mk1-forum.net

Does anyone know why Leyland marked up some of the components with one
digit higher than the official part number? Was it to confuse the Japanese?

Examples:
From the main site, Mark has got hold of this excellent blueprint for the
12G295 small bore head
http://mk1-performance-conversions.co.u ... rawing.pdf
The drawing quotes it as 12G294...

The C-AEG648 camshaft is marked up as "649"...

There is a passing reference to this practice in the Vizard book, but I have
never seen an official explanation. I suppose that in pre-computer days,
it would not really matter as any documentation would be paper based and
it would be easy to find, even if "filed" one digit wrong. In this day and age,
you would probably just get "Computer says 'No'..." as a reply.

Ian

it was always done this way (on cast stuff)

the part number is the id of the current evolution of the part (or at least the 'finished job')

the cast number is the id of the casting

i.e a 12G294 is the bare 'dumb' casting

the 12G295 is the machined item.

they wouldn't renumber the bare casting everytime they changed something other wise they would end up with literally hundreds of casting part numbers for very similar items - just look at the factory blueprints for how many minute changes occur over the life of a casting

it was also probably done this way from a costing point of view - i.e a 12g294 cost '£10', where as a 12g295 cost '£100' as it took into account all the machining costs.

AEG 649 is AEG 648 fitted with the oil pump drive pin.

The crank of the motor I'm currently rebuilding has AEG 479 stamped into it.

The inlet valve in the 12G295 has PN 12G296. Explain that. And if memory serves, the 333 gearbox casing has PN 22g331. I don't think there's any logic to it.

nick rogers wrote: I don't think there's any logic to it.

While there is no logic, there is an answer.

It was done by a Government Comittee.




Nah, as per what Rich has said ^.

Eg, nearly all 1275 heads (from 68-ish on) had the casting no. of 12G940, but n one of them carry that as a part number and there are about 7 versions.

S parts predated government ownership.

940 castings were cast in Wellingborough foundry and then sent for machining for their various uses. Iirc std 1300, 1275 midget, Cooper S, other 4?

rich@minispares.com wrote:it was always done this way (on cast stuff)

the part number is the id of the current evolution of the part (or at least the 'finished job')

the cast number is the id of the casting

Spider wrote:
Nah, as per what Rich has said ^.

Eg, nearly all 1275 heads (from 68-ish on) had the casting no. of 12G940, but n one of them carry that as a part number and there are about 7 versions.

Actually, Now I've posted this and thought more about it, I don't agree. Again, looking at the 12G940 Heads, there were many different raw casting versions of these, but they all bore the same casting no. Maybe they couldn't afford new numbers?

And there are 2 heads with casting number 12A185, and they are totally different from each other.

Spider wrote:

rich@minispares.com wrote:it was always done this way (on cast stuff)

the part number is the id of the current evolution of the part (or at least the 'finished job')

the cast number is the id of the casting

Spider wrote:
Nah, as per what Rich has said ^.

Eg, nearly all 1275 heads (from 68-ish on) had the casting no. of 12G940, but n one of them carry that as a part number and there are about 7 versions.

Actually, Now I've posted this and thought more about it, I don't agree. Again, looking at the 12G940 Heads, there were many different raw casting versions of these, but they all bore the same casting no. Maybe they couldn't afford new numbers?

maybe they couldn't afford a load of new patterns.

Rich is correct.
The part number (of a casting or any other part machined, cast, or whatever) is only changed when an update to the part means it is not fully inter-changeable with the previous version.

-So even though the casting changed over time, it was still fully inter-changeable -it's function/performance was not affected.

The same "rule" applies in the car industry today: if you make a change and the part cannot be used to replace the original version, it must have a new part number.

So what you're saying is the 12g294 was on an actual part at some point in time, then as the casting changed the part was re designated 12g295. So what we're missing is the drawings that relate to 12g295 (or a drawing that is designated a revision)

andy1071 wrote:Rich is correct.
The same "rule" applies in the car industry today: if you make a change and the part cannot be used to replace the original version, it must have a new part number.

Sorry that does not follow in Ford numbering systems.

Every time a part is changed it gets a new number regardless of whether it is interchangeable or not. Interchange between parts is set during the part release by an 'flag' in the system. Without being able to see the release you cannot tell whether one part will fit/do the job, you have to rely on the releasing which is not always accurate.