Newbie/YZ400 motors

Hello all - I'm the new boy, so it's my round at the bar.

Been a member of Bikenet and for quite some time, happened across this site via a link on

I've had a couple of YZ250's (I have a really nice 95 YZ250 for sale BTW), but I have just bought a 99 YZ400.

I've ordered a Clymer manual but know nothing about these motors.

The oil in the frame appears to be way over the max level, and when the motor in running you can hear a noise - doesn't sound like cam chain or small ends - do these motors make much mechanical noise? Can't say I've noticed much from others at Chippenham or Mildenhall?

I'm all ears.

I highly recommend the Yamaha owners manual, it's very good for telling you how to do mechanical work on the bike.

The engines are noisy (at least my '01 is) but it doesn't sounds like bad noises, just like there is a lot going on. If you suspect something then I would recommend finding someone else at the track with the same bike and see if they will let you listen to it and then compare. These things are a blast, have fun!

Congrats on the purchase. I owned a YZ400 for a year, rode two off-road series (total of about 28 races), and tons of play miles. I had to adjust the valves once, and never took the clutch cover off. I think a big part of reliability of the WR/YZ motors comes from frequent oil changes (that and great engineers :) ).

the first thing you should do is check the valve adjustment, change the oil, and perform a compression check (or even better, a leakdown test). The first two will probably make the motor a little quieter, and the third will give you an idea of what the shape of the top end it (rings and valves). Compression reading should be above 175psi, and a leakdown shouldn't exceed 10-15%.


Thanks chaps, received my clymer manual this morning along with rear pads and front wheel bearings.

Gonna try and get the bearings & pads in this evening after work.

If I play my cards right - nip over to Chelmsford for an exhaust on the van early, might be able to get up to Chippenham for about 11.30 - to say I'm gagging for a proper go of this thing is an understatement.

How can i make by myself the compression check and leakdown test?? :D

What tools do i have to buy?? or do i take her to the mechanic?? :)

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now