Questions about piston weights

Ive got a 76 900 that Im in the process of rebuilding
and Ive got a 1000 set of jugs freshly honed and used pistons but the weights are a little off. is this a problem
The weights are .643 lbs,.635,.649,.649 I also checked my stock pistons which are .624,.624 ,.616,.623 lbs. I would think that it would throw off the balance of the engine if you get the rpms up. Yhe other thing I would like to know is about setting valves with the head off the engine If needed Ill start another thread. Thanks

.649 lbs equals 294.38 grams
.643 lbs equals 291.659 grams
.635 lbs equals 288.031 grams

That's an approximate 6 gram difference between lightest and heaviest.

Personally, I'd try to make them all weigh exactly the same, but I don't know if it really matters or not.

If you plan to balance the weight of the pistons you may want to consider doing the rods too.

650ed wrote:

If you plan to balance the weight of the pistons you may want to consider doing the rods too.

i got some advice in my thread on ring and hone stuff last week and someone had one grams out that had made the motor have a humm...he told me to try wheighing mine befroe installing and fileing or sanding any cast marks/burs on the heavy piston to bring it down in wheight...it is repeating info...but...may help

in a perfect world it would be best if all your pistons weighed the same but in rarely ever happens on a street motor it really won't make that much of a differance because your not turning really high rpm's all the time but it can be very important on a high rpm race motor. if you are going to try to match them up match them to the lightest and take out the material from under the piston crown don't take to much from one area and try to spread the removal around evenly.

I would not worry about. The KZ roller bearing cranks are not in very good balance so 6 grams will not be noticable.

Jay

I have always wondered about the whole balance process, and yes I have balanced many a engine, but when you think about it, how much oil was on the counter weight at the last rev, vs the next one, also what happens if there is more oil being suspended on one piston than the other one, all these plus many other factors can change the balance of a engine in motion.
bottom line get it close if you want, but I dont think your gonna see a dimes worth of difference

Hi All; I know nothing about balancing motor components. I do know that I'm hijacking this thread. When a crankshaft is sent to a shop like Falicon for balancing, can they make a "sweet spot" where the crank is near perfect balance at say 4K to 6K? (Where I spend most of my time) Thanks and sorry for the bad manners! Ride safe, Steve

its weight difference is even less if you consider that piston 1+4 and 2+3 are matched.....that is making the same motion :woohoo:

Thanks for the responces. The piston weights I listed are in order from 1-4 The 900 pistons came out of the motor and you can see a pretty big differance in 1 of them I guess I weighed the 1000 slugs first then checked the 900's a few weeks later just thought they would be closer from the factory I guess Ill go 1000cc Thanks againB)

are these stock pistons?well id try and match 1-4 as close as possible then 2-3

Yes Not sure where to take the weight off thogh