cylinder head/spark plug thread

[syncron ice]

Hi,

I was on a couple of weeks ago re: could I replace cylinder head in situ, I cant find the thread (no pun intended!) so I've re-posted. Anyway, the plug in No.3 blew out and the threads appeared to be ok but the plug could be pushed in and out so I presumed the head was cracked as I'm very careful when replacing plugs. I inspected the head insofar as I could but couldnt see anything. I also noticed a bit of thread stripped off the plug. Worst case scenario was a head replacement so I decided to helicoil it just in case.

This I achieved successfully in situ. I bought a 'sav-a-thread' (M14)by helicoil for $21. This included a 'drill' to make a larger hole, 3 different sized inserts and a metal bar to hammer at the end. (Forgive my lack of knowledge of tool names but I know what they do).

The process:

Clean around existing plug hole. Move any hoses/cables that might impede work.

It is recommended to lubricate 'drill' but from experience I heavily greased it in order to catch all the shards which will collect in the perpendicular grooves. ( Have the piston at TDC which also prevents shards from dropping into the cylinder)

Start the 'drill' by hand (hopefully you will have enough of the old thread) and then onto the ratchet (1/4") with short extension as you start the new cutting.

Patience required, a quarter of a turn at a time making sure to keep the extension bar perpendicular to the direction of hole. Square on in other words. It would be very easy to pull from one side and misalign the 'drill'.

Err on the side of caution and withdraw the 'drill' (slowly) when you think you are nearly there. It will be covered in metal shards thank God so clean it well. Check how far you've drilled and if you see a smaller hole with threads further in you'll have to drill more.

Get a kitchen towel, fold in half, roll into a white cigar! Coat half of it with grease and insert it into the plug hole. Twist anticlockwise and withdraw slowly and voila, more shards.

Coat the 'drill' with grease again; re-insert by hand being extremely careful to be on the right threads and when it tightens put the ratchet back on an finish the bore.

Remove slowly and repeat towel etc. Coat a cotton bud with grease and insert as far as possible and rub around in a slow circular motion. Withdraw slowly. More shards.

Repeat towel and bud a couple more times for safety then the same without grease. Clean around hole also.

Now it time to put in the insert. Check that there's no dirt on the threads and coat with high temp silicone (not supplied, about a fiver from motor factors). Screw a plug into insert to hand tight which then aids fitting onto the right thread and screw in slowly until you come to the non threaded part of the insert. Unscrew plug and use metal bar to gently hammer ( a few taps will do it) the insert fully home.

Wait 24 hours for silicone to set.

Refit cables/hoses if you moved them and fit plug and lead. Do a visual check around engine bay to make sure you haven't left tools/rags etc there. Replace engine cover an fire her up.

Hope this is of help.

Tony

[Mr Bean]

Sounds kind of feaseable to me but is it a Helicoil or a threaded sleeve? In either case I don't understand the bashing it with the metal bar at the end of the opertaion or the Silicon stuff. Please enlighten.
Cheers
Wolfie

[syncron ice]

Hi Citizen Smith,

Yes its a threaded insert made by Helicoil. Sorry for the confusion. The top of the insert has no threads just knobbly metal. Yes, I was confused too about this and the high temp silicon but you have to tap it in flush and maybe the knobbly metal provides grip so as the insert doesn't come out when extracting the plug. Silicon to prevent any possibility of loss of compression through threads?

But it works and it's easy!

Tony