Porsche-noob-91

I just changed out the exhaust manifold on my 86 951, including all the studs, new washers and nuts (rennbay kit). I also changed in new exhaust manifold gaskets.

Now with the soapy water test, it seems that I have a few small leaks at several nuts/studs. Also, some gaskets seem to be 'cooking', with tiny bubbles on the top edge. All nuts are torqued to 15 nm.

I'd rather not fail my MOT emissions test again. What is my course of action to solve this once and for all?

Edit: the car hasn't been driven since these changes, just tested. The soapy water test was done when the engine was cold. Can't verify if the manifold continues to leak after engine is warm since the water evaporates so quickly.

944M3

I found I had re-torque the nuts a couple of times after heat cycles. It is a pain for sure.

Gage

M8 fasteners should be about twice that. Did you maybe misread the spec? 15 lb/ft?

944M3

I agree, not tight enough.

I basically ignored the torque and just tightened until they stopped leaking. Within reason of course.

Porsche-noob-91

Hmmm, this may be the solution... I may have indeed done 15 nm instead of 20 nm. 15 lb/ft. If I read the 944 turbo workshop manual, it says on page 26-1 that M8 fasteners should be 20 + 2 nm (14 + 1.4 ftlb). Can someone confirm if this is the correct page I should be looking at? It just says exhaust system flanges so I'm unsure if that includes the manifold.

931guru

This pdf from the 944 factory workshop manual addresses exhaust system tightness and specs...

Porsche-noob-91

Thanks that's the page I was looking at.
So I'll check my torque again and report back ASAP!

Thanks everyone.

Porsche-noob-91

I rechequed the torque today and it was indeed torqued to 15 nm instead of 20 + 2 nm. After torqueing it to the correct value, I tested the car again with the soapy water test. No leaks! Thanks everyone.

951Tom

What methods did you use to remove the studs from the head? My car needs all new manifold studs also. The rear stud on the #4 cylinder has broken off.

Tom
'87 951

Porsche-noob-91

I used the double nut method, and soaked all studs with pentrating oil beforehand. All studs came out easily.