crankshaft 101

[shbop]

I've been reading the back posts, but still don't get it. Could someone please explain, and possible show the difference between a balanced and non-counter-balanced crank for a 2.0. I recently acquired, what is supposed to be, a 68' 2.0L motor in pieces. The crank looks much different than the one in my 66". Thank you!

[tom1394racing]

here's a pic of a non-counterbalanced crank

FS - 66 mm Non-Counter Weighted Crank

[shbop]

Thanks Tom. Could you tell me a little about the application for this type of crank?

[tom1394racing]

The non-counterweighted cranks were used in all 2.0-2.2 911T engines.

Today some racers use them because of their lighter mass and fast revving capability .

[shbop]

Thanks again Tom!

[kenikh]

The counterwieghted cranks were thus designed to create a smoother motor by eliminating high speed vibration. The counterwieghts are designed to offset the weight of the pistons/rods which rotate at 180 degrees from the counterweights. Non C/W cranks do spool up more quickly due to less mass, but if you rev them at high RPM, they can wear out the engine case more quickly due to the abuse (this is exacerbated in magnesium cases due to weaker material). This is a non-factor for racers since these motors are rebuilt in terms of hours, not miles. If you want a street motor to spin up more quickly and still want to rev the motor over 7000 RPM, you are better off lightening the engine's rotational mass with lighter rods and flywheel.

[shbop]

Thankyou for the information. You just made it very easy to understand! Aloha!