Warped Exhaust Manifold

[dave_aber]

Mine's definitely in 2 bits - I had the rear half off recently to change the stat.

[Mark Norton]

Received the second hand manifold which was slightly warped, far less than the original so I have decided to make up shims from the old gasket and fit under the number one port rather than having it skimmed.

Unfortunately on re-fitting the helicoil repair to the number one stud pulled out. Now I was using a torque of 20Nm. I've re-tapped and fitted a larger stud, this time all torqued to up to 17Nm. The Mazda recommended torque setting in the book is unclear 11.7Nm - 22.5Nm ?

Now I believe that the manifold must move around as it gets hot and expands, that's why the gasket is made up of layers so adding shims seems like a sensible way to go. Some other larger exhaust manifold designs that I have looked at use brass nuts or washers at the ends and steel ones in the middle to because of the expansion.

What do you think of the torque settings, would brass nuts be of any benefit?

[Northern Bongolow]

certainly of interest. thanks for the info.
if there is a lot of movement to be allowed for they usually make a split manifold, the holes through the manifold are a tad oversized for the studs as i remember.
looks like it may be down to incorrect torque settings then, if its warping, its tightening and not allowing movement, etc.


can a mod put some add on to the factsheet in the members area maybe.

[teenmal]

Received the second hand manifold which was slightly warped, far less than the original so I have decided to make up shims from the old gasket and fit under the number one port rather than having it skimmed.

Unfortunately on re-fitting the helicoil repair to the number one stud pulled out. Now I was using a torque of 20Nm. I've re-tapped and fitted a larger stud, this time all torqued to up to 17Nm. The Mazda recommended torque setting in the book is unclear 11.7Nm - 22.5Nm ?

Now I believe that the manifold must move around as it gets hot and expands, that's why the gasket is made up of layers so adding shims seems like a sensible way to go. Some other larger exhaust manifold designs that I have looked at use brass nuts or washers at the ends and steel ones in the middle to because of the expansion.

What do you think of the torque settings, would brass nuts be of any benefit?

Hi,
The WLT engine workshop manual recommend 19-22,

Its very unusual to get a range of almost double,ie 11.7-22.5
?
Cheers.

[Mark Norton]

Thanks for those torque settings, I was using a converter to calculate kg.m to Nm and got it wrong.