Cylinder to cylinder deck clearance variation?

[travis]

How much difference in deck clearance would be considered normal? I’m getting.003” to .007” deck clearance after measuring all 8 holes, with most running about .005”. Is this inconsistency normal with budget pistons (FM H336P’s)?

[PackardV8]

These days it’s more likely to be the block, crank or rods than the pistons

[2seater]

I have noticed on three Buick V6's in succession that the center cylinder on each side have right around .003" less deck clearance, while the corners vary less than a thousandth. Switching piston and rod assemblies around has no effect, almost has to be in the crank although stroke measures correct within a thou.. Decks are flat and two were freshly machined?

[FC-Pilot]

If using a factory crank and rods I often use the same rod and piston in the holes first to see if there are any patterns that can easily be identifies as taper in the decks. Then I verify that the rest of the pistons and rods fall close to the same measurements. If need be I can shuffle some around if a crank throw seems short and maybe a rod a thousandth or two long. For a street engine is won’t make any difference, but if it’s mine then I have the time to do it just for insanities sake.

Paul

[ProPower engines]

There is lots of budget pistons that are as good as bang on or as much as -.003 between pistons. This is for cast type econo
build stuff. the stuff they were selling made in India was much worse but they did get better over time but not much.
Since you are measuring at the pin centerline have you checked the pin bore for alignment to the top?

I recently had some new old stock parts a customer wanted to use and the pin bore was off by .004" when the top was on a
surface plate and measuring to the bottom of the pin on either side.
Did you check the fore and aft sides of the 4 corner pistons? That could account for some extra deck clearance if the pins are in crooked.

[MadBill]

Subtly bent rods will also throw off the readings...

[travis]

These rods “shouldn’t” be bent as they are brand new.

I only checked each one as close to the center as I could get. I’ll try some different measuring points tomorrow and swap some stuff around to see if that helps.

I’m suspecting that some of this may be in the pistons...about half of them appear to be a much nicer casting than the other half.

For what it is, I’m probably way over thinking this

[PackardV8]

These rods “shouldn’t” be bent as they are brand new.

I only checked each one as close to the center as I could get. I’ll try some different measuring points tomorrow and swap some stuff around to see if that helps.

I’m suspecting that some of this may be in the pistons...about half of them appear to be a much nicer casting than the other half.

For what it is, I’m probably way over thinking this

You are. Unless the block has been square decked, it’s probably off as much as your variation.

[gmrocket]

These rods “shouldn’t” be bent as they are brand new.

I only checked each one as close to the center as I could get. I’ll try some different measuring points tomorrow and swap some stuff around to see if that helps.

I’m suspecting that some of this may be in the pistons...about half of them appear to be a much nicer casting than the other half.

For what it is, I’m probably way over thinking this

Checking the center of a piston with an offset pin ? You should be measuring directly over the pin and then rock the pistons all the same direction , so you are doing each hole the same.

Some cast dished Pistons leave the dish portion as cast.. your wasting your time putting your dial indicator on that..