Piston to Piston Weight

[JedIEG]

I bought a set of custom Autotec pistons and had to have two of them replaced due to manufacturing defects. I finally got my replacements in and one is weighing in at 464g. All others are at 466g or 467g (specification is for 467g). Should I worry about trying to match all the pistons down to the 464g?
Looking up the density for 4032, I'm going to have to find about a cubic centimeter of aluminum to hog out and that seems like a lot.

 

[PROSTOCKTOM]

That's not a lot to take out. A lot of guys just install them as is. Myself they all have to weigh the same.

Drill bit tip holes in a couple places on the pads and you'll lose 3 grams.

Tom

 

[JedIEG]

Yeah... It will probably bug me if I don't make them the same. There are not obvious pads to drill on with these. Any suggestions?

 

[mopowers]

Have you weighed the pins or the small end of each of the the rods? You may be able to swap parts around to minimize variance. Either way, 2-3 grams isn't much. You'd never notice it.

Does your scale give the same value if you weigh them multiple times?

 

[RustyRatRod]

A little light on the piston end isn't critical. 3g difference, not critical at all.

 

[Bewy]

I wouldn't worry about 3 grams [ varying amount of oil hanging off each piston will probably be greater than 3 grams....]. But if it worries you, I would remove the 3g from the ends of the wrist pins. Being steel, very little metal would need to be removed.

 

[Lefty71]

To me, your first sentence says it all. If you are racing the car (and even maybe not), i would be looking at other manufacturers for the pistons.

 

[ch1ll]

That's .646% variance between heaviest and lightest piston, less than 1 percent. I would think that's really close for a cast piston and would be stupid close for a forged one IMO. What are you going to do? Machine the whole piston? How do you know the porosity is uniform through out the piston? I would be more worried of creating an unbalanced piston than from piston to piston unbalanced. The shaving of the wrist pin may have merit though. I'd leave the pistons alone.

 

[fishmens67]

If you ever checked the balance on a factory rotating assembly the answer is clear, your weight is well within bounds.

 

[PROSTOCKTOM]

It's interesting to me the varied replies to the 3 grams of weight.

It all boils down to the level of precision you expect in your engines.

Yes, it's closer than an OEM tolerance, but if you have an accurate scale and the ability to make everything match then why not do it?

You won't find a NASCAR, or NHRA engines built without matching every component in the engine.

The more perfectly you match the components the better it is for the rotating assembly.

Yes, 3 grams is very little weight, but if that doesn't bother you, or you try to use shortcut ways to remove it, then what else are you cutting corners on?

It all adds up here and there in an engine, car, or racing operation. How successful do you want to be?

These parts cost way to much money to not do it right. Only you can decide how right you want your engine.

Tom

 

[JedIEG]

I'm at bit disappointed with them. They didn't fight with me on replacing the pistons, but QC is obviously not doing their job. I will talk to the machine shop on Monday and see what they recomend.
All of my other parts are dead on the same. All but one rod measure the same, and the odd one is different by 1 gram. All the pins measure the same. And the scale repeats.
Maybe the small ends will measure different but I doubt it. Im stuck trying to figure out where I can take weight off of 7 pistons without impacting the integrity of the pistons, just living with it the imbalance, trying to fix the damaged piston that weighs in good but has a pinched top ring land, or calling racetec and asking for yet another replacement and waiting another month +.

 

[Lefty71]

It all boils down to the level of precision you expect in your engines.

I was speaking more to the fact that he has a need to replace two pistons out of a supposed "custom" set. That does sound like junk to me. Although i hope he has the best of luck in his build.

 

[JedIEG]

Im going to follow HPA's suggestion for balancing after talking to the machine shop about it on Monday.

Balancing Pistons | Safest Place To Remove Weight [HPA Q&A]