33 replies to this topic

[Artful Dodger]

hello:)

i am going to be drilling my block and head tomorrow to accept the 10th and 11th studs. does anyone have any hints / tips oh what to do? i understand how to drill, tap ect but does anyone know if there are depth limitations? can i go as deep as all of the other studs in the block? will i be going through a water jacket? do i have to have a special sized drill bit to drill with and then tap it?

also, when drilling, do i drill it with the head bolted tight on, to stop any chance of mis-alignment?

any knowledge on this subject would be greatly received as, surprise, surprise, i have never done it before!


thanks guys! oh the engine spec, head is a large valve 12G940 standard 1275Gt head. block is also std 1275GT block but bored to +40 thou.


cheers!

[bmcecosse]

Why bother? The turbo engine managed just fine with only 9 studs. The Cooper S engine had an additional 10th stud - and a smaller diameter bolt, not stud, at the thermostat end. The bolt was only tightened to 25 ft lbf. Seriously - these extra studs/bolt are not necessary. And yes - there is a special drill size before tapping. What taps do you have ??

[DAVEY_C]

if you do, could you document it please??
cheers

[Tupers]

Before you even start what are planning on drilling the block and head with. If it's anything less than an industrial milling machine then stop and have an engine builder do it for you.

[Artful Dodger]

Before you even start what are planning on drilling the block and head with. If it's anything less than an industrial milling machine then stop and have an engine builder do it for you.

The block is cast iron and drills easy. if you can borrow a 11 stud head use that as a template/guide. Bolt the 2 heads together, drill the head, using a 5/16" taping drill. Now bolt the head to the block and then drill the block and and tap it 3/8" UNC tape. Then drill the head 3/8" (8mm)

sounds like a very sensible idea, but i dont have or know anyone round were i live that could have an 11 stud head. i have got a head gasket that has the holes for 11 studs, i was just going to use that, secure it to the block, drill it, then to the head.

i have got the right size and types of taps to do the job and have got a mighty big pillar drill from th 80's:) i think im going to be drilling these wholes to the same size / depth/ thread depth etc. of the other head bollts.

if im doing it wrong someone stop me!!

and yes il document it:)

[DAVEY_C]

as said earlier would it not be easier to fix the gasket to the head and drill the head 1st then fix the head to the block etc etc??.... just think it would certainly keep it from misallignment

[freshairmini]

as said earlier would it not be easier to fix the gasket to the head and drill the head 1st then fix the head to the block etc etc??.... just think it would certainly keep it from misallignment

as long as you got the drill in exactly the center of the hole, which can be difficult to do exactly, better to measure it and mark it out properly.

Why do you need an 11stud head anyway?

Edited by freshairmini, 07 December 2011 - 12:22 PM.

[Artful Dodger]

because i want an 11 stud head:) no reason.

didnt get round to it today as i had to leave early to go to work and restoring a 30 year un used pillar drill takes a bit of time 8)

ARP bolts are expensive!

[Artful Dodger]

are the two extra fasteners one stud and one bolt??? if they are is the thread and thread size the same??

[dklawson]

For the block... put the 11 hole head on the block and bolt it loosely in place. Find the drill bit that just barely will pass through the holes in the head and use that to drill a "dimple" on the top of the block. That will give you a centered spot to use with the actual tap drill for the studs.

EDIT: As Bmcecosse said, one bolt, one stud. They are not the same size.

Edited by dklawson, 07 December 2011 - 05:13 PM.

[Artful Dodger]

ok thanks

when i drill the head i will be matching it up to a head gasket, hopefully it wil be accurate enough:)

do i have a choice of fitting 2 studs than 1 stud 1 bolt? i looked at the arp bolt set and there were 11 studs, and a bolt?


edit: you said a tap drill. do i have to use one of these or can i just drill the whole then stick a tap and die through it?

Edited by MiniclubmanGT, 07 December 2011 - 05:21 PM.

[Wil_h]

Before you even start what are planning on drilling the block and head with. If it's anything less than an industrial milling machine then stop and have an engine builder do it for you.

Not sure why?

Having done this a number of times I have a few thoughts.

1) use the gasket to drill the head first, as you haven't yet drilled the head, drill it the same size as the tapping drill.
2) Fit the head on the engine, put all the studs in and tighten down, no need to torque up, just enough so it dosen't move. the key stud is the front central one
2) use the head drilled the same as the tapping dril to guide your drill into the block
3) tap
Simple

If you already have a head drilled then the best way to get the hole central is to make a tube with an external diameter the same as the hole in the head and the internal diameter the same as the tapping drill. You will need a lathe for this though.

As for whether it's necessary, My head gasket kept blowing out of the sides, fitting these cured it. Head and block were flat and all was fine. Just using a lot of boost.

[Artful Dodger]

ok thanks:)

what size is said tapping drill? do you know the sizes i should be drilling these holes at and what thread sizes i will be needing to tap:)

cheers

[Pigeonto]

what size is said tapping drill? do you know the sizes i should be drilling these holes at and what thread sizes i will be needing to tap:)
cheers

I always do it,period. Its a way of pre-empting a problem which commonly occurrs. As per usual, Wil h's advice is bang on,only thing he forgot is that after all that you will have a head with 2 x 8mm holes in it (the tapping drill size by the way to answer your question).So obviously the head's got to go back on your pillar drill to have the 2 holes taken out to 10 mm. How you keep the tap vertical is up to you but it needs to start right. I have one long enough to get a tap wrench on the square of it with the head on,ok its 3/8" dia(9.5mm) in a 10mm hole but thats pretty damn close and you can watch that its central in the hole as you start to tap. Forget about the 1 bolt business and use 2 standard studs.I've done 4 now and all ok, just may need to snick a tiny piece out of the rocker cover and gasket to miss the nuts. You can take the flywheel end hole as deep as all the others, but, the w/pump end one is a different story and I always look for a stud which has a minimal amount of thread on the bottom of it so you can keep that hole as shallow as poss other wise you can go into the water way. Not end of the world but you'd have to lock n seal that stud in.

[samsfern]

It's not hard to do, I've done it many times on a pillar drill, just make sure your drilling it square ( a spirit level and set square can be useful for this), I've never used any sort of template, if you clean the faces up you should be able to see where to drill, it's quite nice soft stuff to drill, you only need to drill as deep as the other studs, Thread size for head studs is 3/8 unc , I'm not 100% sure what tapping drill you need, also, I've always used two regular head studs for the two extra studs. You'll also need to modify the rocker cover and also trim the rocker cover gasket a tad.

Edited by samsfern, 07 December 2011 - 08:16 PM.