1948 engine questions

[Tazmantic]

Hi all new project under way (all others put on hold) so I’ve started with the engine but am getting very confused I now have the Roy bacon book which is great and from this I can see that lots of changes happened in the 40s so I’m worried about the engine I have.

The drive side case is stamped 48/18 6*** B so simple enough though the casting number inside is 39/8/E30 which looking through the parts lists is a model 39/8 would this casting have been used for many years?

The timing side case looks more dirty so doesn’t seem to match but this has a casting number 39/8/E31 once again model 39/8 so it looks like my cases are 1939 so why are they stamped 48?

Further to this the barrel is stamped 39/8/E1 so more to say it’s a 39 or could all of these parts have been hanging about till 48?

So my next concern is the crank as it states in Roy‘s book that the timing side mainshaft went through a lot of changes and though I haven’t removed it (shaft that is) it looks very much like pictures one and two in his book though it doesn’t have the second hole in the shaft just up from the taper which I presume is to oil the bush and as it says on the Ajs parts website the 1946 main shaft won’t fit the 1947 so is there an easy way to tell what I have as any info would be great, the big end is shot and needs doing but I don’t know if this is just through age or lack of oil due to incorrect parts the only numbers on the crank webs are G9.

Think that’s enough of an essay for tonight…

Many thanks

[Duncan]

AMC castings carry the part number for the year that they were first used so it is usual for later year models to have parts with earlier casting numbers.

The oil pump went from single start to two start in 1947, if you look at the scroll on the axle you will be able to see either one starting points or two (180 degrees apart I think). Single and two start pumps and axles can not be mixed and match as the angles are wrong on the pump and you will strip the threads.

[Tazmantic]

Thanks Duncan so these could be older cases stamped up in 48? It’s just it states the timing side case was altered in 47 and again in 48 for changes in the oiling system and the parts books do show different part numbers.

My timing side main shaft is a single start (did wonder what that 2 start meant) so how will I know if my pump is correct?

Many thanks

[Duncan]

It will all depend on what the changes were, for example if it was a post casting machining operation the basic casting would still be the same.

If you have the pump a two start one will have 2S stamped on the end, the single start one will have shallower engagement gears if you look at the picture on page 104 the angle is just noticeable, additionally the single start and 1947 pump used the narrower guide screw again noticeable in the picture.

[Tazmantic]

It doesn’t seem to say just that there were changes to the oiling, and with the book and your explanation it would appear that I have..

1948 cases and the oil pumps (I have 2 one came with it and one I had with some bits I bought a while back) are also for that year or later as although it doesn’t seem to have 25 stamped on it (there is a number but can’t really read it) they both have 1/4 slot in them.

1946 (or possibly older) crank as the timing side main shaft is the single start type.

So the question is where I go from here I was hoping it was just a rebuild job for the engine but as the big end pin is also worn do I get a new pin and 1948 timing side main shaft and use these cases, try and find a good 1948 crank complete or get 1946 cases (as I think the frame is 1946) get a new big end pin and 1946 oil pump.

Thanks again for all the info Duncan

Looking at pic could be 25 but one that came with engine don’t seem to have a number.

[G15 Roy]

I see you are no longer showing as a member have you forgotten to renew.

[Tazmantic]

I will need to check thanks for pointing this out

[Tazmantic]

Renewed

[SPRIDDLER]

If in doubt here's a way to check compatibility of plunger and t/s axle..........

Oil pump plunger compatibility.JPG

[Tazmantic]

That’s just confused me even more

No I think I understand