Yamaha Roadstar Rebuild Update

So, just a quick update on my 2002 Yamaha Roadstar motorcycle. Everything seems to be running smoothly and I have not had any issues with the rebuild so far. I have a little over 1100 miles on the engine at this point and am very happy with how it’s running. I’ve changed the oil twice; once at 300 miles and again at 950. I am using a conventional 20w50 motor oil with a high zinc content. The zinc is supposed to reduced the friction on the moving parts. According to expert suggestions on forums and repair manuals, it is not recommended to use a synthetic oil until after at least 4000 miles of using conventional oil because of the zinc and “heat setting” the rings. I’m okay with that if it’ll extend the life of the engine. In fact, I may not ever go back to a fully synthetic oil for this motor. As far as performance is concerned, I can’t believe the difference between the old, original engine and how the rebuilt one runs. For one thing, the motor is a lot quieter. The old engine had much clatter and I had chalked it up to being air cooled and maybe the valves needed some minor adjustment. (The fact that the valves may have needed adjusting may have been the reason for the catastrophic engine failure). I made sure to adjust the valves to zero lash on both cylinders during the rebuild and had to actually go back and adjust them a second time because of my poor interpretation of theoretical praxis. In other words, applying the knowledge I was learning proved more difficult in practice. But, I did readjust the valves to spec before torquing all the bolts and nuts. There was also the issue of piston thump and loss of power at the top end of the power band. The “roll-on” application of throttle in fifth gear produced clatter and a reduction of power under load. It was as if the engine was “lugging” while trying to maintain speed while navigating a slight incline. I had decided this condition was due to the engine having so many miles on it and was in fact “tired”. However, this lugging and clatter could also have been the product of poorly adjusted valves. Needless to say, the issue had not been addressed before the engine failed. Also, I had been using an “octane booster” gasoline additive with every fill-up just to have the engine run like I thought it should for that size displacement. The rebuilt engine does not have these issues and pulls quite nicely at the top end of the power band. On the other hand, while the low-end torque is sufficient to get the bike moving from a dead stop, it seems anemic and the lack of overall horsepower is evident. My options have been, and continue to be, having the original Midnight cylinders bored and plated for the 1800cc displacement upgrade, upgrading the cams, and boosting carburetion. These mods are all on my bucket list for the 1600cc engine, yet by swapping the current motor with Yamaha’s newer version 1700cc motor (which will almost bolt straight up to my current bike), I gain an extra boost in horsepower:

The difference is not huge, but it is certainly noticeable. Yamaha claims 18 and 15 percent boosts for horsepower and torque peaks, respectively. You can feel the added muscle coming off the line, and the bike passes more aggressively on the highway than the smaller, taller-geared 1600 model. You can ride faster with a reserve of acceleration. The initial getaway is smoother with the taller low gear. (Cruiser)

The difference in horsepower between the 2002 1600 and the 2004 1700 is 22.17 with the 1700 averaging 84.3 hp @ 4400 rpm and the 1600 around 62.13 HP @ 4000 rpm. So, the differences are there but they do not seem to be as definitive as first perceived. Maybe I’ll just keep to the original plan and do the upgrades myself. This way I will have the sense of accomplishment of creating something I envisioned and bringing it to fruition – instead of just swapping one engine for a lager one.