When to replace Wr450f piston and rings?!

OP from Maine, getting help from guys in California, which is cool.  But will the Maine rider suck all that year round dust and use full throttle often through mile long sand washes and rat races over to the next mt range?  Maine riding to me would seem a lot easier on the motor ?


In theory the slipper piston short skirts in the modern short stroke long rod motors "should" have less thrust against the bores and give decent service life.  They do in autos and some other applications  (streetbikes, 4 cycle snowmobiles etc.) with the same engine geometry and metallurgy as these dirtbikes.  The difference IMO is dust, and oil capacity/heat/cleanliness.  Deal with those factors and you can extend it's life.


I earned respect for yamaha's wr400 years ago when I met a girl riding one on the Alcan highway, She had ridden from southern Mexico to Alaska and was on her way home. Her only fail was from a cracked subframe which was repair welded with a coat hanger and a car battery and was still holding when I met her.

Seems people in Maine could be just as hard on an engine as someone in the Cali desert....way too may variables to consider. So I read this thread and I'm starting to get a headache.


Comparing an XR400 or WR400 to a modern 450F is like comparing a tractor to an Indy car. Once I got on a modern 450F my XR400 sat and collected dust until sold. Comparing a modern dialed in FI thumper like the '12 and up WR to a smoker is apples to oranges as well. Now I'm not bashing anyone's bike but I am saying YMMV.


250F motors have to be run harder at higher RPM so generally they won't last as long. That does not mean they are unreliable.


My new WR inspires confidence that this motor is a good one. Still I will stick to the usual routine of tearing down the top end every Summer during the off season. Rings and gaskets are cheap. So the bike is new now with about 20 hours on it only so it'll get torn down next Summer (2015) unless it starts to drink oil or lose power then sooner. Actually I like the bike so much that I could overlook durability and reliability issues; if there were any.


I'm moving back down to the lower desert Western AZ and Southern Cali areas. I guarantee if there are any issues with the new WR they will become apparent very soon. Thumpers don't like sucking that D38 moon dust and I'm too slow to stay ahead of it.

Edited by cubera

Alright, it just seems like people say they go forever on wr400 top ends and never have to tear them apart after years and years of hard riding, where as the 450s have to be torn down at around 200 hours?.. Maybe I'm wrong.

There is some truth in this statement, I don't think the earlier 450s had titanium valves, rather steel, but the newer ones do. And I'm pretty sure the old 400s and 426s had steel valves which where more durable?... Well maybe not durable but steel has less of a tendency to move from what I've read?? (Expansion, contraction etc) So I could see the top ends lasting longer on the older models. Plus everyone says they over engineered the shit out of the 400 and 426 top end as it was sorta the first of its kind, which kinda helped male it really tough... But this is all here-say on my part. Personally I've beat the snot out of my 426 for years, and so did the previous owner. It was even my daily for two years going to college. Runs great and I've only had to touch the valves once. It's time for a yearly tear down to inspect the piston etc though.

The big thing is though I baby my bikes compared to how a lot of people ride, sure I will rev it high and hold it wide open at times, but I'm not doing that most of the time.

Edited by fdme

I've got an '07 WR450 and am still running all stock stuff.  Purrs like a kitten and pulls like a beast.  I do regular maintenance and ride mostly woods (slower stuff).  I'm also old, so I don't rev the piss out of it and beat it to death.

Ive got an 06.  Im 46 and ride it mainly colorado single track and Moab. which means grinding it on rocks, in the mud and going WFO for minutes at a time in sand washes.


Im a freak about clean air filters and clean oil.


valves are still in spec, never had the top end off and it runs great.  *knock on wood*. lll probably pull it apart and freshen everything up next winter 2014/15 to get another 8 years out of it. 


im about to rebuild the linkages and bearings. Ive greased them regularly, yearly but they are alll rusted out now.  Ive replaced teh seal in the shock, ive put 2 sets of seals in teh forks and they need a 3rd.  So the motor is due.


im not going to worry about it though

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