Kdx 300 ????????????

[KIWI KDX]

hey all, im getting bored and looking for something else to
do to my bike...........

its a 91 KDX250,

iv'e been thinking for a while about re sleeving the barrel
and hopefully boring it out to 300

has anyone done this or got any ideas/ advice (apart from buyng the 300 ECX i cant afford!)

 

[mudpack]

Sounds like a can of worms. I'd spend the money on suspension and new tires; you'll be faster, longer.

mud

 

[_JOE_]

That would be a BIG overbore. You have to consider cooling area of the head and cooling system ability, not to mention lower end stress. You would also need someone with pretty good porting skills to make it run right.

 

[julien_d]

I agree with both the above. If you're itching to get more from it, look at your carb and pipe. Those are the easiest bolt on ways to get more juice from it.

 

[KIWI KDX]

hey guys thanks for the input, sounds like i mite have
under-estimated the upgrade!

the other option i had in mind was to try to fit a kx 500 in there as i know where a cheap engine is,
i know it seems like a lot of work for an old bike, but i have the suspension tweaked just rite and the ret of the bike is compleatlly rebuilt.

any advise on that one?

 

[dirt bike dave]

I think an '88 or '89 KX250 cylinder will work on your bike and produce much more peak power. Or you could have your cylinder ported to KX specs.

 

[julien_d]

Man, those 250's are really hard to come by. I'd hate to think of one being torn apart just becuase someone was bored. That machine should be able to produce mad power as it is. I would look into mods for your current setup and get everything I could out of it before scrapping the motor for a hybrid setup. If it's still not enough for you, either there's something wrong with the bike, or you just aren't right in the head! (that was just a little joke :P).

How about some pics of this bad boy?

J.

 

[KIWI KDX]

hey they are getting pretty hard to find over here too...
its not out of compleate bordem, and it does have pretty mad power, to the point of when i drop the clutch to lift the front up, my brand new 130/100/18 just looses traction on most surfaces,......... but i want more!!!!

im only 75kg's so the 500 would probablly be a bit hard to hold on to, im looking into the KX head idea now.

oh and there is plenty of pics on here, just click on my user name and select " find all posts" i have all the pics of the full rebuild. look for "MY KDX (DIAL UP WARNING)"

CHEERS

 

[Tom68]

Gas Gas 300 piston, weld up rear aux' exh ports, stroke crank 2mm. that gives you 293cc, same as KTM300. Don't sleeve the cylinder it can be replated at 72mm, you have to make your own head gasket and you need either a 124mm conrod or a 1mm barrel spacer, don't forget to get your head remachined. If you want your topend back after all that you'll need port work and probably a bigger carby. If you researched all this yourself you wouldn't be bored.

 

[mudpack]

Gas Gas 300 piston, weld up rear aux' exh ports, stroke crank 2mm. that gives you 293cc, same as KTM300. Don't sleeve the cylinder it can be replated at 72mm, you have to make your own head gasket and you need either a 124mm conrod or a 1mm barrel spacer, don't forget to get your head remachined. If you want your topend back after all that you'll need port work and probably a bigger carby. If you researched all this yourself you wouldn't be bored.

Wouldn't it be cheaper (and you'd have a better bike) if you just bought a new KTM??? :rotfl:

 

[KIWI KDX]

tom68!

thanks heaps for that mate!!!!!!
ill start looking into that now!!

 

[Tom68]

Wouldn't it be cheaper (and you'd have a better bike) if you just bought a new KTM??? :rotfl:

Absolutely, but anyone can do that. Even an old KTM300 would be better.

 

[Tom68]

tom68!

thanks heaps for that mate!!!!!!
ill start looking into that now!!

I wouldn't stroke the crank it only gets you 8cc. If you've got the 125mm conrod in it now you don't have to get into the bottom end.

 

[KIWI KDX]

that sounds even better, i just measured the old rod wich was identical to the new wiseco one i put in a few months ago.

it measured 124mm from center to center, is that rite?

what model gas gas? and do i just use the rings to suit that piston?

have you done this or do u know someone who has?
any more info you could give me would be grate!


and "mudpack"
as for a new KTM, that would be grate, but i cant afford one, and i just love pulling up on an old enduro and blowing away all the new 450's

with this mod i should even keep up with the new 2 smokes!

 

[Tom68]

Rod should be 125mm.Piston any GG300, I used Wossner, Wossner rings work in electrosil bore. I've done mine because the bore needed replating and it wasn't worth keping it std as it's an sr model with no ctr exh' valve and needs the extra cap' for bottom end. All the GG300 pistons are lightened around the gudgeon pin which allows the transfer and exh' aux ports to cross pollinate at mid stroke thats why I suggest welding the back aux' exh' ports. Mine aren't done and it ran strong against the 450's at dirt track practice so I'll leave it, some KX500 pistons run this way.Can't say I'm thrilled about the power gain considering the old bore coating was completely worn through at the top, the piston had two cracks and the rings were well worn but at least I can hold it pinned and flat change on the dirt track and not worry about highsiding because of engine failure.

 

[KIWI KDX]

i've had a look on the "wossner" web site, are you running the
8077DB with the rdb7200 rings?

is a wiseco piston ok to use? (just easier to get hold of in NZ)

you said to have the head machined, does it need to be skimmed?

 

[Tom68]

i've had a look on the "wossner" web site, are you running the
8077DB with the rdb7200 rings?

is a wiseco piston ok to use? (just easier to get hold of in NZ)

you said to have the head machined, does it need to be skimmed?

Yeh 8077DB and the rings that were packaged with it, don't know if Wiseco do one, if they do I'd appreciate a picture. The head needs the squish band redone and the bowl deepened (spark plug now runs with a spacer) to get the comp' right. The port timing gets retarded and you can run with that and a 1.5mm head gasket, or you can run a thin head gasket and thick base gasket for topend. I cut a head gasket out of 1.5mm aluminium sheet annealed it and applied a thin coat of GM sealer.Vertex also do a GG piston. I left the jetting alone and it's been fine, done the blue light ride last weekend and felt it might be a bit rich at higher alt's so I've dropped the needle one notch for a ride tomorrow, LH side cover (No plate) broke in a pile up, NLA Kawasaki Australia so we better start collecting plastics. Used PP bumper adhesive for now.

 

[KIWI KDX]

cool thaks for all the help mate.

there is a full set of plastics on australia ebay for $50, i was going to buy them but too much to fright to NZ.

mite be worth a look.

 

[KDX200Kev]

More power will make it more fun to twist the throttle. You may want to talk to Eric Gorr about modifying your engine. He has done wonders for three of my bikes. Interesting enough I find that I'm much faster trail riding on my KX144 EG then all of my other bikes (CRF450R, RMX250 EG and KDX225 EG). My KX is the only bike I can ride with it pinned all the time, which is probably due to me getting along in age. :yikes:

 

[Tom68]

cool thaks for all the help mate.

there is a full set of plastics on australia ebay for $50, i was going to buy them but too much to fright to NZ.

mite be worth a look.

Thanks, had a look on Ebay, couldn't find plastics, any clues?

 

[Tom68]

If you really want to play, try an IT465 piston, make your own barrel, you won't need an exhaust valve and you'll get 397cc. I was giving it some thought until I busted the kickstart out of an IT465 and figured the KDX gearbox etc probably wouldn't like it.

 

[KIWI KDX]

i just serched for kdx parts and they came up, but i cant find them now either, must have sold!