tight spark plug

Post by **brad360** » 12 May 2007 09:10 am

After 2 years and about 18000km I thought it might be time to change the sparkplugs. 3 came out reasonably easily but one is very stiff, I may have turned it 180 deg and it isn't getting any easier, I'm wondering if it might be cross threaded.

Is it likely to be easier to remove when the engine is hot or cold?

This plug change has been prompted by some rough running after several short trips (under 2km) and cool weather.

I noticed two plugs had some weeping around them and smelt of fuel when i removed them after driving about 20 metres, it was running rough.

Post by **pettaw** » 12 May 2007 09:24 am

Hmm, I had this happen to me. Its a real pain. The spark plug is probably partially seized into the aluminium in the head. I would get the car hot first, then you need loads of WD-40 and gently rock it back and forth, pushing it a little further each time.

By the time mine came out it wasn't a pretty sight and had bits of aluminium stuck to the plug threads. Luckily enough the new plug seemed to go in OK and tightened up OK, so fingers crossed, if not then you'll need to drill it and use a rethreading kit. Foggy's used one in the past so he'll be able to advise better than me, but helicoils aren't the best.....they have a habit of coming back out again.

Post by **jtbo** » 12 May 2007 02:23 pm

Also remember that even small chip of aluminium in cylinder is causing engine wear, hygiene of surgery room required

Post by **brad360** » 13 May 2007 12:48 pm

i drove it a few km and it came good, it just doesn't like repeated short trips. it felt like it was running on 3 cylinders for about 2 minutes.

i think i'll just leave that tight spark plug alone.

or do you think it might get seized in worse over time?

maybe i'll give it a regular squirt of WD40 and give it a wiggle every week or so.

Post by **stealthstylz** » 13 May 2007 12:50 pm

That'd be a good idea. If it gets stuck solid they're horrible to get out.

Matt

Post by **shimon340** » 14 May 2007 01:17 am

hi there

I've had this happen to me when I did the first service of a "new" 340.

In my case, after trying to free it a little at a time, the porcelain of the spark plug snapped. Cleaning this up and then using a 1/2" long wrench and adaptor, the plug came out. The thread was totally dry (I've always been taught to add a little oil to the threads) and had a little "dusting" of aluminium. Fortunately, the thread on the head survived unscathed. A New plug fitted in nicely.

however, my friend recently crossed threaded a plug on his 340s. the thread on the head was totally.. well.. totalled!!!

Thw way forward for us was to remove the head and get an "Timesert" spark plug insert fitted. These are better than helicoil since they are 'T' shaped so cant be screwed into the head too far when you put a plug in. They also are non reversable to cant back out when you remove a plug. Just dont overdo tightening plugs as you could damage the insert.

In our case, an engineering shop in manchester fitted one to the head for £15. Pretty good since the timesert kit is over £300!!!

This repaired the thread and normal service could be resumed!

hope this helps

Shimon

Post by **foggyjames** » 17 May 2007 08:24 pm

That sounds like the type of product I've used before, Shimon. Verdict: Use copper grease on plug threads.

cheers

James

Post by **shimon340** » 20 May 2007 09:54 pm

hi james!

I tend to use a little drizzle of engine oil on the plugs but I guess copper works well too!

Post by **brad360** » 22 May 2007 12:59 am

with a hot engine I sprayed some WD-40 on it, waited 15 mins, gave it a wiggle back and forth, went away for about an hour, then gave it another wiggle and it came out, no worries. I will take out the others and put a bit of oil on them.