Head stud suspicious thread

RobertGrieve · Post by **RobertGrieve** » Thu Aug 16, 2018 5:27 am

Hi everyone,

I recently re torqued my cylinder head to find that one of the studs (the LH second row from front) wouldn’t torque up and now suspect the thread in the block is the issue. Interestingly I can undo and redo the the head stud and the thread draws it in and out but it won’t tighten up properly.

I found a small leak of water coming from the top of it when tightened, not good.

The stud is the one that is the unique size and slightly different shape, I’m wondering if anyone knows of this stopping it being withdrawn from the head? It certainly didn’t just pull out, but it is loose!

I’d like to inspect the head stud threads before deciding what to do next...

Cheers, Robert

abowie · Post by **abowie** » Thu Aug 16, 2018 5:33 am

If it's the dowel stud then no I don't think it will pull through the head.

RobertGrieve · Post by **RobertGrieve** » Thu Aug 16, 2018 6:38 am

Hi Andrew,

Dam - had my suspicions that would be the case. Pretty sure it is the dowel stud. Looks like it’s a head off job if I’m to stand a chance of repairing.

Robert

abowie · Post by **abowie** » Thu Aug 16, 2018 7:55 am

I think so. Fortunately your car should have a short stud block so helicoiling the thread in the block should be an easy process.

RobertGrieve · Post by **RobertGrieve** » Thu Aug 16, 2018 11:54 am

Thanks Andrew. Coming to terms with the thought of dismantling everything is a bit painful. Trying to read up if it is indeed 100% the case that the dowel stud doesn’t pull through the head, would hate to dismantle then find it’s not the case - mind you even a new stud would probably not make any difference - if the block threads are knackered, they are knackered.

Robert

PeterCrespin · Post by **PeterCrespin** » Fri Aug 17, 2018 2:28 pm

It is 100% the case, unless someone has previously through-drilled the head to the size of the counterbore.

RobertGrieve · Post by **RobertGrieve** » Fri Aug 17, 2018 3:29 pm

Thanks seems right enough. I believe the cause of the issue was that the dome nut had basically got to the point where it was tight on and not turning anymore at which point it stopped and the stud started turning and so rather than clamping and torqueing up the stud just turned - results is probably a knackered thread in the block.

This morning I have removed the dome nut (by grinding off bit by bit until it broke free

) and re seated the stud as far down as it goes into to the block.

I then cleaned up the threads at the top of the stud and offered up a nut to see if I could get it to clamp and it seems to be OK but I have not fully torqued it yet. Will try with a replacement dome nut and if that fails then head off

Robert

Mark Gordon · Post by **Mark Gordon** » Fri Aug 17, 2018 6:47 pm

You probably already know this, but be sure when you try to torque the new dome nut that the top of the stud is not bottoming out inside the nut before the nut makes contact with the washer on the stud. I.e., there is room inside the dome nut between it and the top of the stud. Otherwise, you're just torquing the nut onto the stud, but not applying any force against the head.

RobertGrieve · Post by **RobertGrieve** » Fri Aug 17, 2018 9:25 pm

Hi Mark, I think I’ve learned that lesson the hard way on this one particular stud, rather annoying

RobertGrieve · Post by **RobertGrieve** » Sat Aug 18, 2018 5:03 pm

Head is off as thread is knackered - anyone got any tips on helicoil process?

abowie · Post by **abowie** » Sat Aug 18, 2018 11:44 pm

It's pretty easy as a general principle.

In the kit you get a drill, an oversized tap and the coil with an inserter tool that breaks the coil tab off once it's seated. You drill the old thread out, tap with the supplied tap and then screw the coil in.

I've only ever done smaller (3/16" to 5/16" non critical) repairs myself as we get anything larger done by he engine machinist we use. You obviously need to be absolutely sure that the hole you drill is perpendicular to the head face.

If you've got one buggered thread you might have more so worth checking them too while you're there.

RobertGrieve · Post by **RobertGrieve** » Sun Aug 19, 2018 3:35 pm

Thanks Andrew i think il try and find a mobile specialist in the area because I’ve not got the gear to do a perfectly perpendicular repair and can’t risk it I don’t think. Seems to be a thing that people do

abowie · Post by **abowie** » Sun Aug 19, 2018 9:11 pm

RobertGrieve wrote: ↑
Sun Aug 19, 2018 3:35 pm
Thanks Andrew i think il try and find a mobile specialist in the area because I’ve not got the gear to do a perfectly perpendicular repair and can’t risk it I don’t think. Seems to be a thing that people do

Good choice IMO.

RobertGrieve · Post by **RobertGrieve** » Mon Aug 27, 2018 6:46 pm

All sorted, thanks for the advise, helicoil did the trick and did it myself with the help of a borrowed electro magnetic base drill, although probably overkill was perfect for the job.

Head now torqued up properly and no leaks at all. Took the opportunity to re shim the head whilst off also.

Robert

abowie · Post by **abowie** » Mon Aug 27, 2018 10:45 pm

Perfect. Shimming the head off the car is a lot easier and a good choice.

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