90 deg crank in Lc

[Antman]

Im thinking of building another motor as Iv'e still got lotsa bits sitting around.

Has anyone heard good results or know someone who has put a 90 deg crank in a Lc.

I know TSS has done them for Rz.

Ant

[2TInstitute]

Can be done easilym works a treat

[DOC03]

What are the benefits ??

[2TInstitute]

Vastly redued 'rocking couple' forces, this is where eah side of the crank is being being bent forward and backwards at the same time.The ends of the crank actualy track a figure 8. Main reason why the crank 'spreads'. Equals more rpm less crank wear/maintenance
Traction as with big bang engines the 270deg break in power pulses gives the tyre time to recover.
KTM 2T guru Harald Bartol didn't go for a paralel twin with 70-110 firing for marketing reasons , 90 deg firing has 1 piston max acceleration and the other max deceleration. Canceling most of the resultant forces out.

[DOC03]

That sounds very benefitial....

What are the downsides - higher engine wear - increased breakages ?

Lozza- if its that easy should I consider it when we do the OL Girl with the Chambers - Porting - Carbs etc ??? I was thinking of doing the bottom end / crank at the same time to make sure everything was all mated well ???

[Antman]

They sound good to both cyclinders firing at once, Steve at tss mentioned the rocking forces associated with a 180 deg crank makes sense.

I need to fing out if the zeal will still work with it i would assume that i will need to get another stator would assume the pickup is different.

Doco i can sell you a crank if you want to experiment.

Ant

[Antman]

Here you go





Whereas, in a 90° crank configuration, a higher inertial momentum (flywheel effect) can be maintained about the crankshaft by having one piston always at or near maximum velocity while the other one comes to a ‘stop’ and then changes direction. The pistons are never both ‘stationary’ at the same time.
This ‘flywheel effect’ also allows the use of smaller actual flywheels.

Therefore a 90° layout will always give the crank an easier life, and accordingly crank life will be extended. This is particularly important for racing applications.

Another advantage of the 90 degree crank layout is that, just as in the GP world, the 90 degree Big Bang gives better feel and grip from the rear tyre on corner exit due to the longer duration of No Driving Force.

This becomes a serious issue, especially with an RS500 race bike with 115HP driving not much more than 100kg.

A tyre is only capable of a total grip factor.This is expressed as a "traction circle" and the shape of the circle is turned elliptical, fore and aft, under acceleration or braking.

This use of the longitudinal acceleration or braking traction capability then proportionally reduces the traction available laterally, i.e. side grip.

So Big Bang gives more available side grip as the accelerative force is applied to the tyre in shorter duration bursts, i.e

[2TInstitute]

That sounds very benefitial....

What are the downsides - higher engine wear - increased breakages ?

Lozza- if its that easy should I consider it when we do the OL Girl with the Chambers - Porting - Carbs etc ??? I was thinking of doing the bottom end / crank at the same time to make sure everything was all mated well ???

Pete only the crankshaft phasing and the stator need to be altered everything else remains the same. There are no downsides, the 180 deg hopelessly underbalanced crank IS the problem.

Have a look at an RD 400 crank for how Yamaha should have done it.

I reckon I could do some 'modernising' on the crank also along with better quality bearings and grooves in the cases to axialy locate the crank more positively. TYhat should see a safe 12,000 rpm redline.

[DOC03]

Lozza, modernising sounds great - a good compromise for it as a road bike.
I can send the end cans up today for the pipes, but I just have to work out when I can get the whole bike up to you now, maybe end of next week ??

[2TInstitute]

If you have a standard LC pipe to send up I probably wouldn't need the bike untill final fitting

[DOC03]

Yep, no probs I can do that - got a right and left from Ant, will try and get em away today so you should semm em toomorrow. Just trying to get the PWK's and Filters sorted so they will be right to go with the modernising etc.

[DOC03]

Lozza, pipes and silencers on the way via Fastway Couriers, will be delivered toomorrow morn.
Cheers
Pete

[2TInstitute]

got them ok

[DOC03]

Thanks Lozza.
Hey in relation to the 400 crank, can they be made ot fit the 350 ?
Ive seen one in the state pretty good nick and can get it relatively cheap ???

[Antman]

Just go banshee mate and run tz big ends ,and 11 ball mains.