exhaust bubbles after exhaust manifold gasket change

[Belgian951]

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.

[ROB III]

Best of luck with the MOT.

[michaelmount123]

Tightening the exhaust manifold to the correct 20nm will probably solve your leaks. A heat cycle will help too.

[Tom]

I'd be curious what brand exhaust gaskets you are using? I've never heard/seen those gasket 'cook' and bubble?? Have any pictures of that?

Normally I drive the car over a couple days and then go back and torque to spec. Invariably some are a bit loose after the header expands and contracts a few times...

[Thom]

I always tighten headers nuts to how tight enough it feels to me and that is way higher than 15 N.m.
Exhaust temperature can get brutally high on these engines and there is no way that 15 N.m can be tight enough. That's the torque figure used for 16 mm motorbike spark plugs.

[Tom]

I always tighten headers nuts to how tight enough it feels to me and that is way higher than 15 N.m.
Exhaust temperature can get brutally high on these engines and there is no way that 15 N.m can be tight enough. That's the torque figure used for 16 mm motorbike spark plugs.

I totally missed that, but yes the factory spec is 15 ft lbs. (or 20 Nm) -- not 15 N.m. That might explain to poor seal.

[Belgian951]

I used these reinz gaskets (OEM normally I believe, 944 111 196 01)

WhatsApp Image 2023-10-24 at 15.09.23.jpeg (76.64 KiB) Viewed 845 times

I'm now unsure whether I did 15 nm or 20 nm of torque... I'll recheck asap and then test again. I'll also try to get a picture or video of the bubbling.

[Tom]

I used these reinz gaskets (OEM normally I believe, 944 111 196 01)
WhatsApp Image 2023-10-24 at 15.09.23.jpeg

I'm now unsure whether I did 15 nm or 20 nm of torque... I'll recheck asap and then test again. I'll also try to get a picture or video of the bubbling.

Try the re-torque for sure. Very curious about the bubbling....? Can't quite picture what's going on there. The shiny side goes toward the headers.

[Belgian951]

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.

Tom, I tried to film the bubbling, which is still present. I think it may be oil or something that is burning off slowly. You can just make it out in this vid, but barely: