Last few bits


For a while now locating the last few bits from the mights Bristol Hercules engine I need has been playing on my mind. A pair of washers snd circlips for either side of the piston. Not huge items but hugely important and a pain to have to make.

I needn’t have worried. A quick call to Patrick at Maddison 4×4 (who does beautiful restorations of aircraft engines) and very generously they arrived next day! Amazing how the universe works sometimes, thank you Patrick!

Last on the list is the castings, which will be ready for collection on Thursday. Can’t wait!

Back to the Keyboard


While we’re waiting for the cases to be cast and heat treated, I’ve started to write some GCODE for fly cutting the mating faces. With such large components travel on the Y axis is very close to the limits, so a trial run over a set of drawings is a must!

The position of the spindle centre is also critical, and this afternoon I brought it forward. I hadn’t done this before but it was fairly straightforward and with Bob’s assistance now in the right place. Bob remains unconvinced that CNC is better than handle twiddling!

I think we’re going to be ok without resorting to larger machines. Great news as it is VERY close to the limit!

Huge Scissors!


Getting an accurate reading from the press proved difficult, any movement was a combination of everything. All the bending moments of the long bolts, give in the jack and twist of the assembly. Bob wrote off that method and we moved onto plan B.

Plan B. Often this is the most successful of all plans, I do wonder sometimes why anyone bothers with plan A? Would NASB have been more successful than NASA?

Anyway, plan B. Bob made a special tool acting like huge Scissors. In order to twist the flywheels around the crank pin, two mandrels will be fitted into the existing holes opposite the crank pin. The tool inserted between the wheels locate on the two mandrels. When opened or closed using the thread and nuts, the scissors will twist the wheels.

There’s plenty of leverage so it ought to work!

CAD Model.


The flywheels have been clocked and have a run out of around 15 thou. Ideally this needs to be less than 5, so the wheels need to be both jacked apart and twisted around the crank pin. Accurately!

Jacking the wheels apart is fairly straightforward, but twisting them around the crank pin is more tricky. The plan is to mount them on the press, then use the press to push them around the crank pin.

The photo shows the CAD model (Cardboard Aided Design 😁😁) for bolting the wheels to the press. Bolts are in place ready for the heavy lift of the crank assembly onto the press.

Patterns completed!


It’s taken a while longer than expected, but the patterns are finished and ready to take to the foundry. Excellent work from Dave and I can’t wait now to see a set in metal. The picture gives you a good idea of the size of things 😁

The plan is to get a couple of sets making, so I can get a set machined in basic order to hold the barrel. This will be a full sized mock up to get the frame started, while the other set gets fully machined.

Bob has the machining plan sorted and a bit of a job on learning the CNC operation on the Bridgeport – but it’s easier than you’d think so I’m sure I can explain it!

Patterns coming along


Dave dropped round with one half of the patterns to show us the progress. Not far off being finished, the fillets, radii and draught angles are going in ok. The timing cover needs a second coat of paint and the main casing a full paint, but another week or two and they’ll be ready to take to the foundry.

I took the opportunity to pair them up with a barrel and for the first time the final dimensions are apparent. Bit of a lump but I can make it work. If the casting isn’t too pricy I’ll have two sets cast, and use the spare set and barrel for dimensioning the frame. The frame builders will appreciate a full sized engine to work with.

With all this activity going on, I need to start thinking about ignition and a carb. Neither of these are particularly challenging, I just haven’t put a great deal of thought in just yet.