bpastorb
XS650 Member
As the title says. I know hugh says on his website he builds both but advertises the 277 degree re phase mainly. Is there a reason that the 277 degree seems to be more popular (more power, better all around, etc.)?
-
Enjoy XS650.com? Consider making a donation to help support the site.
XS650.com receives a small share of sales from some links on this page, but direct donations have a much greater impact on keeping this site going.
What is the difference between a 277 and 270 degree re phase?
mrriggs
XS650 Junkie
The 277 crank is cheaper and easier. You simple split the crank, turn it three splines and put it back together.
The 270 crank requires parts from two cranks, a custom machined center pin, and some fabrication work.
The 270 crank requires parts from two cranks, a custom machined center pin, and some fabrication work.
jd750ace
Front Toward Enemy
What is 7 degrees, Alex! I thought the 277 was the easier one.
It is, like mrrigs said, Use the 1 crank, take it apart and turn one half 3 splines on the shaft and put back together. give you a 277 off set. Cheap and little vibration compared to the 180 crank
divide 360 by 4 = 90 x 3 = 270. theoretically there should be no vibration.
divide 360 by 4 = 90 x 3 = 270. theoretically there should be no vibration.
So you are saying is should be called 83 and 90 re-phased. I was pointing out it is an even no. Commonly called 270/277?
yamaman
xs650 addict
- Messages
- 734
- Reaction score
- 44
- Points
- 16
no, 270/277 is correct. not sure where you got your formula 360/4=90, 90 x 3 = 270? 90* (think ducati) and 270* (think the new super tenere, TRX 850 orTDM 900) are essentialy the same. I think Phil Irving came up with just under 90* as being perfect balance
Posted via Mobile
Posted via Mobile
Punkskalar
Hugh's HandBuilt
I have a few 270 Degree Crank Pins in stock. They are $$$$ so no one uses them. The 277 is more popular due to cost...
mrriggs
XS650 Junkie
Yep, I haven't had any on ebay lately because they are selling faster than I can make them.
Only a true 90° V-twin can cancel all vibration. With a non-counterbalanced parallel twin there will always be vibration, no matter how you phase the crank.
The stock firing order is 360/360, meaning the crank turns 360° between each power stroke. When you re-phase the crank 90° you subtract 90 frome one side and add 90 to the other. That makes the firing order 270/450. Re-phasing the crank 83° gives you 277/443. These are simply refered to as 270 and 277.
If you call it a 90 or 83 then that would be refering to a "big bang" motor where the firing intervals are 90/630 and 83/637. These combos use the same crank configuration as the 270 and 277 but the cam lobes are moved around further.
My formula was referring to the placement of the crank big ends, compared to each other, on a horizontal/vertical axis. 90* offset is an even no and 1/4 of 360 The graph here shows the difference in inertia force. Using that graph on a 277* crank offset if one is 45* the other will be 52* To me i see that is why the 277* gives you the high vibration caused by the offset. The graph shows that a 270 will also give you some vibration.
I realize it is the cost factor, why the 277 is preferred over the 270.
I realize it is the cost factor, why the 277 is preferred over the 270.
mrriggs
XS650 Junkie
That graph is not entirely accurate. It appears to only be showing the primary inertia force. When you add to it the secondary inertia force it looks a bit different.
I ran the actual numbers for an XS650.
On the XS650, maximum piston speed is reached at 74° which is represented by the 286° interval on the chart.
The 270° is slightly better than the 277° but not by much.
The real interesting thing is that the peaks for the 270° are out of phase by 45°, and the 277° is out of phase by 42°. If I'm reading that correctly then the counter weights on the crank should be offset from the center line to properly balance it. [Never mind. It just occured to me that the offset happens automatically since the center of mass of two weights 90° apart will be at 45°.]
Note: This chart is only showing the inertial force of the pistons on a single plane. It is not factoring the forces of the crankshaft or rocking couple. I'll add that in there as soon as I figure out how to calculate it.
Last edited:
mrriggs
XS650 Junkie
Here is the up/down vibration after adding the crankshaft.
Unfortunately, since the counter weights on the crank are moving in a circle, they don't just move up and down but also front to back. So we now have a front to back vibration also.
I set the balance factor for each combo so that the peak up/down force matches the peak front/back force.
360 = 64%
286 = 55%
270 = 50%
277 = 53%
180 = 0%
These are the "perfect" balance factors. As you can see, it is not possible to perfectly balance a non-counterbalanced parallel twin. Increasing the balance factor will reduce the up/down vibes but increase the front/back vibes, and vice versa for decreasing the balance factor.
Notice the 180° has no front/back vibration. This is true regardless of the balance factor. The same with the up/down vibes. No matter how you set the balance factor, the 180° will not change on either of these charts because it has a perfect primary balance. All the vibration you see in the up/down is secondary vibration.
So far, the 180° looks like the best combo but that is only because we haven't calculated the rocking couple yet.
Unfortunately, since the counter weights on the crank are moving in a circle, they don't just move up and down but also front to back. So we now have a front to back vibration also.
I set the balance factor for each combo so that the peak up/down force matches the peak front/back force.
360 = 64%
286 = 55%
270 = 50%
277 = 53%
180 = 0%
These are the "perfect" balance factors. As you can see, it is not possible to perfectly balance a non-counterbalanced parallel twin. Increasing the balance factor will reduce the up/down vibes but increase the front/back vibes, and vice versa for decreasing the balance factor.
Notice the 180° has no front/back vibration. This is true regardless of the balance factor. The same with the up/down vibes. No matter how you set the balance factor, the 180° will not change on either of these charts because it has a perfect primary balance. All the vibration you see in the up/down is secondary vibration.
