Sunday 22 November 2020

Timing Case Machining – Part 1

A couple of weeks after delivering the patterns to the foundry they called me to let me know that the castings had been made and heat treated. As with the crankcases, the material is LM25 Aluminium. They also mentioned that they had made a “spare” of each. I had already asked for 2 castings of each, just in case something went wrong with the machining, but I now had 3 sets!


All the machining went well, so I still have 2 spare sets ….if anyone wants to make a V-Twin like this one that please contact me for a good price!

I was very pleased with the castings and, after boring the 2 holes for the camshaft drives and the magneto in the inner timing case, I clamped the case to the crankcase with the engine in the frame  to check that everything was the right size and in approximately the right place.

It was.

The first machining operation would be to face the inner surface and to then drill and tap the timing case and crankcase for their securing screws. The inner surface was flattened by rotating on the plywood emery board and then the entire engine was built up on the milling machine table for drilling and tapping the holes for the securing screws.

After machining the first 4 holes, the timing case was put on the emery board for a few “laps” to clean up and start flattening the mating surface to the outer.

The effort in making the mating surfaces on the 3  "legs" of the pattern coplanar had paid off – the large “V” mating surface was, as cast, already nearly completely flat and just required a bit of cleaning up.

After machining the last 2 holes, the slot for the chain tensioner retaining guide (this is referred to as the “reaction damper” in the AJS workshop manual) and preparing the surface for the tension-side low-friction strip, the inner timing case could now be firmly fixed to the crankcase. The front cylinder "leg" of the timing case would not fit within the throat of my milling machine but luckily one of my buddies has a much larger Bridgeport and I used his mill to machine that part.

And with the cylinders, cylinder heads, camboxes, dummy camshafts and chains the whole assembly could be placed in the frame and again checked that everything was in the right place.


So far, so good.

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