Winter maintenance and top end rebuild

Hey folks,

My 2001 WR426 will have it's first engine work this winter and I need some advice on what parts I should order before diving into the engine.

Some background:

  • The bike has never had any engine work done since I bought new in fall of 2001. Estimated mileage is somewhere around 7000 miles of singletrack.

  • The valves were still in spec at the beginning of this summer and runs (ran) perfectly.

  • I have been burning some oil on initial startup, but not while running. Because it was only at startup and not continuous, I am assuming this is probably the valve stem seals since I had good compression and no problems starting or running.

  • Last month I fell over in a water hole and wound up sucking water into the engine while trying to kickstart the bike once it was on dry land. I only tried to start the bike for 3-4 kicks before realizing what might be wrong while waterlogged. The entire airbox was full of water as the drain had gotten plugged with grime over the summer. I have been unable to start the bike and steam out excess water because I have lost compression. I can push through the compression stroke with my hand, without using the decomp lever and the plug installed. I changed the oil several times, flooded the bore with tons of WD-40, and regularly roll the kickstart over with my hand to keep the bearings and such oiled and hopefully free of any corrosion.

I figure I will do new piston rings, valve stem seals, and obviously new gaskets for the cases. What else should I plan on replacing as a normal "preventative maintenance" sort of thing while the cases are split. Is there a "top end kit" available and what might it include? I figure I may as well refresh things while the engine is out and apart.

If anything like bearings or other parts that are not typically needed to be replaced during routine engine work are damaged, they will be ordered afterwards.

Hopefully during the week between Christmas and New Years, TrailriderJoe and I will have the bike back in tip-top condition.

Thanks a ton for the help.

Cam chain

I just did a top end on an 02 and replaced all ti valves with WR 400 Stainles Steel OEM valves and springs and cotters for a substantial savings. I replaced the piston and rings and cam chain. I went with the Hot cams Exhaust cam. I had full machine work porting and valve grind on the head since I had well over 10,000 miles.

I did not split the case but if I did I would replace crank assembly and main bearings and seals, oil strainer, and transmission seals.

I would also have a very close look at 3and 5 gear and the shift forks.

How is your clutch?

How is your budget for that matter? I did some reconditioning of other parts while waiting for parts mainly the Carburetor but you get the idea.

Runs great now!

Big question is how much budget. Bike has high hours and you're splitting the cases anyways.....

How many times have you had to adjust your valves?

I would say new camchain and piston to your list regardless.

Delete, double posted...dang goofy internet connection.

Budget isn't great, but I will be doing all necessary repairs, and any preventative maintenance that should be done. For all else, if its not broken I won't be fixing it.

I have never had to adjust the valves at all, and they were perfectly in spec at the beginning of this summer.

Valves are the highest wear item along with cam chain and piston. I'd say if you are not an over-rever and the valves are in good shape, then leave 'em. However, be aware that from what I read when they do start to move (wear), they go fairly quickly so you may be doing a top end job next winter.

All depends on what you can do and want to do. There are people who won't even look at just replace the piston and replace the crank at the same time along with EVERY gasket, o-ring, bolt, etc. And there are those who run it till it blows up and then get mad at it for breaking. Find a happy medium, I say and just have an open mind if your valves start wearing.

If you replace the cam chain--and you should--you will need a puller for the rotor. You will also need a few other special tools for the head work such as a spring compressor, a quality torque wrench, and a good micrometer. Also be sure to follow the head bolt tightening procedure exactly as described in the factory service manual.

Valves are the highest wear item along with cam chain and piston. I'd say if you are not an over-rever and the valves are in good shape, then leave 'em.

After 5 years of riding and racing my wr450, I finally did a top end this last summer after about 8K miles (at least). piston was good, but I replaced it anyways. I changed the timing chain, but didn't really need to. Valves were still in spec so I did not change them.

Bike runs absolutely great still. Turned out to be a $350 top end rebuild.

be sure to mark that position of the cams and chain before you take it apart.

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