Kent Iron head thread sizes

[SteveG]

I'm servicing a Kent iron cylinder head, question -
What are the "normal" bolt thread sizes for the intake, exhaust manifolds and thermostat housing?
I can't remember the specifics and what I'm seeing doesn't seem right.

Steve

[kea]

As I recall, 5/16" UNC

[SteveG]

As I recall, 5/16" UNC

All of them?
So the M7 X 1 threads for the exhaust on my head are not original?

Steve

[Roland V. Johnson]

Yup

[tlracer]

All of them?
So the M7 X 1 threads for the exhaust on my head are not original?

Steve

As original, all those threads are 5/16 UNC. M7 is very unusual, especially in these circumstances as it's smaller than 5/16 (which is very close to 8mm).

A common 'bodge' on this side of the pond is M8 in 5/16unf, because as well as the similar diameters, the thread pitch of the two is very similar.

I really can't think of any reason for M7?

[lbermud]

I’ve serviced a couple of Kent heads before, and from what I remember, the intake and exhaust manifolds usually take M8 x 1.25 bolts. The thermostat housing should also be M8, but honestly, it can sometimes be a little different depending on the year or if someone replaced them before. I’d double-check the threads and lengths, especially if what you’re seeing feels off—sometimes people swap bolts around over the years.

[old 59]

Nope, 5/16 UNC

[SteveG]

So the best I can figure is a M7 X 1 helicoil almost fits in a 5/16-18 buggered hole and they had M7X1 stuff on hand. Only 3 of the 6 exhaust bolts holes where done this way and a M7 X 1 will tighten in a 5/16-18 hole. I was able to drill out/tap those 3 holes for 5/16-18 helicoils and repair the others so I'm good.
I've been doing this long enough to see some amazingly strange fixes that defy logic and marginal mechanical skills.

Steve