Offroad-Express

Toyota 1KZ 3lt turbo diesel. it comes with studs on the exhaust manifold, but why cant you just use bolts? do they loosen more when exposed to large heat changes etc?
your thoughts please!
Cheers, Micah.

Personally I would stick with the studs...
They tend to be stronger....
And also when you are doing them up the threads are already fully engaged into the alloy head....and not turning.
Only the nut turns and the risk of stripping threads in the alloy head are reduced...
Something like that....

Yeah if at all possible stick with the studs.

Metallurgically wise a grade 8 stud is no stronger than a grade 8 bolt. They do have a greater clamping force which will help prevent leaks.

Also when a bolt is tightened it has rotational forces acting on it as well as the stretch of the bolt. Studs dont have have these forces acting on them as only the nut turns on the stud. With the high cycling loads in an exhaust manifold from the temp changes these rotational forces are what can cause bolts to loosen.

ice4x4 wrote:Yeah if at all possible stick with the studs.

Metallurgically wise a grade 8 stud is no stronger than a grade 8 bolt. They do have a greater clamping force which will help prevent leaks.

Also when a bolt is tightened it has rotational forces acting on it as well as the stretch of the bolt. Studs dont have have these forces acting on them as only the nut turns on the stud. With the high cycling loads in an exhaust manifold from the temp changes these rotational forces are what can cause bolts to loosen.

But if i checked them regularly they wouldn't be a problem? its just i already have some HT bolts that are a perfect fit, and half my studs were already missing,(shit quality bolts put in place.) So if i can use the bolts i will. would high temp locktite help?
Cheers, Micah.

retightening the studs will chew out the thread in the head creating a far bigger problem than buying a new set of studs

up to you tho its your motor

Personally I would use studs.

but like mudlva says its your engine you can do what you like.

I think you have your answer, use studs.....
After all this work you are doing it would be a real shame to have ongoing issues re the exhaust manifold.....
I have had threads strip out using bolts on alloy heads.....(not 4x4)

Cheers guys. will use studs. thanks for all your wisdom!!
learning to learn from others mistakes/experiences!

the studs and the lock nuts are available from Toyota,I use OEM ones of these as I know they work and stay tight ( escpecially the locking nuts)
Stud part number =9012610017
Lock Nut part number=9418401041