It may be that 600 numbers denote steel and 700 numbers denote cast iron flywheels. However, in the absence of that being proven (and as some flywheels don't have numbers at all) the best way to identify the two types is the surface finish,detail of the shapes and a 'rust test'.
The two types differ in surface finish and detail because of the very different production methods.
A 'rust test' involves cleaning a small section of the flywheel rim with emery to produce a bright finish and then cleaning the area with thinners to completely degrease it. Exposed to a damp environment the cast iron will develope a light surface rust within 24 hours as a rule. Steel will take considerably longer...a fairly crude test but quite effective....Ian
email (option): julie@wright52.plus.com
Hi Neale...I'm not sure there are 'year specific' parts lists beyond 1948, I've never had any. The latest year specific one I have is 1947. There should, logically be year specific books..they couldn't have written 49-54 in 1949! However, it seems from 1949 they just added the information for the next year and printed another book. The later lists I have that include 'exploded views' all cover more than one year for both M and B model types. The M models supplied exclusively to the AA from 60-63 (the alternator ones) probably would have had a parts list but the bikes were not being supplied to the general public by then.I have got a set of these late 'alternator' flywheels so could check the numbers if required. If a flood of year specific parts books do now appear I would like some copies!..Ian
email (option): julie@wright52.plus.com
Ian,
From Henk's CD I got 1947, 1948, 1949 & 1950 year specific books, also combined 1951/1952.
Hovever, the 1946? 1947? (engine number XM21-3473) change back to all steel flywheels for all M models is then inexplicably reversed in the 49/58 book, with no reference back to 1947 or any other year.
Summary: There is data in the specific year 47/53 books which contradicts some more of your tech section data and also contradicts my 49/58 parts book, hence my "can of worms" description and request for contributions.
Mainly to nail down if and when cast iron flywheels were actually re-introduced for civilian M20 & M21?
Are the early or later parts books wrong? Or both?
"First, do no harm"
Neale
email (option): n.gentner@bigpond.com
Hi Neale,
Here it is:
email (option): unpob@yahoo.com
My reading of this is as detailed in the piece in the tech. section.
The 47 parts list shows cast iron flywheels fitted to the M21 UP to engine number XM21 3472 (part numbers 66-705/7) Then steel flywheels FROM engine number XM21-3473 until 1949? when they reverted to cast iron again. The 1949 parts list shows the correct numbers for the cast iron type.
A look at the 48 parts list (which I do not have) would indicate whether steel or cast iron flywheels were fitted to the M21 for 48 and would show whether the reversion to the cast iron type took place in that year or 49.. So 45-mid 47 M21s would have iron wheels, mid 47 to 48 or 49 M21s steel wheels with the reintroduction of cast iron in 48 or 49 determined by the 48 parts list..Ian
email (option): julie@wright52.plus.com
What contradictions to this do the year specific books make?....Ian
email (option): julie@wright52.plus.com
The 47 parts list shows cast iron flywheels fitted to the M21 UP to engine number XM21 3472 (part numbers 66-705/7) Then steel flywheels FROM engine number XM21-3473 until 1949? when they reverted to cast iron again. The 1949 parts list shows the correct numbers for the cast iron type.
A look at the 48 parts list (which I do not have) would indicate whether steel or cast iron flywheels were fitted to the M21 for 48 and would show whether the reversion to the cast iron type took place in that year or 49.. So 45-mid 47 M21s would have iron wheels, mid 47 to 48 or 49 M21s steel wheels with the reintroduction of cast iron in 48 or 49 determined by the 48 parts list..Ian
Ian,
To the best of my powers of comprehension, I'm afraid the year specific parts books on Henk's CD disagree with the data you are quoting.
1948 page 38, M33 introduced, otherwise as for 1947 (post XM21-3473), no iron flywheels for M series.
1949 pages 36 & 38, as for 1948, no iron flywheels for M series.
1950 page 36, no entries for M20/21 but book states elsewhere that it is for new models only and to use 1949 list for established models.
1951/1952 pages 42 & 44, complete model range, flyweels as for 1948, no iron flywheels for M series.
1949/1958 page 14, iron flywheels re-introduced at an unknown time for M20 and M21, steel for AA M21.
Hence my request.
"First, do no harm"
Neale
email (option): n.gentner@bigpond.com
It appears in the 46 book they have the written description of the materials the wrong way round.
Other than that numbers and descriptions match for all years...Ian
email (option): julie@wright52.plus.com
here is a quetion could you have a crank of half a cast iron and half a steel one maybe bodgers have done this
The 'combined years' parts list for 1949-54 shows the part number for cast iron flywheels for the M21.
If the year specific list for the same year shows the numbers for steel flywheels then it appears there may be an insoluble problem.
There is no way to date flywheels physically, so examination of parts will not reveal the answer.
The conflicting parts lists by definition don't provide the answer.
I based my tech piece on the parts lists I have to hand and there is no contradiction there. (because I don't have year specific books beyond 47 which highlight the differences.) So the 'data I was quoting' was from BSA parts lists.(it hasn't been determined yet whether they were the correct or incorrect ones)
At an early stage in the current discussion it became apparent that the content of that piece contained a number of inaccuracies and the info. relating to flywheel materials may be one of them.
However, with a discrepancy between the parts lists, which currently are the only way of determining what was used in a given year I would be interested to know by what method this point will be resolved...
Ian
email (option): julie@wright52.plus.com
Roger,
It is possible to assemble appropriate model steel and cast iron flywheels together into a crankshaft.
However, that is not the cause of the current flywheel dillema.
Due to their contradictions and or errors, it is now apparent that for the purpose of accurately identifying the year models in which cast iron flywheels may have been introduced, deleted and reintroduced, the BSA parts books and other known publications cannot be relied upon.
"First, do no harm"
Neale.
email (option): n.gentner@bigpond.com
Hi Henri..Cast Iron flywheels were a cheaper option from the point of view of the manufacturer...both the material itself and in the production methods used.
For todays user there is little practical difference if the flywheels are being used in their standard form.
However, if used for tuning applications where extensive lightening is planned the steel wheels should be chosen. The strength of the cast wheels can be seriously compromised by extensive material removal and at high revs there is a risk of the wheels 'bursting' under the increased loads.
In the early days when iron wheels were more or less universally employed the tuners used to machine the iron wheels down and then shrink on a steel 'rim' to prevent this happening...Ian
email (option): julie@wright52.plus.com