brenton.roy wrote:A cammy must be a really expensive restoration. Everything is rare, fragile or both.
What oversize are you looking for Paul?
Brenton, I think I'm going to go for standard...but I'd appreciate your views (and anyone elses):
Having dismantled my engine to address the wrecked big end bearings, I've discovered that the gudgeon pin circlip grooves are in a really poor state on a couple of the pistons --- I wouldn't be happy re-using these pistons in their current state. I have thought about using brass or aluminium "buttons" in the gudgeon pins as many 1920s bikes had; at least that would allow me to re-use the pistons, but I feel this is a last resort.
When I restored the top half of the engine in 1997, the barrel was re-sleeved back to standard. Having measured the barrel today, there seems to be very little wear. At the base of the bore, on the unused part, the size on all four bores is 56.02mm --- std is 56mm. Using the "piston ring gap and Pi" method to calculate wear between top and bottom of the bore, the greatest wear is on #2 and #3 rear cylinders (as expected) but it only amounts to 1.9 thou of an inch; front bores are 0.6 thou of an inch.
So I do not think I need to re-bore to +20 and I would prefer not to have to get a re-bore done on my re-lined barrel. So if I go for std pistons, will they just drop in, or will they be too tight or, worse still, too loose? Too tight I can deal but too loose and I may have wasted my money.
One thing I haven't managed to fathom out is why most of the period literature and piston sellers quote the standard bore as 56.00mm while Draganfly quote 55.80mm as the size....any ideas?