MW AP 132 Piston

PJH

Well-known Member
Tractor is an early JD 50.

Can't find any size stamped on this piston. Should the AP 132 tell me anything?

Rough measurement with a dial caliper is 4.723". I figure the standard bore would be 4.6875".

I've gotta get a bigger mic.

Thanks,
Paul
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AP132 is the M & W piston set number. The size should be stamped on the top, you'll have to clean it up. By your measurements I'd say it .045" oversized.

How did it run? Low on power? Lots of blowby?
 
Mike, the top has a shot peened look, no numbers visible. It actually ran real good, started first rev even below zero, didn't seem low on power. It did have steady blowby, and exhaust smoked a lot on startup. The top ring has been gone for a long time, as evidenced by comparing the ring grooves in the two cylinders.
 
Thanks Kent - I'll get back to you in a few days. I'm gonna have my old retired machinist neighbor look at the cylinders for me, to see if they need work. I'm not good at inside measurements, and not confident in my mechanical skills.
 
I have a very nice set of them ( # AP 132 ) + .045 that will sell for $ 100 plus shipping. My e-mail is open.
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They came in std / + .045 / + .090 / and +.125 all pt # AP 132. From what yours measure (+ or -) they would be .045. "AP" = Add power by M&W. I can get mine measured for any wear if you are interested. There's hardly any noticable verticle scuffing so I don't think they have many hrs on them.
 
Thanks for the reply and the info Randy. I cleaned up the other piston, and it is .045" over, stamped on the rim. After inspecting it closely, the top ring groove is worn out and badly shouldered, so it is not worth putting back in the engine. My retired machinist neighbor is real sharp and helpful, but he's in his 80's and has difficulty getting around on some days, and I don't crowd him. When he looks at my cylinders I'll know if they need machine work. If it needs bored, I'll have to step up to .090 over. I'm not real confident in my skills and knowledge - that's why I'm bothering my neighbor. I'll get back with you in a couple of days. Thank you.
 
Kent, I've discovered that my "good" piston is also a dud, so I'm gonna need a pair of them, and I don't know yet what size. Thank you for the offer.
 
Being that these are aluminum as apposed to the original cast iron ones, there's a good chance the cylinders are fine unless one of the rings dug it up. If the bores just have splotches of aluminum stuck to them , one can use muriatic acid and it will dissolve the alum right away from the cast iron bore. Done it on many "seized up" 2 cycle motorcycle engines. Would be a shame to have the expense of a bore job and new .090 pistons/pins/rings. As you have proved, these engines are real forgiving of things not being perfectly precision like a car. Let me know. Thanks, RB
 

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