I recently had my motor apart (due to third gear retaining circlip failure) and had a good look at the powervalve assembly and it as i have read in other topics the usual wear: was overclosing, center flap pin wear, crankcase to cylinder actuation rod pin wear and idler gear shaft wear. The main modification which i thought was neccesary due to piss poor engineering was the idler gear shaft wear
. The problem is that the gear and shaft are made of the same piece of material being aluminium and an aluminium shaft running on aluminium is allways going to wear. (rule of thumb never have same materials bearing on each other) So the shafts are meant to be 6mm in diameter but had worn down to 5.5mm. What i did was put gear in lathe and clock up shaft to make sure was running true and then chopped off shaft, faced off, center drilled, drilled to 5.5mm then bored with tiny boring bar to 5.95mm diameter. I then removed gear from lathe, gave a clean up, heated up the gear in boiling water, put a hardened and ground 6mm dowell in freeza then pushed pin throughgear with vice and various spacers. This basically removed 90% of the slop in the powervalve rack to gear slop which was causing majorleft to right powervalve drum timing issues. After this i could then turn up the appropriate spacer to make sure the powervalves werent over closing. After doing this i then replaced the center powervalve flap pins with others (i think 4mm diameter). Lastly was the little pin that is on the arm of the shaft that drives the main rack. The pin was worn and so had to be replaced, the original pin was turned with a step to go through the arm and was then peened over to retain it. I ground off the back of the pin to remove the pin. I then attempted to drill the arm to accept a 4mm pin but to no avail, the arm was hard as the hobbs of hell
, so i heated the end up with oxy to red and then let cool slowly, then drilled through it like butter. I then stuck the appropriate length pin into the arm and welded the back up with the mig. I finally got it going this weekend and went for a ride with my mates and was battling to keep the front end down all day
(even though easing the power on due to running in) Also seemingly with the non overclosing powervalve i seemed to get far less violent backfires/missfires when backed completely off and rolling in gear. Very happy and all faith has been renewed in the overly complicated kx500 powervalve setup.
