Stroked Crank

[Rowdy-Yates]

Hey all. The current 125 I just bought has a Stroked Crank. Can anyone explain why you do this? What it does? And How much gain in power do you actually get? I am getting the cylinder set back to the stock bore. I am just wondering the ins and outs of a Stroked Crank?

[Brett]

It gives you more capacity and therefore more power.  Allthough only if you adjust your port timings and compression to suit the longer stroke.

[Johnniespeed]

On a four stroke engine, having a stroker crank adds power to the bottom end, low rpm power. It also makes high rpm less desirable due to reciprotating speed. I have a stroker engine in my short course race truck because I need instant throttle response with high power at low rpm. I had, many many years ago an old Honda 90 with a stroker crank, it was very fast for its size, but very unreliable.
  I am assuming that the effects are similar on a two stroke , but have not tried it yet. By the way, the Honda 90 had 5/8 of an inch stroker pin, how much is yours stroked ?

[Rowdy-Yates]

I am not sure but I have a 2 or 3 mm spacer + 2 gaskets. and lukes is taking .30 out of my head for clearance. If it is insane on the bottom should I get a reed spacer? The only thing I have to compare it too is my rebuilt KX 125.

[KXcam22]

R-Y,
  A stroked crank gives your engine more displacement. Since your engine size in CC is bore x stroke, enlarging the bore or increasing the stroke will make your engine size larger, ie a 125 into a 150 or so.  When I was a kid my friends had XR75 that were  bored and stroked into 100's.  You don't see it that often in 2-strokes because the additional stroke messes up the port timing (as you have found out) and the cylinder must be adjusted upwards accordingly. Cam.

[Brett]

with two strokes stroking is usually left till last due to port timing issues and sometimes a longer rod is required or machining of crankcase to avoid piston interferance.  bore em out first for capacity

[Rowdy-Yates]

Too late im setting my bore size back to stock and ill have a stroked crank. COOL