Click images to enlarge

XPAG Technical Data, Modifications, Torque settings, Casting numbers

How to check your engines Mod. state, and where it originally came from.

Engine Codes.


1936 to 1956.


Consists of four letters, followed by the engine’s number.

MODEL Valves Bore & H.P. Make.
U Morris 8 S Sidevalve H 57mm 8HP M Morris
M Morris 10/4 P OHV J 63.5mm 10HP G M.G.
X Late Morris 10/4 C OHC A 66.5mm 11HP W Wolseley
T Morris 12/4 B 69.5mm 12HP C Commercial
Q 2ltr 6 cyl E 72mm 13HP
O 3 1/2 ltr 6cyl D 75mm 14HP
A Austin A30 D 61.5mm 6cyl, H 69mm 6cyl.



XPAG 1250cc MG TB OHV engine 11HP.
XPJM 1140cc Morris 10/4 ohv engine 10HP.
XPJW 1140cc Wolseley 10/40 ohv engine 10HP.
USHM 918cc Morris Minor MM SV engine 8HP.
XPEG 1488cc MG TF OHV engine 13HP.
MPJG 1292cc MG TA engine ohv 12HP.
MPJM 1292cc Morris 12/4 OHV engine 10HP.
MPJW 1292cc Wolseley 12/48 OHV engine 10HP.
APHM 803cc Morris Minor MM OHV engine, 8HP.
APJM 948cc Morris Minor 1000 OHV engine 10HP.
TPBG 1549cc MG VA ohv engine 12HP.
TPDG 1705cc MG ‘Cream Cracker’ TA engine.
QPJG 2322cc MG WA ohv engine 18HP.
QPHW 2561cc Wolseley 18/80 ohv engine 18HP.


XPAG Modifications During Production.


Before you read through this list, I emphasise that these modifications were during production of the engine, anything could have been done since to the unit. Also, items like cylinder heads do not carry unique identity numbers, and are often swapped about. The number is my own, not that of M.G. or Nuffield.


1) First XPAG fitted into the TB Midget, August 1939. WW2 intervened, and model updated in 1945 and called the TC, using two 1 1/4″ SU carburetters.


2) Up to XPAG 883 (TC) there was no timing chain tensioner. One was fitted from 884, and the aluminium alloy cover has a bulge in it to accommodate this oil pressure fed, hydraulically damper, spring loaded tensioner. The oil is fed from No1 main bearing feed.


3) From 2020 to 2966 a nice alloy rocker cover was fitted as standard. It must have proved expensive, as it was soon deleted and the pressed steel one reinstated.


4) In 1947 M.G. introduced the ‘Y’ series saloon, with a single SU H2 1 1/4″carb XPAG engine. This and the softer cam produced 46bhp. There had been no suffix to the XPAG engine types up until now as there was only the TC using it. In the ‘Y’ the engine became the XPAG/SC, and began at SC/10001. It was both a saloon now termed the YA, and a tourer called the YT, and sold in RHD and LHD. To clear the LHD steering column the dip stick and its guide grew by two and a half inches at SC/13404. Whereas the TB & TC had a ribbed alloy sump, the ‘Y’ type was smooth.


5) In 1949 the TC was replaced by the TD, based on the excellent but modified YA chassis and running gear. The first TD engine was XPAG/TD/501. With the new model a new C45Y dynamo, M418G starter and flywheel starter gear ring were fitted, at TD/501 and SC/14023. The new starter only has two bolts, not three. TD engine numbers very quickly catch up the YA, then overtake it. TD used the Y sump.


6) At SC/14083 the oil pump to filter pipe changed from a two bolt fixing to a banjo-bolt. This required the end cover of the pump changing, and a new pipe. It was done to clear the steering column of the LHD cars. The XPAG/TL and TR engines were in the normal numbering system of the SC units, not separate.( SC means single carb.)


7) At SC/15405 and TD/2985 the oil filter type changed, and its support straps made stronger. The strap fixing bolts to the block were increased from two to three, and the straps made wider, one inch to one & half inches. Anti-crush ends were fitted to stop over-tightening and crushing the filter canister. The pattern for this casting changed to accommodate the three bolts, and hence the casting number changed to 24445. At this time the engine number plate moved from the bell housing to the offside front of the cylinder block, onto a ready cast in raised portion. See Archaeology.


8) At SC/15576 the pistons in the YA were commonised with the solid-skirt type of the TD. It is very doubtful if many Y’s still have their original split-skirt pistons prior to this modification in about mid-1950. Solid-skirt pistons are stronger, but not as quiet.


