Damaged spark plug thread

[Crash Bandicoot]

I was wanting to ask for your thoughts on following:-.

The helicoil insert in cylinder no. 4, has come un-threaded during a compression check.

I re-tapped spark plug with correct tap and re-inserted new helicoil but now the plug cannot be tightened correctly assume in- sufficient thread remaining to secure the helicoil insert.

I am planning on removing the L.H. head, and have some type of insert fitted.

Any recommendation, experience or suggestion of best option greatly appreciated.

Brian

[JohnD]

Just for clarity, "re-tapped spark plug with correct tap and re-inserted new helicoil" means you used the oversized tap so that when the helicoil is inserted its ID was the original size?

Try a thread locker between coil and head?  One of the strengths that are for threads that will never be removed! And heat resistant.
EG Loctite 278 http://www.loctite.co.uk/loctite-4087.htm?nodeid=8802623815681

NB, compression testers should seal on an O-ring on the shank of the connector; they need be more than hand tight.

John

[Crash Bandicoot]

Thanks John,

To clarify, the new helicoil inset is turning in the hole when the spark plug is tightened correctly.

I don't think loctite is going to help me.

Assume insufficient thread to lock the coil in the bore.

I was considering some type of threaded insert to replace the helicoil..

the following inserts as shown on You Tube look promising, has anyone any experience with these or suggestions appreciated.

https://www.youtube.com/watch?v=UTdJUMIcrPI

Cheers
Brian

[DJT]

These are the ones you want: http://www.timesert.com A special insert tool locks the inner few threads so that it won't unscrew, and the collar ensures it won't be screwed into the cylinder. They do a Big-Sert for over-sized holes. Not cheap, but they do the job properly.

V-Coil is a slightly cheaper option: http://www.voelkel.com/en/serv.....ndereparatur-en.html

Helicoil inserts are NOT suitable for spark plug repairs due to the fact that they can screw into the combustion chamber. They are meant for 'blind' holes.