Driving my 954 Fireblade engine 7 today, heard a bang and then it was only running on 3cyld. A spark plug had worked its way out of the head. So i tried to put it back in but the thread in the head is damaged.
Is this uncommon, what could cause such a thing?
Any advice/ideas/help/info would be greatly appreciated. Am going to ring Andy at AB performance tomo as i am due a trip there in the next week or 2; looks like my bill has just shot up!

thanks in advance

Mark

would something like this work

thats pretty cool, i guess i'd have to use a new (smaller) spark plug with it though?

thanks for the link

Helicoil as above.
No it keeps the same size plug.
If yopu're really brave do it in situ, without stripping the engine

I wouldn't say it was common but the same thing happened to Paul Fishers Fireblade engine (929cc) on a trackday a few years ago. Tried to screw the plug back in but it had stripped all the threads. He did get it repaired but I'm not sure where or how much it cost. Might be worth dropping him a U2U.

Phil

if theres enough metal around the plug hole it could be enlarged... and then a standard plug used again.

is the thread stripped all the way down? you might be able to run a cleaning tap through from bore side (head-off job) and get away with it..

Fitting a helicoil is a simple process - if you know what you're doing. Any machine shop can do it.

It involves the cutting of a new thread, then the steel helicoil is wound in and located. Once it's in the visible thread is exactly the same as the old one, so you can use the same plug.

thanks for that; ive sent paul fisher a u2u message.

looks like hellicoil is the way forward then huh. bugger!

As Phil said above,the same thing happened to my 929 fireblade engine,I had a guy at a local engine reconditioning company came out to fit a helicoil,took him about 30 minutes,and cost me £30.
Its a easy job to do with the head off,but not so easy with the head on,theres a little lug on the helicoil thats requires cutting off after it is screwed in place,as the plugs are set deep in the head on the 929/954 engines,so with care and skill it can be done.

Repair methods fairly well covered above but to anybody else reading this thread take heed ---

When replacing plugs always screw them down by hand --
If you can't screw a spark plug in with just your fingers gripping the socket extension stop before you do any damage !
Removed the plug and carefully run a thread chaser tool down the hole provided the threads aren't stripped this will re-align clean and repair the threads rather than recut the threads.

Agreed - Helicoil (or one of their clones) and don't get any swarf into the engine.

You might also like to consider why the old thread was stripped. The two common reasons are:

Cross-threading - the cure is as britishtrident states - start them by hand.

Over-tightening - which can weaken the threads in the head, to the point where they fail. The cure is to use a torque wrench to finish them off when fitting.

[Edited on 15/2/09 by David Jenkins]

Give you dollars to donuts a former owner overtightened the spark plugs ( the reason GM sold the aluminum v8 to Rover in the 60's) Repair that hole and take a real good look at the others.
We used to helicoil all the threads in Hewland gearboxes for the CanAm before we used them.
If it was me I would helicoil all the spark plug threads, and in future use a torque wrench.

hey guys thanks everyone for the replys.

agreed, i guess they have been over tightened in the past.

as said i am due a visit to AB performance for a sump in the next couple of weeks so i will ring him tomo and ask if he can helicoil while im there.

very frustrating!!