KDX250 woes

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Jul 2, 2001
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#1
Riding along behind my brothers KDX250F2, when l notice splashes of milky residue coming off his bike.
My bro knew it was a problem as the bike started to surge and loss power thru pinging. When we pulled over, the white residue was the gearbox oil mixed with water and seeping from the clutch cover and gearbox oil breather hose. On further inspection, the top of the radiator cap was cool and upon opening there was no water. I told him that it was the water pump and maybe a head gasket if the motor cooked enough. We topped it up and the coolant was still green as it spewed out.
Back to the trailer, l unbolted the water cover to find that the bolt had come off the impeller and the whole motor was hot, as in steaming.
After tightening the water pump impeller, it felt a touch loose in it's sideways movement. I emptied out the gearbox oil (filled a bottle and a half) and tighten up the clutch case bolts, filled the radiator and took it for a ride. The power was instantly back during the ride and the bike didn't surge when you are coasting off the throttle but when l returned (5min blast) l opened the top of the radiator and again no water (could see the core), filled it and the colour of the coolant was still green.

Q1. If the motor was still hot, could the water have evaporated from the time l fixed the water pump till the end of my test ride (all up 15-20 mins)?
Q2. Should l replace the water pump seal as a precaution? And how hard of a job is it?

Need all the help fellas.

J :(
 
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#2
Replace the seals and the impeller shaft if it is grooved. If there was play in the impeller shaft, the shaft assembly probably needs replacing. The bearing must be shot. You have to remove the clutch-side engine cover to do this, but it's not too difficult. The head gasket could be blown, replacing it might be cheap insurance.
 
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#3
Thanks Spanky,

I pulled the bike down whilst cleaning my bike (must find better things to do with my time), l found that the impeller was slightly worn, the seal was shot, bearing was slightly worn and so was the shaft.
Verdict: Ordered all the above and a head gasket.

Tell ya how she goes after the repairs.

PS. Any bloody way of lightening the bike, it's nick name is the pig and it feels heavier then my TE400 and very hard to steer but a great bike to learn to muscle a bike in the bush all the same.

J :eek:
 

dirt bike dave

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#4
OZ - The stock pipe and silencer are very heavy and should be replaced. On mine, I modified an aftermarket KDX200 silencer to fit. Other little things you can do are remove the kickstand and remove one of the rear fender supports (if you take off both the fender will crack). You can make a lighter fender support out of sheets of aluminum - make a crescent shape that fits inside the rear fender.

The bike will never be nimble w/out frame modifications, but you can make it turn a bit better by raising the fork tubes 10mm above the top of the triple clamp, shorten the chain and run rear wheel all the way forward in the adjsuters (may require a 13t countershaft), run negative pre-load on the front fork springs and experiment with less than 100mm of rear sag.

BTW, the stock fork valving (too stiff on high speed compression) and springs (way too soft) are horrible. Fixing those things should be even higher priority than shaving the weight off.
 
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#5
Simply fixing the suspension will amaze you at how much better the bike handles. The shock is not terrible, but the forks are attrocious, and the suspension is very unbalanced in stock trim. I run .41 springs in place of the .35 stockers, both ends have been revalved, the fork legs raised about 7mm, and 95mm of sag. You really have to learn to be aggressive with your weight shifting and body positioning in turns with this bike. I have removed both fender supports, but I run a motocross fender, with no tail light. Removing the kickstand was a no-brainer, as it would bend on the slightest hill anyway.
 

dirt bike dave

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#6
Also, shaving the front of the seat foam down will improve the seat/tank relationship and riding position, even if you are 6'+ tall.
 
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#7
Dave and all,

Thanks for the info but the only thing l haven't down is frame mods. When we first bought the bike (shared with my bro until l bought my WR360), it was in bad shape, shot suspenders, levers, graphics/seat but the motor was good.
Since then, l've had a racetech kit fitted with a a .42kg spring, procircuit pipe and expansion chamber, powervalve mods, light porting on the head, KX rear shock and front shocks (for adjustments) and replaced all the bearings, 14/48 gear combo, slimmer seat were big factors.
Yes, it will never be a fairlight bike as it feels like the motor is in the wrong position but as l said, you really learn how to muscle and shift your body on this bike due to the inherit faults in the geometry.
When l stepped into a lighter and more agile bike, the that bike felt like a BMX and all due to The Pig!

J
:p
 

dirt bike dave

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#8
OZ, A friend of mine did modify the frame on his KDX250 by pulling in the steering head angle. I had my KDX250 at the time, and did back to back comparisons. His bike was much improved in the woods and felt at least 20 pounds lighter! I knew the bike would turn better, but was really surprised at how much lighter it felt. This is a pretty extreme mod and should only be done by someone qualified to do the work.

One little thing to do on the KDX250 to get tighter turning is grind a little off the steering stop tab. The stock tab prevents the bars from turning as far as they should.