Club 80-90 Forums

I noticed a drop in power on my way to stableyard. Especially when climbing a fairly long hill. On arrival l gunned the engine a few times and heard a few backfires. Too dark to investigate.
This morning found no. 3 cylinder spark plug loose in head and on withdrawal this...



What the consecquences of such a badly damaged plug?

Regards
Stuart

It looks like the head material around the plug has melted. Or what is that in the threads?

Its lost the tip and thread is damaged and melted.

Get a spark plug tap , re, cut the thread and try a new plug, looks like it wasn’t fully tightened up when fitted , it’s been leaking and melting the threads away , as it’s a long plug there’s probably enough meat left to hold it in

New plug in and holding fine.
Yes agree. Plug loose for sometime. Under local runs it didnt show up.
Once on motorway it cruised just fine at 60mph. Then after about 50 miles on a steep incline very noticeable.

A tad concerned where bits of plug have gone?

Thanks.

maxstu wrote: ↑06 Mar 2021, 11:43 A tad concerned where bits of plug have gone?

Probably burned away and flew out the tail pipe

That is aluminium on the threads of the spark plugs not the plug threads melted. You have lost thread in the head. You may be lucky and have enough thread for a good connection unless it was unscrewed enough during use to melt it all on the way out. Need an endoscope to check it out.

Thanks OBG.

Im pretty certain some thread had burned away. Another photo at this angle shows damage...



Anyway, l drove 65 miles home and camper ran as smooth as ever. So too late for endoscope procedure.
Will check plug again in a few days and report back.
Will be pulling engine later this year to refresh water jacket seals. Then l will check bores, rings and pistons. And get a check around it's heads.

Regards
Stuart

ZsZ wrote: ↑06 Mar 2021, 12:05

maxstu wrote: ↑06 Mar 2021, 11:43 A tad concerned where bits of plug have gone?

Probably burned away and flew out the tail pipe

Let's hope so. .....

Why is it too late for endoscope? The threads in the head will still be damaged. They will not miraculously heal by putting another plug in.

You can clearly see small bits of aluminium at the top on the thread and also melted aluminium at the bottom in the thread.

The replacement plug is holding well. So l assume thread is not totally buggered. But will check thread on Tues or Weds.
Thanks

Looks like you need to get on that engine build get that house move sorted! 

I'd be concerned about the ali welded into the end of the plug thread taking out the threads in the head on the way out. Hopefully you've got away with it.

What brand/spec of plug was it? The last time I recall seeing a plug like that was out of a 2 stroke motorcycle 40 odd years ago

Stesaw wrote: ↑06 Mar 2021, 20:04 Looks like you need to get on that engine build get that house move sorted! 

It is moving surprisingly fast.
Our first time buyers sent a surveyor to our house on tues. He spent 20 mins measuring and checking (but nothing structural). Next day got a phone call from our agent saying all good and buyers' mortgage will be issued in two days.
Engine will have to wait until house move is done and under control...so lve been told by Maxine
Time to start boxing and packing up