Type44 wrote:Been taking stuff apart with screwdrivers for almost 40 years, never heard about this jargon. Cam out? JIS (I imagine that's Japan Industry Standard?).... Translate fastener geek into English, please?
The link in my post explains it all. But for the TL/DR types that still demand knowledge minus effort.
Cam Out is a driver's tendency to lift out of the screw head when torque is applied. Some Screw Drive heads like Phillips are DESIGNED to do this, it's a Feature, not a bug. Or at least it is until you need to remove one that doesn't want to come out. Then the more Torque you apply the more force INTO the screw along the axis of the driver you need to apply or the driver will cam out and probably start stripping the screw head. One way around this is to use an Impact Driver which you strike with a hammer to both drive the tool into the screw head, and break the screw free about 10 degrees or so. If you work on anything older than say 10 years old, you need at least one if not a big one and a little 1/4" bit version.
JIS: Japanese Industrial Standard B 1012:1985 This screw drive is meant to not cam out and is used in manufacturing where torque limiting tools are used, so no cam out damage to the screw, AND no over torque. It's why every older japanese bike has stripped engine screws because people try and remove them with Phillips drivers and mangle the already soft sometimes aluminum screw heads. If you see a little dot next to the drive slot on a screw that's JIS.
Woe unto all foolhardy mechanics who attempt a Japanese motorcycle carb rebuild without heeding the warning of the tiny divot on the screw head. For their life is a sad and angry one filled with screw extractors and praying to the eBay gods that they can find a replacement carb.
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