440 bore measurements - can I run standard sized pistons?

Gentlemen, I had a machinist buddy stop over today and help me measure the bores on my 440 block.

From what I can tell I think I will be good to go with the old TRW 6 pack slugs I got from my neighbor but I am not an experienced engine builder.

The following are the bore measurements we took just below the deck at ring height. (The botom of the bores on all cylinders was 4.321")

The first number is 12 o'clock- 6 o'clock
Second number is 9 o'clock - 3 o'clock

There is no discernable ridge, and crosshatch is easily visible in all holes.

And now to the numbers.


1 - 4.323 / 4.324
3 - 4.323 / 4.323
5 - 4.323 / 4.323
7 - 4.323 / 4.3225

8 - 4.323/ 4.323
6 - 4.323 / 4.322
4 - 4.322 / 4.322
2 - 4.322 / 4.3225

I would think so, but you would have to know the piston diam. You would be ok with as much as .0075 with that type of piston.

I wouldn't hesitate. Numbers look good to me. Are they optimum...probably not, but well within tolerances. Are you running nox or forced induction? If so you may need additional clearance depending on what the pistons measure. They probably measure 4.3175 or there about giving you .0045" to .0065" if your piston is machined .0025" under std. bore of 4.32.

I've run a similar TRW slug with .008" with no issues.

Measure the bores at the bottom of the ring travel and the piston skirts right under the oil rings about 1/4 to 1/2 inch below and then measure the skirts (all eight pistons and bores ) at the bottom and if the skirts are smaller than below the oil rings that piston is junk, don't use it
I'm thinking the pistons skirts come from the factory with the piston to cylinder wall clearances ground into them so a standard piston for the stock 4.3200 bore will have right at .0035 smaller skirts, 4.3165 , not 4.3195 or between the two
Let us know what you find and decide please

Better to hear 'em than to smell 'em.

Post a picture of the oil ring groove on your TRW pistons.

Does the groove have holes or slots ?

I will snap a picture when I dig them out again. I have them in storage at the moment.

No nitrous on this one, just a naturally aspirated M1 dual 4bbl tunnel ram setup.

And either a Hughes Whiplash cam I have on hand, or possibly a Comp Thumper cam. 906 ported heads I had on my 383, Thorley tri Y headers, dual chamber mufflers.

Looking for a fun street build for cruising and such.

3.73 or so gear ratio, 727 manual valvebody, something that will turn the tires, and still be able to run on the highway to get to town.

May even dig out the "quiet" gear drive I bought a couple decades ago.

The bores may meaure out, but it doesn't mean the bores are in the right place.

Not being rude, so please dont take it that way, but, if the guy that was measuring is a machinist, he should have that answer, and know how/where to measure a TRW piston I would think. Remember he clearance is in the piston, not the bore.

Also not being rude with my reply, but being a machinist doesn't make one an experienced engine builder. So while he had the tools to take the measurements, without the experience in building engines those numbers are just numbers.

We were not measuring the pistons, just the bore. My intent was to determine if the bores were still able to use a zero oversize piston. I do not have, and have not found a spec for piston to cylinder wall clearance tolerance. I came here because there are people with the knowledge to help me determine if the bores were within tolerance, or if the block was going to need to be bored for oversized pistons.

There are two styles of forged pistons.

One needs to have more piston to wall than the other. That’s why I asked for a picture or description of the oil ring groove.
While we wait for that info why don’t you measure the skirts for diameter.

Measure at the wrist pin height and compare to bore diameter.

The street slug should work at around .002-.004 p to w.
The race slugs usually run at .007 - .0075”.
New pistons gain .0005 - .001” p to w after they have been run in a bit.

Maybe it is my lack of understand of fine measurements, but I would want one guy, with his instruments to measure both the bores and the pistons, and then provide to me in a semi formal way the piston to bore clearance data. And then I would want to be able to hold him accountable at some level. In essense, this is what happens when you have the work done by a professional.

How many places did he measure in the bore. You should have a sense of bore taper and out of round from the measurements. Did he verify the bore measurement above the ring travel?

That said, the numbers suggest that it is probably okay.

IMO std. size pistons will be just fine.