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Reply to "MTH motor needed"

Sorry, don't have it in front of me at the moment to take a picture, so trying to do this via edits.

The silver Walkera pins are of a smaller shank diameter and then also have the smaller pin tip. It just so happens that that diameter happens to match the typical bore size of the MTH worm gear from the end. The MTH worm gears (at least every one I've touched PS1, PS2, PS3, steam or diesel) is a stepped bore system. The bore through the actual screw section is larger, and then the solid shank section that matches the motor shaft is stepped smaller. It just so happens the length of these pins is near perfect as is the diameters and step shaft size. So you insert the silver pin with the small end first into the end of the worm gear. The sizing is such that the bore keeps the pin straight so the smaller tip aligns and presses on the nose of the motor shaft deep inside that worm gear. Externally, your puller is pushing on a pin, that pushes the motor shaft out of the gear. This puts no pressure on the motor body or the armature (something you already know not to do). I've circled the pins I commonly use.

Then they insert, small end first into the larger bore end of the worm gear.  Again, what folks may not know is that is a stepped bore, not a straight bore. The step is where the threads end typically. So if you use a motor shaft sized pin, it can often kink or bend in the long wider bore section because it has room to bend sideways. If you have a stepped pin, it reduces the length of the small shank and reduces the chance of bending the pin.

Image result for mth can motor

What I'm getting at is one method is a custom machined extra long pin to press these long worm gears off. Extra long for some steamers. If you make that extra long pin the same diameter as the motor shaft, even in hardened steel, it might flex, bend or break over such a long length. You could step size it diameter wise, and that's an option. What I'm giving is a third option. There is a way, with no custom pins, just these 2 puller sets, to mix and match parts such that the silver pins can be dropped into the worm gear bore and act as short of a shuttle pin, a pin that floats inside there and transfers the pushing force. This allows the puller with standard pins to push on this shuttle and press the shaft right out of the worm gear. Those same pins come handy in dozens of other situations and the fact the silver threaded section also matches the black Great planes threads means you can adapt the parts of the 2 pullers for a lot of situations that a single set could not.

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Last edited by Vernon Barry

OGR Publishing, Inc., 1310 Eastside Centre Ct, Suite 6, Mountain Home, AR 72653
800-980-OGRR (6477)
www.ogaugerr.com

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