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MG Midget and Sprite Technical - Engine numbers

I have an engine which has one of the rather odd remanufactured engine numbers. Not sure if it was a Gold Seal or Silver Seal engine (its a grubby yellow colour!)
Is there anything that can be interpreted from these numbers or are they as random as they appear?
8G10 R M413
GuyW

They do mean a lot but you have to find the code !

I thought the 10 is a 1098 engine but not according to Moss numbers ?

The letters ISTR relate to the overbore/ crank undersize - but I don’t know what that equates to - the 413 is I think the actual number of that batch of rebuilds.

Need to research the codes- but where ?
richard b

Exactly, Richard. Asking here was a first step in the researching process. It's like accessing an index database!

This engine came with my frogeye. Part of a box, well several boxes and a pickup load of bits. I wasn't sure that it wasn't just chucked on the heap to make up a 'kit' of parts. But then I got a history record from DVLA at a time when they sent photocopies of all the records they held, unredacted! So I have the earliest record from 1979 listing this engine in the car but showing 997cc

That 997 cc itself is a mystery!
GuyW

ref https://www.mginfo.co.uk/upgrades4mgs/files/MG_Engine_numbers.pdf

GOLD SEAL EXCHANGE ENGINES.
BMC like many firms did an exchange scheme for worn engines, one was the Gold
Seal engine, a complete engine ready to fit and painted gold in colour. The other was the Silver Seal exchange engine, basically a short-block for the owner/garage to fit the old head,sump, and ancillories onto.

Both used a similar system of engine numbering, the original number being struck off.
Initially all engines in the scheme were prefixed 8G, soon a better system followed:-
'A' series engines were prefixed 8G,- 803cc, 848cc, 948cc, 1098cc, 1275cc.
'B' series were prefixed 84G,- 1200cc, 1489cc, 1588cc, 1622cc, 1798cc.
'C' series were prefixed 86G,- 2693cc, 2912cc.
The code after was to do with rebore/regrind sizes and a job number

HTH
Doug Plumb

Thanks Doug. From your message and from the document (downloaded and save) that you link to I still dont get much beyond it being s gold seal engine, with the prefix 8G. from that onwards as it doesn't show the cc capacity the remainder relates to the regrind/rebore and, as Richard says, the batch or job number.

It is still odd that the V5c shows it as a 997cc which was the early mini cooper engine and I am pretty sure was never produced as an in-line engine format.
I know nothing of the car's history between first registration in York, and the first of the DVLA records from 1979. I wonder if it was used in competition and an owner was claiming it as an under 1litre class entrant!
GuyW

Guy,
Moss list8G10E as a 948 early engine.

Is the block marked as a 1098 unit anywhere?

richard b

Guy

As Richard says, there should be an indication of capacity somewhere. I’m pretty sure that 948 engines generally had ‘950’ cast into the block. Some 1098 engines had an alloy plate with ‘1100’ riveted to the block, similar to the early 1275 engines. If no capacity, there should be a casting number.

IIRC the 997 Mini engine had the same bore as the 848 and 948, but a different stroke. The 998 engine was the same stroke as a 948, but with a 0.065” increase in bore.
Dave O'Neill 2

I can't decode the numbers.

But I can say that silver seal exchange engines were not just short blocks. They were complete built engines with head, but no distributor/water pump/stat and housing.

Gold were complete.

Silver reused some parts, gold were all new parts.

Both silver and gold were run to test them.

Silver had a limited mileage 12 month warranty, gold was unlimited mileage 12 month warranty.


anamnesis

This doesn't explain the numbers either, but it's a good read.






anamnesis

..from Terry Horler's book" MG/A-H midget/Sprite"...


David Cox

Good find, David.
Dave O'Neill 2

Here are the rest if the numbers FYI...Dave

The notes do not seem to indicate how a letter refers to a bore o/s or a crank u/s....





David Cox

Thanks David (s) very comprehensive, and very helpful.

I am still intrigued by the V5 entry of 997. Just an error, or intentional? Surely there was never an in line engine with the Cooper S style longer throw crank?
GuyW

The engine size on the V5 was whatever the owner decided to put on it and the DVLC (or whatever at that time the vehicle licensing body was called) accepted.

My old Mini, long since scrapped, had some very dubious entries on its log book in respect of engine size and engine numbers, made by one of its former owners. . .
Daniel

Yes Daniel, that is very much what I had assumed. Particularly as I have never heard of a 997cc capacity configuration of any in-line A series. But the fact I have never come across such a thing, isnt a very robust test! There are some very surprising set ups engineered as one-offs around the world!
GuyW

According to my v5, my Sprite has a 275cc engine. My engine and chassis numbers are both inventions; by me. I didn't get a log book with my Sprite from the breakers where I bought it in 1977. After about 3 years of driving it with 'tax in post' displayed, the local bobby insisted I do something about it. So I applied for a replacement log book abd was told there was no record of my Sprite. The police had no record of it being stolen either. But here it was with number plates. So I filled out the form as best I could, leaving blanks for the engine and chassis numbers. They sent it back to me. I rang them and they said it can't be taxed unless I tell them the numbers. I said both are missing. They said make it up. I did. But somehow they read my 1275 for 275, and despite further tephone calls, and a couple of letters, including a full history request based on my number plate (they said they know less than I do and sent back my fiver), it remains as 275cc. 😅😅.

Yep your numbers may mean diddly squat Guy. Or as you say, something a previous owner did, that was then screwed up by dvla or the previous local council authorities.

You may never know.




anamnesis

Can't remember the origin but my records contain the following in reference to the regrind size letters:
factory recon unit size letters
A = STD
B =10THOU
C = 15THOU (crank only)
D = 20THOU
E = 25 THOU (crank only)
F = 30THOU
G = 35THOU (crank only)
H = 40THOU
J = 45THOU (crank only)
K = 50THOU
L = 55THOU (crank only)
M = 60THOU
David Smith

Up late or very early David?

I found a table like that too. The M was a surprise. I wouldn't have thought the factory would go to 60 over.
anamnesis

Anam, late! I am not, and never have been, a morning person. Born at 5 past midnight and a night owl ever since...
David Smith

Well I guess that my dream that this engine, recorded as 997cc, was an ultra rare, one of a kind, r&D works experimental unit built around the specification of an early 997cc Mini Cooper S on a billet ground crank is finally laid to rest!
🤣🤣😢
GuyW

This link gives some of the meaning of the letters and includes some of what David posted.

https://mgaguru.com/mgtech/engine/be100a.htm
richard b

This thread was discussed between 09/10/2024 and 11/10/2024

MG Midget and Sprite Technical index

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