Re: to tear down or not
I concure and add that tearing the engine apart before installation is not bad advice but, the builder must recognize that a certain amount of mechanical experience will make that step a little less of a potential disaster. One must determine if disassembly of an engine and more importantly, correct re-assembly is within their mechanical ability. If curiosity is a factor and you just need-to-know what's inside and have confidence that you can get it back together right, then go for it.
I feel that the majority of successful motorized bike builds out there are ones that were installed out-of-the-box, with stock fasteners and care during the installation. The performance/longevity seekers will always strive to get the most from these little 2 stroke wonders but if the project is more of a novelty and just something to play with, and you have no experience with small engines and no desire to learn about what goes on inside, install it and enjoy it. The odds are in your favor that everything will work as designed.
Age and Treachery Will Always Triumph
Over Youth and Skill & "Charlie Don't Ride"