Originally Posted by crassius
more depends on the builder than the kit
I have to agree with Map on this as well... I've bought cheaper kits off ebay and spent more time truing the cranks on the lathe, installing the good bearings, cleaning and de burring etc just to get them to run smooth and reliable... They did really nice once the extra work was done, but if someone was to just bolt on and go, the engine may vibrate badly or kill the bearings in short order, some have been lucky and had one last really good without doing all the extra work, but most end up disapointed.
For me, it's so much quicker to buy a good bottom end that's already nice and true with good bearings already installed and very little prep work needed to get up and running. I can take a Dax bottom end right out of the box, install a cylinder and piston setup to it, bolt it onto my bike and go without worrying if it's going to shake it's self to death or eat a bearing after about 10 hours of run time, the other kits I've got off ebay from different sellers almost always needed major crank work just to get them true, then need to be re balanced and in some cases, the bearings were already turning rough or had play in them. One engine I had there was about 1/8" of side to side play at the crank and wouldn't have lasted more than a few miles if I didn't catch the problem and correct it.