26-07-2020, 08:07 AM
Ring gap should be about 6 - 8 thou measured in the bottom of the bore with the ring level. I'd suggest 0.020 is about the limit for wear & this may be a factor in your oiling issue, but there may also be other factors e.g. what about the vertical gap between rings and grooves (off the cuff I'd suggest 2 thou new, 6-8 thou worn)? Are the rings the 'oriented' type and if so are they fitted the right way up? Have you looked at your valve guides? Are you using oil baffles? Come to that, are you using the right plugs? etc.
Personally I've used split skirt pistons all my life and never had the slightest concern with them in sports / touring use, therefore not sure why others recommend slipper type; though I have no reason to doubt they are also OK. Split skirt pistons need about 0.0015 clearance to bore (again, measured at the bottom of the bore) vs 0.004 or so for solid skirts. Wear limit perhaps 6 - 10 thou (bottom - top).
For what it's worth I would never re-bore above the next available step that yields a workable bore. Without delving into your reasons Colin I would regard 0.002 oversize as a useable bore, assuming the other criteria are met.
Others of course are free to hold conflicting opinions or to correct mine if they feel I have something wrong!
Personally I've used split skirt pistons all my life and never had the slightest concern with them in sports / touring use, therefore not sure why others recommend slipper type; though I have no reason to doubt they are also OK. Split skirt pistons need about 0.0015 clearance to bore (again, measured at the bottom of the bore) vs 0.004 or so for solid skirts. Wear limit perhaps 6 - 10 thou (bottom - top).
For what it's worth I would never re-bore above the next available step that yields a workable bore. Without delving into your reasons Colin I would regard 0.002 oversize as a useable bore, assuming the other criteria are met.
Others of course are free to hold conflicting opinions or to correct mine if they feel I have something wrong!