TZ 750 'Crossplane' - 90`- Crankshaft.

[James W.]

Anyone here heard of this being tried?

The standard 180` crank TZ/inline 4 configuration - means that 2 cylinders must fire together.

Yet the potential for run a 90`crankpin arrangement appears even more useful than in their 4Ts which do it.
The even inertia torque & smooth power impulses may well offer improved power delivery, inc' traction.

& the TZ's run a jackshaft between crank & gearbox - which could do double duty as a balance shaft.

This could assist with making the TZ's more competitive in classic racing, perhaps?

[James W.]

Here's a look inside the TZ 750.

http://www.mortons.mortonsmedia.net/med ... TZ7505.jpg

[2TInstitute]

What will it gain? If we look into history the first close firing order NSR500 allowed mere mortal riders to keep up with aliens, then when Mick Doohan switch back to the 90 deg "screamer" format firing he thought it allowed someone to roll the throttle off and modulate the slide better after it went sideways without the fear of a highside......but thats Mick Doohan riding.
Could be worth a try but a lot of work. The 750's just miss out on sheer grunt out of corners, if the Katana's and FJ engines were limited to 1000cc there might be a chance but 1300cc is too much to overcome. Power valves ,triple exhaust ports and programmable ignition would be something I would do before 90deg crank

[James W.]

Sure, & I understand a certain Kiwi TZ 400 builder is keen to do a four, incorporating those kind of things.

He did agree, though, that going to 90`firing would make for a smoother power transition/inertia torque,
with positive effects on stresses throughout the power transmission, from piston to tyre..

[James W.]

Kevin Cameron article on TZ 750, http://www.cycleworld.com/2016/01/18/ya ... n-insights

KC notes the 180` double-firing 'rocking couple' stresses as causation of crankcase fatigue failure.

TZ 750 jackshaft does not run at 1-1 with crank, so it would not be suitable for a simple 'balance shaft' candidate.

[2TInstitute]

Frits Overmars said they hotted up a TZ750 and it was a lot slower due to it wanting to wheelstand at the drop of a hat. Suspension is better today but no escaping the rocking couple even with 90deg phasing, It does mitigate the damaging secondary harmonic though.

[James W.]

Modern rubber is why those big fat over-powered post-classic/forgotten-era 4Ts can go so well now.

Back in the day, when Croz tried to match the quicker TZ's on Ross Hannan's big Z1R Superbike,
or later even on the factory 1000cc XR 69 Suzuki F1 racer, he'd start fast, but chew the tyres up.

No doubt modern reed/port packaging & ignition timing control would soften the hit of a hard tuned TZ 4,
(as would -not not having 180`simultaneous firing, by use of a 'crossplane' crank)) .

Aussie World Champ GP rider & Yamaha Factory tuner Kel Carruthers had to detune the original TZ 700's
- from TZ 350 specs, like-wise, due to the `70s era rubber & suspension limitations.

On Kenny Roberts' TZ flat-track miler, ol' Kel even rigged up a primitive traction control device,
a kill button which cut the ignition to one cylinder, for when the roost was getting too hairy, even for Kenny..