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Old 03-11-2012, 12:06 AM
BarelyAWake's Avatar
BarelyAWake BarelyAWake is offline
Motorized Bicycle Elite Member
Join Date: Jul 2009
Location: Maine
Posts: 7,212
Default Re: to tear down or not

While some suggest a complete teardown & replacing everything, all the fasteners and even including bearings... I personally think this a touch overkill, particularly for such a low cost engine.

Do what you wish ofc, to each their own - but I find a compromise between that and what you've suggested to be "good enough" for these kits. I pull the cylinder, which is a mere four nuts (& perhaps a base gasket, they tear sometimes even on a new motor) - yet allows a visual inspection of all key areas (inc the amount of flash in the ports/removing if necessary), decking/lapping all cylinder gasket surfaces & cleaning the lower end of any potential debris, the only fasteners I feel must be replaced are the mount studs & nuts (too soft) & the acorn nuts used on the head studs (as they can bottom out before full head torque). The side covers you'll be pulling anyway during the build/install (clutch mag & sprocket) and I see no need to replace those fasteners as there's no load on them...

Part of the charm of such a simple two stroke is this light "top end rebuild" is quick & easy and other than a coupla fasteners won't cost you anything but a few moments of your time, yet still ensures there's no garbage in the motor and that everything's put together correctly (& w/loctite) - even if the head studs are properly seated as you'll see any discrepancy in depth (threads remaining) and length.

As for splitting the case and replacing bearings? Well... ya can if ya want to but given the generally low quality of the rest of the engine I really can't see the point aside from the amusement factor. You could replace every one yet it still won't fix the sloppy casting misalignment, out of balance flywheel & crank, sloppy wristpin & other assorted personality quirks these things are known for... you can ofc attend to those as well, but at some point you'll hafta ask yourself if it's worth the effort - or should you seek a higher quality engine? If you enjoy rebuilding for the sake of tinkering, well... that's a different story lol

Honestly? They're toys. Wonderfully fun toys but at some point disposable, no matter what you do. I've one that's got over 10,000 miles on it (all stock parts) and the cylinder's chrome liner (below ring travel) is disappearing. I could replace the piston, rings & cylinder... but why would I bother as for the effort and just a little more money I could get another that hasn't the bottom end wear? I've another engine that ate a cage at 4000 miles & instead of cracking the cases I just bought an $80 replacement motor & kept the old for parts...

Your call

Last edited by BarelyAWake; 03-11-2012 at 12:09 AM.
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