OLIVER TIGER MK III - 5cc ENGINE BUILD
Part 8  by Ramon Wilson
Part four - by Ramon Wilson
I made all the cranks using high tensile En24T leaving it in its as machined state. It is a tough but fairly easy material to machine and produces a good, hard wearing, finish on the bearing surfaces. These engines are never intended to be used in flying mode though I'm sure they would stand up to that requirement if desired; the need for further heat treatment was not felt necessary given their intended display use though.

The cranks were set back between centres for finish turning the shaft diameters then held in a collet for drilling the intake hole. Finally set back in the fixture the crank-pins were brought to diameter. The fine tolerance on the bearing areas was achieved by stoning with a pair of fine grade thin flat India stones.

With those ops completed a simple fixture was made to hold the shafts for drilling the inlet.

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Set at 20 degrees the hole was 'drilled' though first using an FC3 cutter .

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Then the fixture set on its side to machine the inlet timing area

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Then the fixture set on its side to machine the inlet timing area

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And finally set back between centres to screw cut the shafts. Nothing special - HSS ground tool and the tool pulled out at the end of the run ie no run out groove for maximum strength.

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Incidentally if no chaser is available to clean a thread the flanks can be polished to a degree by using the end grain of a piece of wood charged with carborundum paste. Pushed hard into the work the wood will run along the thread until the end.

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The three finished shafts ready to fit.

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I thought it best to finish off the steel parts - rounding off the characteristic 'Oliver' ball ended compression screw - the GFS tool, hardened but not tempered, cuts really well. Note this is En1a - not En8 which I had called for on the drawing below!

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Removing the parting off pip by rotating the tool

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Finished comp screws - all screw cut to a tight-ish fit in their respective heads


Part one here. Part two. Part three. Part four. Part five. Part six. Part seven

Part eight Part nine Part ten

 
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