MG-Cars.info

Welcome to our Site for MG, Triumph and Austin-Healey Car Information.

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - Engine block dating

I have a '72 Roadster. The circular tag on my engine block (type 12H3503) shows a '25' at 12 o'clock, a '3' at 4 o'clock and an 'F' at 8 o'clock. I believe this translates as the block was made on 25th June, 1973.
My problem is that the block tag shows 18GG which only ran up to August 1971.
This is supposed to a reconditioned full engine fitted in 1994, but it also has a 12H2708 head from an 18V.
In the very near future I shall be examining the timing chain to see if it's simplex or duplex which might help as Clausager says the simplex only appeared on 18V engines. Unless someone knows different?
I'm not at all sure what's going on here. Any comment would be appreciated, particularly if it comes with a shining light!
Richard Coombs

Richard. Block tags are fairly easy to remove and replace. In fact, you need to remove them before a block is hot tanked to clean it. Unless one can document that an engine has been in the vehicle since new, everything about the engine must be considered suspect. You have already found that the block markings do not seem to agree with the engine tag, nor does the cylinder head. This type of thing is not uncommon on a rebuilt engine, especially one done by a large engine rebuilder where parts are stripped off of a number of engines, cleaned, machined, stored, then pulled out of the storage areas and assembled into a working engine. At the end of the process, you should have a working engine. But, you may not have the same parts assembled together that were on the engine when it was disassembled.

What is the problem you perceive with this engine? If it is working well, it will be fine for a driving car. If it is to be a show car and everything must be exactly as it left the factory (in truth, better), than the exactly correct parts are worth considering. But, otherwise, it comes down to how the assembly performs.

Les
Les Bengtson

Early 18V engines had a duplex chain fitted. Clausager's book gives the change over date to simplex.
Iain MacKintosh

Les, Thanks for the comments.
There was no problem with the way the engine ran before I stripped the car, although a couple of pots showed blacker than I would like on the plugs. I'm just trying to fathom what I have and to make sure that any wear is minimal. I am still suspicious about the date tag. I don't understand why anyone would bother taking it off and replacing it with one which had no meaning. Nor why they would put an 18GG block tag on if the block was an 18V.
Iain, yes I spotted that. I was expecting that one or the other chain would 'date' the engine a little. I assume that with a rebuilt engine either can be fitted assuming all other required changes are made at the same time so maybe this won't be a good lead after all.
Richard Coombs

Richard - Can't help with the block number.
The 18V was the preferred choice of head for lead-free conversion - the original may have been cracked -many were. The timing chain may be an indicator - but even here you can't be sure whether the original timing gear was worn out and replaced with cheaper new gear.

Sorry
R Walker

Iain. Clausager provides some useful references on what was done originally. But, when something is, at a minimum, 29 years old (1980 MGB), a lot of changes may have taken place during that time period. The second that Richard mentioned "This is supposed to (be) a reconditioned full engine fitted in 1994", things changed. A "reconditioned engine" can be whatever the seller wants it to be--there are no published standards for such things nor any formal definitions. On all of my rebuilds, including the late model 18V engines, I use the duplex timing chain system. Most of us who do our own rebuilds do, considering it a better system than the simplex timing chain. But, what system some unknown rebuilder will use cannot be determined except by a complete teardown inspection. Nor, unless the engine is being rebuilt or is in a show car, does it really matter a great deal.

Les
Les Bengtson

Gentlemen. I see others were posting while I was. My opinion, worth fully what you are paying for it, is that there is no real problem here except one of understanding what has happened previously. Richard is concerned because the engine tag does not match the information on the block casting. I would offer up two possible reasons for this:

First, the engine was destined go into a vehicle which originally had an 18GG engine in it and the original tag was removed from the original engine and installed on the rebuilt engine. The old engine (called a "core") was then shipped back to the rebuilder for inspection, rebuild, and resale. This is why many rebuildable parts have a "core charge" associated with them if the replaced part(s) are not available or in a rebuildable condition.

The second is that, at least here in the US, the larger engine rebuilding companies do not always higher the brightest and best of workers. Seldom does one see someone holding a degree in mechanical engineering, or some related field, working as an engine rebuilder or a mechanic. (I only know of one such individual.) Mostly, the rebuilders hire people who are willing to work cheap, teach them just what is needed to do a specific task, and are not overly concerted with retention of their semi-trained workers--all are interchangable and there are others looking for a job if one worker quits. In such a case, you could well have a marginally competent, minimum wage worker installing tags, on an almost random basis, after the rebuild and painting are completed. I have not seen this with engines (because I rebuild my own), but have seen it on other parts.

Again, worth taking notes on what you can see and might even be worth popping off the sump (if the engine is out of the car) and noting what the rod and main bearing sizes are. But, there is a lot to be said for just leaving an engine alone if it is running well and worrying about what it might be made up of when it next needs to be rebuilt.

Les
Les Bengtson

if you say the F is june what would M be.
Bob Taylor

I deduced it from the contribution to the thread on 'Back pressure etc' by Steve S , Virginia. It's a pity that 'M' is the 13th letter, but if they chose not to use 'I' as it can cause (more) confusion this would make 'M' December. Anyone out there with an 'I'? Or worse, anything later than 'M'?
Sorry, best I can do at the moment.
Richard Coombs

I forgot to thank Les and others. I am sure the essence of what has been said about rebuilds is true and I only care because I'm trying to understand what I have. I intend to remove the sump anyway to check out the wear on the oil pump so I'll have a good look at the rods and bearings.
By the way, is it acceptable/legal to change the engine tag to the original 18V number fitted when the car was made?
Richard Coombs

Well I'm there, I hope!
Les was right on the money re a rebuild being whatever you get. In summary I have:
A reconditioned block with an 18GG label
A 12H2708 head (wider inlet ports), normally fitted to 18V engines
A simplex timing chain fitted to 18 V '73 models
Bucket type cam followers normally fitted to 18V
New carburettors normally fitted to an 18GG but they should be fine

All top and bottom engine parts look to be in excellent condition which at least tells me the PO documentation is correct and the engine has only seen ~20k miles.
As things look good and there were only minor running issues before the strip down I've decided to leave the head undisturbed so I don't know the exact state of the valves etc. I will see how she runs with the new carbs.
So basically I have an 18V engine with the only oddity being the block label! Simple really.
Now onwards to the gearbox!!
Thanks to all for the comments.
Richard Coombs

This thread was discussed between 09/09/2009 and 15/09/2009

MG MGB Technical index

This thread is from the archives. Join the live MG MGB Technical BBS now