Number on Pistons

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archerandethansdad

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Hey Everyone, i just did a head gasket replacement a couple weekends ago and while i had the heads off i noticed that my pistons had a 60 stamped into the middle of them beside a > pointing toward the front of the car. I understand the arrow but not the number. Does anyone have any idea what they could mean? It's a 68 barracuda with a original 318. I've changed the cam but otherwise as far as i knew it was factory. Also the piston is a dish shape not flat top it has a raised edge all the way around with reliefs at the very top and bottom of the piston. I included a stock photo but mine have reliefs this one does not.

piston.jpg
 
All pistons are stamped with their over-size number. In your case, yours are .060 over-size. Your engine has been rebuilt somewhere in the past and these are the replacement pistons.
 
.060 stamped on the piston is the over size.
@ .060 on a 318 (3.97) it equals 327.79 cubic inches, we all round up. 328 CID.
 
Also the piston is a dish shape not flat top it has a raised edge all the way around with reliefs at the very top and bottom of the piston.

View attachment 1715807611
Having a valve notch at the very top and very bottom of the piston and a bowl indicates to me that this is actually a "poly" piston. It'll have a compression distance of about 1.790" instead of the 1.720- 1-745 usual LA range. Any gain to be had by the higher comp distance will be negated by the dish, which is likely about 90 thou deep.
 
Wow, great info guys. I appreciate the feedback. That makes sense too. I'm third in the line of owners with papers to show it. The motor supposedly has 210k but when i had the heads off i could see clear cross hatch on the walls. Which i would not expect to see at that amount of mileage of course i could be wrong and probably am. Thanks again everyone.
 
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