stroking 125 pros/cons

[RMZ450FIRST4T]

I am thinking of selling my kx250 2006 and getting a 125rm/kx/yz (I also own a rmz450). I want something lighter than the kx, rm125 weighs in 22lb lighter than the kx. I just want to know what is the pros/cons of stroking a 125 2t. I know I wil probably need to upgrade the cooling system. please any info wil be appreciated as I know almost nothing about stroking.

 

[arnego2]

I don't think you need to upgrade the cooling system for a 125, as a stroker the max is 153 I think. Maybe just do a upgrade with the 144 as it wil be faster and the half cost. Most people are happy with it.

 

[Rich Rohrich]

Explaining in specific terms what you are trying to accomplish by modifying the engine and what the specific application you'll be using it for will make it easier for someone to give you a useful answer to your question.

 

[RMZ450FIRST4T]

more torque?

I weigh 180lb and would like to have a bit more torque without losing on peak power. Does anyone maybe have some dyno charts comparing a 125 to a 144? And how does stroking affect reliability? The main thing is I want something lite(125) with as much torque(without losing power) as possible without making it too unreliable. I know this is a tall order but thats why I was asking about the pros/cons.

 

[Rich Rohrich]

What you are looking for is a big bore 125 (134cc or 144cc) , not a long stroke engine.

It's pretty rare to increase the stroke on a 125 but big bore conversions are common, very reliable and most of all FUN! Basically the cylinder is over-bored to the new big bore size, and the cylinder ported for more low/mid, more mid/top, or an overall broader powerband. The head is esurfaced and machined for proper squish clearance and the bowl shape is re-contoured to accommodate a choice of fuel; pump or race gas.

Then the bore is re-plated with nickel silicon-carbide composite plating and Diamond honed to final size.

It's a fun and reliable package that has been used for exactly what you described for the last 10-12 years.

Eric Gorr at Forward Motion is innovator behind most of the big bore two-strokes that have been developed over that time. here's some info from his website :

http://ericgorr.com/bbmasterlisthtml.html

I spent a season on one of Eric Gorr's early development big bore 125s and I had a blast. I was 225lbs in gear at the time and it had more that enough torque to keep me amused all day long. They have only gotten better since then. You'll love the end result.

 

[RMZ450FIRST4T]

Thank you that sounds like a good option. Can you maybe post a link where I can see some dyno graphs comparing a normal 125 to a bored one?

 

[Rich Rohrich]

Marcus Gunby posted lots of different dyno charts here : http://www.dirtrider.net/forums3/showthread.php?t=97637

You can also search on posts by Pete Payne of Heavy Duty Racing here on DRN. Pete is a really good engine builder and has posted some info on some of the big bore engines he has put together.

 

[COLEMANAPP]

Some guy in montana has been making a bunch of 165 kits for Husky 125's. I've ridden one and it is the sheeeet. The owner of it races local hare scrambles and immediately jumped up 30 spots when he changed from his yz 250. more info on that could be found at cafehuskydot com. Cool project.