+3 stamped

[SuperRat2110]

What exactly is the +3 stamped on the cylinder mean. Does it have any relevance to the size of piston used or rings? I'm clueless on this stuff.

[thrownchain]

Has something to do with initial assembly. But for all practical purposes, ignore it. Measuring the cylinder will tell you what size piston to get.

[Al Harpster]

Its been reported that cylinders were measured at manufacture & "graded" by diameter. That's the reason for the stamp.

Then, I assume, Pistons were also measured & "graded".

Some degree of piston to cylinder clearance was controlled by matching piston diameter to cylinder diameter.

This is the story as I understand it.

If true, your probably talking about a few ten-thousandths of an inch either way. Maybe less.

As stated in previous post, it doesn't mean nothin' now. It's worn. So it's measure & decide what to do time.

If compression is, say, over 110 psi you might just run it.

If you want a ball park measurement of clearance take the top end apart & place feeler gages between the piston skirt & cylinder. Some guys may hate this idea, but I'm tired of trying to bore gage a cylinder with a bunch of ports in it