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Old 08-08-2014, 07:34 AM   #1
Gundy OP
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Firing order

What are the typical characteristics of the different firing orders?

I owned a super Tenere which I guess is a 270 degree parallel. Nice bike, not so exciting in the engine department, maybe just because it's a giant pig. Same for the triumph scrambler, nice bike but the engine just isn't that exciting. Rode a Vstrom 650, very smooth, but not necessarily adrenaline inducing. Rode a twin cylinder f650gs, and while there wasn't a ton of power, I loved the feel of the motor, which I think is a 360 firing. I mostly ride thumpers, and like them so maybe there is a familiarity thing here. And, there are some other factors at play here like power to weight ratio, total weight, fuel mapping etc.


This leads me to wonder...what other 360 degree twins are out there that would fit a taller rider, besides the F800gs?
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Old 08-08-2014, 08:48 AM   #2
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Talking

Let's see ... firing order of a twin - I think its 1-2-1-2- ... or is it 2-1-2-1- ... shit ... I can't remember!!
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Old 08-08-2014, 09:27 AM   #3
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You are one of the few that prefer the vertical 360 twins. It takes 2 revolutions of the crank to complete all 4cycles of 1 cylinder. On the 360 degree vertical twins, both pistons rise and fall together with 1 piston having a power stroke on each revolution. The cranks slows at TDC an BDC. That is a lot of reciprocal weight that needs to be offset with some type of counter weight. BMW has that, besides quelling some vibes, in changes the direction of them from up and down to fore and aft with a weight connected to the crank that moves in that direction.

The other 3, have 270 degree cranks or are 90 degree offset V twins. 1piston has a power stroke at 270 degrees of crank rotation the other 450 degrees of crank rotation later. Most find them smoother running, because some of engine mass is canceling vibration. In theory the greater distance between power strokes allows the rear tire to gain traction.

Engine design is not why they bikes feel bland to you. They could be tuned for more power, but it would occur higher in the RPM range, Ducati is an example of that. It depends on what the manufacture is attempting to accomplish. These are generally adventure bikes that in theory will see some dirt and low rpm, high torque engines generally are easier to ride in that environment.
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Old 08-08-2014, 03:18 PM   #4
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Quote:
Originally Posted by itsatdm View Post
You are one of the few that prefer the vertical 360 twins. It takes 2 revolutions of the crank to complete all 4cycles of 1 cylinder. On the 360 degree vertical twins, both pistons rise and fall together with 1 piston having a power stroke on each revolution. The cranks slows at TDC an BDC. That is a lot of reciprocal weight that needs to be offset with some type of counter weight. BMW has that, besides quelling some vibes, in changes the direction of them from up and down to fore and aft with a weight connected to the crank that moves in that direction.

The other 3, have 270 degree cranks or are 90 degree offset V twins. 1piston has a power stroke at 270 degrees of crank rotation the other 450 degrees of crank rotation later. Most find them smoother running, because some of engine mass is canceling vibration. In theory the greater distance between power strokes allows the rear tire to gain traction.

Engine design is not why they bikes feel bland to you. They could be tuned for more power, but it would occur higher in the RPM range, Ducati is an example of that. It depends on what the manufacture is attempting to accomplish. These are generally adventure bikes that in theory will see some dirt and low rpm, high torque engines generally are easier to ride in that environment.
Now that is a good rundown.

More here..[excuse the slightly tossy PR video]



And Ash [RIP] did a good article that's a bit dry....
http://www.ashonbikes.com/inertial_torque

360 degree crank...


270 degree crank...


Firing intervals 270, 180, 360..


So I suppose it depends whether you like Krautrock or Jazz.
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Old 08-09-2014, 03:54 AM   #5
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Thanks - all great info. The differences I noticed in the bikes above probably has far more to do with other factors, but still good to know as I am looking around for my next ride.
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Old 08-09-2014, 05:20 AM   #6
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So out of curiosity. What is the BMW engine? I know the Super T is the 270 degree crossplane. What is the BMW? 360? 180?
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Old 08-09-2014, 05:45 AM   #7
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The crank is 180, but the firing is 360 due to the layout. The idea is the pistons(and the mass associated with them) moving in the opposite direction cancel each other out as far as vibration goes.
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Old 08-09-2014, 08:36 AM   #8
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The F800 is a 360 twin, see Graham D's first video. The pistons rise and fall together and there is only 1 way to do that on a vertical twin.

Some Japanese vertical twins have offset 180 degree crankshafts. The pistons do not rise and fall together. They are designated as 180 twins and the firing order is 180 and 540 degrees.

BMW flat twins have 180 degree offset cranks, but the pistons extend and retract at the same time. They are designated as 360 twins, despite the crankshaft being a 180 type, because the firing is still 360 with one piston firing on every 360 revolution.

Confused yet? It is the firing order not the means to achieve it, that determines type.
Argument to follow.
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