Hello,
has someone already tried to balance a 2.4l crank from a stilo or Kappa (2.4l conversion)?!
If yes - how did you balance them???
A friend of me had to realize that with lighter rods and lighter pistons the rebuilt engine has a lot of vibration now.
We did some research and found out that the 2,4l crank has to be balanced with so-called master weights.
These master weights have to be screwed to the crank and should simulate rotating pistons and rods.
Normally the master weight complies with the weight of rod+piston plus about 50% of oscillating inertia from rod+piston. But this 50% is our estimation, only. In reality Fiat uses a specific formula to consider the oscillating inertia.
Does someone know this formula or does someone know the percentage for including oscillating inertia especially for Fiat?! We measured 75 gram of imbalance at each end of the crank, that’s really much. A measurement of an additional 2,4l crank showed the same result – 75 gram.
If we would know the Fiat formula, we could build our own master weights – depending on the weight of the lighter rods and pistons.
Moreover we wanted to remove the balancer shaft. But with this imbalance already this could become a dangerous endeavor.
The normal 2l crank does not have this problem – it can be balanced without master weights…
Would be really interesting to know, how other people in this forum did balance their 2,4l crank…
Thank you very much
Juergen

Hi Juergen,
I was talking to Enry and my mechanic, and both told me that it was not necessary, nor by the twin disc clutch, nor by any difference in the weight of new pistons and connecting rods,and my cranck I bougth new in std measures,!and yet do not feel any vibration in the engine,and I have done 1020km in two weeks...I've done wrong will not balance?I think not, but so far everything is 100%,and I liked the job done...

cheers

Carlos

Juergen, I would ask Guy Croft, but I think the weight of the rod and piston would be the weight to choose nothing else, I know bob weight balancing is de facto on V8 cranks. Prioir to this you want pistons ready for installation ie. they have the correct piston to valve clearance, then piston wieght and rods should be equalised - hopefully if they are quality they will be very closely matched as a set. Then the Flywheel and crank (rod and pistons for wt checking) should be sent to the balancer, you can balance the clutch and Fw assmebly as a whole (I had this done) but the FW clutch and crank must all be assembled in the same orientation as they were balanced. I take it you didnt have the crank balanced prior to assmebly now the counter weights weigh more then the piston rod assembly, any competent balancing workshop would be able to do what you need with little issue.

Nyssa7's engine was build by MBE race engines you could ask there http://www.mberaceengines.co.uk/MBE_Race_Engine/Home.html

I agree with sediciRich, take it to a good shop to have it done.

The problem is that it isn't as simple as adding a weight. There are a whole heap of complex interactions going on in there. Even if you did calculate the dynamic balance points you may not be able to account for resonance. It may also be that the crank webs aren't were the sums dictate the weight be added/removed.