mstg007

I had a friend come over and measure my cylinders and existing pistons in my 302 V8 Engine.
Below is the list of my findings....

Piston----Cylinder------Piston Size
1---------4.051----------4.019
2---------4.053----------4.015
3---------4.054----------4.015
4---------4.054----------4.015
5---------4.048----------4.015
6---------4.048----------4.015
7---------4.046----------4.015
8---------4.051----------4.015

Could you help find what type of (oversized) pistons I need to get?

Thanks for your help!!!!

Shawnb23

Usually when you have the cylinders bored you bore them according to the piston. So you buy the piston's first and then have the cylinders bored accordingly.

JMD

Assuming the measurements are accurate, my guess is that the engine has been bored out to 4.030 previous.

In any case, (if your measurements are accurate!) the block should be bored out to the next size that will clean up the bores which will be at least 4.060.....

There are some who say a 302/5.0 should not be bored out past 4.030, but some others think that 4.060 is ok, put me in group 2.

If the block wont clean up at 4.060, (actually about 4.055 to save room for final hone) most everyone will agree that the block is basicly junk.....

When the block is bored .060 over, you will need to buy .060 over pistons as well. The actual diminsions of the pistons will vary depending on the style, type, and brand. Buying the .060 over version will get you ball park enough to make a final fit.

Good Luck!!!

btw, if you are not planning on boring the block, you will just reuse the slugs you took out.

fakesnakes

+1 on JMDs post. You are at the hairy edge for that block. You didn't say whether you were going to have any machine work done? If not and you are doing what Hotrod magazine called the junkyard rebuild (hand honing the cylinders and replacing the rings and bearings, then I would go with 4.040 pistons and 4.060 rings ground to fit.

However, if you have a ridge at the top of your cylinders, you have a good chance of breaking the rings the first time you rev the engine. If it is an older ingine, there is a good chance the cylinders are not perfectly round. They tend to oblong parallel to the main caps due to wear. When your friend measured the bores, did he measure each one in at least three places? You also need to know the size of the head combustion chambers and deck clearance in order to make sure you have the corrrect compression ratio and clearance. There is a lot to ordering pistons and you need more information.

mstg007

What would you say if I used (Bought) the same Size of existing pistons? I was not planning on boring the block, I was planning on honing it out.

So a junkyard build is kinda what I was leaning towards....

BTW how much is it usually to bore out the block?

MBDiagMan

I would say that you are making a mistake.

To begin with, what oversize is stamped on the pistons?

Do NOT buy a set of pistons and just take them to the machine shop and tell the guy to get to work. Do the opposite. Take the block to the machine shop and tell him the situation. He will do a little micing of his own and if he thinks there is something left to work with, he will make a cut on the most worn cylinder to see if it cleans up at that size. If it does, then HE will tell you what size piston to get, or tell you if you need to find another block.

Shawnb23

In my area is was roughly 250$ and I bought all my stuff and they bored the cylinder's and installed the piston's.

JMD

For a cheap rebuild just reuse the pistons.

IMO there is no point in buying new pistons if you are not going to bore the block,,, case closed...

If you properly use a "ridge reamer" to remove any ridge that may be in the cylinder and the cylinder taper is not severe the block may not need to be bored.

I have in the past done some budget "no-bore" rebuilds on some truck motors (they had very minimal cylinder wear) with great success.

Judging from the cylinder measurements given, I am inclined to think that the cylinders are a bit too worn for a good no bore rebuild, this being the case, if you must do a cheap build don't waste money on pistons.

When cylinders wear, they wear disproportionately at the TOP of the BORE where cylinder pressure (and therefore outward ring pressure) is the highest. So, when the rings go into this worn area at the very top of the ring travel, they expand to take up the space, then as the piston travels down the rings are squeezed down. This happens every time the piston moves up and down the bore. The result over time is fatigued and/or broken rings.

There were "rebuild rings" available that were better suited to this expansion and contraction, but I can't say if they are still made or not.

In any case, the short answer is if you are going to buy new pistons, bore the block. If you don't want to bore the block don't waste your money on pistons.

If you are lucky like me, you should be able to use the old pistons on a cheap, cheap, cheap, rebuild for some time if this is what you are after..... I usually always get away with my shortcuts, others are not so fortunate,,,

SO you have to ask yourself, do you feel lucky? Well do you punk! (Just joking about the PUNK part,,,, sorry Inspector Callahan!!)

Anyway... Good Luck!!

dcohen

use teh cofeee cans


but seriously, i think .060 over on a 289/302 is fine

my 289 is bored .060 over, no problems so far, but then again, its never been started

4reboy

My 351 is .04 over and it runs great, no problems. My machine shop said that they take blocks to .06 over all the time without any issues, and they do a lot of race applications I believe.

but if you do have to rebuild it after .06 over, then you will either need a new block OR you can have the cylinders re-sleeved I believe, but I assume that would cost some money.