How do I tell which pistons I have?

[haubest]

I'm going to have the engine in my 5.0L '97 Explorer bored and I need to know what oversized pistons to buy. My Haynes book says the Explorer comes with one of three sizes of pistons:

Coded red: 3.9987 - 3.9993 inch
Coded blue: 3.9999 - 4.0005 inch
Coded yellow: 4.0011 - 4.0017 inch

There are some numbers and letters cast/forged on the inside of the pistons but nothing that seems very definitive other than, if I remember right, there was a letter R.

How do I tell which size pistons I have? I'm also assuming the oversized pistons I buy will tell me the correct size to bore to.

Thanks for your help.

P.S. Any advice for reboring the engine will be appreciated.

 

[CDW6212R]

The bore size is 4.000000000 inches. Any competent machine shop can handle the boring job. It's unlikely that you can reuse any pistons, and I wouldn't recommend it as they are hypereutectic(weak, they don't last forever). Have them check the block, and bore it the minimum it can take. A 4.030 piston is the most common, but you can likely buy 4.010 pistons and other sizes to bolt right in with the right boring.

 

[haubest]

How dare they use hypereutectic pistons!! Thanks CDW6212R. I'm still curious about the Coded red, blue, and yellow designations though.

Thanks again.