Thread: TD5 exhaust manifold torque - increasing it with larger studs?

Have you removed manifold and checked its mating face is flat across
its full length if not de web and reface is the first thing to do.

There is no point pulling a warped manifold in it will put manifold
or the bolts under uneven tension.
You could crack the cast manifold or get leaks.

Stud holes in head may have been tapped to M10 because of
previous damage to studs due to manifold warping the stud
breaks with warping or when being removed.

Use hi tensile bolts, end of story

Originally Posted by bronson

Use hi tensile bolts, end of story

Repeat post, see next post.

Originally Posted by bronson

Use hi tensile bolts, end of story

I thought the concern is over the thread in the aluminium head! Will high tensile bolts help the aluminium threads in the head?

If you are increasing the torque on the bolts you would need
more thread in the head to spread the load as there will be more
clamping force.

High tensile bolts are stonger so can apply more clamping pressure
to pull the manifold in but the need sufficient thread in the head
to pull on if not you will just pull out the thread.

If manifold is warped and pulled in with stronger bolts the manifold
is being stressed,
to seal the manifold it needs to have two good faces good gasket
and even clamping pressure across its length.

Originally Posted by ScotsD2

Have you removed manifold and checked its mating face is flat across
its full length if not de web and reface is the first thing to do.

There is no point pulling a warped manifold in it will put manifold
or the bolts under uneven tension.
You could crack the cast manifold or get leaks.

The manifold has previously warped and been refaced. It still has it's webs. There is much argument on whether to keep the webs or not, I'm not interested in getting back into that in this thread, I'm keeping them for now. I have previously had a manifold that was dewebbed after being warped and refaced and that rewarped again - so it seems to me that it makes no difference.

Originally Posted by ScotsD2

Stud holes in head may have been tapped to M10 because of
previous damage to studs due to manifold warping the stud
breaks with warping or when being removed.

Yes, we increased the stud size due to damaged threads and for extra strength.

Originally Posted by slug_burner

I thought the concern is over the thread in the aluminium head! Will high tensile bolts help the aluminium threads in the head?

Correct, my concern is about the threads in the head as these are the weakest part, not the bolt strength. If it were possible I would use a weaker bolt as a sacrificial item so that the head remains undamaged as the head is clearly a more expensive and complicated item to fix/replace.

If you are torqueing up more you will need more length of
good fully formed thread in the head good rule of thumb in
alloy use 2x the bolt thread OD as the thread length to give
a good spread of pull across the softer alloy.

Still think you are masking a problem not fixing it if the manifolds
are warping they are getting too hot have a look at all the recent
threads about the MAF and fueling and heat.