Halihat,
Ah well, cam bearings. There you are in luck as that is still a size manufactured. The camshaft uses a single row radial ball unit of Ø5/8xØ1-3/8x9/32" at each end; or what use to be known as an inch size R10. The question you should ask is where they are made. For some odd reason, the majority of imperial size bearing are made in Asia. Even bearings from the house hold names in the ball bearing world are made in China, re-packaged and significantly marked-up in price. Check to see what is etched on the bearing itself as a country of origin, and not what is on the packaging. If you are not worried about where they are made indicating the quality of manufacture, you can buy the same bearing for much less under the trade name "General". They make them for all the well known Japanese, German, and American firms.
Two alternatives are a "Bearings Limited" E15, which seem to be made in Slovakia and perhaps the best choice, "RPH" number KLNJ5/8Y, which are made in Switzerland according to the last batch I got. Note, this only applies to imperial sizes, which are becoming a low-volume product. Many of the big firms like to keep a much tighter control on their metric bearings, and do not outsource them. Also the big names do have their own plants spread around the globe, so you never really know where they are going to come from next.
The cam bearing on the timing side half of the case is retained by a simple steel cover plate, affixed by two 1/4-20 bolts either side. This closes off the bore, which on the timing side is a through hole. I have seen them flat on the side facing the ball race, and recessed. The latter I suppose when they messed up boring the cam bearing housing depth in the drive side half, and there was insufficient end float for the bearings as a result!
These bolts have a rather shallow head to fit behind the cam gear. They are cross drilled for safety wire, which is rather ridiculous, as one can never wire up tight between the two bolts as the cam is right between them! Modify the plate design to take tab washers or use a low strength (non-permanent) thread lock fluid.
The head gasket is a solid copper wire of diamond cross section which fits in the grooves you noted. Some folks just use round cross section wire these days. It develops flats and in time conforms to the groove. I have been using square section wire used for winding large electric motor armatures. This I lay in the groove flat, and like the round wire it gets crushed to conform to the groove. I roll the rings up slightly smaller than required, and then weld the joint with copper wire and a tungsten inert gas welding torch. After dressing the weld flush (easier in square wire than round), I press it over a mandrel that expands it out to the correct diameter, and gets it nice and circular again. It probably would not bee too much trouble to roll the wire on edge and so make the diamond cross section as per original; but a slightly larger square wire would be required. But I never bothered. The important thing when sizing the wire is that the flat surfaces of the head and the cylinder must not touch, there should be a slight gap so that you are always clamped up on the gasket, or joint ring to call it what it really is. If you are crushing the wire, you also have to allow extra as it will settle over time and the gap will close up; maintain at least 0.010" and change the joint ring out if it becomes less.
Two other options are first, just to use flat copper sheet gasket and ignore the joint ring completely. Earlier Douglas o.h.v. engines did not have the joint ring, nor a spigot. I do not know if they used a solid copper gasket or a sandwich composition. I have heard of folks using just solid copper. You may need to flatten the head surface if you intend to go this route as the head lugs may have pulled down over the years ever so slightly. But the cylinder should be fine as it is in compression and there is no stress through the planar portion of the joint surface. The second is to turn joint rings from solid, tube if you can get it (expensive), or plate (expensive as well!)
All the used rings I have seen so far are all solid, but I can not say if they are original ex-factory, or if Douglas possibly made diamond joint rings with an asbestos core. I have had a set of the welded rings in a friend’s touring SW for some fifteen years, and another set has been vintage racing in the UK on road circuits. If you could get a Wills ring big enough in section and clamped the joint faces up tight, you would have the best of all worlds.
Between the barrel and the crankcase should just be a paper gasket. Douglas seemed to favor 0.006” thick material. The shims you have are something someone made to play with the compression ratio. Or perhaps someone has skimmed a bit off the base flange, a very common occurrence over the years, and needed to restore height. For the 62.25x82mm DT/SW engines the distance from the base flange to the head surface is 4.825”. There are several types of barrel, but the two mostly likely encountered are different in the base flange. The early type is thinner, and has four raised bosses where the cylinder through-studs pass. These are prone to crack if shortened too much. I was about to set a record time at the Wroughton airfield vintage sprint (well, perhaps not
) on a borrowed DT Douglas and was let down by this very fault. You will be surprised how much oil can escape from such a small crack. A later style has a base flange a uniform 5/16” thick, and so is stronger and has more scope for re-cutting.
Douglases reputably had overheating trouble when they re-entered the TT in the thirties and had to run on straight petrol. It is said the course fining was designed in the twenties with the 50/50 fuel then in use in mind. Be that as it may, they do not overheat in touring use with the same fining and most folks using a Douglas in anger today are sprinting in 1/4 mile races so there is no cumulative heat build up. If you are planning to use the car for demonstration laps or hill-climbing, you probably will have no overheating problems, depending of course on how shrouded the engine is when installed in the car. But it will run cooler on alcohol or methanol. The late Bill Dent swore by methanol in his famous DT Douglas sprinter. He also said it was gentler on the engine; a softer combustion in the main burn sequence.
The thread on the end of the camshaft is 3/8-20, or it is on the 8-spline drive types. They also made an earlier taper drive and a later small spline drive that may have used a different thread. The crankshaft thread is 7/8-20. Douglas, when not using their own threads (and they had some wacko threads) were partial to the Cycle Engineer Institute thread series, which at that time included two separate systems based on twenty and twenty-six threads per inch. The later of which is all you can get taps and dies for today. Still Douglas applied it to diameters I do not think the CEI system intended! Earlier o.h.v. cranks had a smaller taper and thread. Also over time many have had the threads damaged and re-chased, and are not longer exactly Ø7/8”. Even the ones that are tend to measure closer to Ø0.865” due to the thread crest being worn down.
-Doug
