WR 400 tranny/bottom end question
Posted November 28, 2010 - 12:00 AM
Posted November 28, 2010 - 09:05 AM
I really have no insight into the stainless valves on the four-hundies (I'm just in the middle of a rebuild on my 426 using SS valves from the 400's, so I can't comment on durability), but if they look the least bit suspect, I'd swap em. They are really pretty cheap. If you swap the valves out, get the seats cut as well. While you have it apart, check the guides. Most people overlook these on a rebuild...and definitely replace the valve springs, regardless of whatever else you do tot he valve springs.
As far as the transmission, most of the issues that I'm aware of aren't related to gear failures, but wear of the shifter forks and dogs on the gears. There are instructions in the shop manual for inspecting them...thickness on the fork faces, rounded corners, undercuts, etc on the dogs and slots. Take a good look at the gear teeth for unusual wear patterns as well, and replace anything that looks suspect. I believe most of the issues are with third and fifth.
As long as you're going the full 426 top end, you may want to consider a big bore kit. There's an outfit here inthe states, Luke's Racing, that turns out a great product and really stands behind their stuff. A 444 kit is a bit cheaper than all the 426 parts (unless you buy a good used set up on flea bay or something like that...but buyer beware). On my 426, going to 444 let me run a tooth higher on the c'shaft sprocket. so I can run a bit lower RPM on the higher speed sections of desert or dual sport rides.
As a general rule, when I have the cases apart, I replace every bearing and seal. A bearing supply house can match most of them for you at a considerably lower cost than the dealer.
The WRs, especially the stainless steel valved 400s and 426s are about as reliable as a claw hammer...and the extra performance from the Hot Cams and 426/444 bore increase will really make a powerful, reliable D/S bike. Newer WRs are lighter, have better suspension, and handle better (especially in the corners), but if you have yours set up the way you like it, you can't go wrong. Depending on what you find in the transmission and what you have to do to the valves, you're looking at probably 1200-1500 USD (don't know what that works out to in Canadian) for the rod kit, top end kit, hot cams, timing chain, seals and gaskets, presswork, etc., but you'll have a heck of a fun scooter.
A couple more thoughts...you may want to look into swapping the clutch for an 01-02 426 clutch. They are a bit more reliable. I'm not sure what all you need to do it (or really, even if it's possible), but I know the 01-02 clutch is an improvement in reliability and performance over the 98-00 clutches. If the treansmission and primary drive gears are the same P/Ns, you should be able to just pick up the whole stack and swap it in. If not, at least go for some high quality clutch plates and heavy duty springs, as you will be asking the clutch to transmit a bunch more power. You may also want to think about a Boyesen Supercooler water pump. More power equals more heat as well.
Posted November 28, 2010 - 11:19 PM