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Old 08-27-2008, 01:29 AM
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eDJ eDJ is offline
Motorized Bicycle Elite Member
Join Date: Jul 2008
Location: Wayne National Forest
Posts: 531
Default Re: Brand new engine has hole in cylinder near stud. :(

As I read thru the thread and look at the photos showing the hole it seems simple to me what the problem is. I don't think it's much of a problem though with so many having it and not reporting oil leaks, high idle speeds etc because of it. It appears to be a mold that needs to be ground out further where the hole is occuring.

When the machining for the head studs is performed there isn't as much metal
on that one stud boss as there should be and the drilling cuts thru the "too thin portion" of the cylinder casting and that creates the hole. Continuing to run them in production is just poor quality control but if anyone reads some of the books on China and their industrial revolution they will understand why they are more focused on running numbers over quality. Personally I doubt the Chinese companies that manufacture these bicycle motors would worry much about this problem. The Japanese, however, would be concerned.

The suggestion to apply some liquid steel or JB Weld would be a viable solution. Still, I doubt there would ever be any problems in the usefull life span of this motor to arise because of this. If someone receives such a motor kit it would probably be a good idea to apply the JB Weld before using the engine.

I'm stating this as my opinion and how I would handle it if I were faced with the situation. But somewhere in China a machinist needs to grind a few more mm out of the mold the cylinder is cast from around the location of that one head stud. (so the drilling won't cut thru the casting thus creating that hole) The problem looks much worse than it is.

Last edited by eDJ; 08-27-2008 at 01:39 AM.
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