oil pump oddities

Rob3912 · Post by **Rob3912** » Mon Feb 25, 2008 8:23 pm

i am trying to sort out an oil pump guide screw for a 47 heavyweight crankcase. I have no screw to go by as it was not with it when I obtained the parts. The crank and oil pump are both twin start however the threaded hole to take the guide pin and retainer is smaller than the later (post 48) one I have ( 3/8 26 tpi 1,4 guide pin) and larger than the early one piece (1/4 26 tpi one piece 3/16 guide). The casing appers to be 5/16 26 tpi but I am unable to find any listings of such a guide pin.

Is this a B'strdised casing or a total mismatch. I am aware Plumstead made alterations about this time. Any suggestions or lead to the right part would be of help.

Many thanks Rob

Biscuit · Post by **Biscuit** » Mon Feb 25, 2008 8:39 pm

Thanks for moving this query, I don't know the answer, but Itma should be along shortly.

wilko · Post by **wilko** » Tue Feb 26, 2008 8:49 am

Maybe sombody stripped the 1'/4 in and did a bodge? If i was in the same situation and handy with a lathe(which i am) it wouldn't be too hard to make up an alternative arrangement? Douglas

itma · Post by **itma** » Tue Feb 26, 2008 9:20 am

agreed, As far as I can remember there are just the two sizes

Rob3912 · Post by **Rob3912** » Tue Feb 26, 2008 10:18 pm

Many thanks wilko and Itma, I know what you mean, as I see it I could go even further and fit the larger screw and pin arrangement with a little drilling and tapping.
The 5/16 thread appears to be in good condition, to a factory standard. Either this is a bodge as you say or another one of AJS's little mysteries. The other casing half is numbered M18 4947 B. The B suffix is an unusual reference, not one I've noted before, but then I am a junior in Jampot terms and I have yet to qualify to the plumstead dark arts league.
Many thanks Rob

ps keeping an open mind on this any 47 ers out there?

Duncan · Post by **Duncan** » Tue Feb 26, 2008 11:46 pm

Rob, I have a 47 16m (ongoing project) about 1700 engines later than yours, it also has the “B” suffix, amongst other parts I have had to buy a new “011915 – Screw, guide, oil pump plunger” which I have just checked and it fits perfectly it looks about 5/16”, when I was looking Russell Motors were the only people who stocked them.

Guide pin looks like 3/16"

This might be a 47 only item to match the oil pump which was for that year only as well.

Just looked in Bacon p101 and he mentions “The pump used on the singles has changes to its plunger and guide screw for 1947 and 1948 to tie in with the alterations to the timing-side mainshaft and its oil-pump drive worm”

Edited by - Duncan on 26 Feb 2008 11:56:48 PM

wilko · Post by **wilko** » Tue Feb 26, 2008 11:57 pm

The "B" stands for Bowden cable supposedly. Who knows why they stamped that on the engine no.I think Amal supplied cables too. This is conjecture tho'. Douglas

Rob3912 · Post by **Rob3912** » Wed Feb 27, 2008 9:32 pm

Thanks guys very good stuff. Duncan does the oil pump have a 3/16 guide groove width or is it the 1/4? I wonder if someone has stuffed a later pump in the casing as it matched the twin start crank.

Have checked a 47 parts book and agree with the number it is a shame the description did not include the size.

Please go to the top of the Plumstead dark art league gents,

best wishes
rob

Duncan · Post by **Duncan** » Thu Feb 28, 2008 10:32 pm

Rob

My engine was dismantled when I brought it, I have a suspicion that the crankshaft was not original as it had the earlier 7 3/8” connecting rod and high gudgeon pin piston in the box together with a new, later (lower gudgeon pin) wire wound piston to suit the relined barrel, I have had the crankshaft rebuilt with a 6 7/8” connecting rod and reused the timing side axle which matches the oil pump.

The only real difference I can see in Bacon p104 between the “up to 46” and “47 only” pump is a slightly increased pitch in the gears I believe mine is more like the “up to 46” one (if you have a look can you tell me what the difference is with the corresponding timing side axles on the same page, they both look identical to me, I assume it is the pitch of the thread, but just can not see it).

The pump has the smaller (3/16”) guide pin slot and as I can not see 2S stamped on it I am all but convinced that I have the earlier single start pump.

I am not too concerned with using the earlier pump as it was ok for the WD’s and up to 47, as I still have the earlier tappet guides with three drain holes fitted the twin start pump could lead to swamping of the top end if I ever engage in any sustained “high speed” road work, I should be so lucky!

Don Madden · Post by **Don Madden** » Fri Feb 29, 2008 2:16 am

Hi, duncan. what you cannot see in the pictures is the early, single start plunger has a single worm, the 2S has two interleaved. If you start at one end of the worm & follow it, you will find the 1S has a single thread passing around twice. The 2S has a second thread starting on the opposite side, out of sight in the photo & each makes one turn about the axle.

Cheers, Don.