The Sportster and Buell Motorcycle Forum Motor Stage  

Go Back   The Sportster and Buell Motorcycle Forum > SPORTSTER MOTORCYCLE ZONE > Sportster Motorcycle Motor / Engine > Sportster Motorcycle Motor - Top End
XLF Gallery XLF Classifieds XLF Blogs XLF Shout XLF Arcade XLF Disclaimer/Privacy Statement/Terms Of Use

Sportster Motorcycle Motor - Top End Discuss Sportster Motorcycle Top End issues. Rockerboxes, Valves, Cylinders, Pistons, Rings, Lift Rods, etc...

Members Birthdays
Motor Stage
Figure Machine
Lowbrow Customs
Ironworks Magazine

Lowbrow Customs
Reply
 
Share Thread Tools Display Modes
  #1  
Old 30th January 2006
Lone Wolf in Canada's Avatar
Lone Wolf in Canada Lone Wolf in Canada is offline
Know It All
 
Join Date: Nov 2005
Location: Beaverton Ontario Canada
Posts: 180
Sportster/Buell Model: XLC Custom 1200
Sportster/Buell Year: 2005
Reputation: 247
Lone Wolf in Canada is on a distinguished roadLone Wolf in Canada is on a distinguished roadLone Wolf in Canada is on a distinguished road
Default This is why it sounds like potato potato

The way I understand it, the V twin Harley engine's twin pistons move up and down at the same time, as they are connected to a single crankpin on the twin flywheels, but only 1 piston fires at a time. I realize this gives the classic "potatoe potatoe potatoe" sound loved by most.They have "knife and fork" connection piston rods... what does this knife and fork mean?
Does it not lose power with one piston firing forcing both pistons down?
Why have two pistons if they alternate firing?
Reply With Quote
  #2  
Old 30th January 2006
dmraco's Avatar
dmraco dmraco is offline
Senior Chief Know It All 1st Class
 
Join Date: Nov 2004
Location: Philadelphia
Posts: 1,180
Sportster/Buell Model: Sportster Forty Eight
Sportster/Buell Year: 2012
Reputation: 10963
dmraco is a glorious beacon of lightdmraco is a glorious beacon of lightdmraco is a glorious beacon of lightdmraco is a glorious beacon of lightdmraco is a glorious beacon of lightdmraco is a glorious beacon of lightdmraco is a glorious beacon of lightdmraco is a glorious beacon of lightdmraco is a glorious beacon of lightdmraco is a glorious beacon of lightdmraco is a glorious beacon of light
Default

Quote:
Originally Posted by Lone Wolf in Canada
The way I understand it, the V twin Harley engine's twin pistons move up and down at the same time, as they are connected to a single crankpin on the twin flywheels, but only 1 piston fires at a time. I realize this gives the classic "potatoe potatoe potatoe" sound loved by most.They have "knife and fork" connection piston rods... what does this knife and fork mean?
Does it not lose power with one piston firing forcing both pistons down?
Why have two pistons if they alternate firing?
Not sure this it true. The pistons move up and down opposite of each other, that is why the motor shakes. If they moved up and down at the same time, the motor would "hop." I do beleive what you are referring to is most HD motors will fire the plugs on the exhaust stroke as well as the power stroke. The newer motors are single fire for the most part??? Correct?? Can someone who really knows what they are talking about chime in??
__________________
2012 Sportster Forty Eight
Reply With Quote
  #3  
Old 30th January 2006
Randum77's Avatar
Randum77 Randum77 is offline
Senior Chief Harley Engineer 2nd Class
 
Join Date: Jun 2005
Location: Fayetteviie, NC
Posts: 1,628
Sportster/Buell Model: XL1200cc
Sportster/Buell Year: 94
Reputation: 72
Randum77 is an unknown quantity at this point
Default

To be correct, both the pistons don't go up at the same time. As the previous poster said, it would hop rather then vibrate. Now, there are 4cycles that a piston goes through and only one of them is a combustion stroke. 1. intake 2. compress, 3. combustion 4. exaust. 2 of which are upstrokes, 1. compression and 4 exaust, and 2 of which are down strokes: 1. intake, 3. Combustion.

