03 yz450 issues

Got a buddy who picked up a used 450.......kind of a war horse.....raced pretty hard. He's got it all torn down for new parts...linkage bearings, headset bearings etc. The bike ran well before he took it all apart. The only thing that is left intact is the motor in the frame..... The question is the previous owner said he adjusted the valves what we want to know is do these bikes have any history of valve problems. I know two guys with 00 426s that are stone reliable. While we have the bike torn down this far should the valves be replaced or maybe just check the clearances, do a compression check and ride. I looked through the open slide and the intake passage and valves looked pretty clean in there. Any help would be appreciated.

I've had my 03 yz450 for about a year and it has been stone reliable (knock on wood). I checked my valves last week and they are still in spec. Just my $.02.

i've had my 03' 450 for almost two years. i just took it all down to put in a new piston and rings and to change the valve seals. there wasnt any problem whatsover with the valves...they were almost perfect

Yamaha's arn't the bikes with valve problems, thats Honda. :)

The blue bikes are stone reliable.

HONDAS :) valves :)

I have an '03 that insists on being in spec to this day as well, but that will change sooner or later. The '00 426's had Stainless valves in them and they're an absolute brick because of it.

Yamahas are far better because the quality of the titanium and their processing is better, but all engines with Ti valves will follow the same pattern:

1) Possible early wear in may require reshimming some of the valves

2) After a while (years in the case of a YZF) clearances will drop and require a reshim of about one size lower.

3) Things will go fine and then clearance will suddenly turn up 1-3 sizes smaller. Reshimming will only last 10-20 hours and it will want 2 sizes less. At that point, the Nitride coating on the valve faces is gone, and they need replacing.

If you want to do some preventative maintenence, throw a cam chain in it, and think about a set of OEM valve springs.

Beyond that, your sundial is likely to cause you more problems than your YZF.


How about transmissions? I just got through putting 3 and 4th gear in my 03 YZ450. So much for stone reliable.

Mine's not broken. :)

The 4 spd is notably stronger than the 5spd in the YZ426.

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