spark plug strangeness 2

[cybermini]

14 NOV 2011

Okay, I had a problem months ago when I noticed the round rubber seal around spark plug #3 was flexing like a sub woofer. Pulled the wire and found the spark plug was loose ... so I tightened it and all was fine.

So today I pull my mighty MINI into the garage and as soon as I turned off the key, the motor's fan came on. I thought that was strange, but once had the fan and plug melt down (when the fan came on and it eventually drained the battery and got so hot it melted the wiring harness to the fan) ... so I was preparing to disconnect the battery to keep this from happening again. So the bonnet was open and I was searching for a wrench ... which I didn't have in the garage, so I decided that I would re-start the car while I ran to get the wrench. As soon as I turned the key, there was a loud explosion (louder than a fire cracker, not as loud as a M-80)! I immediately turned off the key and noticed the fan was no longer running. I got out of the car and looked in the engine by to find 1. the spark plug wire for #3 was no longer in place ... and 2. the spark plug (from #3) was laying across the garage on the floor as it had blown out of the engine!!

That plug's threads look fine, so I'm assuming it had worked it's way loose again and that the cylinder head isn't trashed in the explosion ... though I don't yet know... and will have the car inspected tomorrow at my local garage (Auto4N in Cincinnati)

Anyone ever see such a thing?

[mab01uk]

Heard of a few Mini plugs working loose and sometimes get blown out but often damages the thread, meaning head off for a helicoil or can be done in situ by using 'Time-Sert'
Wrth UK Ltd. - the world's number one supplier of assembly products and consumables

TIME-SERT Spark Plug Thread Repair - YouTube

Successful Mini2 repair here:
http://www.mini2.com/forum/first-gen...eads-help.html

[cybermini]

i did try to insert another spark plug and the threads are bad ...

thanks for the link

[dsakko]

So what models does it affect? Ie are the R56-onwards motors more or less succeptible to the R50/R53 Pentagon motor??

[Acallahan]

Have heard of spark plug detonation in the past, hopefully its just the threads that are thrashed.

[MiniMpi]

Sadly this also happened to me recently and it was spark plug number 1
Striped the threads in the head when the plug flew out!!
I had to get a helicoil inserted in the head to sort it.
Seems to be common on early MINI's Gen 1's.

[mab01uk]

It seems more common on R50/53 Mk1 Mini's, but does also happen on other makes and types of car. I think this is due to the much longer spark plug service intervals than in the past on modern cars. Plugs now have more chance to work loose over a longer time or the opposite where they seize/corrode into the cylinder head. The thread damage is caused by the loose plug wobbling around during each cylinder compression and then finally flying out under pressure strips the remaining few threads hanging on...........