Monday, 29 October 2018

Measuring the bores

Before we get into the rest of the strip down, lets have a preliminary look at the bores. From up here they look really clean - there are no ridges at the top of the stroke:

There's a bit of a clonk when you turn the engine over.

Right now I am hoping that is in the timing chest, maybe a loose dynamo chain. Offside piston crown has been scratched by some exuberant decoker in the past:

Nearside piston crown is much the same:

Onto the bores - I measured them each in two positions, at the top and at mid stroke with a comparator and a Moore & Wright 2" - 3" micrometer. Both measurements were in the fore & aft direction which should be worse than the transverse direction:

Here are the results of my preliminary measurement:
  • Offside cylinder, top of piston stroke, fore & aft: 2.818"
  • Nearside cylinder, top of piston stroke, fore & aft: 2.815"
  • Offside cylinder, middle of piston stroke, fore & aft: 2.826"
  • Nearside cylinder, middle of piston stroke, fore & aft: 2.822"
Nominal standard bore is 2.755", so these are a worn 60 thou overbore. We'll measure the bottom of the stroke when we get the cylinder block off - we can measure the pistons as well and decide what we are going to do. Sixty thou is the maximum oversize so essentially if these are too far gone we will be resleeving this barrel... These Ariel barrels are not the same shape as the much more common BSA A10 barrels on which this engine design is based, and we are unlikely to find a better one.

I'm told these dished pistons are not available either, so we will be looking at flat topped pistons and an increase in compression ratio...

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