9) At SC/16463 and TD/6482 the water pump gland seal was improved. Old and new pumps look identical. At SC/16769 dynamo changed to a C39PV type.


10) The oil pump pick up was to the left-hand side of the sump, and it appears that on fast cornering it could cause oil starvation, ( in a ‘Y’? Must have been on racing TD’s.) The pick up was moved to the centre of the sump at SC/16729 and TD/7576.


11) On the Y only, at SC/16831, ( see 12 below as well,) the camshaft timing was altered to that of the Morris Ten series ‘M’ / Wolseley Ten s3 XPJM/XPJW engines, 5;45;45;5 but with the 8mm lift of the TD. It had been 6.6mm lift with the TD timing of 11;57;52;24. The TD always had 8mm lift. Tappet clearance remained at the clattery 0.019″. This was supposed to improve mid-range torque for the saloon.


12) But on both the YA and TD the rocker gear was modified. At SC/16831 and TD/9008 the exhaust rockers had their bushes made longer to increase life, ( Nos 1,4,5, & 8.) Washers were added between them and the spacing springs, and the rocker shaft made longer to suit, the old one was 356mm and the new one 376mm. Inlet rockers remained unchanged.


13) Modification to the drive chain meant that the engines suffixes were to change to SC2 and TD2.( Note a TD mk2** has a TD3 engine!) The clutch was enlarged to a 8″ unit, replacing the 7 1/4″, along with the first motion shaft in the gearbox growing to 3/4″ from 5/8″. The clutch face on the flywheel was enlarged to cope, as was the clutch cover. This moved the starter ring out a little, but it was so machined that its outer diameter did not change. The gearbox release bearing shaft was thicker and slightly higher up the slightly wider bell housing. This all occurred at SC2/16916 and TD2/9408, simply continuing the normal numbers sequence. This was prior to the YB so some SC2 engines can be found in late YA’s.


** TD Mk2 was a special version Midget with a little more power, a bit like today’s limited editions! It uses two 1 1/2″ SU carburetters, as does the later TF.


14) The old disposable, separate oil filter and its associated pipe work were deleted, and a modern for 1952 disposable element type fitted. This used the same element that a huge number of British cars were to use in the 1950’s, to the 1980’s. This entailed a new oil pump casting, that has the filter bowl integral with it, held on by a long bolt. The oil pipe holes in the cylinder block were left un-drilled. The old oil by-pass hole in the block became the oil feed from the pump into the main oil gallery. A by-pass was incorporated into the filter housing itself to relieve excess high pressure with cold oil. If the oil filter itself became blocked due to lack of servicing, it could be lifted off its seating and pass dirty oil, a large spring inside the bowl allowing this. The filter straps were deleted, and holes left un-drilled on the block face. This later oil pump CAN be fitted to earlier engines if the by pass valve is removed, and the old oil filter feed to the rear of the gallery is plugged up, ( by the rocker gear oil pipe.) It is a much neater arrangement, no pipes to leak. SC2/17293 and TD2/14224 onwards were so modified.


15) The un-ribbed 9 pint ( 5 ltr,) aluminium alloy TC sump was recast as a 10 1/2 pint ( 6 ltr,) sump with cooling fins for the new YB due out in 1952, at SC2/17383. It was also fitted to the TD to commonise the engines, at TD2/14948. The oil suction mesh filter pipe was improved, but see SC2/18097, TD2/24489.


16) At SC2/17432 and TD2/17298 the pushrods were shortened to accommodate longer rocker adjusting set screws. The threads were longer, and both rods and adjusters were only supposed to go with each other, not be mixed with earlier parts.


17) For the more powerful Midget TD Mk2 the engine had its waterways improved to help cooling. Whilst the TD Mk2 had both the new head and block, the normal TD and YB had to use up existing stocks. The new items are termed ’round-hole’ blocks or heads, and carry casting numbers for the head of 168422 head and 168421 block. There is no octagon cast into these blocks, as they were also used on the Wolseley 4/44, and have an extra boss for the 4/44 dipstick. This was un-drilled on the M.G. ‘oval hole’ heads are casting number 22952, and M.G. XPAG oval hole blocks are 24146 and 24445 with octagons. (See casting number identity for more.) The round hole cylinder blocks were now being fed onto the production line, the oval hole ones all used up. Alas there were still lots of oval hole heads left. At SC2/17463 and TD2/17969 the round hole block was fitted to the YB and TD, note how the TD numbers are now ahead of the YB, the TD was selling rather well. With an oval hole head and a round hole block, or visa-versa, an oval hole head gasket must be used, part number X24481. Round hole head gasket is part number 168423. See alse item 21 below.


