94 KX 250 rebuild

Related:
Create New Tag

12/4/2018 7:23 PM

So Im new to the forum and haven't touched a dirt bike in 15 years. I picked up a 1994 KX 250 for $200. Couldn't pass it up. I have built several street bike from top to bottom, this will be my first 2 stroke. I could use pointers a long the way, that aren't in the book. I work down from Power seal so they will be handling the cylinder work. The bike came in pieces. Has a brand new Wiseco bottom end kit, FMF pipe, and a jug marked with JM in the side. My plan is mostly trail riding and maybe a few days at Field of Dreams in Nj.

|

12/4/2018 7:33 PM


|

12/4/2018 7:37 PM

It also had a second transmission. I have read that people swap for different ratios. I haven't been able to identify this spare one. the one gear is under cut and has a later style sprocket on the output shaft

|

12/5/2018 12:53 AM

Whats the number on the cases near the oil fill?

99 and up on the newer sprocket.

First thing to check is the power valves. They are discontinued and hard to find. Also look for cracks in the frame and a worn rear brake pivot pin.

|

04 KX125
94 KX250SM
75 Z1-900

12/6/2018 3:44 PM

Kidkawie I have checked that, it is a 94 case. I do have a 94 trans that came with it, one of the gears is a little worn, I was trying to i.d. this other gear set so maybe I could make a best guess on what ratio to run. Or do I just stay with the original set up? Since I have never ridden this bike I have no idea what to base my decision on.

|

12/6/2018 3:49 PM

Today I did get to dissamble the cylinder and exhaust valve. I was excited to see someone has gone through and cleaned up and ported the cylinder, also found someone had broke a screw off in the reed valve. The aluminium gears on the exhaust valves are also a little worn. Any input in what reed valve set up to run? I'm not sure what brand is in there, they are carbon fiber.

|

12/6/2018 3:55 PM

I've got one in the garage right now. Been sitting for years, but should be good to go still.

Check that Wiseco crank and keep an eye on it. Some people don't have issues and others have then lock up.

|

2005 YZ250
1998 YZ250
2005 KX250F

80% of the time it works every time
IG @hamdaddyof2 & @2HRacing
Thanks to : Factory Effex, N2Dirt, Acerbis, DT1, O'Neal, Matix, FMF, ASV, 100% & Mika Metals

12/6/2018 4:02 PM

mattyhamz2 wrote:

I've got one in the garage right now. Been sitting for years, but should be good to go still.

Check that Wiseco crank and keep an eye on it. Some people don't have issues and others have then lock up.

Well I'm still in my tear down and check phase. I wouldn't have thought that brand would have issues. What other brand do you recommend to check out? I'd be pissed if this thing explodes after I replace every nut and bolt and bearing. If you find some spares let me know i have a PayPal account.

|

12/6/2018 4:07 PM

Also if you look in the background of my last pic you can see how trashed the clutch basket is, I have found a good used complete low hour one for $100. Also replacing every bearing in the case, looks like the clutch lever seal let water into the one bearing, so it's worth it to me just to replace them all at this point

|

12/6/2018 4:09 PM

mattyhamz2 wrote:

I've got one in the garage right now. Been sitting for years, but should be good to go still.

Check that Wiseco crank and keep an eye on it. Some people don't have issues and others have then lock up.

rssuby2001 wrote:

Well I'm still in my tear down and check phase. I wouldn't have thought that brand would have issues. What other brand do you recommend to check out? I'd be pissed if this thing explodes after I replace every nut and bolt and bearing. If you find some spares let me know i have a PayPal account.

I bought an 03 yz250 a couple months ago for parts. Brand new wiseco crank with less than an hour of ride time and the rod locked up. It's a pretty common issue from my research. Like I said though, some people don't have issues and others do.

