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.049 Disassembly


Old 02-18-2013, 12:32 PM
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Default .049 Disassembly

Hey guys, how do you get the crank out of the crank case in a cox .049?

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Old 02-18-2013, 12:55 PM
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Default RE: .049 Disassembly

1) Remove the cylinder. If you have a COX wrench and the cylinder has flats on the top fin, you can use the wrench on the flats. The cylinder unscrews counter-clockwise looking down at the top. If you don't have a COX wrench, unscrew the glowhead and you can use a standard wrench on the flats. If the top fins don't have a flat, I usually use a piece of thick leather to wrap around the top cylinder fins and glowhead, then grip with a pair of pliers. Don't use excessive force. If the cylinder is stuck, heating the case near the bottom of the cylinder will sometimes help free it up.

2) Remove the backplate and tank if any - this can be done first or now. Some have gaskets; some do not. If there is a gasket in place, be careful not to tear it when the backplate/tank is removed. If this is a tanked engine, do not lose the venturi tube gasket. This tiny gasket has contributed to about as much aggrevation as any part on the tanked engines.

3) With the cylinder removed, turn the crank so the piston/rod is fully exposed. I usually place a mark in the backside of the rod with a permanent marker so I can have it oriented the same way when I re-assemble the engine. Remove the piston/rod assembly by sliding the rod off the crankpin.

4) Turn the prop screw into the crank until it bottoms out. Some of the later production screws were a little soft, consequently, I always replace the screw with a black oxide socket head screw.

5) Get a block of wood or flat piece of plywood. Place the back of the case on the wood (the wood is soft enough not to mar the back of the crankcase). Tap the prop screw with a hammer - I always use a plastic hammer (when I use a hammer). You can always use a popsicle stick or paint stir stick over the screw head to protect it. The drive plate is a press fit on the crankshaft - light tapping will drive the shaft out of the plate. Be sure there is enough clearance between the plate and the back of the prop screw to allow it to come completely off without binding. Don't heavy-hand it - you don't want to drive the crankpin into the wood!!!

A better way is to use an arbor press or a vice to press the crank out - this avoids the impact shock of using a hammer. If you don't have access to either, just be careful when tapping.

To re-assemble, turn the drive plate so the splines line up as well as possible. Use the prop screw to pull the crank back into the drive plate. You may need to add a prop as a spacer to completly seat the plate.
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Old 02-18-2013, 01:12 PM
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Default RE: .049 Disassembly

And my 5c worth-if replacing the original prop screw with a socket head one, as suggested by Andrew, the thread is 5-40-so you probably won't find it in your local hardware store. Cox International has these in short and long sizes for a very reasonable $1.49 for 2. The short size you'd use with just a standard prop washer, the long with the spinner (the latter being available in a range of anodised colours). Quite apart from the issues of softness of the original Cox prop screw, the black oxide HT steel socket head allow you to tighten the prop up properly, (with an allen key obviously!)-without any risk of slipping or burring the screw slot. [Personally all my small Cox engines are so fitted-from 010 right up to TD15's]

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