After 64 hours on the RM-Z450, my parts tally included just two clutches, a screw on the chain guide and the occasional tire. That is, aside from fixing last year's SX crash damage. I figured I had been lucky and should freshen up the yellow beast, so I headed on down to Hahm Motorsports and picked up a whole-new top end, including a piston, rings, new valves, valve springs and all the gaskets.
Having put in a few pistons and adjusted the valves on my Honda CRF250R last year, I figured, "How hard could this be?" Well, for a rookie mechanic like me, it ended up being just a bit too much. I got the piston in no problem-that was easy. I had some help installing the new valves and springs into the old head; we even checked to make sure they were sealed tightly. Then I proceeded to put the head on the bike. Everything seemed to be going smoothly. The cams were in, the timing chain was on, and the cam locating notches were all lined up (on the cams and on the flywheel, or so I thought).
The bike fired right up. With everything seeming to be in good working order, I headed out to the World's Four-Stroke Championship race at Glen Helen. In practice, while I was just cruising around, kind of lugging the bike, it made that valve-stabbing-the-piston noise and then quit. That's when I got ahold of Dave Dye to help me pinpoint my mistake. He said it was possible that the tensioner wasn't released at top dead center or, most likely, may not have released enough tension at all. So when I was lugging the bike, the timing chain was so loose that it skipped timing and stuck a valve.
When all the replacement parts came in, Dye invited me over for a Mechanics 101 class. He showed me that even though all the timing notches line up when the timing chain is not tight, when you release the cam-chain tensioner, it may offset the notches, meaning I still have to rotate a cam one tooth. He also showed me a section in the manual that tells how many links should be in between the notches at the top of the cam when it's at top dead center. Who'd have thought the manual would have all the answers? With all Dye's help, I'm sure the next rebuild will go as planned.
Since clutches were going fast, I called Hinson Clutch Components, and the company set me up with the full system, hopefully for extra longevity. I also switched over to a Dr. D exhaust, which keeps down the noise and pulls strong all the way through, especially up top. All and all, this bike has been a good working machine as long as this rider isn't the mechanic.
This bike's next fate was to be my practice bike for the 2006 MX Nationals season. I bought a new one as my race bike, and the Dirt Rider bike would be a backup and rack up a lot of hours keeping me in shape. With 20 hours on the rebuilt head and piston and a total of 84 hours on the rest of the machine, I had a bottom end failure. I was riding at a track in Ohio when I first started hearing a noise that sounded like the valves were ticking. It was faint and didn't sound loud enough to be a problem. The noise was consistent, and I didn't really feel any loss of power. I finished my moto, then loaded up and headed back to the house. The next day, I went out riding and the noise began to get a little louder. Then came a loss of power, so I pulled her in. I took off the valve cover and checked it all out. I retorqued all the nuts and bolts in the head and even checked the spark plug and timing chain. It didn't fix the problem. I had a few race mechanics check out the noise, and the conclusion was a bum crank.
Soon after that, Rockstar Suzuki rider Mike Brown and I tore down the motor (who knew he could split cases?!). We found more problems than just the ill crank. The metal shavings (from the disintegrating big-end bearing) ran through the bottom end and moved up through the head and cylinder, causing significant wear and damage. This meant we had to replace the entire head, cylinder, piston, crank and seals. Brown knew a mechanic who would rebuild the motor before I hit the road to go to the next few rounds of the Nationals. I put in the parts order. Most came, but some of them were on back order. I traveled from round to round trying to acquire some of these parts from a few of the Suzuki teams. I tracked down some of them, but even the big teams were short on parts. It was hard to keep track of what I needed while being on the road because we would assemble what we had and realize we needed something else-only to have to put in another order, all while traveling.