re-phase a CS style 2 cylinder engine?

[Quinnf]

Evidently there are tradeoffs.  Two Japanese twin cylinder engines that I busted my knuckles on were used in Honda motorcycles in the 1960s-1970s.  The Honda 350 had a 180 degree crank, while the 175 had zero degree offset.  The 175 was a remarkably smooth and quiet running engine.  The 350 ran rougher, but made a wonderful sound when it was revved up.  Why the Japanese designers chose to make one engine one way, and its sibling the other is something that I've never understood.  And why makers of a popular home-grown v-twin intentionally make the cylinders fire out of synch with the mechanical balance totally escapes me.  But I think the reason has something to do with testosterone and what it does to the brain of the human male.

The reciprocating mass in a heavy slow turning engine like a 12/2 just about necessitates a 180 degree crank to avoid hopping or placing too much load on the bearings.  The downside of that is that the engine will tend to want to rock back and forth along the axis of the crankshaft from the reciprocating forces.  A zero offset twin is inherently better mechanically balanced, and that's a configuration that makes sense so long as the reciprocating mass can be kept low.  

Quinn

[Tom]

I busted my knuckles on a '65 Honda 150 and it was a 0 deg engine too. But strangely enough they were reputed to have crank issues and guess what, this one did too.

[richardhula]

Doug,

I believe the Lister twin cylinder designs are all staggered at 180 degrees... and the power strokes are also 180 apart.

I have heard some commentary about an old John Deere design that they modified in the way you suggest but they kept breaking crankshafts.


dieselgman

Which gives that lovely characteristic twin sound.

With the triples, JP3's at least the 120° crank makes for even firing with a bang every 240°.

Following on from the above references to motorcycle engines, Laverda the Italian farm machinery company who also happened to make motorcycles, produced two versions of their Jota triple 1000cc bike. The original 180° crank version which gained the accolade of worlds fastest production motorcycle in the late '70's, and the later smoother Jota 120 with 120° crank although they did rubber mount this engine as well.

Just imagine what they could have done to a combine harvester

[buickanddeere]

Interestingly, the lister twin exhaust note sounds much like a single. Especially with a 2 into 1 system. My system has 2 mufflers (not a 2 into 1) and I am unable to discern each cylinder individually.

It is a single exhaust note as the exhaust valves opening overlap

[Tijean]

I think the explanation for the sound of the twin is a bit trickier.  On the upright twin the crank throws are offset 180 degrees for balance reasons. Being 4 stroke cycle each cylinder fires once every two revolutions or once every 720 degrees. Thus you will have total of two ignitions every 720 degrees.
Being offset 180 degrees the second cylinder must fire either 180 degrees afterward or 180 + 360 = 540deg afterward depending on which cylinder you consider to be first firing. The other way of seeing it is ignition, pause 540 deg, ignition then pause 180 and repeat. The resulting pp, pp.......... pp, pp,  has the same cadence as a single. Only it were two stroke cycle could the power pulses come evenly 360 degrees apart and give us a pup, pup, pup!

Frank

[buickanddeere]

I believe that was the issue with the experimental John Deeres breaking their crankshafts.

dieselgman

What broken Crank shafts ?  Only two cylinder Deere that broke cranks was the R which was the only diesel with a two bearing crank.If hopped up for more power and lugged hard pulling an oversized plough.

[dieselgman]

Sorry, I cannot remember the JD model mentioned in that conversation but it was stated by a guy who seemed to be in the know. That is a problem with anecdotal and third-hand references to such things. I do not believe there was any intent to complain about John Deere in any way, but rather a general reference to such design changes.

dieselgman