re:20r72r piston

[rick_c26]

I want to replace the pistons in my 1972 Johnson 20. They are obsolete now and I cant find a source for them. I have looked at the specifications for the required 0385338 piston and noticed that the piston 0385339 for the 25 hp of the same year has the same stroke and bore and piston to cylinder clearance. The only differance is the piston ring groove the gap on the 20 hp is min 0.0020 and max 0.0040 and on the 25 hp engine the gap is min 0.0015 and max 0.0040.

or should I go up to 0.0030 over on the 25 hp piston and have the cylinders matched

Can I use the piston for the 25 hp can I have the cylinders bored .0030

[boats.net]

I'm not sure, never looked at them to see what the difference is.