I recently bought a set of oversize piston rings and the end gap when inserted into the cylinder was 1.5mm instead of 0.2 – 0.3mm (60 thou instead of 8-10 thou) as stated by BSA. When I queried this I was informed „The quoted end gap is only a minimum to prevent the ring gap from closing up when hot. A larger gap is not a problem“. I thought such a large gap would result in a lot of blow by and compression loss, or have I misunderstood the case? And if so why would BSA not just quote a minimum end gap?
Cheers
Pete

Had bit of a think and it really is bo**ocks isn’t it?
Too big a ring gap causes: blow-by and pressurisation of the crankcase so even more oil leaks, don’t pump all the spent charge out on the exhaust stroke, allows oil to get past the piston on induction stroke, on compression stroke fuel gets past and contaminates the oil. Have I missed anything?

Hi Pete, The M20 'standards' book gives .008"-.012" as standard... and a condemnation limit of .030" (that would be after a lot of use obviously).

So, starting off at .060" is definitely not a good plan...Ian

email (option): ian@wright52.plus.com