18 replies to this topic

[Minigirl]

Went to torque the head up doing slight turns at a time indicated by the haynes manual and then everyone of them clicked to indicate tightness except number 1 the one right in the middle!!

 

what can be done to repair this headstud thread? My Dad mentioned a helicoil kit but what size do I need?

 

thanks

[Guess-Works.com]

Stud into block 3/8 unc

[Cooperman]

Namric can supply a 3/8" 'Re-Coil' kit which has all you need to do the job, but the head will have to come off again.

The only problem is getting the drill vertical with the engine in the car. I've managed to do it, but it's not easy. Take some time doing this. One way is a pair of short pieces of steel angle which you put at 90 degrees to each other flat on the blockand hold them in position as a guide for the drill. Not easy, but possible. After that it's easy.

[Guess-Works.com]

Just a thought....
http://m.ebay.co.uk/itm/131256288751

[nicklouse]

Just a thought....
http://m.ebay.co.uk/itm/131256288751

I raise you with this. http://www.amazon.co...HAQ97M0KYWAXSCQ

[Cooperman]

It would be easy to make up a drill jig with a 2" high vertical tube, the diameter of the tapping drill plus a few thou, welded onto a flat steel base with slotted holes 3/8" width to enable it to be bolted to the adjacent stud holes and lined up. I might make one up soon.

[Spider]

 

The only problem is getting the drill vertical with the engine in the car.

 

Important point raised her by Cooperman.

 

I use an old head for doing this. Take the good head off, leave all other studs in place, remove the gasket and make one out of some thin cardboard, it only needs to have the stud holes in it, not all the others, plonk the old head on and drill away. On most holes, you can get up to a 10 mm drill bit through them, except for No. 4 on the front and no. 1 on the back, they are smaller to locate the head.

 

If you're willing to sacrifice the old head, you can pre-drill out the one stud hole that's to be helicoiled to the tapping size, but once you get it out to the 10 mm size, you'll find that the next drilling size will want to follow that hole once the old threads have gone. Next trick it to also tap it square,,,,

[Minigirl]

A local store stocks a M10 kit, would I be able to rethread the stud to m10 and use that? Or is it best sticking to 3/8unf? Thanks

[dklawson]

My suggestion is similar to Spider's.  However, I was going to suggest using the head you have on the engine now and wrapping the drill bit with masking tape until it just fits the hole in the head.  The tape will locate the drill as accurately as you need and protect the head at the same time.  You will be able to tap the hole perpendicular "enough" just by eyeballing that the tap's shank is centered in the hole going through the head.  You will have to take the head off for the final step to install the insert.

 

EDIT:  You were typing while I was typing.  Do not use M10.  Keep all the thread sizes standard.  First you would have to find or make a suitable M10 stud and then you (and future owners) would have to be careful to put that one stud in the correct hole anytime the head was removed.  Again, keep the standard 3/8 threads to avoid problems later.

Edited by dklawson, 14 July 2015 - 08:59 PM.

[Spider]

As Doug says, stick with 3/8" UNC (not M10 or UNF).

 

Another option.

 

The threads or indeed the holes are fairly deep, most are usually twice as deep as the thread length on the stud. You can just drill out the damaged part of the thread, run a tap in there (3/8" UNC) to clean it up and if need be cut it a bit deeper, then fit a longer stud, which are available, P/N TAM1617.

[Minigirl]

Got a kit from a local steel works / tool supplier for £23

Drilled it, tapped it, but then confused by instructions as it said to screw the coil in half a turn and remove the tool turn it 90 degree and snap the little tab / tail off.. why do you do this? Why not screw it fully in???

[Cooperman]

You should drill it with the special size drill, use the tap(s) to create the thread in the hole, then screw the coil in using the special tool until it is 1/2 a turn below the top of the hole. Then break off the tang at the bottom of the coil which was used to screw it in. Jobsagoodun!

[Minigirl]

Then do you screw the stud into the spring / coil thats sticking out?

[nicklouse]

It should not be sticking out. You should cut thread so it is flush or lower.

[zerobelow]

I had to helicoil a head stud on a corvair that has a Buick 215 (rover v8) in the back seat behind a roll cage. 

 

It was a very tight space to work in. We made a jig out of a piece of lumber (2x4 over here). We made 2 sets of holes -- one set to do the drill part of the insert. And a second that let us do the tapping part for the insert.

 

All the holes were made with a drill press. One set of holes sized to do the drill out. The second set up for the tap. With that one, we drilled the hole with the tap bit, so it threaded into the lumber. This let us make sure that the tapping went straight, too. 

 

One thing to note: most helicoil sets don't come with the drill bit for the first step, and it's an odd size -- looks like the 3/8 helicoil needs a 25/64" drill bit. Don't try to fudge it with a different bit.