kx85 question

Ok I was about to put this bike together and was about to ask a question,

I thought I bought an 02-05 cylinder that was sleeved. I am putting this on a 2001 bottom end and then into a 2006 bike.

My question was going to be the timing changed a bit in 2006, should I be using the 2001 cdi I have or the 2006 cdi?

Now though I noticed the exhaust pipe wont fit in the cylinder which tells me the cylinder is a 2001. I noticed the 01 and this cylinder have a thicker exhaust collar but small exhaust pipe fitting. I assume I can have this bored out a bit to fit the 06 pipe?

Once I do that, is the timing related to cylinder ports or the exhaust pipe, so should I be using a CDI the same year as the cylinder or the same year as the exhaust pipe.

Thanks for any tips

Well I thought I would easily get the exhaust port bored larger at a machine shop, but it would be cheaper to buy an aftermarket pipe than what they want to setup a maching for this one off job.

Any suggestions on what i could use to bore/hone out the exhaust port myself?

Unless you know exactly what you're doing, don't touch it. Porting on a 2 strokes ports can drastically change alot of things. Usually for the worst. Leave this stuff for the professionals. They have flow benches, CAD, CNC equipment & alot of understanding of how an engine reacts when certain things are done.

Port timing can easily be changed by adding or losing just a few thousandths of an inch.

These aren't your typical Honda B-18 4 banger head where you can just go in a polish up the runners a little.

Look into TDC (Brent) or Eric Gorr. This is what these guys do for a living & they're good at it.

vvvvvvv....Read my Sig........vvvvv

Edited by SAPPERS

I guess I used the wrong term, I'm not working on the exhaust port.

My problem is despite my best efforts I ended up with a 2001 kx85 cylinder, which has a smaller exhaust collar I'll call it.

The slip on exhaust for this 2001 takes a smaller pipe, seems to actually be the same size as a 98-2000 kx80 or kx100 pipe.

The bike im planning to put this cylinder in is an 06 which has a larger pipe.

I actually found an old thread on here where you Sappers said that 01 -05 kx85's take the same exhaust pipe. I think you even called it an exhaust port too lol


But I'm now pretty sure that all kx85 cylinders 02-12 actually have the bigger exhaust collar and have the same factory pipe part number. Leaving 2001 cylinders as the only kx85 cylinders with a smaller collar that takes the older smaller pipe.

And despite me verifying with the seller the cylinder was newer it inevitably is a 2001.

I just tracked down a friend here who has a 99 kx80 pipe, so if that fits, I no longer need to have the exhaust collar on the cylinder made larger.

Edited by thekidd77

If you have both pipes, you could have the 2001 collar welded on the newer pipe, or just use a 2001 exhaust. A machinist could make a collar pretty cheap. You may have to fab some mounts, but that would likely get you the best possible perfomance.

Sorry about your luck, but I was looking at a 2001 KX 85 and passed for parts availabilty / interchangability reasons because it was a one-year model. I have a 2001 KTM 50 with the same issues, can only get OEM parts because it was a one-year model.

Edited by gsa102

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