Can anyone tell me how 270 degrees is arrived at?
As I understand it, the cycle begins with combustion in the right cylinder, after the piston powers down to bdc, the crank has now rotated 180 degrees. The left piston is now at tdc and combustion occurs driving that piston to bdc. Two power strokes have been completed in the first 360 degrees of crank rotation with the two firing events occurring 180 degrees apart. So far, this is pretty clear to me and I think I am on track.
Backing up a little, when the left piston is heading downward on its power stroke the right piston is headed back up evacuating its spent fuel charge. When it reaches tdc it is ready for its fuel intake stroke. But, without a power stroke to drive it onward, it relies on momentum to draw it back down, pulling in fuel charge. At bdc the crankshaft has now rotated 180 degrees without a power stroke. The right cylinder is charged, its intake valve closes and its piston, continuing on momentum, travels back up to tdc, compressing the fuel charge in anticipation of spark and combustion. The crankshaft has now rotated 360 degrees without a power stroke. Left side is following 180 degrees behind compressing its fuel charge in anticipation of spark and combustion. No matter how many times I go through this I don't get 270 degrees or 540 degrees. I keep coming up with 180 and 360.
Thanks
Steve
360 to 180 degree crankThe total cycle for a 4 cycle engine is 720 degrees and a 360 engine fires once every 360. I.e 0 degrees 360 then 720 (back to 0)
If the tw crank throws are 180 apart the interval will be 0, 180 , 720 (back to zero) Subtract 180 and you get 540 as the long interval. The 270 is a 'red herring' which arises from some 360 twins (Triumph, Norton, Yamaha) which have been converted to 90 deg crank throws. G '60 C77 '60 C72 '62 C72 Dream '63 CL72
'61 CB72 '64 CB77 '65 CB160 '66 Matchless 350 '67 CL77 '67 S90 '77 CB400F When I said the pistons are opposite I meant when one piston is at tdc the other is at bdc no matter which stroke its on. This would be better for the balancing of the crank not having the mass of two pistons moving together side by side. The CA set up similar as a big single.
So to recap The Cb engine can rev higher, is easier to start, develops more power and is better balanced so what has the CA got going for it. The only thing is the sound there must be more to it than that. CA fire fire fire fire fire fire fire fire CB fire fire fire fire fire fire fire if its not broke don't fix it.
Aermacchi ss350 Gilera 124 James SC1 Scooter Honda CA77 It's a cheaper engine. One carb, one set of points, one coil etc.. Difficult to do the single carb with a 180 degree motor.
The smooth sound was thought to be important when competing with British bikes. CB160, CD175 and so on kept that nice 360 crank sound. G '60 C77 '60 C72 '62 C72 Dream '63 CL72
'61 CB72 '64 CB77 '65 CB160 '66 Matchless 350 '67 CL77 '67 S90 '77 CB400F that last post of mine didn't work out quite right, the fire fire bit. I left spaces between the fire words but they are missing I will try again.
Ca bang miss bang miss bang miss bang miss Cb bang bang miss miss bang bang miss miss If that makes sense Now then its cheaper to make that makes more sense. I can see that. if its not broke don't fix it.
Aermacchi ss350 Gilera 124 James SC1 Scooter Honda CA77 Sound was very important. I remember back in the early 1970s my friend Alans CB160 sounded quite powerful for its size. It was a very cool bike. He had a single seat, a sissy bar and a Captain America tank. So did snotty Gregs SL175, thinking back on how it sounded it must of also had a 360 crank. Having only owned singles up to that point I didn't know about type 1 verses type 2 motors. I knew Ralphies 305 Scrambler sounded flat out mean, but I thought that was due to its straight pipes. I think this is kind of funny, but until I got into restoring old Hondas I didn't even know Scramblers came with a muffler. The owners must of removed them as soon as they got them home.
Haste makes waste..........my mistake............on the 270...........G-Man has it correct.
Pie.........The CL72 originally had baffles only.......no muffler. In '64 a spark-arrestor was added with baffles in the pipes and one baffle-plate in the "guppy-muffler". I think it was '66 when the twin baffles began in the slip-on muffler. Then in late '66 and all of '67 the muffler was welded to one pipe. When my in-laws sold their 1960s house, my brother-in-law came home to reclaim his muffler that he had removed from his '66 Scrambler. It was still hanging on the peg-board in the garage.
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