YZX500 Project

[scottysg]

Hello, this thread will attempt to document the process I go through to install a KX500 engine into my street legal 2002 YZ250 dirbike.

Purpose: The goal of this project is to have a true, no compromise dirt bike (2 stroke) that also performs reliably for consistent road use, and in motord trim gives quick road bikes a run for their money. Budget has not been decided. In my experience, these projects always break it so I may never set one. Thriftiness will be required.

Motivation: I bought the YZ250 to get back into the off road scene after being away for 5 years. The kicker was I also wanted to get to work on it legally. Something about starting the day smelling that castor oil... I guess we all have our addictions! (another one is boost, so that will come to this bike one day, but not now)

The YZ's been great to get to and from work (17" wheels, 15-49) since the max speed limit is 45 on my route, but it really doesn't have the torque to pull the highway gears (14-40). And don't even get me started on lack of wheelies...Needless to say, for my application there is no replacement for displacement. Enter K500!

The 1988 KX500 motor I bought appears to be in good condition. It shifts nicely, piston and cylinder seem brand new, and it was sold as a fresh rebuild, though with unknown porting, and high compression piston. The inside of the cylinder that I can see looks good, with totally fresh looking crosshatching from hone. I need to get a little mirror to see the other side. The engine did not come with any external electronics, but the flywheel is there with wiring harness coming out from behind it. I have no more info on it, so I should probably take it apart to check everything. If anyone knows how I could do that without needing new gaskets, please let me know.

I have been looking at an ecotrons efi kit, to solve the lack of CDI and it also allows me to upgrade to a turbo setup when I get used to this bike how it is. Its very reasonably priced, around 500. Need to do more research here. I feel like this would be a great possibility for an arduino, but I don't know if I have time for that now. Open to suggestions for this problem.

Check it out!

[umberto]

Is the KIPS valve assembly in place and not cracked?  That's one of the issues I had with my 88.  Also, does your engine have the KIPS cast onto the left side of the cylinder?  For some reason your cylinder looks different than mine, but I can't find a decent picture of mine from that side.

[scottysg]

Umberto, KIPS is cast into the left side of the cylinder.

Tonight I will get a light up into the exhaust and look for cracks in the valve. Then I will remove the side cover for the kips and see if I am able to actuate the valve.

I noticed the rings where the exhaust springs hook onto the cylinder are pretty worn out. The springs have acted like a knife, sawing away at the cylinder material. If I can find a stainless steel grommet that size to put into those holes to prevent it from getting worse, I think it would be a good thing for me to do. I will get some pics of that as well.

I got an email back from ecotrons. They suggest their 2 stroke kit with a 38mm throttle body. They corrected me, telling me that their unit does not control spark, only fueling, so I will need to get the CDI and coil anyway. $799 was the quote price for EFI. Then I would need to upgrade the stator to supply enough power to run it all, another $500 ish. Looking at 1500$ to go EFI yikes.

[scottysg]

Here is a shot up into the exhaust port. Nothing seems cracked in there. Using my fingers, I can rotate the power valve drums, not sure if that is how it is supposed to be.


This shot shows how worn the exhaust spring retainer is!


Using a 10mm on the power valve arm bolt, the two drums are operated and open to just the right location. No visible cracks in them.

Check out this last shot. If you look real close, you can see someone tried to chamfer the edges of the ports. They are not done evenly at all, especially the one left center. Is this really bad?

[umberto]

Can you see if the entire KIPS linkage is in place?  You shouldn't be able to rotate the drums with your fingers.  You may be missing a part or two, which isn't a big deal (I bought several parts for mine on eBay and Rocky Mountain).  The important thing is that the drums are in place and in good shape.

[dave916]

I Would not go moving kipps arm by the 10mm nut
The GOVERNOR roller bearings can fall apart  inside the clutch cover

Looks good  inside that  cylinder

[scottysg]

The whole assembly seems to be there. They move together so it seems ok, but you're right umberto, I probably shouldn't be able to move them with my finger. Also, are you still thinking that my cylinder looks different than yours? Im curious, especially because I really have no way to verify the year mine is.

Yikes thanks for the heads up on not moving the arm dave916. I don't want problems in the cases!

Bought a coil today for 13 $, Im still on the hunt for CDI, kick starter and expansion chamber. Id like to have a compression release too, so Im reading all about that.

[umberto]

Maybe Dave916 could comment, but I think your motor may be an 87.  This motor Foxx posted from eBay looks similar to yours but with paint.

[scottysg]

Umberto, you may be right! If i post my engine serial, would we be able to identify the year?