18) The specification for the steel used in the exhaust valves was improved, very doubtful if any old type now remain in use. SC2/17500 and TD2/18291 gained them.

Note that like the YT engines in the SC-sequence, the TD Mk2 engines also carried on inside the normal TD sequence, no separate numbering.


19) The distributor clamp changed to a cotter bolt, from a simple clamp, at SC2/17670 and TD2/20942. Careful about that distributor at an autojumble, will it fit your car?


20) Once the sump was drained, there had been problems with priming the oil pump. So at SC2/17670 and TD2/20972 the oil pump gained a priming plug. You could fill up the oil pump, and get oil pressure and not heart attack!


21) At last the stocks of ready to fit oval hole cylinder heads had run out. The other M.G’s could now have a cooling system like the TD Mk2, with a block and head that matched. The heads were fed into the production line, ( casting number 168422). This has long reach plug holes (3/4″), so if you have long reach plugs, it is a round hole head. If you have short reach plugs, ( 1/2″), you have an oval hole head. Again if a round hole head is fitted to a round hole block, use the correct gasket, 168423. Old heads use Champion L10S plugs, the new one Champion N8B. This happened at SC2/17994 and TD2/22753. At TD2/22251 the clutch cable became a rod.


22) To improve the mid-range torque of the TD, it gained the YB camshaft, part No AAA3096, at TD2/24116. However, it was not quite the same identical camshaft, see item 23 below. ( Old TD camshaft was AAA5776.)


23) Whilst the ‘new’ cam had the same 5;45;45;5 timings of the YB, it was in fact a more modern profile with wider lobes to improve life. The shape of the lobe profile enabled the tappet clearance to be reduced to 0.012″ from 0.019″, hence it was a lot quieter. It is called the 230 degree cam, with 8.3mm lift. The plate on the rocker cover gave the new clearance, and this was SC2/18097 and the TD2/24116 above. Today we now have the problem of identifying which cam is fitted, see the Valve Gear chapter. The XPAG is one of the more audible engines one hears, it lets you know its tappet clearances are a wide .019″, and even the later .012″ is not so quiet.


24) At SC2/18097 the YB gained a new distributor, 40058F type, and the TD gaining a similar version at TD2/24489, type 40367. These had high lift-short duration cams, and the points gap was 0.014″ to 0.016″ instead of the earlier 0.012″. On the same engines the sump had yet another modification, as oil had been backing up at the longer forward end under braking. So a longer oil pick up was fitted. As it was heavier, it had four bolts fixing it instead of two, and these can be seen on the nearside of the sump. Previous sumps should be so modified, if not already done.


25) The oil level in the oil pump was raised to assist priming, the idea being that if it remained full on draining the sump, it would self prime on starting the engine, ( but see item 30.) This was on SC2/18120 and TD2/26635.


26) From SC2/18272 and TD2/27551 the crankshaft was forged out of E.N. 100 ton carbon steel, a stronger material, part number 168537. Had some TD’s broken a few of the old ones racing?


27) At SC2/18122 on the YB only, the spark plugs were changed to Champion N8, the N8B deleted.


28) In October 1952 the Wolseley 4/44 with its version of the SC2 engine was in production, called the XPAW. Because of the new camshaft timings it was found the springs could become coil bound so the valve spring faces were reduced by 0.5mm on all ‘X’ series engines. This occurred at SC2/19037, TD2/27867, and XPAW/1308. Heads will have been swapped all over the place by now, but they will be round hole heads. This modification was done in early 1953, and records show the SC2 engine ended at 18460, rather odd!! The valve guides were now 24.5mm above the head.


29) At TD2/281167 the rocker pillar bolts were drilled and wire locked, as per normal aircraft and racing practice. The 4/44 remained with spring washers, the YB had gone, the ZA Magnette replacing it with its BMC 1489cc ohv by-pass oil filter engine.


30) At last, by drilling a small air hole up inside the oil pump, the oil pump was made self priming. The TD had by now been replaced by the TF so the Midgets suffix changed but the numbering system continued on. This was at TF/31263 and XPAW/5142. Changing the oil was no problem, oil pressure was instant on starting up afterwards. Both the TF and 4/44 had pressurised cooling systems, at all of 4psi.

