Cylinder head mani stud hole thread spacing

[306Puggy]

I know the cylinder head stud holes are M8 threads, I currently have an M8x1 tap but something tells me they are spaced further apart than that, I am thinking 1.25, can anyone confirm?

[Tom]

Thread pitch you mean.... You inlet manifold holes are M8x1.25

[306Puggy]

Hi, are the exhaust mani stud holes the same? Ruan recommends extending these holes so you can tighten the studs more because the exhaust mani+turbo weigh quite a lot when you have adapter plates on.

[Ruan]

Did I????

I would have said don't use bolts as it weighs a lot doing them up and you'll f*ck the threads... I'd never say extend them... You're likely to punch through an oil or water way..

[Dave]

Run a tap down to clean the threads, you'll probably get the stud in further then, as Ruan has always said dont use bolts, use studs because tightening tight tight on the ally head will strip things out, always best practice to do it properly with studs

[306Puggy]

It was Dave that's why. This is the post I was referring to:

Yeh, when you do this, run an M8 tap down the head too, you'll find you can get an extra 6mm or so of thread out of it, means you can screw your studs in real deep, get them extra tight.

Also I never intended to use bolts for the exhaust mani, I'm not that daft So is there a risk of tapping into a water or oil way then? Should I carefully measure the 6mm or will I feel when it gets to the end of the hole?

Edit: This is the thread that I got it from:

http://306oc.co.uk/forum/thread-14205.ht...ap+threads

Looks like Silverzx wasn't quite clear on it either.

[Tom]

The tap will just hit the bottom/back of the hole, it wont burrow itself in any deeper like a drill bit.

[306Puggy]

Oh I see, Ruan was just being pedantic I meant extending the threads but I used to wrong word. Yes, what I mean is that I plan to extend the threads within the holes.