So far, the 180° looks like the best combo but that is only because we haven't calculated the rocking couple yet.
Both graphs show quit a marked difference between the 270 and 277. Have you built or ridden a 270 and noticed the difference between the 2, vibration wise?
jd750ace
Front Toward Enemy
Looks to me like you would need an accelerometer to tell the real difference between a 277 and a 270, but then again, we are just looking at paper. Isn't and inline 6 cylinder supposed to be the "perfect" arrangement for dealing with primary, secondary, and rocking forces? I think I've read a couple of times that it falls to near perfect balance.
Is the offset of the pulse ( the out of phase part) similar to dynamic angular progression? I know in order to induce forward tilt in a helicopter rotor, the swashplate has to be moved in an advanced position in order for the incidence to change at the desired centerline of the longitudinal plane, same for roll.
The same can be demonstrated with the spinning wheel with the axle in your hands. When you induce action at the axle, the reaction is 90 degrees out of phase with your input, I.E. when you try to turn it in a horizontal plane to the right, what it actually does is tilt to the right in the vertical plane.
Is the offset of the pulse ( the out of phase part) similar to dynamic angular progression? I know in order to induce forward tilt in a helicopter rotor, the swashplate has to be moved in an advanced position in order for the incidence to change at the desired centerline of the longitudinal plane, same for roll.
The same can be demonstrated with the spinning wheel with the axle in your hands. When you induce action at the axle, the reaction is 90 degrees out of phase with your input, I.E. when you try to turn it in a horizontal plane to the right, what it actually does is tilt to the right in the vertical plane.
Tomterrific
XS650 Junkie
Mr. Riggs, I've eagerly followed your posts for a very long time and I want to thank you for patiently sharing your engineering expertise that is so difficult for the majority of XS650 enthusiasts. Thanks!
Phil Irving was the first I'm aware of to suggest the offset on British 360° parallel twins. His thinking was the piston is stopped at TDC so must rapidly brake to a stop and imeadietly accellerate to maximim velocity. He surmised that the point of maximum piston speed of one piston should be when the other is at TDC. This is where the rod and the crank throw make a 90° angle. A Triumph has this at 77° and is the angle Irving suggested. Even though top motorcycle engineers must have understood Irving's concept, it was many years before a few skilled hobbyists proved Irving was right!
As an aside, the rocking couple of a 180° crank is very disturbing to me. I think it must be the frequency or the buzzing of the footpegs that drives me nuts. I have had 360° twins for many years and they vibrate but it doesn't effect me until higher rpm. I'd like to experience a 277° XS but I'm fearful I wouldn't like to live with the lumpy take off or the rocking couple, no matter how slight.
Tom
Phil Irving was the first I'm aware of to suggest the offset on British 360° parallel twins. His thinking was the piston is stopped at TDC so must rapidly brake to a stop and imeadietly accellerate to maximim velocity. He surmised that the point of maximum piston speed of one piston should be when the other is at TDC. This is where the rod and the crank throw make a 90° angle. A Triumph has this at 77° and is the angle Irving suggested. Even though top motorcycle engineers must have understood Irving's concept, it was many years before a few skilled hobbyists proved Irving was right!
As an aside, the rocking couple of a 180° crank is very disturbing to me. I think it must be the frequency or the buzzing of the footpegs that drives me nuts. I have had 360° twins for many years and they vibrate but it doesn't effect me until higher rpm. I'd like to experience a 277° XS but I'm fearful I wouldn't like to live with the lumpy take off or the rocking couple, no matter how slight.
Tom
Last edited:
mrriggs
XS650 Junkie
I'm with you on the 180°. I like the vibration of the XS650 and, compared to that, my XS400 was too smooth. In addition to the smoothness, it also has an obnoxious buzzy vibration. I know it sounds silly to say that a motor is too smooth AND has an obnoxious vibe but that was always my perception when riding it.
I was disappointed the first time I rode my re-phase and felt some of that annoying buzzy vibe. But, unlike the XS400, it still has plenty of good vibes and I was able to get used to the buzziness. It'll still vibrate your feet off the side of the pegs, though.
I can't say I've ever noticed a lumpy take off. Quite the opposite really. Remember that the pistons are adding to the flywheel effect. Yes it has uneven firing intervals but you've only changed the longest interval from 360° to 443° (out of a possible 720°) so it's not like we are talking about a "big bang" motor.
jd750ace
Front Toward Enemy
With a re-phase, you should get a longer torque pulse, with the overlap of the power strokes.
A big bang twin would act more like a single or twingle with a real heavy crank, would it not?
Longer pulse versus stronger pulse?
A big bang twin would act more like a single or twingle with a real heavy crank, would it not?
Longer pulse versus stronger pulse?
mrriggs
XS650 Junkie
The idea with a big bang is to hit the tire with one big pulse while it has traction. Static friction is greater than kinetic friction so the tire will take a bigger initial hit. It will also have longer between pulses to regain traction should it slip.
It seems to me that the full on 720 big bang is a bit overkill. The static friction is not twice the kinetic friction so why hit the tire with twice the force. I'm guessing you would only want to add 25-50% to the peak. To do that you could offset the cycles so they partially overlap. A 90/630 firing order would probably be too far spaced. A big bang Harley at 45/675 would probably be better. Maybe less, 20/700 or 30/690?
It seems to me that the full on 720 big bang is a bit overkill. The static friction is not twice the kinetic friction so why hit the tire with twice the force. I'm guessing you would only want to add 25-50% to the peak. To do that you could offset the cycles so they partially overlap. A 90/630 firing order would probably be too far spaced. A big bang Harley at 45/675 would probably be better. Maybe less, 20/700 or 30/690?
