Should I replace my top end? need feedback

I've got a '98 WR400 with about 3,000 to 4,000 miles on it. I am wondering if I should replace the piston. I have a few questions.

1. Is this time for a rebuild?

2. Should I replace some other things also(wrist pin bearing,valve seats, timing chain, etc.)?

3. Should I hone or deglaze the cylinder wall for the new rings?

4. Is there room in the frame to get the cylinder jug off without removing the whole motor?

5. Will I need any special tools?

Thanks in advance :)

Have you done a compression check? It all depends on how the bike was taken care of. If you rebuild it I would go ahead do the other things as well, although I dont think there is a top end bearing ( wrist pin bearing ) The valve job and timing chain are a good idea though. You will deffinetly need to hone the cylinder or have it done. I am not sure but I think there is enough room to pull the jug with the motor still installed. You will need a torque wrench, hone and basic tools. A ring compressor can be handy but not a must have. If you are going to take out the valves yourself you will need a tool to remove them.

Hope that helps.

Unless you have really trashed the bike, I'd bet you don't need a new top end. Do a compression and leakdown test (might be better handled by a shop unless you have the right tools) to make sure. But the top ends really do seem to last a long time in my experience. If you are dying to do something, I think the above advice is good regarding replacing the timing chain. It's cheap insurance.

You'll know when it's time when you lose compression.. On my 01 426 I had thousands of miles on it.. Gradually I could kickstart it with no compression lever, no compression at all.. Also your bike will be hard to start when it's time. Make sure that your valves are correctly adjusted, it's very important..... Good luck.

While I was having my 5th gear issue resolved, I had my mechanic check out the top-end measurements on my Wr400. I was really surprised to find everything in spec! Pretty amazing for a '98 that has never had the top end apart. I had him do the rings just to be safe....


Does anyone know where to find a compression tester that will fit our bikes?

I bought one at Advance Auto Parts. The deluxe kit contains all of the adapters you'll ever need.


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