View Full Version : Tech Question

07-12-2004, 01:37 PM
Can anyone out there answer the following questions. I'm curious and can't find the info on-line.

1) What is the relationship between the two pistons? That is when piston 1 is at top dead center, how many degrees does the crank turn before piston 2 hits TDC. I have the 1000ds engine. I would assume all ducs have the same pattern but don't know??

2) What does the power/exahust stroke look like between piston one & two. Is it fire fire exhaust exhaust or fire exhaust fire exhaust?

Curious minds want to know :)

07-15-2004, 07:41 PM
This is simple but it is hard to make it sound that way.
To answer the question...each piston fires every 720 degrees of crank rotation(2 full rotations). We have two pistons, so our lovable Ducks would fire every 360 degrees of crank rotation in the British parallel twin world...BUT we are ofset by 90 degrees.
Thus, our engines fire at 270 degrees and 450 degrees of crank rotation respectively. Our engines share a common crank pin so these numbers apply.
If your vertical piston just fired, your horizontal piston will fire 450 degrees after that and the vertical will fire again 270 degrees after that.
This is my best understanding and am open to correction.

07-16-2004, 12:55 AM
And in this configuration (90 degree v-twin) we have primary balancing, correct?


07-16-2004, 12:19 PM
Thanks Mat! good explination.
Zach- I think the pistons would have to be seperated by 180 degrees and go out and back together to completly cancel each other out. However I do believe the 90 degree arangement makes it easier to dynamicly balance...but I'm not an engineer.

07-17-2004, 09:55 PM
Ok, I am an engineer and it is never black and white on this topic.
The 90 degree engine comes closer to a true prefect balance than does any other motor. Balancing a motor is wierd business but the same crankshaft weight that balances the piston at top an bottom dead center, causes serious balance issues when it is at 90 and 270 degrees. The 90 degree V (L) twin quells this issue and the only real vibration comes from the forces of combustion and the minor rocking couple (left right twitching viewed from the top) which comes from the fact that the con rods are side-by-side not on the same line as are Harley's fork and blade design. Harley has a 45 degree v twin which will never be balanced without a serperate balance shaft.
Our Ducks are as good as it gets naturally and with the desmo valves we don't piss away horsepower fighting springs or compromise performance choosing between torque and horsepower.
This is my understanding....I am open to correction.
I have been riding since I was 15 (now 54) and my Ducks have given me more joy than any of my many other rides.
Remember, the only "BAD" motorcycle is
the one you don't ride.