Parts Updates!
       -Used '88 kx250 CDI (fingers crossed its gonna work alright)
       -brand new coil
       -Used fmf fatty with a broken mount (ok since I have to chop it to fit my frame anyway)
       -Used ignition cover and gasket

Still need:
       -Kick start lever (read the '04 is the best) Anyone got one!
       -Sending my head to Larry next Tuesday for a compression release since I'm 6' @ 150 lbs and i need my energy for riding! Im a packaging engineer with full access to multiple cad programs, countless materials and machines so its gonna be the best custom packed cylinder head ever! Let me know if anyone needs a custom package for engine parts, I am the man with the solution!

On another note, work is relocating me from Orange county to ventura county starting jan 1. I just found out a couple weeks ago. Switching from designer to project coordinator and sales. Hopefully more money for buying motorcycle parts! That will delay this project slightly as i will be looking for a place to live and moving. Considering full time motorhome living to save money haha pm me if you have any advice or tips for that. Also I'm going to thailand for 2 weeks starting wednesday then idaho for christmas when i get back. So ill be making pretty much no progress for at least 5 weeks unfortunately.

[reklessj]

I lived in a 40' 5th wheel for 7 years. It was cool you definitely meet some interesting people. RV parks aren't too hip to dirtbikes!! Now that I own a house n have a family I would never do it again. Only tents when we camp n ride, but the wife has been bugging for a motorhome

[scottysg]

Updates today! Been really busy with work this month. finally got time to jump on this project. No mods have been done to the frame. The KX fits with the rear axle and lower engine bolt lining up. will need to modify the head bracket and make some adapter for the front engine bolt.

[scottysg]

Last night I used a dremel, a file, and tap magic to remove 0.315" from the inside chain side of the swing arm because the kx motor is quite a bit wider at the rear mount that the yz motor. Test fitted, and the sprocket looks like its centered pretty good with the rear sprocket. But there should be a slight gap between the swingarm and the engine. So I will remove material to get to .375" total material removal. This is very easy to do, just slightly time consuming.

Now the holdup and the hard part is removing this 0.375" from the bearing pin. I couldn't even scratch that with my fancy file, it is extremely hard material. Ill have to take that to a machine shop to throw on a lathe. I found a bearing online that will replace the 2 bearings that are currently in each side of the swingarm, except of course it is .375" shorter that the 2 oem bearings total width together.

Once the rear mount is sorted out, I can move on to the front mounts. Then figure out what carb I want to run.

As a side note, there is a slight bit of slop on the flywheel. Like its not tight on the crankshaft and it rotates until the key stops it. I don't have a flywheel puller for this yet but if you guys think thats pretty weird Ill have to just pull the flywheel and make sure the key isn't sheared then lap the crank and flywheel to fit more snugly.

Any thoughts or suggestions are appreciated. I don't know what I'm doing here

[scottysg]

Last night I was able to ream the hole in the engine. used a grizzly 43 64 drill bit. (17.07mm, I read about this on the forums as a good overbore to allow clearance, not my idea) sorry my slash button is broken on my computer. its a hss chucking reamer so it was easily able to bore the hole in the soft magnesium. I also started removing .25" of material from the clutch side of the engine mount, so as to let the engine fit in there. I got tired and wanted to eat before I got all the way to .25". I have .125" to go. Unfortunately I am an idiot and in my stupor didn't realize that the swingarm bolt changed from 17 to 18mm from '01 to '02, which my bike is, so the swingarm pivot bolt still doesn't fit in. So I ordered a 23 32 chucking reamer (18.25mm)to bore it again to the next size.

Also, I removed the flywheel, used some valve lapping compound and worked the flywheel on the crank. both the flywheel and crank had surface rust. Now they're polished clean and after a hit with a mallet, it is locked on there. stator looked good, though i have no experience with kx500s so that comment is pretty useless.

Waiting for parts or tools sucks!! Its so close, the hole is going to be very clean indeed. Today i should be able to finish cutting the motor and getting it fit in the swingarm. Cant wait to get this rear mount figured out and get going on the other mounts. hell i can't wait to spark it up.

Im just lost with how I want to fuel it. I have the kx500 carb and the yz250 carb. But I've read that 500's are hard to tune (and I'm nothing special at carb tuning) and I'm trying to spend my time riding not tuning. not to mention if I'm riding at gorman its freezing then I go to barstow or ocotillo and its 100 degrees out. because of that a lectron sounds very appealing. If any one has some advice on this matter, Id appreciate it. Pics to come tonight.

[umberto]

I have a Lectron on my 525. If you are riding that varied of conditions, it's right up your alley. There are only two adjustments, the needle for open to 1/2 throttle, and the power jet for 1/2 to full. It takes minutes to tune, plus they can get it pretty close from the factory. I bought mine from Packard racing. I have a post on my 2003 conversion showing what mods I did to get it installed.

[ozrider]

now you need black plastics and paint frame green