Corvair Forum

One of the spark plug holes is now stripped and nearing 18mm in diameter, don't know what the PO did to achieve this situation.

What are some options available for repair?

A fairly common failure - there are a number of kits and with care you can do it with the head on the engine.

DO NOT USE A HELICOIL. A helicoil is great for repairing normal bolt threads, but a spark plug threaded hole has different properties compared to a normal bolt hole.

See Clark's page http://www.corvair.com/user-cgi/catalog ... N&page=173

BTW - the main reason an insert fails is the top of the insert is not installed BELOW the head surface. This causes the spark plug to seat and lock on the top of the insert, not on the head flange as it should and when you remove the sparkplug it will unscrew the insert.

If you are not good with this type of work, get someone experienced to do it.

X2 on using time-serts versus heli-coils.

I ran into the same issue with my 63 spyder. I had two spark plugs that somebody, some where in the past, had stripped the threads out. Hey....it can happen. I ended up trying each of recommended Clark's methods for repair. They both worked fine.

Within a few short months of making those repairs, I was still fouling and pulling plugs for other major engine related issues. I hated to pull the plugs from where I had made the repairs for fear of having to do them again.

In the end, I had the heads reworked, I had 6 inserts installed. And it's now the way it should be.

I like the save a thread repair kits as they have serrated top threads that embed themselves in the aluminum when installed properly and they don't come back out, I have used these a lot and have never had one come out

Jsr wrote:One of the spark plug holes is now stripped and nearing 18mm in diameter, don't know what the PO did to achieve this situation.
What are some options available for repair?

nearing 18mm.................too big for a timesert........your going to need a bigsert or some other oversize insert repair.

-Scott V.

Thanks guys for the quick responses.

davemotohead wrote:I like the save a thread repair kits as they have serrated top threads that embed themselves in the aluminum when installed properly and they don't come back out, I have used these a lot and have never had one come out

DM - thanks for the confirmation, I had used the save-a-thread on one of the other spark plug holes seemed to install rather secure.

Scott V wrote:

Jsr wrote:One of the spark plug holes is now stripped and nearing 18mm in doiameter, don't know what the PO did to achieve this situation.
What are some options available for repair?

nearing 18mm.................too big for a timesert........your going to need a bigsert or some other oversize insert repair.

-Scott V.

Scott - that's what I was concerned about the dang size... I was not seeing any large size timeserts... I'll search out bigsert.

Thanks again!

Jsr said: Scott - that's what I was concerned about the dang size... I was not seeing any large size timeserts... I'll search out bigsert.

Big-sert info: http://www.timesert.com/html/bigsert_sparkplug.html
Hopefully you can find a shop nearby that can do it for you, the kit is rather expensive.

Marty Scarr