ALFAGTV6.COM

Hello.

Does anyone know the balancing factor(amount of weights not to be counted with the bob weights) of the Alfa Romeo V6 12 valve 3 litre?
Numers from 30-50 are normal....

Jarle

My one got done at 47%, engine loves to rev.

Thanks Que!
Can anyone comfirm this number? JJ? Barry?

Jarle

For what it is worth, I used 50% on a 2.5L V6.

Thank you Reale. The machine shop thought it was 50 % but they need a confirmation before starting to balance.

Jarle

I tried to ask several people about this and most that knew regarded it as 'secret' info and would not tell me. I had one balanced at 35% and it is fine. I spoke to Dennis Black (Don Black's son) and he said it was 'probably' around 42-45%. In talking to my machine shop, they said you would probably go with a lower percentage for higher RPM use and a higher percentage for lower RPM (street) use. Ultimately I don't think it matters exactly what it is, but I would like to know!

You take one complete piston/rod/ring/bearing combination - even the wrist-pin and wrist-pin retainer rings and weigh it and balance all 6 assemblies to each other.

Once you have all 6 of the complete assemblies completely balanced to within minimal differences of each other, you take one assembly, weigh it and take 33.3333% of that weight - this is the weight that must be applied to the crank balance...

Then you take 50% of that number and apply it to the flywheel balance - this is the way that we have done the 3.7s and they are smooth as silk at idle and have virtually no twist under throttle-blip....

junglejustice wrote:You take one complete piston/rod/ring/bearing combination - even the wrist-pin and wrist-pin retainer rings and weigh it and balance all 6 assemblies to each other.

Once you have all 6 of the complete assemblies completely balanced to within minimal differences of each other, you take one assembly, weigh it and take 33.3333% of that weight - this is the weight that must be applied to the crank balance...

Then you take 50% of that number and apply it to the flywheel balance - this is the way that we have done the 3.7s and they are smooth as silk at idle and have virtually no twist under throttle-blip....

The way I read this, it sounds like you're fitting your bob weights at 33.3333%, balancing the crank, and then doing the flywheel seperately?
please tell me that its actually being balanced as an assembly (crank/flywheel/front pulley)??

It is all being done in one run at the engineering shop, but there is no way to compensate for that huge weight inside of the crank-pulley, so they do things in stages...

Lighten the flywheel first
Get the rod/piston assemblies all to even and neutral
Then balance the 6 assemblies to the crank
Then do the overall internals to flywheel and pulley.

The only way to eliminate the pulley all together is to go with a custom unit, but there is so much counter weight tha would have to to go to the crank and flywheel then that you will be drilling for days...

Custom flywheel and pulley wuold be best I am sure, but why...? All of the engines that I have been involved in with Dawie now (14 all together) are all smooth as silk and rev-happy!

So you're effectively achieving a neutral balance, and then slapping a big counterweight on each end (pully, flywheel)? or am I missing something?

Over the other side of the fence in Ford V8 world, theres stock and stock like cranks that use a counterweight in the front harmonic ballancer and one in the flywheel, and then there's the race cranks wich are internally ballanced (helps stop the flywheel and the nose of the crank falling off at 8,000rpm) These things, from my understanding are balanced with the flywheels on...
So unless you're operating the machine for a known imbalance at each end to compensate for the pulley and flywheel effects, you wind up adding weight to balance and then removing it again?

Yeah, well, it's not like an in-line 4 where you have a zero balance factor and everything is brought to zero - because of various factors (such as the number of cylinders, degree angle of the V, FWD and the tolerances between various assemblies, you have a balance factor.

Where they use 33.3333% on the V6 I think that they use 50% on the American V8s.

Some shops over here will just do 30% and call it good like on Chevy and Ford V6s (and it does work...), but Kevin Brink at Alan Y. swears that it is very important to use exactly one third if you ant to be right on with the Alfa V6.

Crank with bobweights.NO factors will be posted due to ongoing work.

Speaking of cranks, here's a pic of Plastigage being used to measure clearance. The example shown is somewhere around 0.045mm (.0018"),correct for high-performance use.
Jim K.

Hey Kartalamakis,now that youve posted ALL your pics for everyone to see,no one is going to buy yer book!!

hehehe....

The select few Barry, the select few!
Jim K.