TO20 Piston Identification

pburchett

Member
I am rebuilding a TO-20 for my wife. It was her pappys tractor.

When I took the head off all the pistons were evenly coated with carbon.

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The exhaust valves were all not the same color.

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I was really confused after cleaning off the piston tops. All I notice is the direction indicator and the letter "P" stamped into the top. I was expecting "STD" or something like a number indicating a over sized piston. What does the "P" stand for?

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P for plus? Might be over bored piston and sleeve. Looks like a good engine though, just need to be lovingly rebuilt.
 
The P is probably a factory sizing mark or an inspection stamp.

I've never seen overbored sleeves, typically they are purchased as a new assembly fitted with a piston, rings, and pin.
 

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