Part eleven - con rods - by Ramon Wilson

The con rods were milled - material is Alumec 89 which is a tough aircraft grade and has stood up well in the past. First up was to mill to block size plus 1mm all round then drill and ream both holes before removing the waste on each face.

The taper coincided with the difference in diameters so setting to mill the sides was straightforward using a couple of dowels.
A couple of pins were turned up to match the relevant holes and the ends rotary milled.
Then set on small expanding mandrels the waste was removed around the ends.
A bit of fettling on the sides with needle files, emery and Scotchbrite...
...saw them ready to fit the phos bronze big end bearings.
The pistons were made and a new lap was made to the usual (for me) design using a piece of 10swg copper around a 12.7mm mandrel. With the copper annealed and wrapped around the mandrel it was silver soldered along its leading edge then set up for turning.
Initial cuts were done with a sharp pointed tool with a fair degree of rake.
Then the last 0.2 mm finished off with a more round nose tool to improve the finish.
It took just over an hour to make from cutting the material to ready for use and is another addition to the steadily growing collection. Using 320 first then 600 grit Silicon Carbide powder, the lapping itself did not take very long at all. The piston was honed with an external hone then lapped to the liner with a micro amount of 1000 grit using the usual T-bar driver. Due to the length of piston that took much longer but a good result was achieved - quite tight at the top of the stroke, it should soon bed in to a nice fit once assembled.

With all parts for both engines now complete and cleaned up, here they are.

And a closer look at the bits for one - the screw in the case is to prevent the liner rotating as the head is screwed up
Finally it's all together. The only 'fettling' was a whisker off the con-rod big end face and some relieving of the case to give the con-rod some clearance.
Despite my foreboding that this would be difficult to obtain a run, after just a few low rpm bursts and a tweak of the compression it was off - it ran the tank out would you believe!
Next week: the two completed engines.

part one    part two   part three   part four  part five   part six   part seven   part eight

part nine  part ten   part eleven   part twelve