A couple of months ago I bought what seems to be a 2003 klx250. (by the looks of the frame, saddle and tank at least)

​I use this bike to guide dual sport tours in Northern Vietnam so the last thing I want is it breaking down on me while I take guests to remote areas. During my last trip I started to hear a resonating sound coming from the engine at a certain rpm (mid range) so it's time for me to open it up. I have no idea how much mileage the bike has done and what the service history is.

My thoughts are to open it up and replace
- big end
- piston
- cam chain

And possibly the crank bearings while I am at it.

What are you guys take on this? Should I replace something else while it's opened up?
Any advice would be appreciated!

Cheers

 

I'd check to see if the noise is coming from the cam chain tensioner first.

 

I agree with canklx. The automatic cam chain tensioner is about the only known point of failure on these bikes. Did you check for any sparkly bits in the oil?
KLX678 makes a manual cam chain tensioner if that is what is making the noise. The manual one won't fail. He has a European distributor too.
Krieger Cam Chain Tensioners

 

I do sell them and can ship to Vietnam - have done it already. It does sound like what you describe is the typical noise when the cam chain tensioner quits working. Replacement is non-invasive and even shipped to Vietnam is under $75 total.

 

Thanks for the response guys.

I'll definitely check out the cam chain tensioner. I doubt the sound is coming from there though because it's not so much the sound of a slapping chain but more of a bearing that's running dry or something. Bit hard to describe and maybe I'm completely wrong but that's also why I want to open it up to find out more. I'll definitely keep the Krieger Chain Tensioner in the back of my mind.

I'm used to competative dirt bikes/enduro bikes such as wr450f, yz450f and exc450 where you have to change all the things that I mentioned in the opening post on a somewhat regular base.

Did you guys ever change one of those things on a klx?

 

I thrashed mine for 64,000 miles before it gave out.
My cam chain is still in spec, thanks to KLX678's cam chain tensioner.
Change the tensioner first.
I bet that fixes the noise.
This motor is super reliable if you change the oil and check/adjust the valves on a regular basis.

 

If your KLX250 is a kick start model, check the idler gear in the kick start mechanism for slop on its shaft.
https://www.bikebandit.com/oem-parts/2003-kawasaki-klx300r/o/m141888#sch294575
p/n 59051B