Maintenance & Technical > KX500 Original

1988 kx5 motor

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boost165:
Just after a bit of info about the 88 kx5 engine I have got this engine for my 2000 kx 250 hybrid I now that the 88 motor has only the kips in the cylinder but now kips power valve in the exhaust port like the 89-onwords  models and the intake port has now bridge for less piston wear I assume, The power valves are in really good condition witch I have read are a hard part to find, what I wanna now is if  this year engine any good with it not have the exhaust kips.is there much power loss ? Any advice on this year motor would be grate :)

dave916:
88 motor is fairly similiar to later 89/on motors {crank/transmission/ port timing 

top of exhaust port is about 2mm lower than 89on but overall is got more area and alot cleaner port roof
the  89on centre kipps is pretty crude and may and also has issues with cracks in exhaust bridges

main differance on the 88 motor are
differant top end/ larger and heavier more water a kips capacity no centre kipps,
 differant intake area  and top reeds run closer to piston than 89on{not good}
bigger crankcase volume {differant cases  with no centre kipps hole ]  holes in 88crank could be plug for less volume
lighter flywheel /slight differant timing 2degree

current  building a 88 will post pictures when i get off my ass in gear :-D

boost165:
Thanks for the info I did wonder about the two big holes in the crank but as the bottom end is all done and built with new rod and new gear box from an 87 model witch didn't fit but does now . What a Ballack that was so it can stay like that lol is the power around the same as later models would you now? Many tanks

dave916:
Have not drove them back to back but if both motor were set up the same they should be pretty similiar , 88 should be the faster of the earlier motor / probably slight more of a hit compared to 89on [lighter flywheel and no centre kipps}
Not sure how case volume would effect performance?
With the top end u probably need to kipps bolt mod and mod the inlet for reeds your using/ radvalve wont work well without reed spacer and  filling rear inlet voids

88 std exhaust port


86  std smaller ex port

boost165:
I have done the kips bolt mod ready for when the top end goes on I have already got a boyesen reed block  came at rite price so is this not the best one to run on this year ? What sort of spec engine are you building or hoping on building if you don't mind me asking  :-)

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