Here is a question I have been meaning to ask for a while and Andy sending me some pictures of his KM20 engine has given me the opportunity.

I used to own a Morris Commercial C8 gun tractor, the cylinder head which for a while I was removing with annoying regularity had the "QAULCAST" emblem cast into top surface, recently I saw a similar logo on a smaller car engine, and I assume this meant that component production was passed around during the war years.

BSA M20/21 barrels sometimes had a number or letters cast into the barrel, and I wondered if in some cases this could mean something similar, BSA motorcycle production during the war was greatly increased at the same time the factory took on multiple orders for other war work often in gun production which may have involved subcontracting some components?

Here are some examples, there are probably others?

Andys KM20, "DB" could it be David Brown?


"B"




"66-88?"


"66-133?"


? Higher on the barrel

email (option): robmiller11(a)yahoo.co.uk

David Brown sounds like a logical option Rob. They had their own foundry which carried on after they took over Aston Martin (hence the DB model range) Some Hillman Imp engine blocks were cast by Aston Martin in the 60's and had AM cast into them. Ron

email (option): ronpier@talk21.com

Pattern makers often applied their own marks to the patterns when they produced them...The 'Star of David' mark seen on many BSA castings is rumoured to be there due to the high number of Jews that worked in the pattern making shops. Birmingham had (and still has)a large Jewish community based around the jewellery quarter...

The barrel base flange was also increased in thickness at one point, so there would have been a change of pattern there and these may have been marked to indicate use with the longer barrel base studs used after the alteration......Additionally, each pattern would only produce a limited number castings so they were periodically renewed, no doubt by multiple pattern makers at different times over the 10 stud barrels 25 year production run...

There was the change to a different barrel material when cylinder liners were deleted and, of course, there are numerous post war examples around which have been thoroughly mixed up with wartime examples...BSA, at some point, also decided to add the part number...

It must certainly be a possibility that castings were sourced from other suppliers. BSA themselves owned a number of companies that produced castings, both for themselves and for other manufacturers and aircraft companies supplied the castings for some companies..I would imagine the pressures of wartime production could well have led to an increase in that type of 'cross supply' but it is clear there are many reasons why the various markings might have been changed...Ian

email (option): ian@wright52.plus.com

I'm not aware of BSA using a dating system for the various engine components and to do so with just the barrel would seem illogical...The full set of 'month' code letters would be very common though if that system were employed and it should be relatively easy to confirm whether that was the case....
However, there would be barrels with the same letter that could have been manufactured 5 years apart...or 25 years apart if the system was employed throughout the total production run of the model.....

The year of manufacture of the engine was, under normal circumstances, denoted by the engine number prefix letter, though this was suspended during the war and all engines carried the 'W' prefix from 1940/41 onwards...

Certainly on post war crankcases the full engine build date was also stamped on the crankcases, either just below the tappet chest on the exterior face of the case or inside the timing chest adjacent to the intermediate gear spindle (e.g.19-2-54)...Ian

email (option): ian@wright52.plus.com

The full name "Qualcast" usually appears on the rear of Ariel W/NG brake drums.....

A lot of castings for the motorcycle industry (and car) were made by Birco/Birmid based in Smethwick and West Bromwich, there used to be lot of other foundries in the black country that were also used, I'm sure Birco logo is on some Triumph 3HW castings, BSA, Norton etc could also have used them as they were local to them, most of the foundries a round here closed in the eighties/nineties, a few still survive but when they stop making petrol/diesel engines they will also close down too.

email (option): robmiller11(a)yahoo.co.uk

When I upped my M20 to 600cc, Ian told me that I'd probably have to open up the inlet port to accommodate the M21 1 1/16" carb, but I found it already was big enough and the few other M20 barrels I've look at or worked were also already 1 1/16". Ron

email (option): ronpier@talk21.com

The extra capacity of the M21 was achieved by lengthening the stroke to 112mm from 94mm..This demanded a change to the piston crown height as the con rod remained unaltered so the M21 piston is different as well...The bore remained unaltered at 82mm....I've seen variations in port sizes...Ian

email (option): ian@wright52.plus.com

I guess that since they used exactly the same barrel and valves for both M20 and M21, it was easier to make one barrel fits both.

