Piston weight difference issue

[Mas]

I recently purchased 2 NOS vintage pistons for my '57 Lark 35 HP. In wanting the best running motor, I decided to use a gram scale to compare the two pistons' weight. The results showed the two pistons 10.01 grams apart...exactly. This is the weight of 4 U.S. pennies.

I have not yet weighed the rods yet and I doubt they're exact. Should I match a heavy piston with a light rod and call it good, or remove weight from the piston. Unfortunately, I do not have the weight of the rods since I have not removed them from the old pistons...yet

This seems too big of a difference, but also seems like removal of a lot of aluminum?? If in agreement with the former, where is the best place to remove weigh for those with experience balancing pistons?

Mas

 

[F_R]

Re: Piston weight difference issue

Forget everything you ever learned about weighing that stuff and go ahead and use them as is. If you want to be persnikity about it go ahead and match heavy piston with light rod, but you won't know the difference.

You should see the huge difference in weights of some of the replacement connecting rods on some models. Some were twice as thick. But they worked just fine.

 

[a70eliminator]

Re: Piston weight difference issue

10 grams seems like alot, you may want to measure the diameter, the heavy one may be oversize.
The reciprocating assy. flywheel and all could be spin balanced, then weight removed or added to crankshaft throws to achieve a dynamic balance. Again I don't know enough about how outboards are balanced.
I was typing while FR posted, way more knowlagable outboard guy than me so what he said.

 

[Faztbullet]

Re: Piston weight difference issue

Stick it together as it a short stroke cross flow.. as F_R posted you wont see any difference

 

[Mas]

Re: Piston weight difference issue

Pistons are standard bore & both have the same casting numbers embossed...but I guess all would be cast the same...just standard bore milled more?? Anyway, none are stamped with oversize markings as I would expect...but I have yet to put a mic on them. I guess I better do that to make sure! Anyway, an oversized piston would seem to be a bit more than 10 grams???

Assuming they're both STD bore for the moment, how much a difference would 10 grams make in wear for example?

Mas

 

[Dhadley]

Re: Piston weight difference issue

As stated, you'll never notice the difference. At the rpm you'll be running you'll be fine. The motor will last for many years, don't lose a lot of sleep worring about it.