2 stroke comeback.

[Keltik]

Crossplane crank for novelty purposes?

I'm sure there's an engineering reason to do it but I just want to hear what it sounds like.

[Paul]

Crossplane crank for novelty purposes

On a 4-cyl 2-stroke? It would be terrible for vibration.

[Jeff B]

On a 4-cyl 2-stroke? It would be terrible for vibration.

I will have to have cross plane crank if I want even 90 deg firing order....
That was the plan....

[Kakapo76]

Crossplane crank for novelty purposes?

 

I am now fully aroused.... 

[Jeff B]

Am I missing something here? What's good about a crossplane crank? It's just the firing order....
I don't really want to go flat plane like a 4 cyl 4 stroke as that will be firing 2x cylinders at same time.
I'm not sure why Yamaha did it on their R1? It just makes an uneven firing order and sounds like a v4...

[Paul]

Crossplane only really makes any sense on a 90degree V8.

I don't really want to go flat plane like a 4 cyl 4 stroke as that will be firing 2x cylinders at same time.
I'm not sure why Yamaha did it on their R1?

Smoothness and vibration - controlling the opposite mass-oscillations.

[Kakapo76]

a good explanation of the relative merits.

https://www.youtube.com/watch?v=-s5bSQIQQsY&ab_channel=EngineeringExplained

[Keltik]

One consideration for your crank phasing could be running dual expansion chambers with cylinders paired together.  I think snowmobiles might do that kind of thing

[Kakapo76]

Hey Jeff,

I found a channel you might find interesting/ useful- got some cool experimental 2 stroke tuning stuff.

https://www.youtube.com/channel/UCHRXYmO1vdp-Bi1-w11R7WQ

[powerband]

Hi Jeff,
The Yamaha TZ750 straight 4 is 1&4 TDC then 2&3 TDC. Folan, a Swedish engineer built a 1,000cc twin both @ TDC for torque, then split crank to 180 for power, fast or slow tracks for MX sidecar racing.
Paul.

[Jeff B]

Hmmm interesting, weren't the TZ 700s and 750s in essence 2x TZ 350s joined together? (2x seperate cranks)
I guess glavine 1,4 down and 2,3 up @ 180 deg will be the best for balance but I'm not sure if the crank will like firing 2x cylinders at once?
All the 2 stroke 4 cylinder outboards seem to fire at 90 deg evenly (cross plane crank)
And I think that would sound better,?
In motorcycles, the "twingles" always sounded a bit off....

[orac12]

I think there is a couple different theories in the motorcycle world to do with big bang or screamer firing order setups. The big bang, giving more time for the tyre to relax and regain grip between combustion cycles.
Where as a screamer the combustion cycles are evenly spaced and provide more consistent power.

Not sure how it would affect a jetboat,big bang firing order might be hard on splines ? 

[Jeff B]

I think there is a couple different theories in the motorcycle world to do with big bang or screamer firing order setups. The big bang, giving more time for the tyre to relax and regain grip between combustion cycles.
Where as a screamer the combustion cycles are evenly spaced and provide more consistent power.

Not sure how it would affect a jetboat,big bang firing order might be hard on splines ?

Yeah that's what I believed also.
An even firing pulse always seemed like a better option to me.
I'm not sure why Yamaha adopted the cross plane crank for their R1? Lots of mumbo jumbo about torque transfer and traction but I just cant like the sound it makes Haha.
I dont need uneven torque pulses or traction aid.....I hope....

[orac12]

I think the smoother output of the screamer setup would be the way to go in a jetboat.

[Warwick Marflitt]

Next project will be 9 cylinder radial powered Gnome style engine...with a stationary crank,the block and cylinders all rotating en mass!! Jeff's trickiest waterjacket creation yet???
Power strokes evenly spaced across the cranks duration is more linear and smoother than twin firings at 180.... imagine a two pole electric motors power/torque delivery?? And then a 30 pole/cyl = one power stroke/push every 12deg of crank rotation probably why the Americans built the 36cyl 127litre  Lycoming XR-7755 5,000hp radial...