Ouch! broken engine head studs stuck in block

[melanddoug]

Hello,

Help!

I've ended up with a broken engine head stud which is stuck on the bock, and it's broken such that none of the stud is sticking out. Ugh.

I've managed to drill the old stud out leaving a smooth hole (slightley smaller that the stud) which has no thread. I'd hoped to be able to kind of 'peel' the old stud's thread out from the inside of the thread hole, but sadly it's stuck fast and virtunally none of it is showing.

I'm guessing my next step is o ap a new thread (actally, hopefully re-establishing the old one) ..

Is that the best bet ? Anyone know whee I can get a tap for the righ thread ?

Or any ther suggestions ? (I'm even considering a new engine..)

Thanks

Doug

[chrisryder]

if you can get your hands on a correctly sized tap you might be able to salvage it. if not, there is a kit called a 'helicoil'. you drill out the hole to a certain size (bigger than the orginal thread) and then you tap it to a set size. then you screw in a 'coil' which has the outside thread of the hole you've just tapped, and the inside thread of the head stud.

if you google 'helicoil' there must be a website for them.

[MarkyB]

A picture would help a bit, but you need to use a slightly bigger drill bit than you have, be it metric or imperial until you can see thread somewhere.
If the drill shank will slide into a studless hole it should be perfect.
How much more metal need to come out before you get to that stage?

Roy will faint clean away at the idea of getting a new engine for this

[melanddoug]

Thanks Mark-

I think a picture wouldn't help much. It just looks like a stud hole in the engine block, but with smooth sides.
It's the front short stud hole, front-offside.

I'm pretty sure the metal I've drilled out means the 'peaks' of the thread are exposed. but the old stud thread seems to be really stuck. I've tried driving it out with a small sharp scredrivier but it won't budge.

I too balk at the notion of buying a new engine just for this! (or a new block anyway)

Doug

[fussyoldfart]

Helicoil is a good way to repair this. The kit they sell includes the correct drill bit, usually several coils, and a tool to put them in with. They claim that the result is stronger than the original threads. Getting the new hole perfectly straight would be my biggest worry. A drill press would be best or at least some kind of jig to hold your electric drill vertical.

Darrell

[MarkyB]

Something really sharp and hard is what you need to pick away at the old bolt thread.
I've got a metal scribing tool which would be ideal.

Keep tweaking away at the top till you get it started, the metal of the bolt should be softer than that of the block.

You could trying spraying some dark aerosol paint down there then wipe it out with a Q tip or something, that should reveal if you can actually see any thread tips.

[bmcecosse]

I did indeed 'take a wee turn' at the idea of a new engine........ Just carefully work with it - you will get it out in time. The block thread is 3/8" UNC which is very very close to 3/8" Whitworth. How did this happen - were you removing the studs - or tightening the head nuts ??

[melanddoug]

I was tightening the head bolts - the gasket had blown again (not sure why..) so I was re-tightening the bolts to see if that would buy me some time. I think it broke at about 45 lbs torque.

Looks like the Helicoil idea might be the way forward. Owing to a particularly subborn and hard blob of old stud (f'nar), I think I've accidentally drilled slightly off-centre and nobbled some of the thread.

The engine smokes quite a lot anyway. I'm not sure if it' the head, which I was about to rebuild, or the rings, which I'd earmarked for replacement in the summer.

I'm going to have a think about what to do. There comes a point where time is more valuable than dosh....

thanks for your help.

Doug

[fussyoldfart]

Looks like the Helicoil idea might be the way forward. Owing to a particularly subborn and hard blob of old stud (f'nar), I think I've accidentally drilled slightly off-centre and nobbled some of the thread.

That's the very problem with drilling for a helicoil too. If you are going to put a stud in it has to stand perfectly straight and exactly in the right place. You might try bolting the head back on with one or two nuts to hold it in place and then use a long drill bit through the vacant hole to straighten things up. If you have to strip the block completely and take it to a machine shop a replacement engine might become a more attractive proposition.

Good luck!

[melanddoug]

I did indeed 'take a wee turn' at the idea of a new engine........ Just carefully work with it - you will get it out in time. The block thread is 3/8" UNC which is very very close to 3/8" Whitworth. How did this happen - were you removing the studs - or tightening the head nuts ??

