Help,............blown out spark plug

[maverick]

Please any help advise would be helpful to my V7 Stag !

.Spent a lovely Bank Holiday cleaning the Stag,hard top off,ready for a enjoyable drive with the wife,when after about 3 miles heard a tremdous bank form under bonnet ,and could see spark plug nearest dip stick hangin down on H.T lead,completely blown out.

Managed to gently limp her back to base.

Must admit this wasnt a total surprise,as I had noticed this particular plug weaping.and was afraid to overtighten,think this thread was damaged along time ago.

Now I know I need to get this Helicoiled,hopefully in situ,but has any member,got any experience of this ,or got any tips.

I have searched back to previous posts,and there seems to be v.little entries.

Thanks in advance,

Mark

[John]

imported post

Helicoiling is pretty easy, though doing the sparkplug hole in situ might be a minor challenge. Assuming you can get the tap etc. in position and square on the whole (might be tough depending on what cylinder you're doing), you also need to ensure the swarf from cutting the new thread and the tang from the end of the helicoil don't fall into the cylinder. I've not done this myself, but I've heard a good way to avoid this is to turn the engine over so that the piston in that cylinder is a bit below TDC and fill the cylinder with grease. Once you've cut the thread and fitted the insert, you can turn the engine to TDC to expell the grease and swarf out of the spark plug whole. My only other advice is to make sure you keep everything square on, and take it steady.

[european voyager]

imported post

My car was given helicoil with the head on , it was awkward but done , I put the piston up and made sure the helicoil tail was broken off with long nose pliers and didnt go into the engine , I blew as much swarf out as I could with an airline then turned the engine over a few times with the coil disconnected to blow any excess out , fitted the plug and its been good as new since.

[alan_thomas]

imported post

I was talking to a engine reconditioner this lunchtime about this very subject, he had stopped using helicoils for plug threads and swears by these http://www.timesert.com/

The advantage is they have a shoulder (much better with a thru hole like a plug) They are a full thread profile of the correct thread angle and they have no 'tang' to break off and lose down the cylinder.

Not the cheapest but the best (he says)

- Alan

[Mpower738]

imported post

My Father and I fitted a helicoil thread repair to my 1961 Mercury outboard when one of the plug threads stripped. Because the engine is monobloc, ie no cylinder head, I didn't want to strip the whole thing to get the piston out in order to do it, as parts are virtually non-existent.

Instead of drilling we used an adjustable reamer to take the hole out to the correct size for the helicoil tap, with plenty of grease on it to pick up the swarf. Then tapped out the thread, again with loads of grease, and fitted the coil.

I think a correctly fitted helicoil insert is the easiest, quickest and cheapest repair, but you do need to be very careful or it can all go horribly wrong.

Those inserts do seem to be a good idea, but without removing the cylinder head the problems remain the same as helicoiling, and the price is bound to be higher.

I must say I regret not helicoiling the stag plug threads the last time the heads were off, it would have been so simple to do at the time. Now what has happened to you is always a possibility as I know a couple of the plug hole threads were stretched.

Hope you manage to sort it out.

Doug.