Thread: Dropped a piston

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Originally Posted by kitz

I just wouldn't use it. If it came like that you sure as heck wouldn't take it, right? Get another and match the balance.

Kitz

do you think by buying just one new piston, that I would have to re balance it? If so, how would they balance it? because i just got my rotating assembly balanced for $175
thanks

Originally Posted by facemelter

do you think by buying just one new piston, that I would have to re balance it? If so, how would they balance it? because i just got my rotating assembly balanced for $175
thanks

you will need to weight match it with old one like i said

Thanks Pat, I did notice that. Thanks for the advice, I will just have to purchase a new one.
Thanks

well, i now ordered a new piston. What im wondering, is whether it is really necessary to balance it being its only 1 piston? Would it really make much of a difference?

Thanks

Originally Posted by DennyW

As mentioned. You need to check the weight of the new piston, and compare that weight to the (new) old ones.

Think of it like this. 7 pistons weighs 1 lb. The 8th one weighs 1.5 lbs. Will it make a difference ? Yes, it will at the upper rpm's. Just like anything that is not balanced in a rotating mass.

Check to see what the tolorances are with the people that make the pistons. They should have a set weight they go by, or they are not very efficent makers.

Alright, thats understandable. What I want to know next, is when I bring the piston to the shop. Do they just compare one to the other, then add weight, or subtract, etc. or do i need to bring my crank, all my pistons, bearings, back down to the shop so they can re weigh it all out. I would rather not have to pay $175 for a full balance if not necessary.
Thanks

i would just match the new one to the old one..... i'm sure they can weigh each one for you and tell you how close they are for free...... if they're the same then no balance required...... if not then they can probably just balance the new one to the old ones weight

if the new one is heaver they will mill some grams off the piston if lighter them you can use a heaver pin if close with a gram or so it will be ok but it should be check you just need the one rod /piston not the hole mass . the piston s new should be match in weight but now you have a broken set. it need to be check to old piston this stuff i know i balance engines

Originally Posted by pat mccarthy

if the new one is heaver they will mill some grams off the piston if lighter them you can use a heaver pin if close with a gram or so it will be ok but it should be check you just need the one rod /piston not the hole mass . the piston s new should be match in weight but now you have a broken set. it need to be check to old piston this stuff i know i balance engines

Thanks pat, thats exactly what I needed to know. Its appreciated.

That is more than runnable.........Jeweler's file, go easy, don't disturb the skirt coating, use the ring you plan to run for fit (remember, even the factory has ring clearance specs found in shop manuals and ring manufacturors for such a situation). The areas you displayed do not "see" the cylinder wall unless you raised the material to astronomical height. It was designed to place the ring for control, not hold the engine together. If all else fails, mic it again and again to be sure then get anal and replace (better safe than sorry). If you cracked a skirt or severely gouged the ring lands, I'd be replacing it. You don't have anything to worry about if handled properly. You should see what a fuel motor goes thru in one run and they re-use and re-use....etc.

by the way......you should have the old card from balancing......grams per piece....they can do it whith out having the assembly in their possesion. Food for thought, if a small block chevy has 1/4 gram off of the balance placed at 6 inches from the centerline of the crank, It's like swinging a 6 lb weight at 4000 rpms which robs about 18 hp.