Originally Posted by East82
I believe the general agreement is that a standard HT 80cc will give you from 2000 - 6000 miles, maybe more, with decent care. At which point do you stop replacing parts, i.e. cylinder rings, piston, etc ... and get a new engine??
The "general agreement" would be more that it's a roll of the dice, it's dependent on far too many variables to really state what the expected lifespan could be, even up to and including "decent care" - mostly due to the highly random quality control the 49/66cc in frame kits are known for regardless of "brand" or vendor.
There are folks (including myself) that have replaced/upgraded everything from fasteners to bearings seeking to improve and extend the service life of these inexpensive engines, only to have it fail catastrophically anyway - then there are those (including myself again) that slap a motor on their bike, doing little to nothing to upgrade it in any way & then pound the snot outta it, only to have it last seemingly forever, no matter the abuse...
For example the pics below are of my Schwinn beater/commuter that now has well over 10,000 very hard miles on it, yet it's about as basic a build as they come with a "generic" 66cc that aside from some maintenance & general repair (plug & cap, head gasket, carb, a coupla fasteners that rusted) just refuses to quit... almost all the fasteners are stock factory originals, as well as the mag, CDI, seals, clutch pads, bearings, head, etc. (all the stuff some say to replace immediately) on an (omg) aluminum frame lol - I've even always had the dreaded white wire kill switch connected, with lighting no less o_O
(cyl pics taken during head gasket replacement)
There are those that will advise a complete overhaul, replacing absolutely everything
with "quality" components, even before the motor is run... while you can ofc do this and there are some items that most likely should be upgraded (like filter, mount fasteners), after a coupla years building & riding these things I've come to the conclusion that it's not really worth the bother, if fact may even be defeating the point of these inexpensive, comparatively disposable engines as you can easily spend the same or more in time and money "upgrading" & repairing one as just buying a replacement...
TBH aside from an attentive, careful installation and keeping an eye out for potential failures - if/when it gets to the point that you're considering "replacing parts, i.e. cylinder rings, piston, etc" you might as well get another, keeping the old for whatever parts are still good... Much as I do love these lil things, I really do believe that if you find yourself thinking about a major
rebuild and/or modifications equal to or in excess of the engine's value - I would seriously recommend looking into just getting a better quality engine as these things aren't going to be able to live up to expectations as you're either racking up a lot
of miles, suffering from poor quality, or just want more than they can give...
Other'n that - I'd reco jus' riding it like ya stole it & replacing it if/when it blows.