Rebuilding my 1987 KX 250

[dinkyguitar]

Engine looks great Dinky well done.

The power Valves one is alloy one is steal?

Yes, I noticed that too, they are made from different materials. Not sure why...

When you install the power valves the manual says the valves will have "dots" on top of the gears to align with the rack but mine didn't have any.

On the valve with the bigger gear, one of the teeth are ground lower. On the other valve if you look closely the top of the gears are beveled....one is beveled slightly more than all the others. This is what I used as an alignment mark to the rack. Not sure if it's right, but once installed the valves are open when the rack is fully out.

Also both alignment marks are straight in line with the edge of the power valve cut out.

This area:



dinky,

[Goat]

Very nice job. Looks brand new

As far as power valves go... If they are closed with the rod all the way in and open with the rod all the way out then it is set up properly.

I do break in a little different than SB. I do a half dozen heat cycles. Retorque head and cylinder bolts between heat cycles. Then for the first 15-30 minutes on the first ride I play in first gear at various rpms. After that it's balls out for 10 minutes and let it cool down completely. Every ride after that I ride like I normally do. Been doing it that way for 20 years and have never had a problem.

[dinkyguitar]

Very nice job. Looks brand new

As far as power valves go... If they are closed with the rod all the way in and open with the rod all the way out then it is set up properly.

I do break in a little different than SB. I do a half dozen heat cycles. Retorque head and cylinder bolts between heat cycles. Then for the first 15-30 minutes on the first ride I play in first gear at various rpms. After that it's balls out for 10 minutes and let it cool down completely. Every ride after that I ride like I normally do. Been doing it that way for 20 years and have never had a problem.

As far as I know, if you pull the rod out both should be open, and you should see a smooth transition between the jug through the power valve opening and out the exhaust. They also open at different rates. So on mine, if memory serves me right, looking through the exhaust the left power valve will open first followed by the right and then both fully open.

Thanks for the advice on the break in.....I'm currently trying to find a way to take the bike somewhere for break in. My yards on big enough ride....

Any northern NJ riders out there?
dinky,

[bens87braap]

Thats correct Tom u have set them up correctly I also asked that question somewhere on here and the 87 doesnt have the dots.   the beveled teeth are our indicator and the bigger gear makes that valve open slower. Great job u can come break it in on my property in Australia hehe

[dinkyguitar]

Great job u can come break it in on my property in Australia hehe

Always wanted to visit Australia  .

dinky,

[dinkyguitar]

Progress today...

I got the motor in, and made a kickstand....still needs some tweeking to fit right.







dinky,

[reklessj]

Lookin killer man!! Keep us posted with you progress!

[sandblaster]

It's purdy.

[yeomans]

I've seen all alloy sets of valves and all steel sets as well.
I think someone broke a valve in the past and replaced it.
In 1987 kx 500's and 250's you start to see the use of both alloy and steel valves sets that year (86 are all alloy). They also used both timing marks that year as well ( short gear tooth and the stamped dot).
When you would have ordered a nos valve the replacement would have been an alloy valve. I've never come across a nos steel replacement valve.
My guess is that it originally had a set of steel valves in the motor.

Beautiful bike by the way.

[dinkyguitar]

Another update...

Here's my home made kickstand....I later changed to a heavier spring and it's perfect. That satisfied feeling you get after you made something and it came out exactly how you wanted it.





More pic's.





A little set back that I has was a leaky sprocket.

It was strange that it started leaking after having oil in it for over a week. It wound up being that o ring between the sprocket spacer. I didn't install one, but now I do.

And the grand finale was that I got to start it     

After months of putting her together I gassed her up and she started on the 3rd kick  . Kind of loud with any baffle material.

I'm happy she started....and with a used CDI I bought $40....That was a hard to find part and I just wanted another one in case mine didn't work. Really was the only part I didn't have a duplicate of. Everything else I could find.

So far I've done 2 heat cycles...more tomorrow.

Oh, and another set back was that my left radiator is leaking  down on the bottom. Only leaks after it has a little pressure. I'll have to see if I can fix it.

Maybe I'll post a video of it running tomorrow.

Very happy I got her running.

dinky,

[bens87braap]

Great Dinky yeah post a vid I wana see 

[Foxx4Beaver]

another set back was that my left radiator is leaking  down on the bottom. Only leaks after it has a little pressure. I'll have to see if I can fix it.

I've used the 2 part liquid epoxy J.B. Weld, not the 2 part putty, on a very small hole on my 500 due to the radiator screen wearing through...this was 2 years ago, and it's still holding strong.

[dinkyguitar]

I've used the 2 part liquid epoxy J.B. Weld, not the 2 part putty, on a very small hole on my 500 due to the radiator screen wearing through...this was 2 years ago, and it's still holding strong.

Thanks for the tip...

dinky,

[Foxx4Beaver]

took me a little while to find it so I could post a pic...but this is what I used...

[dinkyguitar]

Got it!

I think the trickiest part will be finding exactly where the leaky is....Probably have to use compressed air.

dinky,