XR400R, what is the valve adjust principle and interval?
 

Is it done with shims or the like or with the good old counternut method ?

How often are they to be adjusted ?

How often is the timing chain to be adjusted, changed ?

Don't worry, it's the good old counternut method (if by that you mean screw and locknut)...

If you are buying secondhand it's probably best to give them a check, then I've found once a year or 12,000 miles is fine as long as you are not murdering the engine...

The cam-chain should be good for 18,000 miles at least - I changed mine at around 22,000 miles and there was plenty of life left in it, although it had stated to stretch.

The whole valve train on the XR400 is pretty robust... some people say the auto cam-chain adjuster can wear/stick, but I've never found that myself...

xxx

just to add the valve settings are.........

0.10mm {0.004in } intake
0.12mm {0.005in} exhaust

Hope this help's