I believe Falicon can stroke your crank!!

[ToXicD]

Ok guys i just got done reading on Falicon's website and they mention that they can stroke your crank!!! I have not talked to them yet to see if its possible on the xr650r but i dont see why not Now all i need to find out is how many mm's i can go without running into valve clearance problems. If anyone knows about how many mm's you have till the valve hits the factory piston please let me know.

Also by increasing the stroke, i believe you will ultimately increase the compression because the piston will be traveling closer to the cylinder head so does anyone have any ideas how to calculate the compression ratio when doing something like this?? I am hoping to be able to go at least 2mm and still have enough clearance for the valves, if not i would like to go 4mm and have a custom piston made. I am going to call Falicon tomorrow and talk to them and see what my options are. I will let you guys know what they say.

Falicon makes custom length rods so as of right now the plan is to get a 4mm longer rod and having a spacer plate m ade for under the cylinder which should bring my cubic centimeters to over 700!

[dylanr]

Interesting, let us know how that works out, dont know much about strokers, sorry

[zrt1]

A longer rod isnt going to give any extra cc's at all. It will give you a better rod to stroke ratio. Unless you change the stroke of the crank the pistons travel will always be the same no matter how long the con rod.

[ToXicD]

Yes, that is why I asked about the stroker crank. Since I am buying a new one anyways we are gonna try to machine the old one to get more travel

[pwrpapa]

If your going with a long rod kit you have to have a custom piston made to relocate the pin hole, and a different skirt too. I like the long rod because it gives the piston more dwell time at the top an bottom of it's stroke.

The 650 already has a long stroke. A

longer rod 650 would benefit by reducing piston speed which allows it to turn more rpm's safer. slower piston speed generates less friction and reduces pumping losses due to better ring seal. it also allows the piston to remain at tdc and bdc longer allowing for more cylinder filling and more complete combustion. since the stroke is not changed it does not destroke it and you definetly see gains over a regular rod 650 provided you select components to optimize the setup. Also the rod angle is better with the longer rod compared to the stock rod.

you would have to contact ross or chp or a similar piston manufacturer to have a piston made to the right specs.

[ToXicD]

thanks papa, i was thinking about trying just that, figured it would be the easiest just didnt know if i could get a piston for that particular application. as far as rod angle i havnt looked to close at it but i am assuming there is enough room so it wont hit the cases. if not no big deal, i machined the cases on my 250r motor to clear the rod.

pwrpapa,

i will think about this more tomorrow after i get some much needed sleep, but cant you accomplish this same thing by just using a longer rod and makeing a spacer plate to put under the cylinder to raise it for the piston clearance?? lets say you go 4mm longer on the rod, you could compensate by using a 4mm thick base gasket correct?? as long as the skirt on the piston isnt too long i dont see why it wouldnt work but i could be wrong.

[Ryanthegreat1]

A

longer rod 650 would benefit by reducing piston speed which allows it to turn more rpm's safer.

As I recall a longer rod will not slow piston speeds. The piston still has to travel the same distance in the same amount of time.

Acceleration of the piston from one direction to other is slower at least at the top and bottom of the stroke as the dwell time is much longer. I would think because of this extra time spend at either end of the stroke the middle of the stroke has to be much faster to travel the same distance in the same amount of time.

[pwrpapa]

You are 75% correct in your reasoning. Consider this: Using the identical bore and stroke and using a longer connecting rod with the piston wrist pins located closer to the bottom or in the oil ring groove actually reduses the piston speed. This directly correlates to the exact rpm the shorter rods had given you. Even though the long rod motor is turning at the exact RPM, the piston speed (up and down motion) will be slower. This causes less friction, side thrust on the piston, reduced rod angularity and better intake and exhaust filling and expulsion of the combustion chamber. This age old trick is most advantageous building a high RPM motor. However it is detrimental to low rpm motors.

Using a compass, ruler and protractor you can draw a cylinder, piston and crankshaft and prove this to yourself.

This may be somewhat difficult to grasp untill you've actualy seen it done in an engine shop.

[Beyond The Pale]

You have to remember that it's not so simple on a four stroke. Any spacer under the cylinder to make room for that longer rod, or stroke means a different cam chain. Not sure which bike you are considering doing this too, but my 600 has a top engine mount. That would have to be redone to make room for a spacer.

[martinfan30]

Sounds like way too much work for the amount og HP gained IMHO.

[pwrpapa]

I agree...........

