See Vans video below to see the proper tension on the belts. More precisely, the balance shaft belt at 3:48 and the timing belt at 6:55.

plumbum

Thanks guys!

The belt was new in the spring and I had the tension checked a week ago and was told it was good (they did not re tension it) I don't have the tools to check it so I am waiting for someone who does.

I read the balance belt will seem loose when it is tensioned properly gut didn't expect to see it and the timing belt vibrating so much

V2Rocket

the balance belt idler will sound awful when it goes out, and the balance belt 'orbits' quite a bit if it is too loose. the idler stops it from orbiting too much but if set wrong it will go all over the place.

plumbum

So I had another look today and listened with a stethoscope rattle seems to be around the water pump but sounds like plastic. If I check near the rear timing cover by the water pump I can hear it but if I check a bit higher on te water pump I hear nothing. I think it was the timing cover hitting the water pump area that was louder due tote hood being open.

I hope that is it as I don't hear it with the hood closed and it seems to have gone away for now.

robert944h

How many miles are on the car. Hopefully you're not hearing a rod knock....

plumbum

It's defenatly in the upper front cover area...was more cam speed than crank speed.

John_AZ

Have you checked the cam gear bolt?

If the cam gear bolt is loose, it will damage the keyway on the cam shaft.

http://www.944time.com/porsche/944-cam-tower.php

There is an upgraded 12point/triple square bolt available on Pelican.

GL
John

plumbum

I dont think that is quite the same noise but I will check it out tomorrow! Easy enough to have a look...Like the self check on belt tension..and the flapping belts look like mine so I guess I am good! I must be too use to seeing serpintine belts that dont move.

Thanks for the link John!