Monthly Archives: October 2021

Tap tap tap….


It does get a bit monotonous, but I like a job where you can switch off and let your mind wonder. It wondered, long and far – it was great! But now I’m back, and the 16 holes in the second case are tapped M10 right to the bottom. Thankfully Bob did the other set.

32 holes in total, 3 taps per hole. 96 tapping operations. Tap tap… ta-da!

And drilled…


Drilling the compression plate using the rotary table. The bottom of the barrel isn’t round, but rather a series of flats like an octogon. No idea why, that information Sir Roy probably took to his grave.

Anyway, the outside edge will be milled out to a round profile using the rotary table. It’s been a bit of a pain, taking longer than anticipated. But soon it’ll be all done and ready to transfer the hole markings to the cases.

Plate in situ for marking.


The compression plate has been bored and cut to fit on the barrel. Here it is clamped in place to allow the stud holes to be marked out with a custom made punch. Once we have the holes drilled we can fit a couple of bolts and cut the outside to size.

The plate will be used to mark the holes through to the barrel, which can then be drilled and tapped for the studs. Once the plate is bolted up, the job can be centred on the plate ready for boring.

It won’t be long before the two parts come together for the first time!

On a plate..


At the bottom of the barrel there’s a spigot, which has a location protrusion. Rather than machine the top of the cases as originally planned,, Bob suggested we make a compression plate to fit, keeping the cases flat at the top. I like this idea as by skimming the plate, or making a few of various thicknesses, we can alter the compression ratio.

The original Hercules is only 7:1 as it was supercharged. This engine won’t be (at first 😉) but should run ok. With a sleeve valve engine, higher compression interferes with the valve opening times. The piston effectively gets in the way of the ports, much like with 2 strokes. Next job is to make the plate, so we can get on with marking & drilling the cases.