I'm just a bloke doing some stuff, the more interesting bits I post on my blog. Scroll down far enough and you'll see me riding from Melbourne Australia to Birmingham, England in 2014. But now I'm working on another project, a single cylinder motorbike engine at 2750cc!
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.
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!
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.
I hid quietly in the back of the shed, waiting patiently. After what seemed like hours, one came cautiously around the door. Another following meekly behind. Eventually they relaxed enough to start work, when I was able to take a quick photo on my phone!
Probably a world first, photographic evidence of the existence of shed faries! Here, they are drilling a set of engine cases to be reamed later, to accept silver steel dowels for accurate location. I managed to leave undetected and lived to tell the tale.
The shed fairies have been busy again, working on making the Denbeigh mill a better machine. Bob is certainly very through! The vertical head has been stripped and greased, then re-assembled with a new drawbar assembly. The head has been set parallel to the table and the machine run for 15 minutes to make sure nothing gets too hot or stiff.
The drawbars took some work, with the rear of the machine sawn off by 2 inches to allow the shorter ones to be fitted and tightened. Spacers and locators made and in general, the machine is now much better and ready for use. We’re waiting for the steel plate to arrive, so we can bolt the enormous cases to various machines.
I love seeing this kind of work. Some of those items might not be required for 10 or 20 years, but one day in the future that will might save a load of time.
The original idea of boring the cases would have worked, but using the boring head in that position would have meant we couldn’t see inside the bore. Blind operations are ok, but I prefer to be able to see what’s going on. It’s fair to say that your ears tell you a lot, but even so it’s good to have eyes on what you’re doing!
We looked at making an adapter plate to swing a vertical head through 90 degrees. (Sideways, so to speak!). When we dug out an old vertical head from under the bench, it turns out it’s adjustable anyway 😁 So with a bit of fiddling to get it parallel to the table, the boring operation is all worked out.
Here’s one half of the cases plonked onto the table of the Denbigh mill. You can see the flailing belts which have to be hand pulled to help start the motor to the rear of the machine!
The boring head in the photo will automatically expand to perform a facing operation. It was second hand and hasn’t been used yet, plenty of old stuff that ‘might come in useful one day’ is being pressed into service – and it’s good to see. Shed recycling to save the planet 💪
The second set is being drilled and the second timing case milled. Once those jobs are complete, we can look closer at fitting locating dowels. Finally, we will come back to the Denbigh….