I always recommend OEM. OEM OEM OEM for cranks.

|

2005 YZ250
1998 YZ250
2005 KX250F

80% of the time it works every time
IG @hamdaddyof2 & @2HRacing
Thanks to : Factory Effex, N2Dirt, Acerbis, DT1, O'Neal, Matix, FMF, ASV, 100% & Mika Metals

12/6/2018 4:23 PM

mattyhamz2 wrote:

I bought an 03 yz250 a couple months ago for parts. Brand new wiseco crank with less than an hour of ride time and the rod locked up. It's a pretty common issue from my research. Like I said though, some people don't have issues and others do.

I always recommend OEM. OEM OEM OEM for cranks.

Do you recommend O.E. pistons also? I can still get those and ebay O.E. rings

|

12/6/2018 4:31 PM

rssuby2001 wrote:

Well I'm still in my tear down and check phase. I wouldn't have thought that brand would have issues. What other brand do you recommend to check out? I'd be pissed if this thing explodes after I replace every nut and bolt and bearing. If you find some spares let me know i have a PayPal account.

mattyhamz2 wrote:

I bought an 03 yz250 a couple months ago for parts. Brand new wiseco crank with less than an hour of ride time and the rod locked up. It's a pretty common issue from my research. Like I said though, some people don't have issues and others do.

I always recommend OEM. OEM OEM OEM for cranks.

rssuby2001 wrote:

Do you recommend O.E. pistons also? I can still get those and ebay O.E. rings

OEM or ProX. ProX pistons are OEM with a different box. I've never used them before, but Vertex is another good one. A lot of guys have good luck with Wiseco pistons, but I've seen a lot of them break in less than 5 hours.

|

2005 YZ250
1998 YZ250
2005 KX250F

80% of the time it works every time
IG @hamdaddyof2 & @2HRacing
Thanks to : Factory Effex, N2Dirt, Acerbis, DT1, O'Neal, Matix, FMF, ASV, 100% & Mika Metals

12/6/2018 4:36 PM

mattyhamz2 wrote:

OEM or ProX. ProX pistons are OEM with a different box. I've never used them before, but Vertex is another good one. A lot of guys have good luck with Wiseco pistons, but I've seen a lot of them break in less than 5 hours.

Yea i have seen the pro x come up. Thanks for the help, I have built plenty of air cooled 4 strokes, this is my first 2 stroke, completely different animal

|

12/6/2018 6:36 PM

rssuby2001 wrote:

Today I did get to dissamble the cylinder and exhaust valve. I was excited to see someone has gone through and cleaned up and ported the cylinder, also found someone had broke a screw off in the reed valve. The aluminium gears on the exhaust valves are also a little worn. Any input in what reed valve set up to run? I'm not sure what brand is in there, they are carbon fiber.

That intake looks like a boyesen rad valve, they still sell the replacement reeds for that...also inspect the rubber boot for cracks, boyesen sells the boot & gasket also...and they are also in Pa...

|

12/6/2018 6:40 PM

rssuby2001 wrote:

Today I did get to dissamble the cylinder and exhaust valve. I was excited to see someone has gone through and cleaned up and ported the cylinder, also found someone had broke a screw off in the reed valve. The aluminium gears on the exhaust valves are also a little worn. Any input in what reed valve set up to run? I'm not sure what brand is in there, they are carbon fiber.

sandman768 wrote:

That intake looks like a boyesen rad valve, they still sell the replacement reeds for that...also inspect the rubber boot for cracks, boyesen sells the boot & gasket also...and they are also in Pa...

Thanks, yea the boot needs replaced, it's a shame when people don't know what they are doing when they shove 2 big screws in aluminum and break it

|

12/6/2018 6:49 PM

A lot of really good info about Kx building on "KX riders.com" ...make sure you surface your case 1/2"S good before reassembly to prevent air leaks, the KX"s donot use a gasket, so a nice clean surfaced set of cases is important ...

|

12/6/2018 6:56 PM

sandman768 wrote:

A lot of really good info about Kx building on "KX riders.com" ...make sure you surface your case 1/2"S good before reassembly to prevent air leaks, the KX"s donot use a gasket, so a nice clean surfaced set of cases is important ...

