SOHC.co.uk Forums > CB350/400

Are my pistons standard or oversize?

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Bryanj:
The gap is the same as the cicumference is not much bigger for a 1mm overbore, also the oversize should be on the rings, usually at the gap on the top side on the opposite side of the gap to the manufacturers mark

DayvW:
Thanks. I cant see any marking on the rings at all whether a manufacturers mark or an overize.  Think I will be safer with new rings .. all I need do is find some.  Any idea of a good source anyone?

Trigger:
Davy, you dont want to be buying new ring's untill you know that the bore's are not worn out. Classic Motorcycles sell +1mm pistons , but i am not sure if they do ring's without the piston's .

DayvW:
Thanks Trigger6969 - the bores if anything seem a little under 52 (more like 51.9) - am measuring with a Vernier gauge so difficult to be precise.  The pistons are marked as 1mm oversize (as confirmed above) - but also seem about 51.7- so allowing for my inaccurate measuring it all sounds about right (the pistons are snug - but not too tight (and she has been running well). The oil rings in particular seem very worn (the gaps are visibly way over .9mm) - which perhaps explains why the pistons were pretty mucky (carbonised stuff that was quite damp).  I hadnt noticed much oil burning when running it has to be said though - but with gaps that large I guess it would be?  I'm thinking perhaps I should fine someone to measure the bores a tad more precisely to be sure?

Lynx:
Last time I looked Partzilla did oversized rings on their own. I has some. Have to wait for them to come from America though. About 2 weeks.

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