Both pistons alternate in the combustion stoke inorder to create a consistent powerband. I could explain more, but I don't have the time. I am sure a more techincal person will kick and and straighten things out. Also, feel free to correct me if I am wrong w/ something.
__________________
"America has bred a society that is innocent and incapable of accepting responsibility, but yet, is able to place blame on others without guilt."
[
Reply With Quote
  #4  
Old 30th January 2006
xl1200r's Avatar
xl1200r xl1200r is offline
Senior Custom Bike Builder
 
Join Date: Nov 2004
Location: North Greenbush, NY
Posts: 2,956
Sportster/Buell Model: Buell 1125CR
Sportster/Buell Year: 2009
Sportster/Buell Model #2: XLCH
Sportster/Buell Year #2: 1964
Other Motorcycle Model: Kawasaki Ninja 250
Other Motorcycle Year: 2006
Reputation: 1866
xl1200r has a spectacular aura aboutxl1200r has a spectacular aura aboutxl1200r has a spectacular aura aboutxl1200r has a spectacular aura aboutxl1200r has a spectacular aura aboutxl1200r has a spectacular aura aboutxl1200r has a spectacular aura aboutxl1200r has a spectacular aura aboutxl1200r has a spectacular aura aboutxl1200r has a spectacular aura aboutxl1200r has a spectacular aura about
Default

Techi person, here I go...

The pistons move sort of together, they are actually 45* apart on a common crank pin. What was said is true, they alternate which piston is firing. So while on piston fires and forces both down, the other has the intake valve open and is drawing in fuel (4 strokes...Down(intake), up(compression), down(ignition), up(exhaust).

What makes the "patato patato" sound is that the engine is "odd-fire", in that the spacing between the firing is not equal. You get cylinder 1 to fire, the crank turns 315*, then cylinder 2 fires, but the crank has to turn another 405* for cylinder 1 to fire again. This is due to the 45* piston angle and the common crank pin. This means that there's almost a 30% difference in the amount of time it take for each cylinder to fire from the other cylinder firing.

I wish I could find this animation of the whole thing happening - it's be much easier to understand when you see it.

Try this:

Hope that helps.

Last edited by xl1200r; 30th January 2006 at 16:53..
Reply With Quote
  #5  
Old 30th January 2006
ed_in_az's Avatar
ed_in_az ed_in_az is offline
Senior Custom Bike Builder
 
Join Date: Dec 2004
Posts: 2,500
Sportster/Buell Model: Nightster
Sportster/Buell Year: 2008
Reputation: 54554
ed_in_az is a splendid one to beholded_in_az is a splendid one to beholded_in_az is a splendid one to beholded_in_az is a splendid one to beholded_in_az is a splendid one to beholded_in_az is a splendid one to beholded_in_az is a splendid one to beholded_in_az is a splendid one to beholded_in_az is a splendid one to beholded_in_az is a splendid one to beholded_in_az is a splendid one to behold
Default

Here's the animation:

http://www.sa750.com/vtwin/vtwin.htm
__________________
2005 Black 883XL / NRHS 1200, 9.5:1 Comp, .497 Cams, SE A/C & Pipes, Jagg oil cooler
_________________
Don't throw your pearls to swine! They will trample the pearls, then turn and attack you.
Well ... that explains a lot.
Reply With Quote
Know Thy Hog

  #6  
Old 30th January 2006
xl1200r's Avatar
xl1200r xl1200r is offline
Senior Custom Bike Builder
 
Join Date: Nov 2004
Location: North Greenbush, NY
Posts: 2,956
Sportster/Buell Model: Buell 1125CR
Sportster/Buell Year: 2009
Sportster/Buell Model #2: XLCH
Sportster/Buell Year #2: 1964
Other Motorcycle Model: Kawasaki Ninja 250
Other Motorcycle Year: 2006
Reputation: 1866
xl1200r has a spectacular aura aboutxl1200r has a spectacular aura aboutxl1200r has a spectacular aura aboutxl1200r has a spectacular aura aboutxl1200r has a spectacular aura aboutxl1200r has a spectacular aura aboutxl1200r has a spectacular aura aboutxl1200r has a spectacular aura aboutxl1200r has a spectacular aura aboutxl1200r has a spectacular aura aboutxl1200r has a spectacular aura about
Default

That's the one...there's a lot of good info on that site too.
Reply With Quote
  #7  
Old 30th January 2006
Y2K's Avatar
Y2K Y2K is offline
Senior Master Custom Bike Builder
 
Join Date: Apr 2005
Location: Yacolt,Washington
Posts: 3,956
Sportster/Buell Model: XLH 1000
Sportster/Buell Year: 1974
Other Motorcycle Model: Electraglide classic
Other Motorcycle Year: 2000
Y2K has disabled reputation
Default

[QUOTE=Lone Wolf in Canada]They have "knife and fork" connection piston rods... what does this knife and fork mean?
QUOTE]

