My recommendation would be to buy a grubee from a reputable dealer. If not a grubee, then from a dealer that has a good reputation. Most all of these engines are about the same quality (grubee's are a notch above), but a good dealer will offer a warranty and send you parts if you have trouble. This will make the engine more expensive. You can go cheap and buy from a dealer that offers no warranty, but if something goes wrong, you are the one that needs to buy the parts. When dealers buy wholesale, they get a box of assorted spare parts. When they run out, he has to start parting out kits. This is what makes offering a warranty expensive if someone stands by the warranty. I have found that most failures are due to over revving and improper installation. (over torquing hardware, improper clutch adjustment) People love to run them WFO, but in their domestic market they were workhorses to move people and merchandise to town - not to provide 35mph thrills on a bicycle.
When I got into these kits, I bought from the cheapest vendor with the full understanding that there was no warranty whatsoever. Last year, a 66cc HT kit would set you back about 150 bucks (with shipping) from the cheap vendors. If you bought one from a "reputable" dealer with a warranty, it would cost you $200-250. That's a lot of parts. Now you can get a 50cc kit for $125 shipped from the "cheap" dealers and $179 shipped from a more reputable dealer. Like I said, many times the "reputable dealer" is buying in bulk from the "cheap" dealers but will stand behind their product. The choice is yours.
