Piston to Bore Clearance and Ring Gap.

5/7/2019 11:24pm
After some opinions on the following;

Piston Diameter - 97.953mm
Bore Diameter - 98.008mm
Piston to Bore Clearance - 0.055mm / 2 thou
Ring Gap - 16 Thou

This is from a new aftermarket Big Bore kit for a 450

What is your ideal expectation on piston to bore clearance? I have been told that above is acceptable, and also it is to tight from different people.

Also are big bore kits for dirt bikes generally torque plate machined?
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Paul_Pitzonka
Posts
693
Joined
5/1/2018
Location
Grand Terrace, CA US
5/7/2019 11:59pm Edited Date/Time 5/8/2019 12:27am
After some opinions on the following; Piston Diameter - 97.953mm Bore Diameter - 98.008mm Piston to Bore Clearance - 0.055mm / 2 thou Ring Gap -...
After some opinions on the following;

Piston Diameter - 97.953mm
Bore Diameter - 98.008mm
Piston to Bore Clearance - 0.055mm / 2 thou
Ring Gap - 16 Thou

This is from a new aftermarket Big Bore kit for a 450

What is your ideal expectation on piston to bore clearance? I have been told that above is acceptable, and also it is to tight from different people.

Also are big bore kits for dirt bikes generally torque plate machined?
The Ring gap should be about right... bore size multiplied by .004 or .0045 seems to be the general consensus by ring companies on top ring gap of a naturally aspirated engine so that would give you a minimum gap range of 015”-.017”... the piston to bore clearance of .0021” is correct... the ideal clearance on most modern Nikasil plated aluminum cylinders is .002”-.003”... and I don’t know if they’re bored and honed using a torque plate from the manufacturer... (although I surely hope so)...
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