Ask the Editors: Mini Troubles and Shady Mechanics
This is a pretty difficult question considering we’re not certain what exactly failed in this engine. We’re assuming you purchased and installed an oversize head for this machine (rather than had the stock 50cc bored out) to achieve the bump in displacement? If this were the case, is there no way you could have the stock head reinstalled?
As far as the damage in question- break in is generally a fairly simple procedure to insure tolerances and machining quality and the little imperfections within meld with their counterparts. The process in a simple air cooled 4-stroke should have been nothing more than a few heat cycles. We would have started the engine, let it idle for 8 minutes, giving it a couple of revs in that time, then shut it down to cool off completely. Repeat. And perhaps repeat again one final time before riding.
It’s very unlikely failing to follow this procedure would have resulted in the type of catastrophic damage you describe. Unfortunately, without knowing exactly what happened (did the piston seize within the cylinder? Did one of the valves come loose? Did the timing chain snap?), we can’t be certain how the damage occurred but we would certainly steer clear of any mechanic telling you that it’s all your fault and not bothering to explain the problem.
In fact, we would likely take that 80cc head to a new mechanic and have him check it over for a clear explanation as to what’s damaged and how to avoid a similar fate in the future. It would seem repair would be a more affordable option to purchasing an entirely new head.
