SOHC.co.uk Forums > CB500/550
running on unleaded !!
Bryanj:
I would also say a slightly bent valve mate
Johnwebley:
looks like a head-off job !!
just as summer is finishing!! LOL
Johnwebley:
OK,update,
so I took the head off,
looked like Foreign object damage in cylinder No4,
lots of marks both on piston,and head,
valves removed,good seals on inlets valves and seats,exhaust seats good,but valves in need of lapping,
not happy about state of No4 piston,so off with the barrells, result,top ring broken,and 50% vanished !!big damage to top ring groove,
and top land,
No3 piston also has broken top ring,???
1 and 2 pistons OK,
no marks on bores,
ordered new (std) piston, 4 X sets of rings,
waiting for them to arrive,
SQ, why do you think the rings went ??
John
K2-K6:
It's quite unusual to break rings on a 4 stroke engine if everything is normal, possibly more influenced by the assembly last time it was built.
Also a possibiltiy if it had been stored for a long time for the bore/rings to rust and cause damage when someone tried to start it.
matthewmosse:
Sounds familiar, my first running and taxed 550 had all 4 pistons like this when I bought it, mostly the top rings were completely awol and the gaskett goo pointed to bodged rebuild in the past and the missing rings had scorred the head badly. Ran really well with a good used set of pistons and barrells fitted. I found 1/2 of one ring in the sump, rest either was removed in the bodged rebuild or possibly found it's way out through the exhaust valve which I find unlikely. Appart from being tempremental to start when hot there were no symptoms.
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