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!
The cases have been cast, along with a batch of Aston Martin gearboxes 🙂 They’re away being heat treated and I’m expecting them back in a week or so. Not much more can be done until then, the mighty Bridgeport CNC conversion is patiently waiting!
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!
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.
Into the press for an asymmetric push, the idea is to move the flywheels around the crank pin. A sound plan, but unfortunately the flex on the long bolts made it difficult to get a decent reading on the DTI.
Getting a twist reliably measured to 7 thou was not possible, so another think is required.
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!
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.