Thanks, yea I have a few kz750, I use yamabond, I have one half completely cleaned, other is almost done. I will dry assemble and check, since I got the bike in pieces

|

12/6/2018 6:56 PM

rssuby2001 wrote:

Kidkawie I have checked that, it is a 94 case. I do have a 94 trans that came with it, one of the gears is a little worn, I was trying to i.d. this other gear set so maybe I could make a best guess on what ratio to run. Or do I just stay with the original set up? Since I have never ridden this bike I have no idea what to base my decision on.

People generally swap out the 99-01 trans for an earlier model because the 1st gear is too tall. I can only assume its a L model (99-02) used replacement trans for the damaged one you have. I'll be removing my 94 trans after the holidays (KDX swap) if your interested and not in a hurry. It works just fine.

Lose the Wiseco crank, its junk. Hot rods, OEM or Mr Crankshaft for a rebuild.

I spent over 6 years doing a factory resto on my 94. It was built with all oem parts. I just turned it into a supermoto, tired of seeing it in my livingroom.

|

04 KX125
94 KX250SM
75 Z1-900

12/6/2018 7:08 PM

Kidkawie wrote:

People generally swap out the 99-01 trans for an earlier model because the 1st gear is too tall. I can only assume its a L model (99-02) used replacement trans for the damaged one you have. I'll be removing my 94 trans after the holidays (KDX swap) if your interested and not in a hurry. It works just fine.

Lose the Wiseco crank, its junk. Hot rods, OEM or Mr Crankshaft for a rebuild.

I spent over 6 years doing a factory resto on my 94. It was built with all oem parts. I just turned it into a supermoto, tired of seeing it in my livingroom.

Yea I see a lot of people don't like that crank, I guess I will make other plans for that, i was thinking of grabbing a used own and sending to out for a rebuild and wielded. I mostly was trying to find out why that one gear was under cut on the one side on the newer transmission. I have done more reading, as you said it seems people want the earlier ratio. I have seen a few supermoto running at Summit Point in West Virgina. It looks fun, this is is my 6th bike, I may have to unload a few before I do another.

|

12/6/2018 7:13 PM

I don't mind researching and building a $200 bike from the ground up, instead of a $1,500 bike that went bang on the trails

|

12/6/2018 7:27 PM

I paid 750 for mine and put probably 4k into it before the SM conversion. That was another ....1600 or so.





|

04 KX125
94 KX250SM
75 Z1-900

12/6/2018 7:38 PM

Kidkawie wrote:

I paid 750 for mine and put probably 4k into it before the SM conversion. That was another ....1600 or so.





Good looking bike, how do you like it as a supermoto? I wasnt sure how the 2 stroke wound feel on the pavement. The local KTM dealer had a demo day this past fall, I got to ride all of the street models, i did enjoy they 690 enduro, but while i was riding i was trying to think how a 2 stroke would be

|

12/6/2018 7:48 PM

It is what it is. A mx bike is not good on the street thats why Im doing the trans swap. Im running 14/43 gearing right now. 1st gear is great, then I just up shift to 5th in like 4 seconds.....just cruising. BTW, its plated, I get tons of looks. lol

|

04 KX125
94 KX250SM
75 Z1-900

12/6/2018 8:03 PM

Biggest drawback is the mx trans, after tgat its trying to cruise/maintain speed without the bike going on and off the pipe. Since you're new to 2 strokes, its like someone repeatedly pushing a nitrous button.

Fun as heck tho!


|

04 KX125
94 KX250SM
75 Z1-900

12/7/2018 3:27 PM

Kidkawie wrote:

Biggest drawback is the mx trans, after tgat its trying to cruise/maintain speed without the bike going on and off the pipe. Since you're new to 2 strokes, its like someone repeatedly pushing a nitrous button.

Fun as heck tho!


That bike looks really good, I hope mine will get there by the spring. Im currently trying to build this one while finishing my kz750 track day/daily bike. I did locate a fairly cheap O.E. crank. I will have to sent out, rebuilt and wielded.

|