The oil pump used on the M20/21/33, B31/33 and other models had a change to the gear tooth form at some point..Presumably to improve its pumping performance...
To date I haven't been able to find any BSA literature that details when that change was made and which is the later type of gear...
It is also unclear whether the two tooth forms are interchangeable, though I suspect they are not.
Something to look out for if you are building up a pump from the component parts of more than one unit..
Does anyone have any information on this?....Ian
email (option): ian@wright52.plus.com
Are there different part numbers for the components Ian ? I presume we are talking post-war here ? A check of parts lists may provide clues but apologies I have none for the post-war period........
A different tooth form could prove disastrous over extended use by mis-matching of components..........are we certain they are not interchangeable...?
Wartime part numbers (from the next to last contract) are...Scavenge gear 65-2590..(2) feed gear (driver) 65-2592..(1) feed gear (driven) 65-2591...
A look at a 1947 parts list shows different numbers Scavenge 65-2599, feed (driver) 65-2600, feed (driven) 65-2601...
So a change took place, possibly, with the introduction of the B31 for the 46 season...and definitely by 1947....The change also applies to M Series models...
BSA literature clearly states that in the case of the gearbox tooth form change early and late types are interchangeable...
I haven't been able to find anything so far regarding the change to the oil pump gears..Without confirmation one way or the other the sensible thing would obviously be to not 'mix' the two types...Ian
email (option): ian@wright52.plus.com
I'll have a look through my literature Ian and get back to you on this.........
Interestingly, the oil-pump (spindle ?) on 1947 AMC singles also altered around this time if I recall correctly and is not interchangeable with the earlier type......
This could get complicated...I have checked a 1942 WB30 parts list and this model has the 'later' numbers for the pump gears...So they are not in fact post war but ran concurrently with those fitted to the M20...
A postwar change to the M Series models was therefore a 'standardisation' change...
Next stop is a 1940 parts list for the B29/B30..which I do have...
However, I don't have anything for 1939 OHV models...and the numbers need to be traced back for their introduction date..Ian
email (option): ian@wright52.plus.com
And now I'm confused...The 1940 parts list for M,B and C Series models shows the same numbers for all models..and they are the same as the post war numbers....
So, in conclusion it appears all models had the same pump in 1940...
Then the pump for the M Series models only was changed (in 1941?) for the 'duration' (not the WB30 though)...
and finally the pump for the M Series models was changed again post war to conform once more to the previously used type...
Odd indeed..Why did the M20 have this change made?...and the question of 'interchangeability' also remains...Ian
email (option): ian@wright52.plus.com
This is making my brain hurt 
Dunno if this is relevant to this problem but the Draganfly site says something about a change to the pump gears around 1955 which appears to be related to the number of teeth on the gears (so not interchangeable except as a set. Or is this query more tooth form related than tooth number?
http://www.draganfly.co.uk/index.php/bsa/bsa/a710--b3133--c101112--m202133/category/893-oil-pump
Cheers
Pete
I have a bumper box of pump gears in the workshop that I'm going to sort into the two (tooth form) types today....
Both tooth forms and corresponding part numbers were in evidence before 1955, as detailed in my previous post..
I believe the number of teeth was changed at some point for the Gold Star...perhaps this was standardised across the range post 55?....
While I'm sorting I'll look for other differences...Ian
email (option): ian@wright52.plus.com
OK...The number of teeth on the pump gears was altered from 12 to 13 along with the tooth form change...However, the gears were made to fit into the same sized hole in the pump body so the PCD remains unaltered...
You can mix the two types and they will turn..albeit that one runs at a slightly different speed...
Whether they function as well when 'mixed' in terms of oil delivery is debateable and there might be wear problems between the two types if used together..Personally, I would avoid mixing the two types...
Looking again at the parts lists from 1940 through till 1958 it appears I got myself confused and there was in fact only one gear set change from 1958 onwards..
These gears have part numbers 65-2592, 65-2591 and 65-2590...
I can't find any reference to a part number change for 1955 so I assume Draganfly may have got this wrong...the change was for 1958 according to the lists....Ian
email (option): ian@wright52.plus.com
I've now found a note in a parts list that includes 58 and earlier bikes detailing that the oil pump gears were replaced by the later type and noting that..
'for replacement purposes gear sets are only supplied in sets of four'...
So early and late types obviously can't be mixed together....
Which brings me back to where I started really...If you are building up a pump from more than one 'donor' check that the gears match...
My head hurts as well now...
....Ian
email (option): ian@wright52.plus.com
None of the above Rik... ..The confusion over when each type was used was all my own work after getting a large pile of parts lists mixed up...
As you will see in my later post I realised the mistake and noted the fact there was only one change to the gear type and that was post war...
When the originals do all crumble to dust (and I have some that aren't looking too good) there are a number of alternative sources for modern replacements courtesy of the Gold Star suppliers and others..
There's an even higher capacity one available from ABSAF in Holland....Ian
email (option): ian@wright52.plus.com
[' I have to say that if quality new pumps are available, I wouldn't mess around with older parts...although uprated delivery is not always a good thing without other modifications.']
Careful Rik...It might be the first step on the road to purgatory for a rivet counter...
Also,
['and with sharing aforesaid boards with sad old buggers who answer their own threads !']
I must admit I laughed myself (in an ironic way) when I realised I'd answered my own question.. ....Now I just need to work on answering them before I ask them...Ian
email (option): ian@wright52.plus.com