Anyone do their own HeliCoils?

[jthm]

I have managed to cross thread the lower half of my rocker arm thread. I do not want to take the head off and buy new head bolts and a new head gasket, so I'm considering doing a helicoil I have had them done in the past by machine shops but I am considering buying a helicoil and tap set for myself. Has anyone done this with the head still on the motor? My main concern is the straightness of the drill.

[onefastV6]

Have you tried to use a tap to chase the threads? If the threads aren't damaged too bad they might be repairable.

[jthm]

I have not yet tried that, but was hoping it would be an option. Do you know what size tap I will need? 96 corsica 3100

[RacerX11]

I helicoiled one of my rocker arm mounts for a '99 3100 head. You will need a special extra-deep heli-coil, as the threads on the rocker bolt are longer than a standard helicoil. I just bought the seperate helicoils and used a regular tap. I think I had to buy a package of 5 or 10 helicoils. I will see if I still have the leftovers. I don't have the specs on the tap in front of me, but I will check tonight.

You need to be real careful about lining up the hole when you drill out the original threads. If you don't get it perfectly straight, this will affect how the rocker lines up with the valve tip. Also, be careful about dropping metal chips into the engine.

Marty

[Guest]

IEEEEeee.

I don't know that I would trust a heli-coil for teh rocker arm.

[RacerX11]

Raven,
Why not? Helicoiled threads can be stronger than raw tapped threads in the parent metal.

jthm,
The helicoil inner thread is a 10mmx1.25, so the outer thread requires a 12mm-1.25 tap. I checked my metric tap set, and only have 12mm-1.50 and 12mm-1.75; I must have bought the special tap for these helicoils, but can't seem to find it. I think these run around $5-$7.

The inserts can be purchased from www.mcmaster.com in 10mm, 15mm, and 20mm lengths (I couldn't find 15mm or 20mm locally). With the gen3 stud, there is ~16mm of thread protruding into the hole, but there is several mm of unthreaded bolt that sticks out past this. You will probably have to either use a 20mm insert (if hole is deep enough) or break the tang off after install using an 15mm insert.

Marty

[Ryan from Ohio]

The problem is drilling hardened steel thats sitting in Aluminum. Your drill will want to wonder towards the softer Aluminum.

I did this on a head with a broke off exhaust stud bolt. It was a giant PITA.

However I understand not wanting to buy another set of $28 bolts and $15 gasket- I cant blame you.

If you already have the other bolt out- disregard my first comments. That should be fairly easy really. Just make sure you drill as linear as possibly. Use both hands. Have someone watch you to make sure your going in at a right angle.

HeliCoils are good stuff. Ive done a few in my days in the shop also. Im a machinist by trade.

Good luck!

[geoffinbc]

You can find or make a cheep drill guide.

When you tap your hole just find a nut the size of your tap and thread it onto the tap. Then rest the nut on the top of the hole you are repairing. be sure it is sitting down evenly and begin tapping. The nut will guide the tap in square and once your have started tapping your good to go.

[ForcedFirebird]

I have managed to cross thread the lower half of my rocker arm thread. I do not want to take the head off and buy new head bolts and a new head gasket, so I'm considering doing a helicoil I have had them done in the past by machine shops but I am considering buying a helicoil and tap set for myself. Has anyone done this with the head still on the motor? My main concern is the straightness of the drill.

You could also use something like this...
http://60degreev6.com/showthread.php?t=35763

[CNCguy]

I have managed to cross thread the lower half of my rocker arm thread. I do not want to take the head off and buy new head bolts and a new head gasket, so I'm considering doing a helicoil I have had them done in the past by machine shops but I am considering buying a helicoil and tap set for myself. Has anyone done this with the head still on the motor? My main concern is the straightness of the drill.

I know this is late but a Helicoil will work great. Some military parts are made with Helicoils since the threads are probably twice as strong as a threaded aluminum hole. If you are concerned about straightness, have a block of steel drilled with the Helicoil drill size and use it as a drill guide. Also, have a second hole drilled in the block as a guide for the tap.