When to change pistons?

I know there is a time to change rods, but is it best to change pistons at the same time or do you ck wrist pin holes and continue to run them? We are changing rods after 42 passes, pistons also have 42 passes....blown alky hemi.

Josh

 

hi josh. I think if it was mine I think now would been a smart time..Dave

 

First I would look at the inside of the piston where the rod and wristpin meet. They will crack there and the piston will still look like new , also I take feeler Gage's and check to see if the ring land compresses .

 

I measure them about every 10 passes....they are born with .003-.004" positive taper in the skirts...so the bottom is just a little bigger than just under the oil ring...i change them when they do not measure more at the bottom.....on my previous combo the skirt measured 4.300" just under the oil ring and 4.303"-4.304" at the bottom of the skirt...so I pitched em (gave to kids at the track) if the bottom measured 4.300" or less...we ran a little nitro and had fairly thin skirts (.125"-.130").....so 10-15 passes was average life before they started banging around in the hole....maybe with straight alcohol or thicker skirts you could run em longer before it starts to crush the skirt....

 

Pistons

going to make you all swallow hard!
I am a tractor puller, with a 3 chevy engine tractor, I run 8-71 blower hi helix kobelco 70% over.
One of my motors is a 572 big M, the Pistons are Ariias that I bought used in 1995 in a package deal. The engine is a spare, runs from 15 to 40 runs every year, never have replaced the wrist pins. One is Washed {burnt} a little between the top and 2nd ring. Has been that way for 10 yrs or more. Does not seem to affect the leak down. Never have changed the wrist pins. .990 heavy wall.
Compression ratio is 10.8.
I am not advocating this, just saying this is a spare motor. BTW, the rods are a used set from one of my other motors! Those have a lot of runs also.

I give them a complete Physical & check and put them back in!

Note I am not saying to do this. Some times I think failure is a result of what we do to them, rather than fatigue.