KDX 400 Questions

[Justinsavs]

I recently aquired a 1980 KDX 400 for $700 and I've been searching for motor stuff for the last 2 weeks, and I'm probably pretty close on giving up. Anyone have any idea what I can do? You can't buy the Pistons online unless you special order them from Wiseco, (which I heard you can't order just one) and I'm not sure what it takes to rebuild a bottom end in the motor. Since finding a piston is hard, is it possible to use a kx500 air cooled or liquid motor in the KDX frame? Would it bolt up without modification? Are parts easily obtainable for this? What do you guys think? So far the motor starts up pretty easy, 3-5 kicks when cold, 1 kick when warm. I don't want to push this motor very hard in case I might break something and not have the ability to replace it.

Also what year did they start using the square light on these? I'd like to use one instead of the round light. I'll leave a couple pictures.

[david]

The piston has been unavailable for several years and everyone that asks this question get the same answer. Don't know if anyone has found a solution because no one posts one, I'm sure everyone just gives up. I would just enjoy it for as long as you can then part out what's left. There is a NOS set of rings on eBay for $145.00 right now.

From what I can tell, it's an 80mm bore. The Kawasaki ZXI/STX 1100 jetski is an 80mm bore also, but I have no idea if the pin size is compatible or if the pin height is correct or if the ring end gaps are in the correct location, ect.

[Rd400pi]

First thing I did was Swaintech coat the piston. This built up enough thickness to get back to where it needed to be. I used their "thick" option. I found a set of rings through a dealership. Later on after much watching of the fleabay, I stumbled upon an NOS piston and seperatly, another set of rings. I used the NOS one and have the coated piston on the shelf. This is a painfully long story to encourage you not to give up.

Mike

[KDX Geoff]

First thing I did was Swaintech coat the piston. This built up enough thickness to get back to where it needed to be. I used their "thick" option. I found a set of rings through a dealership. Later on after much watching of the fleabay, I stumbled upon an NOS piston and seperatly, another set of rings. I used the NOS one and have the coated piston on the shelf. This is a painfully long story to encourage you not to give up.

Mike

I've done the piston coating thing too (put on a thou coating to increase the diameter by 2 thou) but not got the engine back together yet.

Persistence beats resistance