Binding Exhaust Manifold studs (Doorman, non-Volvo)

[beewstew]

I'm working on putting the head back together on a 2004 xc70 after replacing the head gasket.

The old exhaust manifold studs didn't look great (picture below) so I bought some M8 1.25 studs at the local auto parts store. Labeled "Ford" but the thread pitch and overall length was the same, so I thought these studs would work. They're driven in w/ a 6mm bolt head that's shaped into a hex on the outside end of the stud. Then there's a flange nut that you thread on (like normal).

When I torqued the head back on, the gap between the exhaust manifold and the head was zero on the turbo side, about 1/4" on the timing belt side - maybe a bent turbo support bracket? I thought I could close this gap by evenly tightening the ex manifold nuts, but they're quickly binding up.

I'm realizing now that I should have just pulled the engine at the start of this head gasket repair - oh well... I don't want to trash the (aluminum, female) exhaust threads in the head!

How tightly are you supposed to insert the exhaust manifold studs? There's no torque spec that I can find. Suggestions on where to go next? There's no movement in the exhaust manifold, which makes me think it's somehow bound up "diagonally" on the studs.

Old studs:

Old exhaust manifold studs with bound/galled nuts and damage to threads

New studs that don't quite fit:

New generic M8x1.25 Ford studs with nuts.

Screenshot 2024-10-26 185625.png (852.08 KiB) Viewed 546 times

[jonesg]

don't know but i would remove everything and check the manifold for flatness and order the oem studs.
a warped exh will crack, cast iron.

[jonesg]

i would do this.

[beewstew]

Thanks @jonesg no torque value though? Just "tight when it bottoms out"?

[lrock]

A note regarding engine removal: the engines are installed from the bottom into a raised vehicle. Maybe you have a 2 post lift, but something to keep in mind if not, before attempting to remove it.

[dikidera]

A note regarding engine removal: the engines are installed from the bottom into a raised vehicle. Maybe you have a 2 post lift, but something to keep in mind if not, before attempting to remove it.

I've been told it can be removed from the top. But someone else said re-aligning it correctly took some time.

[lrock]

A note regarding engine removal: the engines are installed from the bottom into a raised vehicle. Maybe you have a 2 post lift, but something to keep in mind if not, before attempting to remove it.

I've been told it can be removed from the top. But someone else said re-aligning it correctly took some time.

Did they remove everything else from the bay?

i'd probably just roll the backend up on ramps and use two farm jacks to raise the front, wheel it under with a tranny jack, raise it level and lower the front back down on it. But i do things the hard way.

[chrism]

I can’t think of a situation where you would ever want to torque a bottomed-out bolt (or stud) especially in an aluminum head or block. You could do some serious damage like busting into a water jacket. Check the depth of the hole before you insert the stud and mark the stud accordingly. Then screw the stud in to a depth a little shy of the hole’s depth.

[beewstew]

@chrism I think it's a problem with the Ford studs+nuts. There's an extra crimp on the outside of the nut you install onto the stud. I think it's there to make the nut one-use and no-wiggle-off. There's no way to tighten on the nut without driving the stud - hard - into the block. I put in an order for volvo-specific studs and nuts today.

Here's a picture of Ford/Doorman vs Volvo OE exhaust manifold nuts. I think the crimp on the last ~2 threads of the Ford nuts is part of the problem I'm running into.

Ford vs OE exhaust manifold nuts.

Screenshot 2024-10-27 201750.png (776.16 KiB) Viewed 466 times

[vtl]

Your manifold is likely warped. They all do that. Also supposed to tighten the nuts from center outwards

Volvo nuts are mishaped to oval, so they unavoidably drive the studs, too.

Torque is 25 Nm.