winter repair

Last winters project was new valves, guides and seals on the head. The shop wanted to "deck" the head which I was reluctant as it's a combat and has enough removed by the factory. Went ahead anyway with minimum removed. On assembly the right front head stud nut wouldn't tighten....pulled the helicoil loose. I suspect it may not have had enough thread on the stud for the nut to seat which caused over tightening of the stud into the aluminum head all due to to the removal of metal from the head. After I get this repaired at Phil's shop Fairsparesamerica, I don't want a repeat of pulling the new insert. Anyone have this experience?

It pulled the Helicoil out? What size was it? I asked Comnoz about bronze inserts vs Helicoils when I was getting my head together and his comment was only if the Helicoil fails. Or something along those lines. He would be my next call!

Got a source for repair. Any opinion why the helicoil pulled loose?

The visible threads are what remains of the Helicoil? Did the stud bottom out and break the coil? Or did the stud not engage all of the threads of the coil?

If the visible threads are in the aluminum then I would say the coil wasn't long enough.

Russ

rvich said:

The visible threads are what remains of the Helicoil? Did the stud bottom out and break the coil? Or did the stud not engage all of the threads of the coil?

If the visible threads are in the aluminum then I would say the coil wasn't long enough.

Russ

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The threads are in the aluminum and are from the larger tap used for the helicoil insert. This part of the helicoil didn't fail. I pulled what was left of the insert to get the head ready for the next repair. Will contact Phil Radford later this week. Want to let him have some uninterrupted time off for the new year.

When ever possible, I will always go with a thread insert. This will double, if not triple, the fastening capability of an alloy structure.
Helicoil only when no other option is available, like if not enought meat, or if you need a quick temporary fix. The soft alloy of the head simply does not offer the integrity to hold helicoils where as the deep grip of the thread insert surpasses the required torque.

Although they have their application, I personally do not trust helicoils.

In my case the helicoil survived for more than 30,000 miles. It failed after last winter's head rebuild. I suspect due to the head being resurfaced reduced the distance on the stud threads to where the nut didn't have enough distance to tighten against the head. By tightening the nut the stud then pulled the helicoil loose....that's my theory. Anyone else have this experience? Fixing the thread won't prevent the same thing happening again. Maybe I'll cut a bit more thread on the studs just in case.

Just curious...how much more was shaved off the head? Have you recalculated the compression ratio? You might have just gone past the holding limit for the size of thread used. If this is a concern you could use a thicker copper head gasket to get back to the stock compression ratio. JS Motorsports offers them, probably others as well.

Russ

rvich said:

Just curious...how much more was shaved off the head? Have you recalculated the compression ratio? You might have just gone past the holding limit for the size of thread used. If this is a concern you could use a thicker copper head gasket to get back to the stock compression ratio. JS Motorsports offers them, probably others as well.

Russ

Click to expand...

Exactly what I suspect. I believe I ran out of thread and the long front nut bottomed which made the stud pull the helicoil. Compression ratio wasn't my quest, rather cranking compression. Before changing to a Norrix RX cam a previous owner had installed a standard cam in the combat engine which was giving 183 psi per cylinder. As gas got worse with the alcohol, the engine wouldn't stop pinging. The additional duration/overlap of the RX cam fixed this and it runs very nice now....just leaking oil from the head due to the pulled right front cylnder head stud. Anyway just got back from dropping the head off with Phil Radford. I'm planning to use one of my copper head gaskets when I assemble it.