Probably a simple question,why on the front frame is the tube boss under the seat open at the top,also on my frame the nearside seat spring lug on the rear frame is 5mm lower than the other side,am i being fussy?
I also wondered about the hole under de saddle, maybe it has something to do with the bracing process ?? to speed up the heating ?? But when the frame has sidecars lugs there is no hole at all...
Another thing I did recently noticed about the frontframe is that both tubes that go into the headstocklug are closed at the end, so that you don't have to pump the whole frame full to get the grease at the headstock bearings. simple and clever....
Probable real reason for hole in WM20 frame: More efficient and cheaper to bore casting right through during manufacture.
Alleged reason for hole: Original spec said to have called for M24 frame i.e. sans sidecar lugs (M24 also have hole, ditto lower front lug, presumably for lightness, along with thinner wall tubes)
Problem with alleged reason: WM20 frame has many differences to both JM24 & KM24 frames, including the saddle lugs. If the actual M24 frame had been specified, most, if not all of them would have broken in service and intact WM20 frames would be as rare as intact M24 frames.
Reality likely to be that: in general terms, the M24 frames were closest to what Army wanted i.e. basic dimensions and no sidecar lugs.
Yes, I do know of WM20 rare exceptions which do have sidecar lugs.
To the best of my knowledge, no pre-war, war, or post-war rigid 500-600cc frames with sidecar lugs have the hole bored right through saddle lug (presumably for strength).
The hole is a source of water entry which can cause the lower bolt to rust solid, also led to demise of many M24 frames due to the more aggressive corrosion of the high-tensile, light guage tubing.
Series A Vincent frames also have the top of saddle lug bored through and presumably the same potential to rust inside the saddle tube.
In the interests of long term conservation, I recommend treating the inside of frame to prevent further rust and a bung to keep water etc out.
Re variations in tank mounts etc
There was a war on, "war finish", "war tolerances", short life expectancy.
No 70 year old I know looks exactly like the day they were born, or even when they were 20.
Many frames have been damaged, some repaired better than others.
Many tanks have been damaged, some repaired better than others.
I use stacked 3mm thick rubber washers for rear tank mounts, primary objective is to get the best "fit" possible between tank and frame so no destructive strains are induced on tank.
If one side ends up with a different number of washers on top and bottom to other side, this is far preferable to a later leaking tank.
Ditto saddle springs, many saddle stays are slightly twisted, many saddle frames are slightly twisted, many springs are not exactly identical lengths. Try swapping springs side to side, use the adjustable lower bolts for their intended purpose, or place a couple of packing washers on top of one spring, this is far preferable to a "leaning" saddle.
If you are doing a major "proper" restoration you will of course check all these things and correct as necessary.
