Misfire and plugs?

[feef]

2002 MX5 1800, supercharged

The car has been running fine until earlier this week where it developed a misfire

I checked the plugs and found that the plug in cylinder 3 had had the electrode bent to the point that it was touching the center electrode, but there wasn't any obvious signs of contact

I re-gapped the plug and refitted it (as it was sunday evening and everywhere was shut) and went for a run, and all seemed fine

Today, I swapped out the plugs with some new ones and did an oil and filter change while I was at it

Went out for a short blast and noticed some hesitancy at the top end under load, and on returning home, the misfire had returned, however, it was the plug in cylinder 1 that had suffered the bent electrode now, number 3 looks tickety boo

Cambelt was changed less than 10k miles ago
both coil packs were replaced last year (2 packs for 4 plugs, wasted spark)
Both misfires developed after a blast with high rpms

Any ideas?

[Oldandslow]

I was thinking it could only be some catastrophic failure of piston bearings but a quick google suggests excessive detonation (US forums) or knock might be it. They said to look for specks of metal around the plug tip. Not sure of the mechanism by which the electrode gets bent.

[feef]

ill be inspecting the combustion chamber with a borescope tomorrow. It seems ofd that it's now a different cylinder. However, I'd expect such failures to continue in their respective cylinders and also, perhaps, have a much more catastrophic effect on performance than I've noticed.

I'll take a look tomorrow and see what's what.

[feef]

Let's play Spot the Difference

[Oldandslow]

Ouch! So you've got bits of ring land bouncing about.

[trackerjack]

Very interesting as when I track dayed my special which runs an MX5 engine that has an HSK turbo conversion and the pressure regulator pipe blew off causing massive overboost. This resulted in similar damage to the piston edge and replacement was done and I make sure the boost is sensible now, however it still goes very nicely thankyou.

[feef]

I've decided to drop in a 4.0l 1UZ engine instead

[Rickyy]

feef said:

I've decided to drop in a 4.0l 1UZ engine instead

Build thread please!

[feef]

http://www.pistonheads.com/gassing/topic.asp?h=0&a...

And I'll be updating http://kickingtyres.co.uk with posts too