I was wondering if I might impose on the good members of this forum for a bit of advice regarding a gearbox.
I recently purchased a quantity of M20 parts which includes some WD parts. There is a gearbox which appears to be the WD type but I think this box was used post war as well.
My question relates to the selector drum assembly. The gearbox I have has a quite large diameter drum, 1 1/8" in diameter. The part that fits into the bush is 15/16" dia. Now I have not had one of these apart for some time but have had the later rigid/plunger ones apart and they have a much smaller diameter selector drum. Unfortunately its been many years since I have had the gearbox out of my WDM20 and I cant remember what it was like.
Does anyone know when these gearboxes had the larger diameter slector drum assembly ?
Brian.
email (option): brimorest@icisp.net.au
Hi Brian,
The pre war, WD and post war boxes all used the same selector shaft the only difference was that the track for the selector forks and the diameter of the peg heads changed. I'm not sure about your 15/16" shaft end, it might be for the '46-'48 B series.
email (option): spacemonkeym@gmail.com
Hi Matt,
I am sorry to correct you but the pre war M type gearbox definitely had a bigger diameter selector shaft. Have you ever wondered why the steel bush in the cover has this huge outside diameter and a very small inside diameter. That is because the earlier shaft was much thicker. When the smaller shaft was fitted they just adjusted the inside diameter of the bush instead of changing the hole in the gearbox casing.
So What Brian has, is probably a pre war M group gearbox.
Regards,
Leon
email (option): leonhop3@planet.nl
I am sorry to correct you all, yes it is pre WW2, but also pre 1937.
4 speed BSA box appears to have been introduced for 1932, many M20 bits will fit, biggest difference is a shorter mainshaft.
If you have sand-cast housings, they are also pre 1937.
1939 g/box virtually identical to WD and up to 1948.
The early 30's shifters with 15/16" shaft also have the small diameter pins for cam tracks.
37-48 used big pins
49-63 M g/box reverted to early 30's type small pins
The small pins give a better shift.
You can't re-machine an early 30's 15/16" shaft down for later box because shaft is drilled axially and not much left.
You can use a 49-63 M shifter in a 37-48 box.
Merry rivet counting, I am working on another update for my gearbox tech article
email (option): n.gentner@bigpond.com
I stand corrected. Always good to learn something new.
email (option): spacemonkeym@gmail.com
Thankyou Gentlemen,
it appears I have a pre war box although I am still a little unsure of just what year.
Looking at pictures of the 1936 and earlier boxes they appear to have a slightly different outer cover where the clutch arm attaches. My box appears the same as a WM20 externally. It has 9/32" cam pins.
It would seem that it is from 37' or 38'. That would make sense as there was also a 37' or 38' tank with the stuff. (looks the same as a M20 tank but with panel in the top)
email (option): brimorest@icisp.net.au
extract from my unfinished gearbox update for tech section:
1950-1963
66-3140 gearbox shell with fixed fittings M20 M21 M33
NOTE: No bare shell listed in 49-58 parts book.
These later versions of new style M shells have casting number 66-3141 and foundry mark PBM within a hexagon (possibly star) located beneath number, the entire number/mark is located on left-underside. These have provision for proper oil seal, but no oil filler which was deleted from main shell and moved to outer cover for 49 and later.
………………
Summary of 37-48 gearbox shells:
Part numbers and functionality of M shell used from 1938 to 1949 inclusive remain identical. Casting number of M shell used from 1938 to 1949 inclusive is 66-3030.
However there are also some variations in the actual 1938 to 1949 shells.
66-3028 gearbox shells have foundry mark J.H.L. with casting number 66-3030 beneath. Foundry mark and casting number located on Right underside of shell and is read with the open end of shell facing towards reader. Due to die wear this casting number and foundry mark becomes fainter during years of production, barely discernable, unreadable on some WD gearboxes.
Some main shells from war production WM20 gearbox have no foundry mark, but have casting number 66-3030 located differently, clearly visible on upper outer edge directly behind clutch arm.
Some main shells from war production WM20 gearbox have casting number 66-3030 in both locations.
Sole known example of shell with number 66-3030 at top and also underneath, was found on loose gearbox from unknown machine, located in Australia.
Sole known example of shell with casting number 66-3030 at top only, was found on gearbox fitted to 1944-1945 WM20 located in Poland. (outer cover with casting number 66-3103 also fitted)
Shell presumed to be otherwise identical to 66-3028/66-3030, probably wartime production.
No users of Henk’s forum responded to my enquiry for additional information regarding gearbox shell with casting number on upper surface.
Speculation: Possibly made by an outside manufacturer contracted to BSA very late in the war? In event of problems, the easily viewed shell number used to quickly identify?
