A Matter of Timing

Getting the cam/valve timing right. 99.5 % of my engine building experience is on two stroke motors. Almost everyone who has owned dirt bikes or two stroke street bikes had to tear down the engine for an over pop or rings. You had a couple of options, you could pay someone to do the rebuild for you or you could do it yourself.

I have had a ton of two stroke bikes, mostly street bikes. Most of them were Yamaha RD 400's and a couple of Kawasaki H2's. My dirt bikes where of the Suzuki RM 125 and 250 variety Those of you who have owned these bikes, usually messed with the engine to get more performance. Or in the case of the 79' Daytona Special had the two piece crank split in two on you. I have no idea why Yamaha went with this set up for the Daytona, but in the end you would have to replace it with a single piece crank from a 78' or earlier RD. My collection of RD’s were in various states of repair, and I was constantly messing around with them so I became familiar with their motors in a hurry.

I do not have a whole lot of experience with four strokes other than giving them tune ups, adjusting the valves and carbs every now and then. This is the first four stroke rebuild I have done other than a lawn mower engine or two. And the biggest concern I had was timing the cams. This procedure turned out way easier than I thought it would, at least on this bike.

After tightening the 10mm bolts to 29 ft. lbs. the 6mm bolts to 7.2 ft. lbs. and the head nuts to 14 ft. lbs in the proper sequence, it was time to install the cams and line up the timing marks. The intake cam has a I on it for intake and the exhaust is marked with an “ex”. Then you need to Align the flywheel T mark with the stationary pointer on the crank case.
Next step is to rotate the exhaust cam to line the timing mark with the left side cap mark. Do the same for the intake, put the cam chain on and adjust the whole shooting match till both cam marks and the timing mark are aligned in their proper positions. Torque the cam caps and timing chain guide bolts to 7.2 ft. lbs.

Now it’s time to reinstall the tensioner assembly. First remove the blind bolt, then insert a screw driver into the blind bolt hole and turn clock wise until it stops completely. Install the tensioner and gasket and torque to 8.7 ft. lbs. pull out the screw driver to release tension and set the blind bolt to 4.3 ft. lbs. Reinstall the valve cover and gasket (not in that order)and you’re ready to install the engine in the frame.

Just a case of following the manual and every thing fit together like a glove. This procedure was not too bad on this single with overhead cams, but I suspect it is just a tad more complicated as the number of cylinders increase. Next is the electrical and charging systems, I suspect this is what took this bike out of service in the first place. It basically needs to completely rewired as most of the wiring is shot.

Till Next Time......................