To add to what has been posted, the knife & fork means that one rod has a slot that the other rod fits into like sticking a knife between the tines of a fork.
both rods and connected together to a single crankpin.
__________________
Electraglide Roadtripper
Reply With Quote
  #8  
Old 30th January 2006
xl1200r's Avatar
xl1200r xl1200r is offline
Senior Custom Bike Builder
 
Join Date: Nov 2004
Location: North Greenbush, NY
Posts: 2,956
Sportster/Buell Model: Buell 1125CR
Sportster/Buell Year: 2009
Sportster/Buell Model #2: XLCH
Sportster/Buell Year #2: 1964
Other Motorcycle Model: Kawasaki Ninja 250
Other Motorcycle Year: 2006
Reputation: 1866
xl1200r has a spectacular aura aboutxl1200r has a spectacular aura aboutxl1200r has a spectacular aura aboutxl1200r has a spectacular aura aboutxl1200r has a spectacular aura aboutxl1200r has a spectacular aura aboutxl1200r has a spectacular aura aboutxl1200r has a spectacular aura aboutxl1200r has a spectacular aura aboutxl1200r has a spectacular aura aboutxl1200r has a spectacular aura about
Default

Quote:
To add to what has been posted, the knife & fork means that one rod has a slot that the other rod fits into like sticking a knife between the tines of a fork.
both rods and connected together to a single crankpin.
This makes it so both pistons can be right in line, rather than being offset.
Reply With Quote
  #9  
Old 31st January 2006
nzsailor nzsailor is offline
Chief Harley Engineer
 
Join Date: Feb 2005
Posts: 504
Reputation: 3397
nzsailor is a jewel in the roughnzsailor is a jewel in the roughnzsailor is a jewel in the roughnzsailor is a jewel in the roughnzsailor is a jewel in the roughnzsailor is a jewel in the roughnzsailor is a jewel in the roughnzsailor is a jewel in the roughnzsailor is a jewel in the roughnzsailor is a jewel in the roughnzsailor is a jewel in the rough
Default

my daughter had a two cylinder fiat bambina 500cc car
both pistons go up n down together so that you get power 360 degrees apart which makes sense for the power band
once it was running even at idle it was quite smooth
but the way the back end of that little car bounced up n down when the starter was cranking over was absolutely lewd!!!!!!!!!!!!!!!!
Reply With Quote
  #10  
Old 31st January 2006
xl1200r's Avatar
xl1200r xl1200r is offline
Senior Custom Bike Builder
 
Join Date: Nov 2004
Location: North Greenbush, NY
Posts: 2,956
Sportster/Buell Model: Buell 1125CR
Sportster/Buell Year: 2009
Sportster/Buell Model #2: XLCH
Sportster/Buell Year #2: 1964
Other Motorcycle Model: Kawasaki Ninja 250
Other Motorcycle Year: 2006
Reputation: 1866
xl1200r has a spectacular aura aboutxl1200r has a spectacular aura aboutxl1200r has a spectacular aura aboutxl1200r has a spectacular aura aboutxl1200r has a spectacular aura aboutxl1200r has a spectacular aura aboutxl1200r has a spectacular aura aboutxl1200r has a spectacular aura aboutxl1200r has a spectacular aura aboutxl1200r has a spectacular aura aboutxl1200r has a spectacular aura about
Default

"a couple octaves lower" was the main point. All engines sound like crap with no exhaust on them - it's just the nature of it. Even my racecar with a 400 small block, all juiced up sounds like ass with just manifolds on it (can't run headers in my class).

There are some bad sounding big engines out there, just as there some really good sounding small engines.

Quote:
my daughter had a two cylinder fiat bambina 500cc car
both pistons go up n down together so that you get power 360 degrees apart which makes sense for the power band
once it was running even at idle it was quite smooth
but the way the back end of that little car bounced up n down when the starter was cranking over was absolutely lewd!!!!!!!!!!!!!!!!
As for the 360* crank thing, this would be the same setup the triumph twins use. I'm not sure why your fiat didn't hop around when running, but I understand those triumphs have a little shake to them since both cylinders are moving up and down together, even thou they are on different strokes.

As for the powerband thing, on paper the 360* firing order makes sense, but from what I've read it's not the case. According to that link, the 45* Single pin V-Twin makes the most "real" power per "rated"power. The scentence in the link is worded poorly, but what it's getting at is that a 45* V-twin that makes 70hp has more "actual" power than a 360* parrallel twin making the same 70hp. I don't know the science behind this, just relaying some info I came accross.
Reply With Quote
Know Thy Hog

Reply

Bookmarks


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


Custom Search

All times are GMT +1. The time now is 19:24.


Powered by vBulletin® Version 3.8.5
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
XL Forum - Linson Media LLC