Extra 25BHP for £80 !!!!

[DEYAN IYI]

Balancing must be done for sure. The machine shops can add weight to the pulley, flywheel and crankshaft if needed.

Yes, that link is not active now, but hopefully one day... Lot of info in there.

[Rusty's Uncle]

The thing is that the heavily weighted pulley on the Bis must work in conjunction with the flywheel which is a very heavy piece of metal. Also the pulley will not fit an aircooled as it is much deeper so you would not be able to align the fan belt 

[DEYAN IYI]

Yes, the pulley and the flywheel are different, so we need the aircooled ones. All together with the clutch plate and the calculated additional "bob weight" on the place of the con rod/piston group go to balance.

[smallcox]

This is true the crank from the bis was a more dynamic set up allowing higher revs to be achieved with less deflection. The only rule to fitting this setup to a aircooled would be if you use the flywheel and pulley from a aircooled 126 then the benefits will be lost even if you get the crank balanced.
 The only way I would see to use a bis crank in an air cooled engine is to use the flywheel from the bis then have a front pully made from steel machined to fit with the same counter weight that the bis front pulley has already, then get it all balanced together. Only problem with this is cost

[Rusty's Uncle]

OOOOW this is making my brain hurt and I am well confusificated 

[DEYAN IYI]

Well, the Cinquecento 700 flywheel and pulley are different, and it's still worth.    The pulley has a bit more weight, just like Panda 30 (the only difference with the standard AC pulley). Additional weight is possible to attach even using screws (better welded maybe), but how much, the machine will say.

The Bis's flywheel, I'm not sure, if will fit, cos the ring gear is thinner than the aircooled one, and the starter will need to reach deeper. But I don't see any reason not to use the normal one. You can drill the 4 holes at the same place. One good thing about the Bis's one - it has less peripheral weight.

PS - Standard 650 flywheel is 7,370kg vs Bis 6,590kg.

[Rusty's Uncle]

Now that crankshaft pulley is different to a Bis in that the Bis has a much larger counter weight. The flywheel also is different in that it only has two large holes for lightening as opposed to four on the Bis. So it looks to me that there are more variables here where the crank pulley and flywheel have to be matched. Smallcox , our UK Guru , has explained the theory of the weights and balencing to me. It all made sense and seemed to come down to the dynamic bending moments on the crank as the power and revs go up with the pulley and flywheel opposing the bending force coming from the pistons.
So if the Bis crank is a higher spec then I guess that it could be fitted to an aircooled for normal running. But what is normal ? My 499ccs motor will rev to over 6,000 rpm when you push the noise peddle 

[GTMaster]

Standard 650E engine: 24hp @ 4500rpm, 41.5Nm @ 3000 rpm
As you can see there's no point in revving it over 5000-5500 rpm (especially with points ignition).... so normal running (dynamic running  ) would be between 3000 rpm and 4500 rpm.
 

[Konstantinov]

crankshaft from CC is different than this one from BIS