Boxerworks.com

After cleaning up my heads for dual plugging I just noticed that one of the heads I've been using for the last 21 years has a Heli-coiled spark plug hole. A magnet doesn't stick to it, so it must be Stainless. I've read about how steel inserts change the heat range of your spark plugs (and can even act as a glow plug) and that aluminum threads are prefered for aluminum heads. I haven't really noticed a problem, but I'm increasing compression and will be using a 336 cam so things might change.
It looks like there's only two options for aluminum inserts. Timesert http://www.timesert.com/html/bigsert_sparkplug.html
and Locknstitch http://www.locknstitch.com/sparkpluginserts.htm. The Locknstitch seems like a superior product because it's designed to prevent cracking, but one kit costs more than a completely rebuilt head.
The Timesert version is cheaper, but cracking could be an issue.
Anybody have experience with either one? Should I even worry about re-doing the threads?

mattcfish wrote:Should I even worry about re-doing the threads?

I wouldn't. If the current insert is working fine, I'd live with it. If you want to be anal about it, but a little less anal than you're considering, Heli-coil the other head so that at least they will be identical.

I have steel Timeserts in my dual plugged '74 Harley Super Glide (aluminum heads) on the right side and steel Heli-coils in the left side. No problems for 7 years.
I'd leave the Heli-coil alone.

I'm surprised there isn't more debate on this subject. There's a lot of banter on the Hot Rod cage driver sights. I'd hate to have to cut up the good threads on my other head to install a matching Stainless Heli-coil. I'm moving compression up from 9:1 to close to 10:1. Is the unbalanced heat transfer on the plugs really a non-issue on airheads? Maybe with the dual plugging it really is less of an issue.

You can always get the one head welded up and redrilled and tapped into the aluminum, eliminating the helicoil.

Technically there is a difference in heat transfer with a helicoil just because there is the extra interface that the heat has to pass through. I seriously doubt that anyone has ever actually measured the difference. I can't believe it would make a heat range difference.