I'm helping my buddy rebuild his LT1, so far he had the crank polished and purchased a new set of PM rods from the machine shop. The block had minimal wear so it only needed a hone job new freeze plugs and cam bearings all done by the machine shop. The pistons he ordered where Speed Pro 2v relief -5cc flat tops coated pistons and they came with moly rings and ordered SP bearings. Since, this is a performance build with LE2 H&C and a simple upgrade on a stock motor is the balancing necessary? our machine shop said it wasn't and would be fine since we're only changing pistons but I have my doubts. Pistons are mounted on the rods and rings are already installed pending assembly. So whats the verdict??

 

Unless you want the bottom end to rattle itself apart, it is necessary.

 

Ditto

 

Yes..most definitely. The lt1 is externally balanced by the flywheel. The changes in pistons will be enough to throw it out of balance enough to be problematic at high rpms. Always better to be safe than sorry.

 

Since it was only $200 to get my $1800+ assembly balanced I would say it was worth it- even if your parts aren't that much or are way more its prol the best thing you should spend money on IMO..

 

I say don't waste your money balancing it. 300hp vibrator.

 

Jlo, I know this will run counter to the info in the above posts, but keep in mind everything has a tolerence! If your new pistons and ring pack are within +/- 8 to 10 grams of your old piston and ring packs original weight ....... your machine shop is right, you will NOT have to re-balance this motor.

If your new pistons and ring pack are up to 10 grams lighter than the OEM setup, your motor will now be slightly "overbalanced", something many NASCAR and performance engine builders do anyway. If your new piston/ring setup weighs no more than 8 to 10 additional grams per rod/cylinder you will still pretty much be within the OEM factory tolerance for GM line built engines.

Finally, from my personal experience, about two(2) years ago we re-built my cousin's '94 Z28 LT1 Camaro engine with stock rods and crank but "upgraded" to forged pistons so he could more safely run a small (50-75 hp) nitrous shot, and, even though the forged pistons and ring pack he used were about 10 grams heavier than stock ........ that motor runs "smooth as silk" right up to 6,500 RPM day in and day out.

Hope this info helps.

 

I just think that a balance or balance verification should be part of any rebuild when a part of the rotating mass is changed with other than oe stuff. Speed Pro makes good products but even they are subject to a quality glitch on any given day. 97 6 Speed is absolutely right and you may be ok..but then on the other hand...you may not be. Guess all depends on how much you like to gamble. Best of luck on either way you decide to go.

 

get a good scale and weigh each rod/piston combo. Make em all the same.