No users of Henk’s forum responded to my enquiry for additional information regarding “star”, JHL, PBM & BA foundry marks on BSA aluminium castings.
OUTER COVER…IDENTIFICATION
1937-1938
66-3064 Gear box cover outer, foot change, less bush, (bare cover)
66-3063 Gear box cover outer, foot change, with fixed fittings.
1937-1938 M19 M20 M21 M22 M23, also (KJM22 i.e. 1938 restamped by BSA with additional K to signify unsold 1938 machines as 1939 models, (these outer covers have also been found some proper KM23, possibly some carry over into early KM 1939 models, or possibly later change).
Casting number 66-3064 D (inverted) on inside.
Externally: has deep recess for 66-3066/1 special sleeve nut for screw which retains kickstart return spring, cover has deep groove in clutch arm pillar for 65-3161 rubber boot, cover has no external protrusion on outside at front in indented area.
Internally: has strengthening ribs around kickstarter shaft area, has no internal machined clearance slot for wide kickstart spring, cover can only be used with narrow 4 coil kickstart spring. 37-38 covers were normally polished.
1939-1940
66-3103 Gear box cover outer, foot change, less bush, (bare cover) 1939-1940, KM20, KM21, KM22, KM23, KM24… WM20, WM21, WM23.
66-3102 Gear box cover outer, foot change, with fixed fittings, 1939-1940, KM20, KM21, KM22, KM23, KM24… WM20, WM21, WM23.
Casting number 66-3064 D on inside, but 3064 is crossed out and 3102 added above, (indicating earlier casting dies were altered for new cover, casting numbers are inverted. But as casting dies wore the numbers became less readable, until they all but disappeared.
Externally: has deep groove clutch arm pillar for 65-3161 rubber boot, has slightly raised machined boss for hex locknut for kickstart return spring, has an external protrusion on outside at front in indented area.
Internally: has machined slot at rear of kickstart boss for spring clearance of wider spring (6 coil), has no strengthening ribs around kickstarter shaft,) 39 & 40 civilian covers originally polished.
1940 military
66-3102 Gear box cover outer, foot change, with fixed fittings, WM20.
NOTE: no bare cover listed in 1940 military parts book.
Fitted to machines 25001-42000.
1941 military (RAF data but probably applies to other 1941 contracts)
66-3102 Gear box cover outer, foot change, with fixed fittings, WM20.
NOTE: no bare cover listed.
Casting dies changed:
Internally: has casting number 66-3102 only, in smaller font and number is in normal orientation. But as casting dies wore the numbers became less readable, until they all but disappeared.
Externally: has no groove for rubber boot, still has an external protrusion on outside at front in indented area)
Ex WD covers were rough cast, “war finish”, not polished.
66-3102 Gear box cover outer, foot change, with fixed fittings, WM20, probably later WW2 production.
Casting dies again changed.
Internally: casting number 66-3102 still in small font and normal orientation, but now number is more distinct.
Externally: protrusion at front in indented area has been deleted by altering casting die, die joint line is visible where die insert installed.
Ex WD covers were rough cast, “war finish”, not polished.
1945
66-3102 Gear box cover outer, foot change, with fixed fittings, WM20, machines 104818 – 116817.
No bare cover listed in 1945 parts book.
66-3102 (presumed) Gear box cover outer, foot change, has casting number 66-3103 (inverted) no groove for rubber boot.
Probably made during war, example found in 1944-1945 WM20 located in Poland.
All other 39-48 WD type outer covers have casting number 66-3102.
So far only one example known world wide, no users of this forum have responded to request for more information re gearbox cover with casting number 66-3103.
Summary:
Most 1939-1948 outer covers appear to have casting number 66-3102.
Rare exception outer covers have casting number 66-3103.
All 1941 and later outer covers appear to have no groove in clutch pillar.
1949-1963 M outer covers have horizontal clutch arm and large screw-in filler/adjustment plug.
email (option): n.gentner@bigpond.com
I dont know if it means anything but my gearbox has the numbers 15-4177 and Birmal 4569 cast on the underneath.
The main housing seems much heavier (thicker) than the later ones. The only marks I could see on the inside was a 2 cast in the sprocket end.
email (option): brimorest@icisp.net.au
Does it actually say Birmal? or just BA?
4177 around 35-36.
Case is thicker, it is sand-cast.
email (option): n.gentner@bigpond.com
Hello Neale,
yes it has the word Birmal cast into it. So it looks like its 35' or 36'.
I dont use any external image hosting so cant post pictures.
email (option): brimorest@icisp.net.au
Hello again Neale,
I got your e-mail but for some reason I am unable to send you a e-mail. The e-mail keeps coming back as undeliverable. The problem could be with my system as I have had this before. I will try again in the morning.
Brian.
email (option): brimorest@icisp.net.au