Those are safe clearances, given the 400EX has sub-rockers to contend with. I wouldn't go less .080" with a hi-rev ignition box though. A good direct acting cam set-up, without rocker arms, can get away with a lot less. I just finished putting in a GTT cam last weekend. As a "quick & dirty" clearance check, I adjusted the valve lash to spec., then individually put a .100" shim in between and slowly turned the motor over (w/o spark plug!). Nothing touched so I got a good feeling that piston to valve clearance would not be a problem. If you ever do it that way, NEVER use a ratchet handle to turn the crank. ALWAYS use a fixed handle, such as a breaker bar and turn the motor very slowly. Sometimes when a valve is closing there is enough pressure to spin the crank with it and a regular ratchet will not offer any resistance. If there's not enough piston/valve clearance you will probably bend a valve! Also check one valve at a time. If any of the valves are canted towards each other (on the big end) they can touch, again resulting in bent parts. It's a relatively easy way to set your mind at ease. BTW, that was with a decked cylinder (piston now even with gasket surface). Also noticed that the Wiseco 440 piston had larger than stock diameter valve notches, so oversize valves wouldn't be a problem either. >>>>>Be careful and check when putting a shim in there, I remembered that I used a Honda car valve stem seal which was much shorter on top than the one Marcum's sells. Don't want anyone to ruin their valve seals.
Last edited by MIKE400EX; 03-06-2002 at 07:12 AM.
Mods: Big Gun FS w/MM quiet core, no lid , K&N, FCR41, 11.3:1 440 and Web 479 cam, porting, no choke. Works TRS fronts & Ultracross rear shock, a few other goodies
450R,250EX, Blaster, Banshee
