I got this motor a while back, and I plan to build it up a little and drop it in my currently smoking 88 Iroc. When I took the heads off I saw this:




Some say 10 or 11 or 12 or 14. What do those numbers mean?

 

they look like alignment marks.... piston pins are off centered and "need" to be installed with the pin offset to one side... looks like it is for directional purposes.

 

The forward-facing mark, yes. I think there's a different explaination for the numbers.

Two guys in the piston shop got bored (no pun intended) one day. They got to talking, and one said, "I bet if we started stamping random numbers on the top of these pistons, it'll really drive somebody nuts 15 or 20 years from now when they try to figure out what they mean."

 

Seriously? Weak. I was hoping it was a sure sign of a rebuild or something!

 

A "20", "30", or "40" might indicate that. But, I'd hope they were all the same number in that case.

They're probably some sort of production tracking #, like shift, lot, date, or some such number.

If you want to know if the engine has been rebuilt, check the bore diameter.

 

What should the bore be, if it has not been bored?

 

Looks like it should have been a 4.000" bore block.

 

Well, I took a micrometer, and the inside diameter is almost exactly 4". I know that doesn't make sense, I think it was 3.99 or 4.01 or something like that. Is that stock, unbored?

 

it was almost 4? are you sure this is a 350 and not a 305?

 

Yes, the block number checks out to be a 1969 350.