[Eric750]

has any one ever split the crank on a cb350?
i mean trun it 180 and make a thumper out of it.


eric750

 

[Geeto67]

I'm sure someone has but why would you want to? There are bigger singles out there than the cb350 (you can bore and stroke a new enfield 500 single to 750) plus I think you would actually lose power by going to a twingle.

 

[jbranson]

I think he means turning it into a 360 degree engine. Common misconception that 360 degree twins fire both cylinders at the same time. Both piston go up and down at the same time....they fire alternately....like many many british twins and some small Honda twins.
Problem is you have to have the cam reground..a 180 degree cam won't work with a 360 degree crank of course.
JohnnyB

 

[Geeto67]

quote:
I think he means turning it into a 360 degree engine. Common misconception that 360 degree twins fire both cylinders at the same time. Both piston go up and down at the same time....they fire alternately....like many many british twins and some small Honda twins.
Problem is you have to have the cam reground..a 180 degree cam won't work with a 360 degree crank of course.
JohnnyB

He said thumper, a thumper is a single or twingle so I assumed he meant a twingle (both pistons fire at the same time). Of course a true twingle also has a shared combustion chamber so that the rods have equal pressure exerted on them. Neat idea but too much work for not enough gain. These days you can get a brit single for the price of a nice condition cb350.

About the small honda twins, a trick a friend of mine told me about how to get your cb77 superhawk to sound like a brit twin was to swap the bottom end with that of a honda dream.

 

[FR]

I've only heard the term "twingle" in reference to V-twins, where the crank and cam timing can be altered to fire the cylinders sequentially, to allow for a longer period between power pulses, as opposed to alternately. The advantage to sequential is that it allows more time between power pulses, which enhances traction.
I would think that in a vertical twin if both cylinders fire at the same time you'll have other things than traction to worry about...like reliability.

FR

 

[Geeto67]

quote:
I've only heard the term "twingle" in reference to V-twins, where the crank and cam timing can be altered to fire the cylinders sequentially, to allow for a longer period between power pulses, as opposed to alternately. The advantage to sequential is that it allows more time between power pulses, which enhances traction.
I would think that in a vertical twin if both cylinders fire at the same time you'll have other things than traction to worry about...like reliability.

FR

puch used to make a parallel Twingle, there are others too but I am blanking on them. It was basically two pistons with a shared combustion chamber. It was a fairly reliable engine. I'm not exactly sure why they built that instead of a regular single or a true twin. A true twingle has a shared combuston chamber so that equal pressure is exerted on both pistons so as to avoid unequal stress on the rods.

 

[jbranson]

The Puch Twingle was a two stroke wasn't it? Sold under the Alstate name by Sears. Also I'm pretty sure the cylinders were one behind the other with a very strange crank setup.

Didn't think you could build a four stroke twingle. I'm pretty sure the origin of the word twingle was in description of these strange Puch and other European twin cylinder two strokes.

Course...who knows...maybe it means a set of unmarried siamese twins.
JohnnyB

 

[Geeto67]

quote:
The Puch Twingle was a two stroke wasn't it? Sold under the Alstate name by Sears. Also I'm pretty sure the cylinders were one behind the other with a very strange crank setup.

Didn't think you could build a four stroke twingle. I'm pretty sure the origin of the word twingle was in description of these strange Puch and other European twin cylinder two strokes.

Course...who knows...maybe it means a set of unmarried siamese twins.
JohnnyB

Ossa and puch both had 250 and 350 cc 2 stoke twingles. I can't think of any factory produced 4 stroke twingles but I do know that in the 60's and early 70's a lot of dirt and hillclimb riders would convert brit 360degree crank bikes to twingles because the powerpulses worked better for traction in the dirt. There used to be a kit to convert 500 and 750cc triumph twins, I think one of my father's freinds still has one (came with cam and a mag ign).

 

[jbranson]

I guess and advantage to a two cylinder "twingle" four stroke would be that effectively you'd make close to the same hp as a 4 valve single of the same displacement. And like you said...leave plenty of time for the tire to hook up.
JohnnyB

 

[chewbaca]

They used to twingle 650 yamahas on ocasion for certain dirttrack situations. Decreased power plulses for tire grip. Lower horsepower higher torque.

Sweet can only be completely appreciated if you have experienced sour.

 

[mikeo]

The Puch "twingle" was a two stroke and the front smaller piston was actually an exhaust scavange device. It didn't actually transmit powet to the crank but I think it enhanced compression and helped pull exhaust gas out of the main piston.

The Honda 305 engine was made as a 360 degree engine for police work. Its designation is "CP" and not "CB" "CA" or "CL" etc. The Dream (CA) had a 360 crank I believe but a really wrong cam shaft for any serious power. I suppose one could get the cam ground for better power but if you go the 305 route why not get the kit and make it a 350? The only advantage to a 360 degree twin that I know of is that tuned length collector pipes add power. It just seems like a lot of work for not a lot of result.
Just my two cents worth.

Mike O

 

[jbranson]

Same thing I've heard Mike....there have been people that have changed the 175 360 crank to a 180....no apparent difference in power either way...just a different sound. Never heard anyone say it was worth the effort on bikes tuned to the moderate level our vintage race bikes are.
JohnnyB