Difference in VRod & Airhead Timing?

Ed1955 · Sep 20, 2010

Could someone educate me a little on the timing sequence difference between the Revolution and the Evolution Engines? I once read (but have forgotten) that the air cooled HD's had the "Potato, Potato, Potato..." sound because after one cylinder fires the next one doesn't fire until a 415 degree rest or something like that. So I can sound like I know what I'm talking about could someone tell me what the timing sequence difference is between the two engine designs? I recall something like the airheads firing at 415 degrees and then again at 115 but it was a long time ago that I read it I and forgot the facts and I hate sounding like an ass when talking about stuff like this for obvious reasons. Thanks in advance!
Ed

OutToWinPAHC · Sep 21, 2010

Depends on displacement, compression, cam, but most evo's and shovels run 30-35 BTDC. The sound is actually from the engine design.

"the crankshaft has only one pin, and both piston rods connect to it. This design, combined with the V arrangement of the cylinders, means that the pistons cannot fire at even intervals. Instead of one piston firing every 360 degrees, a Harley engine goes like this:

* A piston fires.
* The next piston fires at 315 degrees.
* There is a 405-degree gap.
* A piston fires.
* The next piston fires at 315 degrees.
* There is a 405-degree gap.

Ed1955 · Sep 21, 2010

Thank You!

That's the answer I was looking for. That being said, does the Revolution engine fire evenly then at 360 degrees or one firing while the other piston is at it's lowest point?

Thanks for the answer on the Airhead motors!
(Below is a photo of my Dream Bike!)
Respectfully,
Ed

OutToWinPAHC · Sep 21, 2010

Yea they are conventional much like a car, and fire every 180 degrees apart.

Vambo · Sep 21, 2010

The Revo has a more standard or conventional firing pattern where 1 cylinder is TDC the other is at bottom. The Evo's fire very quickly 1 piston is TDC and the other is right behind it and fires very quickly, hence the "potato" sound. This is a big reason for their unique sound.

Z16monte · Sep 21, 2010

Vambo said:
The Revo has a more standard or conventional firing pattern where 1 cylinder is TDC the other is at bottom. The Evo's fire very quickly 1 piston is TDC and the other is right behind it and fires very quickly, hence the "potato" sound. This is a big reason for their unique sound.

I disagree,with a single pin crank and a 60deg vee. when 1 cyl is at TDC the other is either 60deg behind or ahead of tdc. Cam timing will determin whether its on compression or exhaust stroke In order to be at TDC/BDC the crankpins would have to be seperate or it would have to be a flat twin ala BMW.

Ed

Vambo · Sep 22, 2010

Z16monte said:
I disagree,with a single pin crank and a 60deg vee. when 1 cyl is at TDC the other is either 60deg behind or ahead of tdc. Cam timing will determin whether its on compression or exhaust stroke In order to be at TDC/BDC the crankpins would have to be seperate or it would have to be a flat twin ala BMW.

Ed

There is a thread here somewhere documenting this but I don't care to search. That was just a loose description to make the point. Not 100% sure of the "exact" firing sequence but absolutely NOT nearly as close as the Evo fires. NOBODY else fires that close!!! LOL! The Revo is a more commonly used and efficient pattern.

Z16monte · Sep 22, 2010

Vambo said:
There is a thread here somewhere documenting this but I don't care to search. That was just a loose description to make the point. Not 100% sure of the "exact" firing sequence but absolutely NOT nearly as close as the Evo fires. NOBODY else fires that close!!! LOL! The Revo is a more commonly used and efficient pattern.

I'm guessing, but not sure. 720 deg to the combustion cycle, piston 1 fires at 0, 2 fires at 300 deg, 1 fires again at 720.
Ed

Difference in VRod & Airhead Timing?

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