The TF 1250cc engine was in fact the TD Mk2 slightly more powerful version, with an extra 4bhp over the standard TD unit. This block had been re-cored to enable it to be bored out to 72mm, giving 1466cc, and becoming the XPEG, the TF becoming the ‘TF 1500’. The TF 1500 head was the TD2 one, with bigger valves, inlet 36mm, ( TD 33mm), exhaust 34mm, ( TD 31mm.) The TD had used a 7.25 to 1 compression ratio, but in the TD2 this became 8 to 1, with 60bhp. The TF 1250cc produced 57bhp.


31) To reduce oil feed to the rockers, the banjo-bolt at the oil gallery on the rocker feed pipe, had its internal diameter reduced to 0.055″. This was at TF/31943 and XPAW/5300.


32) On the 4/44 only, at XPAW/6809, the water outlet angle at the thermostat was changed to face the offside, in readiness for the BMC ‘B’ series to be fitted as the Wolseley 15/50 ( 1500cc, 50bhp) radiator was being fitted. This outlet looks just like a TF one to me, and I suspect it was to commonise parts, as the 4/44 carried on for another 23,000 cars!! Or was the ‘B’ series in short supply?


33) Again, the 4/44 had a completely different sump casting to its M.G. cousins, with a floating oil pick-up. Air leaks had occurred, so it was improved with a four bolt fixing instead of two. These can be seen on the outside of the sump under the oil pump, from XPAW/7642.


34) The TF had gone, the 4/44 the sole user of the ‘X’ series of engines, with the BMC ‘A’ and ‘B’ series taking over. On XPAW/20901 the timing chain oil thrower was enlarged from 2.6″ to 2.812″ to try to reduce oil leaks at the front end.


35) We are into 1956, the front asbestos rope seal on the crankshaft is replaced with a modern neoprene sprung lip seal, at XPAW/24110, part number AEG133, ( a Morris part number, not BMC.) Sump and timing cover were machined to suit, and the sump gasket modified. Watch out at auto-jumble’s that you buy the right sump gasket for your engine, the late 4/44 one is too short at the front end, for your M.G.


36) Last ‘X’ series engines off the line, October 1956 in a 4/44. The 4/44 ran for 34,000 units, and had just a few engine modification’s, perhaps it was well sorted by then. However the column change gearbox fitted with its selector rods entering the casting under the oil level line, adapted from the YB, was another story. It leaked till the end. Both the TF and 4/44 used the later crankshaft part number 168557.


Torque Wrench Settings.

Cylinder head stud nuts. 500 lb/in; 5.7m/kg; 50lb/f.
Connecting rod big end bolts, then on to next split pin hole. 320 lb/in; 3.7m/kg; 27lb/f.
Main bearing cap nuts, then on to next split pin hole. 750 lb/in; 8.6m/kg; 63lb/f.
Rocker shaft 10mm bracket nuts. 42 lb/f.
Rocker shaft 8mm bracket nuts. 27 lb/f.
Flywheel bolts. 50 lb/f.
Small end, ( gudgeon pin,) . 33 lb/f.
Timing chest cover. 20 lb/f.
Clutch cover bolts. 33 lb/f.
Sump bolts. 27 lb/f.
Manifold clamping nuts. 20 lb/f.
Oil pump stud nuts. 12 lb/f.


Casting Numbers.

Model/Item. Casting Number.
Early Morris/Wolseley Ten 1140cc ‘X’ cylinder block, oval. 22500.
Later post war 1140cc cylinder block, oval water holes. 24144.
Early M.G. 1250cc ‘X’ block, octagon cast in, oval water holes. 24142 & 24146.
Later post war 1250cc M.G. block, octagon cast in, oval holes. 24445.
4/44, later TD, & TF block, no octagon, round water holes. 168421.
Early 1140cc cylinder-head, no centre oil drain, oval water holes. 22812.
Later post war 1140cc head, same as early ‘T’ type, oval holes. 22952.
Later TD, & Y oval hole cylinder head, short reach plug. 22952.
4/44, TD & TF head, round water holes, long reach plugs. 168422.
Late 4/44 head, round water holes. 168425.


These can be found on the cylinder block behind the dynamo, or on top of the head.


Casting numbers are often quite rough, the wooden pattern getting knocked about with use and age, so numbers can be difficult to see. On the block it is under the tappet chest cover, behind the dynamo, above the octagon if the block has one. On the cylinder head it is easy to see on the top, though often not fully clear, casting ‘flash’ obscuring it.


This comprehensive technical data supplied by Neil Cairns.