As Ian said to increase the capacity to 600cc I simply dropped in a pair of M21 flywheels and a piston through the plug hole. :thinking_face: Ron

email (option): ronpier@talk21.com

BSA spares list show

1939 Civilian
Cylinder Barrel 66-88 M20 DL and M21
Cylinder barrel 66-81 M20 std
Base studs 24-1620/1 x 4 66-1627/1 x 1
Carb 76/014 M20 Std & DL
Carb 76/024 M21

1940 Civilian also used for Contract C7370
Cylinder Barrel 66-88 M20 and M21
Base studs 24-1620/1 x 4 66-1627/1 x 1
Carb 76/014 M20
Carb 76/024 M21

Contract C6126 (the earliest military spares list available)
Cylinder Barrel 66-88
Base studs 24-1620/1 x 4 66-1627/1 x 1
Carb 276/014

Contract S7218 (the last military spares list)
Cylinder Barrel 66-88
Base studs 24-1620 x 4 66-1627 x 1
Carb 276/014R

1946 Civilian spares list
Cylinder Barrel 66-88
Base studs 24-1620 x 4 66-1627 x 1

1949-1958 Civilian spares list
Cylinder barrel 66-132 M20 and M21
Base studs ? (I'm missing this page)

It would appear from the base studs part numbers remaining unchanged from 1939-1946 that the bottom flange thickness variance wasn't a deliberate alteration, more a manufacturing difference?

The pre war barrels were the same for M20s and M21s and presumably the same inlet size of 1" or 1 1/16", but then there is the unexplained difference with the M20 De-Lux & standard models barrel in 1939?

The pre war carburetors had a different number, but that could be the body length rather than the bore, post war the M21 used an alloy spacer to increase velocity, longer bodied carbs exist, was that the case in 1939?

Can anyone confirm inlet sizes for the variously marked barrels, a large number of replies could be useful as some barrels have been enlarged for tuning.

Rob

email (option): robmiller11(a)yahoo.co.uk

The 014 carb was 1" and the 024 was 1 1/16".

C7370 was the odds and sods Civilian and ex-Dutch contract and the implication is that they still had pre-war Type 76 carbs with open pilot airways.

C6126 is odd, unless it's a misprint as it suggests that the early M20s didn't have the 'R' suffix carbs...i.e. they used the flat-milled Norton type jet block with two small pilot inlets rather than the centrally machined slot. That would surprise me, as even pre-war Nortons had the cast gusset under the inlet to allow for the extra machining.

In the supplementary parts list for spring frame models fitted with an alternator and supplied to the AA, that is within the 49-58 parts list, another barrel is listed... 66-141..Though there doesn't appear to be any alternative numbers for the base studs..

This supplementary list is a surprise as I am pretty sure alternator models were supplied from 1960-63 only...I suspect the list I have is a post 58 reprint and the supplement has been added to cover later models rather than to reprint a complete new list..

In the main parts list the barrel base stud numbers are the same as the earlier ones you have listed...24-1620 and 66-1627 indicating the base flange wasn't altered at least up to that point...I'll have to take a look at what barrels I have to see if I have an example each flange thickness..I think I do have both lengths of studs if I haven't disposed of all the old ones in one of my 'clearouts'....Ian

email (option): ian@wright52.plus.com

It may be 66-132 was the one with the thicker flange and 66-141 was the unlinered one...That would mean the unlinered barrel was only fitted for 3 years and would explain the fact they aren't very common...Ian

email (option): ian@wright52.plus.com

Ok as far as carburetter bodies go prior to the war Amal had four holes around the base above the big nut which specified 6 then after 1933 used 76, in 1939 the war Office in England decided that it wanted to be able to filter the air going into the carbies so changed the design to delete those four holes by putting the hole within the opening at the front. The 1939 Amal list shows M20 having body 76/014(four holes) and also WD M20 as 276/014R both one inch opening and M21 76/024 (four holes) had inch and one sixteenth opening. It also lists Export Models of M20 and M21 as all being 276 prefix. All war time M20 and M21 had the standard Amal body which is 1.5 inches from centre line of body to face of flange. M21 for A.A. use from 1949 to 1953 had the extended body which was 2.5 inches from centre line of body to face of flange whereas the standard M21 from 1946 to 1954 had the shorter length body. Normally a longer carby body was to clear the magneto. Just to mess with our minds AJS continued with the four holes all the way up to the monobloc in 1956. Matchless had a 275 or 276 body until 1946 when it reverted back to the 76 type four hole body. WD Ariel NH had a 76 body whereas NG had both types of bodies and VG had 76 type body. Triumph also reverted to the 4 hole type for its racing engines in 1949 to 1953. Velocette MAC WD had 76 body whereas MAF WD had the 276 body. I believe that all M20 carbys had the one inch hole and M21 the one and one sixteenth hole. I have seen heads opened up to take 289 carbies at one and one eighth and new owners think this was the norm on M20. WD M20 had a carby 276C/1B with body 276/014R and also 276L/1E with body 276/014R all the same specifications except the 1E bowl did not have the horizontal fuel banjo it had the standard vertical threaded part under the bowl with the thin nut under the bowl. I have only seen a few of this carby although I had a lot of the 1E new old stock bowls. WD M21 had a carby 276P/1B with a body 276/024R.

