hi. i did a bit of search and found almost all inline 4 motorcycles have the below piston running pattern ( including my baby Blade).

which means the outer 2 pistons reach TDC simultaneously and the inner 2 pistons reach TDC simultaneously. (only different engine i've ever encountered was the Yamaha crossplane inline 4 engine)

so is there any specific reason to make it run the outer and inner pairs simultaneously? isn't there any other different piston running pattern for an inline 4 engine? like 1 and 3 reach TDC simultaneously and 2 and 4 reach TDC simultaneously?

according to my search almost all inline 4 motorcycle engines run like the above mentioned pattern. (just the piston running pattern not the firing order). if someone can give a mechanical explanation it will be great thank you

 

A few reasons behind the thinking of Yamahas Crossplane Technology on inline 4s
and
https://www.yamahapart.com/page/crossplanecrankshaft

 

Even though 2 pistons are at tdc at the same time, they are on opposite strokes, thus only 1 is firing at a time. Each piston makes 2 revolutions to fire once.

 

I think that Yamaha crossplane video broke my brain. Okay so instead of a nice 4/4 time, you get a weird jazz drum thing, and that's an improvement...?

Surely the inertial momentum on the crank would be tiny compared to the forces generated by combustion, right? Otherwise the engine wouldn't slow down when you chopped the throttle but just accelerate til death. So I'm no engineer but wouldn't the goal be to get those combustion forces as uniform as possible and live with the smaller inertial force? Maybe tune/balance the crank to minimize? The graph at 3:30 is pretty suspicious to me - would be nice to see some units

But to the OP's original question, now I'm curious too. I would have thought the symmetrical arrangement would be to minimize vibration but that's a wild guess on my part. I'd also like to hear a better explanation

 

F2 firing order is 1 2 4 3. So with that being said it fires from the outside to inside 1,2 then jumps to the outside to 4 then inside to 3 then outside to 1 then 2 so on and so forth, kind of like leap frog, fire two in a row then jump one, then fire two in a row jump another, and on and on.

 

Mmmm I'm staying tuned to this thread.
Well im nit even a mechanics buthole but I'm
thinking it has something to do with balance of the engine
hope some has the true answer as I'm keen to know.

 

You've heard the phrase, 'know enough to be dangerous?' Well, here we go...

The biggest reason is to even out the power pulses. This reduces the forces that the bearings are subjected to. Also, in a flat plane crankshaft, balancing is simplified and manufacturing costs are reduced.

It's also not a good idea to have adjacent cylinders firing. In most engines they'd share a water jacket and localized overheating is a real possibility.

In a four-stroke engine, generally you'd have a cylinder fire at 720°÷N, where N is the number of cylinders. This results in the smoothest stream of power pulses, and in a 4 cylinder, that would mean firing every 180° (1/2 crank revolution). This is NOT written in stone*, but it IS the way to make an engine smooth, and generally that's a desirable thing.

Here's a little vid I found:


*What IS written in stone, of course, is that every cylinder has to fire once every 720°. Whether that follows the 720°÷N formula or not is up to the designer. There have been lots of past examples of what are generally termed 'odd-fire' engines, and in the automotive world these have usually been the result of 'trimming down' a larger motor.

One of the best examples of this is the Buick oddfire V6 motor. In the early 60's, Buick made a very cool 215ci 90° aluminum V8, dubbed the 'Fireball' V8. An aluminum block, heads, and intake from the factory in the early 60's was quite an achievement. In high school, one of my teachers had a '62 Buick with the aluminum 215 engine, and me and other motorheads would pester him after class to pop the hood for us.

Needless to say, this was an expensive engine to produce. Buick sold the blueprints and tooling to British Leyland/Rover in the late 60's (years after Buick ceased production of the motor), and it was only a few years ago that Rover retired the design.

Anyway, also in the early 60's, Buick saw a need for a compact V6, and in essence took the 215 Fireball and lopped off cylinders 7 and 8. This motor was built for mainstream use, and thus was cast iron and not the expensive aluminum. Since they retained the crank journal degreeing (the sharing of crank pins for opposing cylinders) and the 90° cylinder banks, the cam timing was modified to suit a 6-banger and what was left was a bit strange when compared to conventional designs. Only three connecting rod journals on the crank, with opposing cylinders bolted to the same journal: 1&2, 3&4, and 5&6, each one in 90° opposition, with a firing order of 1, 6, 5, 4, 3, 2 (odd on one bank, even on the other). At 0° crank rotation (do not confuse with 0° TDC), #2 fires. 90° later, #1 fires. Now we have a gap from the 'missing' cylinder from the V8 motor, and after #1 fires, we wait 150° till the next cylinder fires, #6. Cylinder #5 is on the same journal, 90° apart, and thus fires 90° after #6. Now another 150° gap, and then #4 fires, followed by #3 on the same journal 90° later. One last 150° wait, then #2 fires, followed 90° later by #1 and we're through the whole order (and then some). So starting from crankshaft 0°, it's 90°, 150°, 90°, 150°, 90°, 150°. The key here is understanding that the odd-fire nature of the engine is forced by the retention of the same crankshaft degreeing and 90° cylinder opposition as the original 215ci aluminum V8 (minus the #7 and #8 cylinders).

What you end up with is BangBang - pause - BangBang - pause - BangBang, the 'pauses' more or less substituting for the missing two cylinders of the 215ci V8 that composed the base design.

No, this is not a smooth motor, but it does have character. Got one in my '69 Jeepster.

RE: The Yamaha above. I suppose you could consider it an oddfire motor, as the firing intervals are 90-180-270-180. Not sure I fully buy Yamaha's reasoning, but I guess the success of the bike more or less speaks for itself, eh? The Honda RC30 and RC45 were also oddfire motors at 90-270-90-270.

Every engineer has a reason for doing what he did. Whether that reason makes sense or not is another question altogether.

 

read all the replies. thank you all. they are very informative

 

Then there are Harley Davidson motors....

2 cylinders both on the compression stroke at almost the same time. The entire next 360 degrees are nothing. The flywheel is so heavy that there is enough momentum to carry the rotation until the next power strokes. They stall every rotation, resulting in the iconic Harley gallop.

 

right got it thank you