Piston & Head Damage (Detonation???)

[Hey Jimi]

Hey, years ago when tuning a 150 I put the piston in back to front. Got the exact result you have.Just make sure the top ring groove hasnt tightened up and restricting ring movement.

Cheers Jim

[Frautzi]

If you have measured the port "as said" but then flattened out the card and measured (now flat) then this is a safe width...
IMO

yes spot on J1MS, i also curved the card to the bottom of the barrel and measured that and i think it was roughly 47/48mm

Jay

[Frautzi]

http://www.forums.ilambretta.com/viewto ... 16&t=29695

More info on here as well fellas

Jay

[Frautzi]

I see you found the problem, is the crank a Tino Sachi 62mm crank?
Ive had weights come loose twice in one of those cranks, but mine locked the rod rather than chip bits of the weights away, the rods must be good to chip titanium with out braking.

Hi eden i have no idea what make the crank is, it going to Harry Barlow to be checked trued and welded.

Update:

Spent some time last night checking all components, Had phoned Harry Barlow and spoke to him regarding other possible causes, he said have a look at the weights.
Found one of the weights had worked its way toward the con rod and has two sizable chunks missing. This would explain why the ports aren't damaged and the fact it continued to run after the event and then built up deposits on the head and piston. The amount of the weight that has come through the crank is almost the same thickness of the rings... how's that for coincidence.
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I'm hoping this was causing the original issue of the spark plug failure issue possibly causing some sort of detonation due to the damage in the squish band. but time will tell .

After the information regarding the rings it was easy to see why most people was thinking foul play..... so looks like its component failure. sorry if things were a bit miss leading

Lessons learnt, check everything twice,

Thanks for the guidance and the theories, much appreciated.

Jay