I'd more or less finished the MS restoration, made up a box-section tubular steel mounting frame and decided to fit one of my ex-Merlin compressors for it to direct drive. To facilitate this, I'd brazed in a vertical section of tube in order to bolt up the mounting plate.
I'd got this far just before Enstone but was a bit unhappy with the compressor I'd figured on using as the mainshaft felt seal had failed. In the original conception, the compressor's crankcase is open to the cam box and is lubricated by oil mist. When pressed into other service, one must close off the case and fit a splined shaft in order to drive it. There must have been a lot of these efficient (3-400 PSI) little compressors about after the end of the war, as they turn up quite often at engine jumbles and I've yet to find one that's worn out. The one I had in mind has a nicely-made 1/4" steel mounting plate with the compressor bolted to it. The drive shaft is supported in a small ball race and a felt seal separates it from the outside world. But the years march on and when left to stand, it weeps oil.
At Enstone, I found (was directed to!) another of this breed, a much better thing altogether with a proper cast aluminium crankcase with feet and even sporting a pulley on the shaft. This I bought for not a lot and yesterday got around to mounting it on the MS' frame. As the MS has a lot of exposed aluminium, it blends in very well. The addition of a couple of pieces of the aforementioned box-section tube under its feet brought it - amazingly - into direct line with the MS output shaft, which ends in a rubberised canvas three hole drive coupling.
Now I needed to make a drive plate. Looking through my boxes of bits, I found a steel boss that was a good close fit on the compressors' shaft, an old lipped seal carrier with three holes on exactly the right diameter and a small valve spring cap from a pre-war bike. Centring them carefully by eye, I brazed them all together. 10mm screws secured with Grindle washers and plain nuts went through the holes to act as the drive pins and a hole was drilled and tapped through the boss so I could use an Alan screw to tighten the boss on the shaft.
Assembling the compressor to the MS, I was delighted to find it all lined up and that the small amount of slack in the mounting bolt holes was all I needed to get a wobble-free drive. The petrol tank was already sprayed up and just required assembling, although it was too late in the evening to fire it up.
Photos later ;o))
Regards,
Kim Siddorn