Quote:
Originally Posted by gmanelan
Thanks for this info. I have been looking at the aa package you mention. Given I was hoping to go for 86mm your comment is a bit worrying!! - how did you remedy the excessive ring gap? Did the replace the rings?
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We've seen the same issue with the AA 86mm Biral cylinders.
What we've done in the past was to have the cylinder Nikasil coated. This does three things. It allows us to control the bore size, RA factor and the Nikasil reduces friction so the cylinder runs cooler. Nikasil may also reduce heat transfer keeping the energy in the cylinder but that is simply speculation. I have no data to prove that.
Of course this requires an attention to detail beyond, plug and play. The ring pact is different (Nikasil vs cast iron) and piston clearance can be slightly tighter to reduce piston noise. We've had pretty good luck using Wossner pistons in conjunction with Biral barrels. Very quiet running. They make a shelf 85mm that is easy to source. 85mm is a safe bore size for cast iron and Biral 84mm. The benefit to coating the stock cylinder is that you can reuse 84mm pistons if they are still in spec and by reusing the older style Biral cylinders you can maintain the concours aesthetics.
As for boring the cast 84 to 86mm: you can do it but it gets very thin. We've seen at least 2 different attempts at this modification result in cracked cylinder just above the spigot. Sometime "it woks" is simply a reflection of attention to detail or lack there of.