I finally got my hands on some parts and first impressions are that they’re big! Not unfeasibly large, just big – and I love it.
A job lot of spares came up at the right price so I took the lot, even though I suspect some of them are Centaurus parts. One sleeve is slightly longer than the other, which leads me to believe it’s from a Centaurus. I have three heads, two aluminium and one cast iron.
I prefer the look of the iron heads, but they weigh a tonne! Not as heavy as the crank and rod assembly I picked up. That’s too heavy to lift onto the bench!!
It will take a couple of days to plough through what I have and decide which parts (if any) are serviceable. I’m still holding out for a matching set from one engine, but the special spanners are proving to be quite elusive.
Those parts are out there somewhere I know it!
Well actually no. What we have here is a freehand sketch of the crank case, one side. The sleeve drive side (or timing side I suppose if you follow convention). To assist the pattern maker this view is quite useful. It’s also good for anyone wanting to visualise the finished engine.
The chain and sprockets driving the sleeve will be visible with the side plate removed. The side plate will house the oilways for feeding the shafts and the ignition pickup. I’ll post a pic of the side plate shortly.
Bob is finalising the full sized drawings, after which the design work will be all but complete. The only remaining task is to source a Piston and Sleeve along with a few extra parts. I’m waiting until I have those in my hand before I press the tit on the pattern maker.
Parts wise I’m waiting for people to come back to me regarding a special spanner to remove the Bristol cylinder. I can make one if necessary but I will still need to find a nut first! It’s a slow process…..
Finished drawing of the sleeve drive by the talented Mr. Bob. As it turns out having the sleeve drive shaft rotating in the same direction as the main crankshaft really helped us. I’m sure that Sir Roy Fedden didn’t imagine we’d be doing this to his state of the art Aero engine some 70 odd years later! But even so, he no doubt faced the same design hurdles (and some more!).
Chain drive will be easy to achieve and adjust. The oil feed will be modified however as it is much easier to oil the sleeve ball joint by taking a drilling down the centre of the shaft. This means we won’t be able to run a points cam on the outside, so an alternative ignition system will need to be found. I think a hall sensor located close to the sleeve drive sprocket is probably the best solution, but I need to do some research.
Great progress though, I just need to get my hands on some parts first. Fingers crossed!
Here’s a photo of the nuts holding the barrels on. No doubt that the right tool is required to remove them without damaging them. Hopefully the threads are a standard size, as our design doesn’t warrant using original nuts. Finding them would be tricky for starters!
Today I managed to get my hands on a Bristol Hercules engine! The contact I made a few weeks ago at the Newark aero jumble came good, and true to his word Graham had a few engines around. The one in the picture didn’t look too bad on first inspection, but it had stood with no exhaust manifolds for some time and the sleeves were quite rusty. Some of them looked pretty bad, I doubt that the barrels could be removed without causing damage. (and that’s the last thing anyone wants!).
However, there’s another engine stored elsewhere that is apparently in much better condition. I will need to go back again to see it, as access to that part of the airfield needs to be pre-arranged. Graham is kindly sorting this out, along with (hopefully) the loan of some special spanners. The nuts holding the barrels on are almost splined and will certainly require care in removal to avoid damage.
Looking at the amount of room to swing a spanner, particularly on the rear bank of cylinders, an ordinary hex nut would be no use. You couldn’t swing a spanner through the 60 degrees required to get on the next flat, so Bristol came up with a solution.
Graham seems a nice chap and is willing to help. With any luck, this time next week I might have some actual parts!
Just a quick scribble as he puts it! But really its a fair amount of work and very clever. With Google and computers at our disposal its all too easy to take things like this for granted. Given the size of two sprockets and length of chain, work out the distance between the centres of the sprockets. Easy!
But this is proper old school engineering. No computers, no Google. Not even a calculator! You need to know the formula and do the maths.
Be like Bob!