XS650: Twingle

The Urban Dictionary describes Twingle as:

• A contraction of the words Twin and Single. A twin cylinder motor running a close firing order ignition timing that mimics a single cylinder motor to provide better traction. Most commonly used in reference to motorcycle flat track racing. Referred to as a “big bang” motor when used in reference to multi cylinder machines

• To twingle : such a state of euphoria that your entire body has the feeling of being asleep, but doesn’t hurt. It’s like when your foot falls asleep but covers your entire body from head to toe, and doesn’t hurt when you walk

• An internal combustion engine in which more than one piston is actuated by a single connecting rod (often “V” or “Y”-shaped)

• to play with

• When an individual, usually a young pre-teen girl, decides to “save herself” for Edward Cullen, forgetting he is a fictional character.These individuals are usually found in groups, and can be heard screaming at the mere sight or mention of said fictional character.

• The slightly painful tingling, itching, arousing feeling felt in the balls when thinking about, watching, or hearing the “dog-in-a-tub” sexual manoeuvre being performed.

Originally these were 2 stroke, pistons travelling together, sharing a common combustion chamber. One cylinder was responsible for intake. The other for exhaust. When more than one exhaust pipe was used, they came from the same cylinder.

From Wikipedia:

• A twingle is a 4-stroke twin cylinder engine with an altered firing order designed to give power pulses similar to a single cylinder four-stroke engine. It is well known that four-stroke singles “hook up” better than two-strokes in the dirt. This is because four-stroke singles have half as many power strokes per crankshaft revolutions as a two-stroke single. This creates a recovery gap  during which the rear tyre regains traction.                                   Inline twins with a 360° crankpin offset or flat-twins can be easily converted into twingles by firing both of the cylinders at the same time and installing a camshaft or camshafts that operate both cylinders’ valves in parallel. Because many such engines already employ the wasted spark principle, only the camshaft modification is necessary. The Vintage Dirt Track Racing Association (VDTRA) 2010 Rules have banned vintage motorcycles from being setup as a twingle

This became popular in flattrack racing. ‘Big Bang’ engines. Due to the recovery gap. Banned in ’07 (AMA). Harley riders will tell you this was because of the cost of replacing parts. More likely the Harley lobby was concerned about losing it’s advantage.

Twingling is easily done on our XS650s. A matter of replacing the cam. Ignition is already wasted spark.

 

twingled cam

 

 

twingle vs standard cam

 

 

The bloke that made this cam had this to say:

• This is an XS650 cam which I reground for .060″ more lift intake and exhaust, then parted on a lathe, sleeved, and welded back together 180 degrees out of phase.  This cam will make your XS650 fire both cylinders at the same time! …  This cam was from a 1978 XS650, but should be used with an earlier compression release system in which there is an extra lever on the bar that keeps the left side exhaust valve open.  I tried installing pop off compression release valves, and there still wasn’t enough relief!  I recommend this cam for race use only.  The only way I could get the bike started was on a jumper.  It ran like a demon, with double the torque.  The front wheel would come up in first and second on the throttle!  The problem was that I couldn’t stop anywhere because I’d never be able to get the bike restarted without the jumper.  The sleeve in the cam is 4140 tool steel bored through to accommodate a Boyer ignition.  The weld is extremely strong.  The cam looks a little rough because I reground it on a WWII era tool grinder!  Please keep in mind that I have made race winning cams reground on the same grinder!  This concept was never intended for the street…