Retapping spark plug hole threads

[Money$hit]

Has anyone had a bad experience with the spark plug holes on an M50 NV? Im trying to remedy whats gone wrong with my engine.

Basically, I went to do a full spark plug change, and got into what seems like a deeper project. I pulled the plugs and tried inserting new ones. All went well except in cylinder #5, which gave me issues. I basically couldnt get the plug to tighten down, as the plug just keeps spinning. I tried running the same sized tap through the threads to get anything out of the hole that could be impeding the plug. I think the threads on the head are dunzo. Is there anything I, or a machine shop can do to restore the spark plug hole on this head?

[gazellebeigem3]

Short of removing the head, a helicoil would probly do the trick

[Money$hit]

ill try that tomorrow.

[318isbmw]

Yep, helicoil for the win with those. Dad's done a few on vw motors, always worked and ran like hell w/ the helicoil w/ no issues.

[1fastcosmo]

Id pull the head and insert a timesert if i was you.helicoils suck.I know its a pain in the ass to do it butbetter to do it once than twice.

[Farbin Kaiber]

Id pull the head and insert a timesert if i was you.helicoils suck.I know its a pain in the ass to do it but better to do it once than twice.

Truf.

[Money$hit]

pardon my ignorance, but what is a timesert?

[Farbin Kaiber]

http://www.timesert.com/html/sparkplug.html

Much better "clamping/locking" in the bore. Less likely to fall thru, or come out with a plug later.

[JGood]

Isn't there a decent probability of metal shavings in the head, if it stripped out and was just spinning?

[Farbin Kaiber]

Isn't there a decent probability of metal shavings in the head, if it stripped out and was just spinning?

Nope, you can strip the threads without tearing the metal out. More of a forced thread crush.


If there are after tapping, Cornwell IIRC carries a shop air adapter that creates a vacuum with a small tube to remove them all.

[JAM]

teflon tape?

[JGood]

Nope, you can strip the threads without tearing the metal out. More of a forced thread crush.


If there are after tapping, Cornwell IIRC carries a shop air adapter that creates a vacuum with a small tube to remove them all.

Ahhh, cool. Good to know.

teflon tape?

Fail

[Farbin Kaiber]

In the past few years the Ford 4.6-5.4l v8's strip like v6 4Runners blew head gaskets. I think there is a kit for it, based around the Ford application but will work with other tap/die sets. I prolly saw 15-20 of 'em done without cylinder head removal in the last 12 months.