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.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.
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.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.
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).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.