# technical question

6 replies to this topic
• # wsmcrobert

Posted January 11, 2006 - 09:42 PM

2002 xr 650r
i need to know where the motor's longitudinal center of mass lies in relation to the rear motor mount or in relation to the countershaft sprocket. (one-off project). thanks!

btw, i will soon have a nice california plated rolling chassis for sale. has desert tank, good tires, pro taper bars.

• # Fordskin

Posted January 12, 2006 - 03:14 AM

mc square the diagonal root of the qaurtex then equalize the verticle sylindrum thus forming the qaudrant mass. Done it heaps of times.

• # Fordskin

Posted January 12, 2006 - 03:19 AM

That was just a joke by the way just in case anyone thought it could really work. The real answer is %#\$%+**\$ ok i'll behave myself now.

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• # snaggleXR650

Posted January 12, 2006 - 05:22 AM

Nobody can know that. However, a guess would put it somewhere in front of the counter shaft and just behind the cylinder. I would put it .750" back from where the rear of the cylinder wall comes down into the tranny.

What is this "one off" project you are attempting. You can't leave us hanging now!

• # XR650L_Dave

Posted January 12, 2006 - 09:29 AM

If you have the motor out, I recall a trick for this (but it may not be true):

If you hang something from a point on its circumference (like from a motor mount), and draw a plumb line, and hang it from another point, and draw that plumb line, the intersection of the lines will be the CM in that plane.

By longitudinal, do you mean where "left/right" looking from above, or "front/rear" looking from the side?

Dave

• # sorenlaf

Posted January 12, 2006 - 12:00 PM

...If you hang something from a point on its circumference (like from a motor mount), and draw a plumb line, and hang it from another point, and draw that plumb line, the intersection of the lines will be the CM in that plane...
Dave

Believe that is correct.

The center of mass should be between the suspension point and the ground.

Sounds like someones building a forumla singles bike!

--Soren

• # wsmcrobert

Posted January 12, 2006 - 02:12 PM

yeah,
the 650r motor is going into a tz250 chassis. it will be a formula singles road racer. something simular to this ktm single in an aprilia rs250 chassis:
http://www.motobits.com/Boris.htm

balancing the motor in the chassis from front to back is not the problem as long as i can get somewhat equal weight on the front and rear tires (i have hung the motor in the chassis and weighed the bike and am 20# heavy in front but i think that i can overcome that) btw, stock the tz 250 is about 10# heavy in front. the problem i am having is deciding where to mount the motor in the chassis left and right.

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