email (option): ukcarbsathotmail.com

That's interesting so it appears that in 1939 M20DL and M21 models both had the same barrel but different size carb bores then the situation was the same as post war with the larger size 1 1/6" barrel inlet being used?

There are several more numbers in the C6126 propriety list, I was just too lazy to type them all.

AM/276L/IE Carb complete less cables
AM/276/14/RMC Body

This is from the contract C7370 propriety list which would have accompanied the 1940 Civilian spares list, only two carbs listed for 3 models B29 M20 & M21?

1940 Edition









1944 Edition

email (option): robmiller11(a)yahoo.co.uk

I have measured 6 barrels in total....The first one on this list is a 1936/7 '8' stud barrel...Flange thicknesses seem to have quite a tolerance...I measured all of them on all 5 stud holes and measured on the machined barrel base and the machined nut seat, not on the raw casting, to try and get a more consistent result...

To summarise those results the average thickness for the 4 exterior studs was .478" (31/64ths) with a considerable variation in the readings spread across all the holes measured irrespective of the barrel..The dimension for the stud inside the tappet cover averaged .384" (nominal 3/8")....This difference explains the part number difference for the 'inside' stud...

1) 1937-38 barrel...Inlet port 1.062" Part number 66-73
2) Unlinered barrel...Inlet port 1.062" Part number 66-132
3)Unlinered barrel...Inlet port 1.152" (I ported this one).Part number 0 132
4) No flange marking...Port diameter 1.087"
5) No flange marking...Port diameter 1.062"
No.4 could be 1.062" plus tolerance...Hard to say...
6)Inlet port 1.091"...Part number 66-88
No.6 as number 4..?
Note: both '132' numbered barrels are unlinered.....Ian

email (option): ian@wright52.plus.com

So all at least 1 1/16"?

Does anyone have an M20 barrel with a 1" inlet?

Rob

email (option): robmiller11(a)yahoo.co.uk

Not on me..:laughing: ...What's the part number on your unlinered barrel?....and does anyone else have an unlinered barrel with a number?....and does anyone have a 66-141?(2)...Ian

email (option): ian@wright52.plus.com

Hi

I have both types nos here

I can measure tomorrow

Br
Job

email (option): jonnyob1@googlemail.com

Hopefully I can check my M20 tomorrow to see what numbers are on the barrel, it is an unlinered 1 1/8".

Rob

email (option): robmiller11(a)yahoo.co.uk

Here is my unlinered barrel with 1 1/6" inlet, it appears to say "6 133", presumably these numbers are often 1 out from the actual part number because they are the part number of the unfinished casting?

But this one would probably be manufactured some time between 1949 and 1958, I suppose I could grind off the part number to make my M20 more correct for 1943 but I probably won't.

Rob

email (option): robmiller11(a)yahoo.co.uk

I wasn't sure whether one of mine was a '0' or a '6' as the definition of the casting was poor..I guess it was a'6'..So '6 133'

My other unlinered barrel has 66-133 cast on it...Ian

email (option): ian@wright52.plus.com

Hi, mine has no barrel casting only H to the neck. I am pretty sure it is a postwar one.
John ☹️

email (option): john.kater@chello.nl

Hi John, is it a definite "H" or could it be that odd star thingamy I illustrated in the first post?

Rob

email (option): robmiller11(a)yahoo.co.uk

email (option): john.kater@chello.nl

A question.
I have a spare cilinder with 27 mm inlet.
It has also dubble valve springs (like an OHV).
Anyone ever seen that ?
Should I remove the inner springs..?

Michael, it's been known by other forum members, who do some tuning/tweaking to fit double valve springs to minimize valve bounce at higher revs. Mick Holmes told me he fits BSA C15 valve springs inside the M20 springs. Ron

email (option): ronpier@talk21.com

Yes, I've also used C15 inners...The M20/21 didn't use inner springs as a standard fitment...I think A10 inners have been mentioned on the forum as well...

There's no real advantage in using inner springs on a standard engine.....Ian

email (option): ian@wright52.plus.com