Would that be 3/8" UNC 16tpi ? I assume that's "turns per inch" .. so each line of thread is 1/16" apart ?

cheers

Difficulties Doug

[bmcecosse]

I can't access my Zeus tables at the moment - so can't say if 16 tpi is correct or not...... It's 'threads per inch' BTW!
Edit - but looking on internet it does seem to be 16 tpi - and 5/16 drill bit.

[melanddoug]

I did the hi-tech solution . I measured it.it's 16 per inch.

Helicoil ordered. Let's see how it goes!
what a polava
thanks again

D

[bmcecosse]

You can only safely tighten to 45 ft lbf IF you have the later studs with either the 'dimple' end or the 'Y' on the end......... Actually I believe the Y studs are good for 50 ft lbf when used with the flanged head nuts. Otherwise 40 ft lbf for the very old studs. But I am surprised the stud broke like that - are you confident of the settings on the wrench ? For years and years I had no torque wrench and simply tightened by hand until I felt the stud begin to 'yield'. Never broke a stud - nor any head gasket problems.

[rayofleamington]

Just in case anyone gets this in future - you can remove broken studs without drilling, or if you drill then it's worth to get an 'easi-out' kit.

To do it without drilling you need a fairly high power mig welder - use some hardboard over the block face with a cut out for the stud as you need to ensure that no weld spatter gets in the oilways or cylinders (adding a thick layer of grease helps to catch it). You weld an addition on to the end of the stud - as big as possible. Then use an oversize hex nut and place it over the new lump and weld the two together. Let it cool for a minute or so but you don't need it to go cold. Then provided the weld was solid, use the nut to unscrew the remaining stud. If the weld wasn't solid it's likely to come off the top of the sud - then you are back to the start and be more careful next time.

I've had to do this on head studs, manifold studs, sheared wing bolts, a sheared wheel bolt etc.. on classics and moderns and I've never had it fail. On big stuff I've used landrover wheel nuts, as I had them to hand.
When I had to remove some locking wheel nuts (on a company vehicle that came with no key) I got our machine shop to knock up some large hex pieces for me, and 20 minutes later I'd got all 4 off.

I had to do that again on a friends car - one locking wheel bolt had siezed. I told him to leave it alone until I had sorted it but he took it to a tyre place and they used an extension on their wheel brake and broke the key That left me with 4 locking bolts to remove instead of just one I left the siezed one until last, but the heat from welding really helps to loosen them and it wasn't much harder than the others!

The one advantage of a sheared wheel bolt is that you don't need to worry that much about where the weld sparks are going - doing a head or manifold stud takes a bit more care.

[phurn]

Cricket! The leaflet with my head gasket said tighten to 51lb/f which I promptly did! Guess I'm lucky not to have snapped anything...

[bmcecosse]

Sure it wasn't 51 Newton Metres? which is almost 40 ft lbf.

[phurn]

nope definatly lbf. the carstarted to creep back on its hand brake abit but other than that i didnt notice it giving at all.... i replaced my inspection gaskets too, those i did over tighten, as they pushed out and spewed oil everywhere, cleaned them up, put them back on abit looser, and all is well!

[melanddoug]

I had wondered about the welding-someting-on trick, but had read elsewhere that it doesn't work so well and you stand a chance of messing up the block (different car though - triumph stag v8).

Thanks loads to everyone for your help! Group hug .........

Doug

[rayofleamington]

It probably doesn't work on a Stag V8 beacuse the studs are at an angle to the block.
Therfore if you sit a nut flat on the block, it won't turn far before locking up.

Fortunately for us, the Stag V8 is a very different animal (often reffered to with a lot of swear words).
I wouldn't want to work on an engine where the cooling circuit only seals between the heads with a wing an a prayer and the head studs are at an angle to each other
Removing studs that have been sawn off at the block face is much more aof a common job for those guys

[bmcecosse]

The studs on that Stag engine (and the TR7 engine which is half of the V8) are at right angles to the block - which is of course at an angle. The bolts go in at an angle. Once the bolts are removed the head can be slid up the studs - except the steel studs often 'weld' to the alloy head unless they have been greased. That's when the fun starts........