Balance factor for a twin flywheel?

[vince998]

After rebuilding a freinds Egli (EV6) i was told that the standard vincent balance factor doesn´t work well in an egli as well
you live and learn (the vibration is bearable.
I believe that you can get the crank well balanced dynamically, but what causes the vibrations is compression and firing stroke once the engine is running?
How to balance a crank for all throttle settings?

This is a sticky wicket with the Vin.... usually in the range of 45 to 55 is quite usable.... but as far as ideal or perfect.... that can depend on so many things, like an Egli frame for example. But, most vibration problems with a Vin
have nothing to do with the balance at all.... the usual culprit is poorly fitted main bearings: a bearing is as only as good as it's housing and with these soft cases I always line bored and fitted aluminum bronze sleeves for dead
true crank alignment and perfectly round bearings using a .0006" to .0008" radial clearance.

 

[riptragle1953]

IS the Egli vibration fairly consistent or does it worsen with engine RPM.... and does it lessen at a higher R.P.M.? If so about what R.P.M. or M.P.H. is it at it's highest level?

 

[vince998]

From what i can remember (the rebuilt was a good 7 years ago) the vibration was constant up to aroung 3500 rpm, and increased steadily (everything was new so we didn´t ring its neck).
Vibration increased with throttle opening (ie full accelaration)
Relatively smooth on a neutral throttle
Mk 2 cams, 9:1 compression, Concentric Mk 2s (32mm)
The explanation i got afterwards (from the egli expert) was it was all down to frame harmonics. (something to do with the rear subframe?)

IS the Egli vibration fairly consistent or does it worsen with engine RPM.... and does it lessen at a higher R.P.M.? If so about what R.P.M. or M.P.H. is it at it's highest level?

 

[davidd]

Some builders have very specific targets with only two of three points difference between stock, Egli and Norvin. I asked Terry Prince several years ago what he used and his reply was 60% for twins and 74% for singles. I forgot to ask him if he changed the numbers for Eglis. However, I have noticed that the Egli and Norvin values tend to be in the 60% to 70% area. If you have a stock bike I would stick near the Albervin and Rip figures. If you have an Egli or Norvin, I would talk to one of the experienced engine builders in the club and get an opinion.

David

 

[Big Sid]

We had marvelous success with 60 percent with our Vincati , perfect for the Ducati GT chassis . NO vibration , liquid smooth . This balance factor in fact works in all types of Vincent frame configuration , original , Egli , Norvin , for all who ride fast , use higher revs . Generally the lesser factor , 46 , 35 , is smoother at lower speeds , better for touring types who mind the legal limits , but this buzzes more at higher speeds . Much has to do with the flywheel runout . The factory accepted 1.5 to 2 thou total runout and these motors varied on the rougher side . If runout is held to tighter limits , no more than a half thou total then the motor is much smoother , the rods and pistons of being identical weights also a factor in achieving the smoothest running . Attention to all these points gives more satisfaction .
You pays your money and takes your choice . Sid .

 

[Big Sid]

For what it's worth , the advice I just gave came directly to me from Neal Videan some years ago . Sid .

 

[Big Sid]

More on the subject , or related . Dave Matson said that he had found there were three variants of rod widths and thus weights , this due to the forging die being non to carefully closed together during the process of rod forging . he would select a pair of the heavier rods to process for his racer . Later went to Carillos .
Videan was central in building big end assemblies in Australia for Vincatis and all manner of other Vincent configurations . At first he built to several different balance factors for whatever it was used in , then went to building ALL to 60 percent . All buyers were satisfied . But these Aussies are fast riders . Something in the water . Sid .

 

[Vincent Brake]

I think when reading this all, with a big thanx for all your resposes, that I will settle for a mid.: 55%, I will skim the flywheels true, will rework the rods to an equal weight, at both sides: the small and the big end.
As I like to drive it a bit faster than the usual pottering around. (bit costly though with all those speeding tikets)

I will let you all know in the spring time when it will be ready (with megacycle MK II and 7,5 comp. ratio. Suzuki pistons) The cases (remachined, CNC, I will post a youtube video soon) are having my own new oversise bearings (no sleeves) with a (on the big rollers) a clearance of 0,01-0,015mm and on the small roller 0,02mm (lapped in) and the ball roller is yust a bit free.
Maybe its all a bit over the top, but I cant help myself, I have to do a job, in the only way it can be done.-ABAP- (as best as possible)

Vincent Speet

 

[Vincent Brake]

see for re-machining or skimming cases:
http://www.youtube.com/watch?v=wAarnSU2ooo
Bit more preparation as you see now

 

[Big Sid]

To Vincent brake , send me your E address and I'll send you a vid of a head casting being made out of a round billet . In minutes.
sid@bigsid.com