Stripped Spark Plug Thread in Head - help

[Ultimatt]

Hi all,

It's been a while since I've been on here - which is usually good news as it means all is well in Elan Land...

However a recent development has exceeded my technical knowledge and I cannot see any previous posts addressing a similar problem.

The car has been driving near perfectly for months (only reason I say 'near' is that it's 24 years old and has the normal creaks and groans you'd expect); 2 minutes from home in the morning and at no greater speed than 30mph from start and no hard acceleration, there was a loud pop/bang and a slight puff of smoke form under the bonnet. - Never good!

I stopped the car immediately and popped the bonnet. It appears that one of the spark plugs has literally popped out of the head, forcing the HT lead into the housing cover.
Got myself towed home and had the chance to inspect and attempt a fix today. My hope was that the spark plug had simply worked lose and popped out, so I replaced all spark plug with new ones. The plug that popped would not tighten into the head, suggesting that the thread into which it goes has in some way stripped. All other plugs went in fine, initially by hand and then by torque wrench. Incidentally, the cap on the top of the spark plug that goes into the HT lead had come off and was wedged inside the HT lead. I managed to get this out with a threaded bolt of the same diameter.

Has anyone any experience of this and or know what my solution options are? - other than buying a new engine?
She's my daily driver, has 120k on the clock and I have owned her for nearly 15 years, so I know she has been cared for.

Many thanks

Matt

[dapinky]

Hi Matt,

Probably not the answer you'd hope for - but it's all I've got......

..... the options all depend on how much metal is left around the stripped thread - and the first step would be to remove the head and have a look.

Hopefully, there is enough clearance between the spark plug hole and the valves to not have caused any structural integrity issues with the valve seats.

If that is the case, then any reasonable engineering shop (or enginne reconditioner) should be able to do a satisfactory repair to the head.

The 3 options are:-

1) Drill and tap a larger hole and fit a wider sparkplug (not my favourite choice).
2) Have a thread replacement insert (Helicoil) fitted to enable the original sparkplug to be used.
3) Have the damage 'built up' with aluminium welding and thread re-cut into the new material.

Both 2 and 3 are considered to be 'proper' repairs and will be a good job.

Obviously, it will need a new Head Gasket, and is possibly a false economy to not look at replacing the timing belt/tensioner/idler at the same time (unless it was done fairly recently).

If the plug getting blown out has caused damage (cracking between plug and valve seat), then it will need specialist welding, and a good used head may be a better option - but until it is off, you won't really know.

I have had good results from both welding/re-cutting and from helicoils on other engines, but I've not had the necessity (yet!) on an elan.

(I've even seen on other forums that people have 'bodged' the repair ny not removing the head, and using 'chemical metal' to re-build the threads -but I wouldn't really consider that as an option.)

[Ian T]

Also there is another fix that is similar to a helicoil but both quicker and easier to fit. IIRC it is called 'Timesert' or something like that and I had to have it done to a Carlton head where the owner had not tightened the spark plugs adequately and a loose one had rattled and worn its thread away before popping out and rendering the car pretty undriveable. Had the car towed to Hayes Engineering in Bexley (near me) and they drilled the hole to a larger size and fitted the sleeve, so the original plug went back in. Also considered a 'proper fix' and the process manages the swarf you get from drilling with the head still fitted, so the whole process only took about an hours work and cost approx £80 (about 8 years ago).

[Jeemy]

I just happened to read this in Car Mechanics magazine a couple of hours back.

A guy with the same question, given the same advice including a kit that prevents scurf from entering the cylinder - I'll look it back up if thats helpful.

Then at the end the guy giving the advice said:

"a tip I've been told about is to drop the piston to BDC, and then fill the cylinder with shaving foam! It prevents any material from entering the bore and when finished, can simply be pushed out by cranking the piston. I have to admit, I have never tried this myself".

So make of that what you will, but I thought I wouldn't with-hold it!

[Ultimatt]

Thanks chaps - Really appreciate your input.

Dave, I know you are a man experienced with engines and the Elan.
Are you aware of these alternate methods mentioned and any risk they may pose to the Elan engine?

Matt

[dapinky]

Matt,

I have to admit that I'm not a great believer in trying a repair with the head in situ....

....and (maybe because I've never seen the results, and am panicking unneccessarily) wouldn't be confident that there is no damage between the plug hole and valve seats unless I've had a good look.

I suppose that sticking a boroscope down the hole may help to establish if it's a viable proposition, and if the system is tried and tested elsewhere, it *may* be the simple answer - just something I've never encountered, and wouldn't necessarily consider.....

...sorry, not really a lot of help

[Jeemy]

OK as you are still struggling here is exactly what was said about a stripped plug thread in a BMW 1998 E36 M3:

Somewhat abridged, and I will have the June 2014 issue somewhere if you want it posted. Enright will testify I am not the fastest at getting to the post office…..

Car Mechanics covered thread repair kits in June 2014. The BMW has 12mm plugs. There is a kit available that does not require the thread to be drilled, using a pilot nose on the tap to carry out the job. The kit for the 10mm (sic) thread is available here: bit.ly/1jSNIQN and the 12mm version is just over £40.

The best advice I can give when fitting the helical is to work slowly and steadily and to use plenty of grease on the tap to pick up the swarf as it is cut. After the thread has been cut, blow down the plug hole with an air-line to remove any debris that has fallen into the cylinder, and then slowly turn the engine over by hand to ensure that nothing is obstructing the throw of the piston.

<shaving foam anecdote ensues.

I hope that is helpful especially the link.

[Enright]

Enright will testify I am not the fastest at getting to the post office…

Aha, glad you've not completely forgotten me then!

[ccb056]

A keensert is a bit higher quality than a helicoil, it can withstand a bit more torque.

Had a stripped out lug nut hole in a rear hub, originally replaced with a helicoil which eventually failed, then replaced with a keensert and it's been running strong since.

[Ian T]

Here you go - this is what was used on my car.

http://www.timesert.com

Sounds the same as a keensert, from a different manufacturer. Either way, you might prefer to get your local engineering shop to fit it as they do them day in and day out so have the experience and confidence to get it right.

This is one job I think my heart would be in my mouth for and I'd probably worry a bit too much given the value of a head.

Ian.

[Ultimatt]

Thank you all. Appreciate your input and help.
Haven't had chance to tackle it yet, but will aim to get it to a local engineer to see which they have experience of.

Matt

[Simon_P]

...that prevents scurf from entering the cylinder

Those little blue people get everywhere!

Haven't had chance to tackle it yet, but will aim to get it to a local engineer to see which they have experience of.

You need to use the right tool for the job - An engineer won't be able to help you. You need to speak to a Mechanic or a technician.

Phone and speak to a few people that do the job, it is a bread and butter job them - Let them worry about the method, the swarf,and the guarantee.

Start here
http://www.fer.co.uk/

[muley]

Matt

You have PM


Jim