125cc Stroker Motor Question(s)

Arkmx
Profile picture for user Arkmx
Posts
1625
Joined
10/6/2006
Location
35 miles west of PHX..., AZ US
Arkmx
Edited Date/Time 1/27/2012 11:58am
.

Is it possible to build a "Stroker" and still maintain the 125cc displacement?? Zach is wanting to get a KX 125 that says it's a 125cc with a stroker motor in it.

I thought that if you make a stroker motor using the stock cylinder you would have to install a base plate to get the clearance for the longer rod etc., thus increasing the volume and thus the cc's... Am i correct? If not can you enlighten me on this before we move forward on this bike.

Thanks in advance!


.
|
mxtech1
Profile picture for user mxtech1
Posts
1968
Joined
7/21/2011
Location
Galesburg, IL US
mxtech1 12/27/2011 9:23am
12/27/2011 9:23am
If you increase the rod travel you will have to decrease the size of the piston to keep the same CCs. I would like to know how you would decrease the size of the cylinder bore? If you stroke it, add a base plate, keep the stock piston, you'll be over 125 CCs.

CC's are calculated using the rod length X piston diameter.

Why not just do a big bore and keeo the we 125 stickers on it?
mx5471
Profile picture for user mx5471
Posts
986
Joined
7/10/2008
Location
AL US
mx5471 12/29/2011 6:27pm
12/29/2011 6:27pm Edited Date/Time 12/29/2011 6:44pm
It's really not a stroker motor as you would normally think. PR2 built a "long rod motor" for my son' s RM85 years ago, and it rocked. I had people waiting in line to by that bike when he moved up to a big bike. They don't change the position of the crank pin on the flywheels,they put a longer connecting rod in, and then have to put a base plate below the cylinder to allow for the longer rod. CC's are not calculated by the length of the rod. It's calculated by the stroke, "how far the piston travels up and down", and the bore, "diameter of the cylinder". If you put on a rod a mile long without changing the stock position of the crankpin, you still have the same stroke, and if you have the stock bore, then you still have the same 125cc's you started with, but you would need a mile long base plate. What it does is add crankcase volume,and it works great. I would ask some questions, the first one is was it a KX125 or a KX100 built to a 125. In that case,pass on it. Who did the work and, call them to ask what they did. Find out some more about it, and maybe the people here can help.
jsmx97
Profile picture for user jsmx97
Posts
205
Joined
12/28/2011
Location
NH US
jsmx97 12/29/2011 7:47pm
12/29/2011 7:47pm
Im assuming the seller means to say that it has a stroker crankshaft and is no longer a 125. MXtech1 your info is a bit off as far as calculating CC's and what a stroker is, as it looks like mx5471 has explained already the correct meaning of a stroker and how to calculate CC's.

Get some info on who did the stroker build before you decide to buy the bike.

Post a reply to: 125cc Stroker Motor Question(s)