2003 KX 250 SF Conversion

[dave916]

These motors are never ending when you start doing work to them
As u are gone so far i would check for side movement on the complete crank
I reckon 50% of kx500 have either worn crank journals or main case races

A steel set of valves is what u need {think the 86 had them}

A modded Steel set with a 4mm spacer {nut} loctite to the kiips shaft{see black arrow}

[dave916]

If your kipps valves were not fitted to cylinder i presume the kipps chamber would be opened all the time which kill top end
Bottom end would also be affect as the exhaust sub port would also be opened

Hopefull the valves fitted would have big gain bottom to top
Only down side it may be a bit harder to kick

[umberto]

Luckily, there was no side to side either.   All in all it seems to be a very solid motor. 

I wasn't that impressed with the 88 KIPS valves, they seem to be made of some pretty cheap metal. I wasn't able to locate any 86 valves.  Do you know if the later model valves will work?

[dave916]

Luckily, there was no side to side either.   All in all it seems to be a very solid motor. 

I wasn't that impressed with the 88 KIPS valves, they seem to be made of some pretty cheap metal. I wasn't able to locate any 86 valves.  Do you know if the later model valves will work?

All the KIPPS  valve 86/88 will interchange/ alloy and steel {
IF  You had a steel set i think the should last for ever
The steel one have a narrower stem than the alloy ones

[umberto]

I pulled the cylinder off my bike last weekend, and was going to install the exhaust valves from the 88 head I bought on eBay.  I stopped because I wanted to see if a buddy of mine could make new ones out of steel.  While the cylinder was sitting on my work bench, I noticed that the exhaust ports that tie to the KIPS ports are very different from the 88 head I bought, and the one that came on my bike.  

Here is the 88 head from eBay:



Here is the head from my motor:



Does anyone know why the exhaust ports would be so different?  Maybe the head was sleeved with a later model sleeve?  I'm not that familiar with the K5 heads, and was hoping someone could help me figure it out.  Thank you!

[DoldGuy]

Umberto,

Your original cylinder has an "89" & later sleeve, the eBay cylinder is the correct layout for the "88" & earlier....

DoldGuy

[umberto]

Thank you for clearing that up for me.  Do you think the later model sleeve will cause any issues with the engine's performance?  Both of the exhaust ports flow into the hole for the KIPS opening, I just don't know if they line up with the holes in the valves anymore.  Do you think I should clean up the 88 cylinder and use it instead?

[DoldGuy]

I personally like the 88 cylinder (eBay one). There has to be a huge loss of power with your current cylinder as most of the top of the port is being covered by that sleeve & the sub port windows are a big restriction too. Just my $.02

DoldGuy

[sandblaster]

I say open her up and let her flow... 

[motopunk]

I say open her up and let her flow... 

mike, this mod, youve done, will take low end and add topend power  ... 

[dave916]

Both being sleeved is a pain,
The ebay88 sleeve is going to a bit restricted on the inlet side{ inlet ribs on sleeve}

Not sure how your orginal  cylinder will work out
issues will be higher exhaust centre port {and no centre flapper valve} will loose bottom end
Sub port not matching outlet
matching sleeve on inlet side miight have issues

Are the kipps chambers stiil opened on orginal cylinder? {since no valves were fitted]

I  i would run the ebay cylinder {if no wear} or try and find a  cheap 88 plated cylinder
A stock 88  for example {88 is one of the best early cylinders}
inlet side




 

[umberto]

The 88 cylinder does have the KIPS valves, they are just out right now. I have a buddy trying to make me a copy out of steel. I think I will take a closer look at that cylinder and see if it will work with this engine.   Thank you for the advice everyone.  If I get adventurous, I will get out the air grinder, harken back to my hot rod days, and give Sandblaster's port mod a try.   

[alexander-vmann]

after reading this i kinda wanna put my 87 k5 in a 2006 kx 250, thats for sale near here 

[umberto]

It's really not that tough to do. The 06 should be even easier than this 03 has been, because it's a little bit bigger bike.

[zz3gmc]

Actually, the 05-07 KX250s have a narrower frame. My 07 feels like a 125 compared to the 03/04 KXs. I prefer the 03/04 over the newer gen frames. 05 up have a quirky handling trait that would just be accentuated with a 500cc mill bolted in place.
I believe it would be pretty much the same amount of work to do though.