Numbers on Piston Surface

While cleaning carbon off piston surfaces last night (before installing new head), I saw the number +.020 on the top of each piston.

Does that mean that they are that much bigger than the originals? The PO told me when I bought the car that the engine had been rebuilt about 30,000 miles ago. When I got the carbon off, I was surprised to find the piston surface looked brand new. I don't know what I expected to find...pitting, charring, just didn't know.

Tonight, I hope to get the head installed.

Depends what you mean by "much bigger" - the +.020 means they are 0.02inches bigger than standard - not exactly a lot but it is the typical "first overbore" size.

Gottcha.

No, I didn't mean "much bigger" like it was a large number....just that it was .020 inches larger than the original piston/cylinders.

Larry,

Are the pistons a shallow dish or a larger dish? Can you post a close up picture of the top of a cylinder. Hopefully the PO installed High Compression pistons!

David,

I will get pictures when I get home tonight.

I don't know the difference in "shallow" versus "large" dish.

By the way, thanks for the deal on the head. I looks great. I'm working my usual 12-hour shifts this week, but I hope to wrap the job up by the weekend.

Larry

Almost certainly this means the cylinders have been bored out by 20 thousandths. As stated, a very common size overbore size. You've got lots of metal left for another bore or two.

My pistons said .030 on them, and had the > symbol over the three as well, but the machine shop confirmed they were actually the stock, original size. I figured maybe the pistons were sourced as if they were an overbore size for a smaller, but still british engine as they were Brit parts. Does that make sense? Couldn't figure any other reason.