[Mk2] [Turbo] anyone running with a lightened crankshaft?

[TUBBY-DEUCE]

i dont know how to make it any easier. pistons are 180 deg out of phase so forces completly cancel each other therefore no counterweights on the crankshaft are needed. as for balancing the rod/piston assembly you just make sure there all the same weight. simple. if you dont know what your talking about dont give advice. especially if you intend people to act apon it.

from what ive read and researched so far, that seems to be the rule, as long as rods and pistons and connecting parts are the same weight things should be fine. thats why i was getting at the forge rods and pistons should be withing tollerence and evenly weight matched, is that true?
its to my understanding they should be matched to whithin <.5grams of one another

[arome]

the pistons and rods i use normally all come out of the box within 1 gram of each other. if you weigh them all seperatly then for example match the heviest piston with the lightest rod they should all come pretty close. if you want it perfect it requires you take a little metal off the piston. but as you say most people will accept a 5 gram diffrence. it depends on the application of the engine your biulding.

[TUBBY-DEUCE]

as for the application of the engine, just want a quick point to point car with a revvy engine, im not bothered about top speed as it very rarely gets used, and the driveablity issues i can live with as it wont be doing alot of miles.

[TUBBY-DEUCE]

recieved this the other day from a company im considering using:-

Yes under normal circumstances rods and pistons get zero balanced to within 1gramm. And rotating assembly can be left independantly in which case it's around £95 for the crank assembly on it's own. My only concern is that if the crank has been made too light for the piston rod assembly it will need to be balanced as a complete unit and compensated accordingly.

[BrianUK]

arome wrote:
i dont know how to make it any easier. pistons are 180 deg out of phase so forces completly cancel each other therefore no counterweights on the crankshaft are needed. as for balancing the rod/piston assembly you just make sure there all the same weight. simple. if you dont know what your talking about dont give advice. especially if you intend people to act apon it.

Silly question - if the counterweights are not needed then why do Toyota go to the expense of manufacturing them?

I took the route of fitting a Fidenza Flywheel - which at only 4kgs is a considerable weight saving

Brian

[arome]

the counterweights on the crank are to balance the crank. i was just trying to make a point that they are not used to balance the piston/rod assembly. in an application where the pistons are 180 out of pahse

[TUBBY-DEUCE]

the counterweights on the crank are to balance the crank. i was just trying to make a point that they are not used to balance the piston/rod assembly. in an application where the pistons are 180 out of pahse

thats basically what the company said, the only thing they were concerend about was if the crank had been lightened too much, to an extent where the rod/piston assembly wieghed more than the counter weight i gather

[Century Motorsport]

i dont know how to make it any easier. pistons are 180 deg out of phase so forces completly cancel each other therefore no counterweights on the crankshaft are needed. as for balancing the rod/piston assembly you just make sure there all the same weight. simple. if you dont know what your talking about dont give advice. especially if you intend people to act apon it.

Can you please explain the reason for counter weights?

I see you thinking in the fact that 2 pistons are down and 2 pistons are up - being 180 deg out of phase but you seem to be missing the fact that each piston is balanced with the opposite counter weight... go ahead and remove your counter weights and lets see what happens.

I only give advice on things i understand, and this is one.

Thank you.

[Century Motorsport]

Just another reason for counter weights...

Without counter weights the rocking couple between cylinders would break the crankshaft due to harmonic vibration.

Nathan

[GeoffC320]

arome wrote:
i dont know how to make it any easier. pistons are 180 deg out of phase so forces completly cancel each other therefore no counterweights on the crankshaft are needed. as for balancing the rod/piston assembly you just make sure there all the same weight. simple. if you dont know what your talking about dont give advice. especially if you intend people to act apon it.

Silly question - if the counterweights are not needed then why do Toyota go to the expense of manufacturing them?

I took the route of fitting a Fidenza Flywheel - which at only 4kgs is a considerable weight saving

Brian

I would think that the flywheel would have more effect than a lightened crank as you're removing mass from much further out from the rotational axis. Like having light rims on your wheels makes a lot more difference than light centres.