The engine is easy to disassemble and to assemble, with exception of the main bearing of the shaft, which is integral to the shaft and the piston-pin, that is sometimes not easy to get out of the piston.
For disassembly Allen keys of sizes 1/8” ( cylinder bolts on crankcase UNC8-32 5/8”), 3/32” ( head bolts on cylinder UNC 6-32 1/2”) and 2mm (backplate screws M2.5 6mm) and a special key for the clamp ring of the front bearing (see sketch in fig.2) are necessary.

fig 2. Tool for clamp ring of front bearing. back side to be used to push front race in crankcase . Material: steel, brass or dural. Pins can be taken from needle bearings.

Tool with clamp ring

5.1 Crankshaft and main bearing (see fig.3)

To get out the crankshaft take out the clamp ring of the front bearing and heat up the crankcase gradually to 110 – 120 degrees Celsius. (not higher, there are plastic cages in the bearings)

Heating up the crackcase with shaft

Don’t use a gas-flame, but an electric plate to prevent deformation, and use a thermo-couple in one of the bolt holes (now cheap to buy, e.g. from Conrad Electronics in combination with a multimeter) to keep control over the temperature. At 110 to 120 degrees C it will be easy to push back the shaft (with a 6 – 7 mm or M8 * 0.75 thread pin in the front of the shaft) and

fig 3. Section crankshaft and bearings.

push out the front bearing ( preferably with a special tool, see fig.4). When the front bearing comes out, mind the shims!

Push out the front bearing with tool  

When the front bearing comes out,
the shims!

fig 4. Tool to push out front bearing. Material: aluminium or Tufnol.

If the main bearing of the shaft needs disassembly for cleaning or inspection of the balls or the groove in the shaft, push the cage forward from the back side. The crank web has cut-outs (also for balance) for this. This should be done by appr. 1.5 mm diameter rounded pins, preferably with two on both side of the crank pin, so the cage is not distorted too much. After the cage is off, the balls may fall out immediately, so take care they don’t jump away!

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