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I had to be towed a few miles home today, thanks wifey, took the head off & the piston's literally disintegrating. Metal flakes everywhere, a small bite size of the piston crown nearest the valves gone. I can see the top ring. Barrel scored horribly.
Any advice on theoretical causes of this? I'd had the head off about 1000 miles previously to fit a better gasket & everything looked OK then.
This sort of damage is very often caused by weak mixture and over advanced ignition.
Which valve is it nearest to?...Ian
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I would certainly check the ignition timing before any further dismantling. Pre-ignition would be my first thought.
Grad a MM21flywheel.
Mr.Wrights 720 piston up grade.
They will see only the tail of ya bum.
PS.R30 in the mix is ok 2.
Hi All with Respect
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Pinking can be tollerated but full blown detonation can blow a hole in a piston in as little as 2 combustion cycles
Ask race tuners about how quick it can happen.
Thanks for the thoughts.
The engine is currently a standard 600 with an alloy head. Only deviation is that the barrel is one of the linerless types, recently fitted with a standard size liner & piston.
The carby is a brass Allparts 276 replica in good condition. It has a 170 main jet with the needle in the #2 position. It's been like this for a fair while.
Plug colour is a milk chocolate brown, hard to read plugs these days.
I'd given the timing a quick check recently & it was a shade advanced, about 1/16". Will do so again.
The hole in the piston is a neat arc equidistant from both valves. A dainty bite size. Most of the scoring's there.
I hadn't heard any pinking noises.
Compression was a bit down lately & I was thinking of investigating- should've done so sooner.
Well I have to eat humble pie regarding the ignition timing. Measuring with the head off, the points are starting to open at about 9/16". I've no idea how I got that so wrong, it doesn't do much for one's self confidence.
It happens Bob, your a brave man to admit it. Best of luck with the rebuild.
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