i am pulling apart a 302 that i bought awhile back to get ready for a rebuild. this engine was supposed to be stock with 60,xxx original miles, i get it tore down to the bottom end to discover the pistons are stamped with "040" on the top of them. and pull the first rod-piston assembly from the block to discover the rod bearings are ".010"....no big deal...but my focused question is that when i look up the part number "273AP" it says nothing about oversized pistons, just standard size, any help with finding out if the piston is oversized would be greatly appreciated.......note: all the pistons have "040" stamped on top

 

With those markings, it is 99 44/100s sure you have a rebored, crank-turned engine with more like 160 or 260,000 on the clock.

That's the bad news.

To find out if there is any good news, mic the cylinders and see if they are in spec for a simple hone job. I doubt you can go beyond the .040 overbore if not....

As for the crank, you're probably going to put a 3.10, 3.25 or 3.40 stroker in there anyway.....()

Who did you buy it from and can you take one of those .040 pistons back and stuff it up his nose?

 

Engines are commonly overbored to .060", crankshaft journals down to -.030".
Unless this is going to be a blown or Nitrous Oxide fed motor it should be no problem to overbore to 4.060".

"...my focused question is that when i look up the part number "273AP" it says nothing about oversized pistons..."

Ummm, focussed? What does this number refer to?

 

the number 273ap is the actual part number on the piston....the top of the piston is stamped with 040....does this mean the piston is a 4.040 piston.....the crank journals are .010"

 

Yes it does.

 

Before you get ahead of yourself, have you mic'd the bores? It might very well be that the bores are in good shape and you could just rering it.

If this is the case, boring the engine to the next oversize would accomplish nothing more than lightening your wallet.

Same goes for the crankshaft. Mic it and inspect it.

Engine tear down is exploratory surgery. Measurement and inspection is EVERYTHING when it comes to the rebuild process, or at least a huge part of the process.

 

thanks

i tore it down for head gaskets, so i figured since it was tore down this far then i will put new bearings and oil pump in the engine, and while i was at that i figured it would be best to put new rings while all the hard stuff was done

 

AGAIN!!!!!

Have you inspected and measured? If you rering an engine with worn cylinders you will be wasting your time. If you put new bearings on a badly worn crankshaft you will have low oil pressure best case.

You are putting in lots of sweat and money. Don't waste it!

 

Agreed. I'l go even further and say that you are guaranteed an engine failure with the new bearings in a very short time. The bearing and crank/rod bearing surfaces wear together and form matched pairs much like a flat tappet cam. Therefore you cannot change half of the pair, you have to change both. If the motor was in good running order before the teardown leave the bottom end completely alone, don't even remove a rod cap for a look see.

 

By now you know you have .040 oversize pistons, but to find them wherever you were looking them up, simply add "-40" to the end of the part #. They don't have different part#'s for each oversize, just suffixes, ( 273AP-40, 273AP-60, ect.) The same holds true for rod and main bearings, and both are stamped with the oversize.

Don't feel like the Lone Ranger, I had already bought .030 oversize pistons before I cleaned off the tops of the old pistons and found .040 stamped in them.

Personally, I would shop around for another motor. If you need to go more than .040, you have one of the worst blocks Ford made to attempt that. Depending on the year, it probably has the worst performing heads that Ford ever made.

You can certainly clean up the journals if they are in good shape, hone the cylinders if they are close to specs, throw in a high volume oil pump, new rings, bearings and gaskets and get on down the road. How long a motor like that will live is a crap- shoot.

It's cheap and easy, and if you are the kind of person who drives like grandma, it may be worth your while. If you want performance and longevity, it is definitely not the road to go down.

What are your goals for this build? You really need to go one way or the other: extremely cheap or done correctly. Spending half of what it takes to do a correct build is most likely wasted money.

 

Too late, re-read the OP!