The earlier pump has a smaller feed plunger, I believe the later one has a 1/4" feed plunger. The return plunger is the same. The body in the vicinity of the feed plunger is a bit broader on the later pump, but the earlier pump can still be reconditioned to fit a larger feed plunger. When I last had this done by Draganfly (a long time ago using an earlier body) they fitted a feed plunger that gave approx 15% greater feed output than the later type pump. However, the ratio between feed and return plungers is large, so the return can easily cope with this greater output.
I'm sure its a Triumph pump, possibly preunit triumph. It is possible to modify it to fit an Ariel single, some of the competition guys did so in the earlier days to get greater oil feed at low revs (trials use, etc). However, the ratio between the feed and return rate is much reduced, and with a roller big end, there is not much benefit for normal use, indeed it is suggested that the churning effect of passing a lot of oil through a roller big end can heat the oil and lessen the lubrication qualities.
excuse me for jumping in the thread, but, (havnt got the paperwork on me at the moment) I was reading up about Bruces cam oiling kit he mentions Morgo being better than MAzac or something oil pump coompared to BSA style. am I right in thinking the one he mentions is the brass coloured one compared to the bigger aluminium coloured BSA A65 ones?
The BSA twin (and Ariel Huntmaster) oil pumps are gear pumps, not plunger pumps. The original pump bodies were of a mazak type material, having stripped and refurbished several pumps of this type, it can be pot luck as to how the pump body behaves when stripped down, and some have had to be junked when the mazak gave way. I think SRM (and possibly Morgo) used cast iron bodies for their remanufactured oil pumps for A10/A65 BSAs, as a more durable material than the original type. I don't know why mazak was originally chosen, was it more suitable (softer metal against hard gear teeth lessening wear), or just the usual cost cutting?
The picture below is of another Triumph pump alongside an Ariel single pump. The Triumph pump is not an exact match for the Ariel oil ways. When fitted to an Ariel, the timing case was generally altered slightly rather than altering the Triumph pump. Dont ask me why it was done this way though.
the next photo shows a 48 Ariel pump (on the right) that has been bored out to fit a 49A or later delivery side plunger. As you can see there is not a lot of material left around the plunger.
Ariel huntmaster and later square 4s were fitted with mazac body geared oil pumps that were from an A10 A65 BSA. Some of the BSAs however were fitted with a cast iron body pump. Those pumps were sought after by Ariel 4 and Huntmaster owners to replace the mazac pump. Apart from being cheap nasty rubbish Mazac will continue to expand and distort throughout its life. It is normal for a mazac pump body to grow into the gears and completely seize the pump if it has not been in use. The pump in my own 4 was an example of this. After eventually getting the gears out of my pump I had to machine the gear housing a couple of thou larger to fit the gears again. There were indents around the body where the gear teeth had prevented the mazac body from expanding. Shortly thereafter I found Drags supply CNC machined steel bodies to replace the mazac body. Below is a photo of a MK2 pump fitted with a steel body. A decent nose body for the pump would also be nice. David