I have a 1986 TRX 295R (actually 300cc's) with the stock jug and a big bore sleeve and am thinking about stroking the crank. The bike is used strictly for dragging in the sand and maybe 300' dirt drags in the future. What is a good amount to stroke an R crank, 4mm, 7mm,... without losing too much reliability? If I stroke the crank what will happen to the porting? Will it need to be reported or will anything need to be done to the porting to compliment the longer stroke? Also, how will stroking affect the overall balance of the motor? Will the counterbalancer need to be modified? My motor is very close to being "square" (72mm stroke and 72.95mm bore) which I know is beneficial to the overall performance and durability. Any help/suggestions are appreciated.

 

4mm is a good setup for the small bore 250's

 

I don't know about the 2 strokes, but a 4 mil on a 400ex has a slight wobble. It viberates a little more then before, but a rubber mounted steering stem made it go away. My quad pulls so much harder than stock crank 440's. I say spend the bucks and stroke it.

 

some say you need a fresh cylinder to be 100% stout on the set up for the + stroke to begin with before you have any other porting (stock stroke porting). beech or someone else can elaborate im sure. ive heard of motors still running strong when the cylinder is setup for stroke and it goes back to stock stroke.

 

If the motor doesnt have an exotic port arrangment then more than likely a +4 wont kill it. You would almost need to put a degree wheel and map the port timing to see where it falls. That's the only real way to know what you have and get what you want. There's a lot more than just putting a stroker crank into a 2-cycle and taking off.