bonneville piston movment

[phil]

I have a quick question do the pistons on the Bonneville move up and down at the same time or do they alternate.. This was the conversation at the coffee table tonight I though I would ask the experts.. :up: thanks guys. I feel kinda silly asking , but if you don't ask you don't learn.

 

[sweatmachine]

up and down together, on opposite strokes.

 

[sharp21]

Depends on which motor you have, a 270 or 360.

This is determined by how the crank shaft is staggered. For a 270 the power stroke of the first piston is followed 270 deg later by the power stroke of the second piston. So the piston rods connect to the crank 90 deg apart from each other if that makes sense.

On a 360 deg motor they are connected on the same plane & DO travel up & down together, but one piston will be on its power stroke while the other is on its suction stroke. So the crank rotates through 360 degrees between the power stroke of one cylinder & the power stroke of the other.

So the answer is... maybe! Depends on which motor is in your bike.
S.

 

[Speed3Chris]

No silly questions really. Sharp pretty much nailed it. To elaborate....it takes two complete crankshaft revolutions and one complete camshaft revolution to complete the 4 cycles on an internal combustion engine. Intake and compression are one crank revolution and power and exhaust are the second.
The pistons on a bonny motor go up and down at the same time. Their power stroke is one crank shaft revolution apart or 360 degrees. A further nuance is the common coil for each cylinder fires redundantly, i.e. every time both pistons come up to TDC on both sides. When the spark plug fires on the exhaust stroke for the uncharged cylinder, it doesn't do anything on that side. The Scrambler and Cruiser models don't do this and have two separate coils and igniter or ECM depending on carb or EFI bike tells the individual coils when to fire separately based upon staggered crank throws.

 

[BlueJ]

Depends on which motor is in your bike.
S.

Bonneville/Thruxton: 360, they move up and down together.
Scrambler: 270, they are 90 degrees apart on the crank so when one is all the way down, the other is only halfway down.

 

[phil]

Clear as mud gentlemen (lol) , so is there any advantage to both of them going up and down at the same time, or is it just a engine design. .

 

[thearcticsea]

I love that video.

 

[Nick Morey]

Clear as mud gentlemen (lol) , so is there any advantage to both of them going up and down at the same time, or is it just a engine design. .

If I remember right 270 provides more torque at low RPM & 360 is smoother at high RPM

 

[sweatmachine]

I love that video.

Thanks. Just imagine, every time those pistons come up, BAM BAM BAM BAM BAM BAM BAM and your ass is hauling ass down the road!

 

[Kirkus51]

4 stroke Suck Squeeze bang blow

Think of a guy in a wheelchair race, both arms go together to get maximum push on the tires. Same with a 360 crank both pistons go together. That's my bad analogy for the night.

 

[KingBear]

Think of the pistons as a nice pair of tits on a hot woman walking toward you. The tits move together in that just-the-right-amount-of-wobble kind of way, separate but in unison.

I have no idea where to go with this but I enjoy thinking about it.

 

[Speed3Chris]

Good analogy KB but keep in mind some tits don't bounce.
See below

 

[sharp21]

Clear as mud gentlemen (lol) , so is there any advantage to both of them going up and down at the same time, or is it just a engine design. .

Balance.

If they were 180 opposed, ie one going up while the other going down, the vibration would be unbearable.

Also it produces torque like a single (which produces more torque than any other configuration), is light in weight and produce almost double the singles RPM. Good horsepower and top speed as well.

It's not used as much in recent years due to newer engine designs, so it has the vintage street cred & that great 270 sound that I love.

S.

 

[phil]

4 stroke Suck Squeeze bang blow

Think of a guy in a wheelchair race, both arms go together to get maximum push on the tires. Same with a 360 crank both pistons go together. That's my bad analogy for the night.

no, no . That totally makes sense. cool thanks. :cheers: I brag about guys lots , on how helpful you guys are. Thanks.

 

[sweatmachine]

4 stroke Suck Squeeze bang blow

Think of a guy in a wheelchair race, both arms go together to get maximum push on the tires. Same with a 360 crank both pistons go together. That's my bad analogy for the night.

no, no . That totally makes sense. cool thanks. :cheers: I brag about guys lots , on how helpful you guys are. Thanks.

well not really. It would be more like he's putting both hands on the wheels but only pumping with one hand each time, alternating which hand is actually putting force on the wheels.

 

[Stars&Bars]

The Bonneville motor is also known as and is referred to as a Parallel Twin