I just got a set of pistons I bought off ebay today. By measuring them they don't look like what was advertised. The bottom part of the skirt is measuring 4.014. One of them has 4.020 etched on the bottom. They were advertised to be for 4.035 bore. Numbers on half the bottoms are JE 521FR, other half is JE 521 FL. This isn't a part number. Can anyone tell me what this is?
Thanks.

I would imagine it's the forging number. The R and the L indicate the position of the intake valve, so in a small block Chevy you have 4 R's and 4 L's. If it's 4.014 at the skirt it's probably for a 4.020 bore.
Flatlander Racing has an extensive list of JE pistons for you to compare.

http://www.flatlanderracing.com/jepistonchevys.html

Race,
Why not call JE and ask them ??????? If anyone would know ....

I looked inside some of my old JE's today and they have the 521FR and 521FL mark. These particular pistons are 181920's, one of the standard duty flat-tops.

THANKS!!!!
That is what I needed to know. They were supposed to be part number 181917. As long as they aren't the pistons made for 400 hp and under I will be fine. Think I will go put them on a scale to make sure the weight is correct for standard duty.

Niether the part number you gave or the number on the box I have are on JE's website. Must have changed.

They're listed on the page I linked to Flatlander, and they also appear in this section of the JE catalog. Did you ever click on the Flatlander link? If you did, you would see that the 181917's are for a 4.035 bore with a 1.25 CH, weigh 403g and use 1/16", 1/16", 3/16" rings.

http://www.jepistons.com/pdf/2002-je4-13.pdf

I was looking under the wrong link. If they are the pistons you listed they are for 3.75" stroke and 5.7 rod. That won't work for me. Is the comp height measured from the center of the pin to the top of the piston? If it is measures 1.25, that sounds like a 3.5" stroke piston, that would work. I think I better get these to someone that can tell me for sure if they will work with what I have or not. Thanks for all your help!

The formula for figuring out what works is:
1/2Stroke + Rod + Comp. Height = Deck +/- .010" or so.
If you have a 1.250 CH and a 3.5" stroke you will need a 6" rod. If you have a 3.75" stroke and a 1.25 CH, you will need a 5.875" rod.
The 181920's I listed are the ones we use in our 327. 3.25" stroke, 5.94" rod, 1.425 CH.
Believe it or not, I thought you called your pistons 181917's, which would be as described above. If they're .020" over, they could be 181915's.
You seem to be reluctant to provide information on exactly what you are trying to do with these pistons. If the skirt measures 4.014", you will definitely not be going .030" over.

I can't tell you what I have because I don't know. The pistons are supposed to be the 181917's. That is .035 over with a 3.5" stroke and 6" rod. The pistons measure 3.019 (I read wrong earlier) so I know they are NOT for a .035 over bore. The guy sent me the wrong pistons. I'm just hoping they will still work with the crank and 6" rods I have.

Would it be fair for us to assume that you have a crank with a 3.5" stroke even though you haven't actually come right out and declared as such? It's real easy to just say "I have a crank with a 3.5" stroke and a set of 6" rods." If you reply you can copy and paste this sentence if it's true.
3.019"? What's this measurement?

lol, Sorry, could get more confusing? 4.019 not 3.019. My crank has a 3.48" stroke. 6" rods.

Where is the 4.019" measurement taken? JE will explain how to measure pistons if you call them.

http://www.jepistons.com/faqs.asp