[ToXicD]

yes i have considered the cam chain length and i am hoping there is enough slack in it, if not i will just find one that is one link longer. also the motor will be going into a custom built frame so the top motor mount wont be a problem guys.

[Frank ZX]

Like someone else said,You don't gain more CC by installing a longer rod.The crank throw stays the same,as does the bore.

[ToXicD]

well of course i am gonna have to bore it out to get the cc's but i am hoping i can find someone to modify the crank to get more travel out of it. i am a machinist and have access to the right equipment, but i think i would prefer someone with more experience to do this kind of work. it seems like there are only a few here who are interested in trying to go all out with their motors, im sure because for a bike it makes plenty of power. as i have mentioned before the motor is going into a quad frame so the more hp i can make the better. dont get me wrong i dont want something i have to rebuild every weekend, but you can make alot of horsepower and still be reliable if you know what you are doing

[Ryanthegreat1]

You are 75% correct in your reasoning. Consider this: Using the identical bore and stroke and using a longer connecting rod with the piston wrist pins located closer to the bottom or in the oil ring groove actually reduses the piston speed. This directly correlates to the exact rpm the shorter rods had given you. Even though the long rod motor is turning at the exact RPM, the piston speed (up and down motion) will be slower. This causes less friction, side thrust on the piston, reduced rod angularity and better intake and exhaust filling and expulsion of the combustion chamber. This age old trick is most advantageous building a high RPM motor. However it is detrimental to low rpm motors.

Using a compass, ruler and protractor you can draw a cylinder, piston and crankshaft and prove this to yourself.

This may be somewhat difficult to grasp untill you've actualy seen it done in an engine shop.

http://www.stahlheaders.com/Lit_Rod%20Length.htm

"Another concern in selecting the rod length is the effects of mechanical stress imposed by increasing engine speed. Typically, the concept of mean piston speed is used to express the level of mechanical stress. However, the word "mean" refers to the average speed of the piston in going from the top of the bore to the bottom of the bore and back to the top of the bore. This distance is a linear distance and is a function of the engine stroke and engine speed, not rod length. Therefore, the mean piston speed would be the same for each rod length."

Longer rod = slower piston acceleration = less stress on con rod

So yes longer rod to a point will hold up to high rpm's better than a shorter rod in the same motor.

[dmvmechanics]

seems like you'd be adding more moving mass as well. why did yamaha go to a shorter stroke then when they redid the R1 motor for high revs?

[martinfan30]

seems like you'd be adding more moving mass as well. why did yamaha go to a shorter stroke then when they redid the R1 motor for high revs?

Short stroke/big bore = top end HP...

[Nailpounder]

http://www.stahlheaders.com/Lit_Rod%20Length.htm

"Another concern in selecting the rod length is the effects of mechanical stress imposed by increasing engine speed. Typically, the concept of mean piston speed is used to express the level of mechanical stress. However, the word "mean" refers to the average speed of the piston in going from the top of the bore to the bottom of the bore and back to the top of the bore. This distance is a linear distance and is a function of the engine stroke and engine speed, not rod length. Therefore, the mean piston speed would be the same for each rod length."

Longer rod = slower piston acceleration = less stress on con rod

So yes longer rod to a point will hold up to high rpm's better than a shorter rod in the same motor.

Now you're a 100% correct.

I've' built tons of race motors an you always want to put the longest rod you can in it for a better rod to stroke ratio.

[ToXicD]

Ok guys i just got done reading on Falicon's website and they mention that they can stroke your crank!!! I have not talked to them yet to see if its possible on the xr650r but i dont see why not Now all i need to find out is how many mm's i can go without running into valve clearance problems. If anyone knows about how many mm's you have till the valve hits the factory piston please let me know.

Also by increasing the stroke, i believe you will ultimately increase the compression because the piston will be traveling closer to the cylinder head so does anyone have any ideas how to calculate the compression ratio when doing something like this?? I am hoping to be able to go at least 2mm and still have enough clearance for the valves, if not i would like to go 4mm and have a custom piston made. I am going to call Falicon tomorrow and talk to them and see what my options are. I will let you guys know what they say.

[ToXicD]

i just talked to falicon and the guy said he believes you can use a 1/4" base plate and still have enough play in the chain. that increases the stroke by 6mm which ultimately brings the cc to 725 with a 102mm piston!!! i will also be having the crank supermodded which includes all balancing and polishing. i cant wait to see what kinda horse power this thing is gonna make