Originally Posted by eDJ
From what you've seen of the insides of the motors, does it seem like the design
is satisfactory for a service motor that can give 20 to 35 mph performance ?
I seem to remember you indicating you thought the materials and machining of the
case etc were OK whereas the cylinder and porting left much to be desired.
Is it more of a question of better training for those who put these motors together,
along with better inspection, and quality control ?
Perhaps a definitive manual for how to do a complete tear down and rebuild would
be what's most needed now for the markets outside of China. Even if it were set
up online as an eBook.
Yes, the design is fine for its intended use. From what I've discovered the majority of the problems are caused by improper assembly.
As a means of high speed manufacturing, the castings are die cast. This results in a superior casting when compared to sand casting.
Most of the engine internals are fairly good...totally serviceable. This has to be taken in the context of what we are paying for. A 70cc engine is capable of producing 15HP reliably, so one could say that this Chinese engine is junk. All things considered they really aren't that bad. If the parts are made to the intent of the design, and assembled properly; this engine should provide years of fun.
The engine that is shown above with the countershaft problem is a recent exception. A new local customer came in this week to have me check what he thought was excessive gear noise. He was certainly right, and it's a good thing he didn't ride it any more than he had. The entire countershaft assembly is scrap. I replaced the countershaft, and gear assembly with a new one I had here at the shop. We'll see how the rest of it holds up.
"Is it more of a question of better training for those who put these motors together,
along with better inspection, and quality control ?"
This is it! 99% of the problems would be resolved if this were done. It would take so little to train someone to assemble these properly. One day, tops, to train 30 assemblers in a class-room type enviornment.
Same thing for the quality inspectors...One day of class room instruction: combined with the simplest collection of standard measuring tools, and a few custom gauges would make a world of difference in the finished product.
I have just about enough material...photos from tear downs, to put together an assembly manual. I plan on doing this eventually and putting it up on my website for everyone to use.