Piston Weight

[Pellwood]

I am doing a top end rebuild and was wondering about the tolerances for piston weights.

I have a set of Mahle cast pistons including pins & rings with 3 that weigh 504 grams and one that weighs 498 grams.

Is the difference between them acceptable or should I machine the other 3 down to the weight of the lightest piston?

I know that ideally in order to balance an engine you should include the weight of the entire reciprocating mass, which means the con rods as well but I don't want to split my case.

Any thoughts ?

 

[ozziedog]

:mrgreen: Just to chuck in a thought and I'm not an expert by any means , a balance can not be achieved unless everything is balanced so any weight difference will give you a locomotive effect which is great but it does limit revs but then again I'm guessing you're still looking for torque. I'm wondering if it is actually meant to be that weight, did you gather them separately or get them as a set?

Ozziedog,,,,,interesting

 

[atafonso]

The balancing will make the engine run smoother and last longer. VW tolerance was quite large but they were producing in large scale and also this engine was not made to exceed 4.5k rpm. It can be greatly improved if you balance the crank, flywheel, conrods and pistons. I balance conrods and pistons to 0.1g in all my engines. Crank and flywheels separate to 1g and crank with gears and front pulley. VW tolerance was 5g on conrods for example.
Today's pistons can be around 10g. I am finding the new Mahle's to be almost unbalanceable as if you remove too much it can weakens the piston. AA's are pretty good within 1g most of the times.
Abel

 

[Pellwood]

Thanks for the responses, they were bought as part of a top end rebuild kit from Machine 7, i will try to swap the pins around as well to get them as close to each other. At the moment im just after a stock setup.

Maybe i will put a thread up when i start the rebuild. At the moment i have just finished the teardown and clean up.