Maintenance & Technical > KX500 Original

1988 kx5 motor

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dave916:
spec of motor i am building will be stock[port timing}  [look for smooth power rather than more top end}
there will be a few little differance to normal builds
running roller bearing on flywheel side/ shimed on clutch side to centre crank  /balanced crank /epoxy cases
top end will epoxy inlet {dercon f} to reduce boyese port size and flaws /going to run a boyesen radvalve with 10mm spacer
top reeds of radvalve will almost hit piston /complete block boost port/ damage or jam reeds on casting flaws of boyesen ports

unfinished work i am currently doing


stock top cating flaws is where your radvalve reeds will jam


reduced boyesn port size

motopunk:
you could use all gears of the 87 motor , but you need the 88-2004 shafts...

i have an 86 and 88 engine and love to ride both . the 88 has a smoother power delivery and handles better on hardpack . also know the 89 and 99 motors from testrides on borrowed bikes ...  the 88 is very close to the 89 and up motors in performance. i think its the cylinder and slower second gear , that also was changed in 89 to faster second gear...

boost165:
Love the work your doing I'm going to have to tidy my inlet up to stop reeds jamming that's  a good tip thanks  :) the complete gearbox from an 87 will fit with with some changes I had to cut the input shaft down on the left hand side wear it sits in the bush and has a needle roller bearing so I had to change it to a normal bearing and also the inner clutch hub is different only 6 splines unlike the 88 onwards I couldn't find a 87 clutch hub. parts are really hard to find in the uk but I did find on eBay a kx 250 hub witch had 6 splines apparently it was from an 86 model 250 I don't now but I took a chance on it and it fitted :) happy days ,, thanks for the info guys it all helps

dave916:

--- Quote from: boost165 on February 27, 2015, 08:04:45 PM ---Love the work your doing I'm going to have to tidy my inlet up to stop reeds jamming that's  a good tip thanks  :) the complete gearbox from an 87 will fit with with some changes I had to cut the input shaft down on the left hand side wear it sits in the bush and has a needle roller bearing so I had to change it to a normal bearing and also the inner clutch hub is different only 6 splines unlike the 88 onwards I couldn't find a 87 clutch hub. parts are really hard to find in the uk but I did find on eBay a kx 250 hub witch had 6 splines apparently it was from an 86 model 250 I don't now but I took a chance on it and it fitted :) happy days ,, thanks for the info guys it all helps

--- End quote ---
A Reed spacer is the way  to go/will need less work on casting flaw area
the reasons i used epoxy is to fill the huge rear void{for reed screws} dont need it with reed spacer
the rear void {reed screw area] and the boyesn ports are far bigger in  88 than later years
Dont go mad grinding casting flaws{boyesen ports} as the cylinder is prone to cracking in that area[like kr1 cylinders}

boost165:
Oki I will just smooth of wear the reed petals hit this is all much needed info :)

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