Rebuilding my 1987 KX 250

[bens87braap]

All new to me i havnt done it yet but my 87 will need cases split at Christmas time wanting to do it myself so i following this thread.

[dinkyguitar]

So I finally started putting the bottom end together.

I took all the bearings and bushings on both cases and stuck them in the freezer.

I then took a hot air gun and started heating the case where the bearings would go and was able to install them.

The crank seals went in fine (those I stuck in the freezer also). 1 I had to persuade using a socket and hand pressure. I kept checking the other side to make sure they were all seated properly against the ridge.

1 main bearing dropped in while the other needed some tapping with an hammer with the old bearing stacked on top. I kind of expected this since 1 bearing is always stuck to the crank when you remove the crank, while the other remains in the case.

There's 2 bushing for the trans that were also installed. Both needed a little persuasion but I got them installed.

After that, I mocked up the trans with all new cerclips and made sure I could turn the shift drum through all the gears.

1 thing that pissed me off was, there's a c clip on the trans that holds the bearing by 1st gear. I had to spread the clip pretty far to install it and eventually stretched it. I couldn't install it without this happening. And it's because when you install the clip using the c clip pliers the clip edges get in the way. It ovals the c clip and the edges of the clip hit the shaft. I'm not sure if I should file the edges of the c clip.

On the old c clip, the edges are rounded a little and you don't have to open the c clip as much to install.

The other thing that has me confused is, with both crankcase halves together laying upright, I can spin the trans through all the gears and get it in neutral. But the minute to tilt the motor, the gears bind on each other.

Is this normal? The only other thing I can think of is that my 4th & 5th gear shift forks are reversed, but I'll check that again tonight.

Not much to see here, but this is the cases with new bearings and bushings.



dinky,

[sandblaster]

Scroll down about half way...
You can tighten your C clips right up...
It's a Motorrad thing 

http://www.oem-cycle.com/forum/viewtopic.php?f=5&t=661

[dinkyguitar]

Thanks for that link...

And here's the clip I'm talking about.....and that's the edge causing the problem. I haven't screwed the cases together since I'm still checking the trans works, so I can take it apart. (picture taken was when I was disassembling the motor)



I'm also freezing my crank to install it....

Question on whether this will work for getting the crank in, and screw both case halves together.

1. Freeze the crank.

2. Apply yamabond to one side of the crankcase half.

3. Heat the other half of the case in the oven.

4. Heat the main bearing on the other crankcase with a hot air gun.

5. Quickly get the crank and drop it into the case.

6. Get the other case from the oven and hopefully close both cases.

I'm not sure how yamabond will hold up to 1 case being clod while the other hot. I'd imaging just as long as you don't exceed 200 deg f., you should be OK. You might not even need to heat the case to 200.

When I used my hot air gun, my case only got to 130 deg f.

dinky,

[dinkyguitar]

So I was able to get my crank in, and seal the cases following my steps.

It was very nerve racking making sure I had everything ready.

1 case half was on the barbecue heating up while the crank was in the freezer. I had the case heated to about 170f.

Then I had to lay a bead of sealer on the other half. After that, heat the bearing with my heat gun, run to the freezer, get the crank, and  nervously, slam it in. Then run and get the other case off the grill, position it and it dropped in. I gave the back end of the case a slam with my hand to seat the 1/16" gap.

While it was cooling, I hand tightened the case screws, then followed by little turns of the screws to evenly seat the cases.

After I calmed down, I looked it over and everything seems OK.







I read somewhere that you shouldn't put to much yamabond on, and I was pleasantly surprised after tightening the screws it looks like I used just enough.

And here's the next project I have to tackle. Cutting that sprocket bushing shorter. They don't make that part anymore, but I was able to find a thread where someone listed this part as an exact fit, but you need to make it shorter....



It should all down hill from here....hopefully anyway.

dinky,

[bens87braap]

well done dinky top job

[Oblivious Maximus]

 Now that's good news. But what was the problem with the gears jamming up when you tilted the engine?

 My primary drive shaft leaks a (very) little and the collar is slightly grooved. I remember reading that same post somewhere.

 Could you please post the part # for the spacer you bought, or the year bike it was for ?

 If you have a machine shop nearby they could trim it up pretty easily.

 Your gonna love this bike..

 










 

[dinkyguitar]

 Now that's good news. But what was the problem with the gears jamming up when you tilted the engine?

 My primary drive shaft leaks a (very) little and the collar is slightly grooved. I remember reading that same post somewhere.

 Could you please post the part # for the spacer you bought, or the year bike it was for ?

 If you have a machine shop nearby they could trim it up pretty easily.

 Your gonna love this bike..

I think the problem might have been because the cases were not screwed together. I just tilted the case so there might have been a slight gap between the cases.

Now that I got the cases together I think it should be OK. I looked over the gears several times, and made sure the 2 clutch forks were in the correct order. Plus I have all new cerclips. It seems to be shifting good now.

So the collar part number is 92152-0150. It's a 30x25x13.2 from partzilla for 06-12 KX & KLX 450's. The stock collar is 30x25x9 so it needs to be cut down.

This is how I did mine. I slipped the collar on a 1" drill drum sander and used grinder. I actually used a "thin" cutoff wheel. Spin the drill and grinder in opposite directions and stop several times to cool it down otherwise you'll melt the rubber. Scribe a line and hold the grinder steady. Put a level on the blade to get an idea of how you should hold it.



Cut it "a little" thicker than you need and shave it down. When you start shaving it down, use the drum sander with the collar to hold so your hands don't get hot. Also, the collar is made of hard steel so it will take time to get it right.

Also, as far as how much to take off, with the stock collar is had about a 2mm space, so my collar wound up being about 9.5 to 10mm thick. It varied in thickness because it had a slight wobble when I was cutting it. Plus grinding it by had is very hard to get accurate.

I think as long as the collar fits with the sprocket and cerclip, you should be OK. It's rotating with the bearing and sprocket anyway, so the assembly should be forgiving as far as wear.

[sandblaster]

Love how you did this.
I have to do stuff like this all the time.
I'm glad I am not alone... 

[Oblivious Maximus]

Thanks dinky, for your time and info. It's now on my to do list.

[dinkyguitar]

Motor is finally assembled! Every bolt cleaned, new gaskets, all new bushing, bearings, new rod, & piston.

I hope she starts  









Here's my power valves before,



And after cleaning...soaked in gasoline.



That's also the grease I used for the power valve gears, and on seals and parts that operate by high temps such as around clutch and exhaust. It's that high temp moly grease.

My next steps will be to install it in the bike, make the final connections and see if she starts.

My only concern is that I don't have a place to ride her yet.

Can I break in the motor just putting around the yard?

dinky,

[sandblaster]

You could do your heat cycles no problem but to finish the job I would think you would need it under load..

[dinkyguitar]

My manual doesn't really say how to break a motor....nor do I have any experience.

I remember in high school my friend had dirt bikes and he never broke them in...In fact he always used to say "break a motor in hard and it will last forever"....

What is the preferred way to break a motor in?

dinky,

[sandblaster]

I use a very similar method to this:
http://www.oem-cycle.com/forum/viewtopic.php?f=5&t=769&p=2866&hilit=engine+break+in#p2866

[bens87braap]

Engine looks great Dinky well done.

The power Valves one is alloy one is steal?

Do we run any specific oil or mix on the run in cycle I have purchased stock needle and jets?