454 Piston problem

[Gerkin]

Hello all.
I have twin 454s that I am tearing down and putting back together with new rings, oil pump, gaskets, etc...
Heres my problem. I ended up breaking a piston skirt on 1 piston.
I cannot find a replacement piston.
My part number is 353062. Its a std 4.25
Anyone know where I can find that part number?
I have another piston that is same size, the only difference is it weighs 12 grams less.
I heard it is not good to use a different weight for a piston.
I also heard that if I replace all 8 pistons, it could still through the engine off balance if its not close to the original weight.
Please help
Thank you all

 

[alldodge]

Correct if wrong
You have a old 454 and you want to take old pistons and put new rings on them?

 

[Gerkin]

correct, but I have to replace 1 piston that I damaged. Or possibly all 8 if need be.
I have the correct rebuild kits for the engines

 

[alldodge]

Suggest don't do it

Just rebuilt a 454 Mag MPI and if top of the bore looks good and within tolerance the low bore will not be. All rings bores wear from top to bottom, and bottom will be wider, not to mention will not be perfect round

Now if your wanting to do this for a cheap fix and then sell it I understand

 

[Scott Danforth]

The pistons are GM truck motor pistons. A year will help identify if it's a Mark IV, Gen V, or Gen VI

 

[Scott Danforth]

Agree with AD, only way to put new rings in an engine with more than 100 hours is a bore and hone

 

[Gerkin]

So, it is a Gen IV 1986
Low hrs
Cylinders have been honed.
Block is in good shape

Just looking for a piston or a possible solution to my broken piston skirt problem

 

[Scott Danforth]

The mark 4 pistons didn't change for GM much between 1968 and 1989. There are basically the lower CR dished used in the 70s and the flat tops.

Measure the bore in 3 locations with a bore gauge

 

[alldodge]

Measure the bore in 3 locations with a bore gauge

Could also put a compression ring in the bore and measure ring gap, right ??

 

[Scott Danforth]

Could also put a compression ring in the bore and measure ring gap, right ??

if you have the bore at the top, and know the ring gap at the top, you can then measure 3-4 points down to get taper

I personally like to take the bore gauge and measure side to side, then rotate 90 and take same readings. that give me taper and eggality

 

[Gerkin]

I inserted a ring and leveled it with the piston head and took 3 readings. Top, mid, lower. All were identical. I could get a .020 feeler gauge in but met with decent resistance.

 

[Gerkin]

The piston that I removed has a weight of 889 grams.
The one I bought that had a cross reference number to the one I pulled weighs 877 grams.

 

[alldodge]

Can do what I use to have done in my younger days, before matched pistons.

Weight all pistons and the use the lightest. Then drill out a bit of every other piston from underside to make all match

 

[Scott Danforth]

The piston that I removed has a weight of 889 grams.
The one I bought that had a cross reference number to the one I pulled weighs 877 grams.

Unless you spend money on a balance job, don't worry about the 12 gram difference. Stock motors were off as much as 29

 

[Gerkin]

Really? 29 grams off seems like a lot.
I am new to the whole piston weights, so I am relying on you professionals

 

[Gerkin]

What about replacing the wrist pin with one that is a little heavier to get closer to the other piston weights?

 

[ScottinAZ]

that 29 grams relates to just a hair over an ounce. your 12 gram difference is less than half an ounce. From the factory, frankly I am surprised they kept it that close. They dont balance every motor as it goes out the door, close is good enough for them. Really the only folks that DO worry about the tightest of tight tolerances and balancing are those either with a LOT of time on their hands, or building a race engine that is going to rev to the moon. For general applications, the factory tolerances are "good enough"

 

[Scott Danforth]

Really? 29 grams off seems like a lot.
I am new to the whole piston weights, so I am relying on you professionals

I do this as a hobby, professionals get paid..... LOL

you are dealing with cast pistons. so weight is all over the place.

if youre not going to spin that motor over the published 4600 RPM range, no need to worry about it. especially since you have cast pistons

if you are going for an 8000 RPM zero balance motor with forged pistons, then the guy doing the balance job will add or remove weight as needed.