The XPAG and XPEG engine block is a cast iron four-cylinder unit with dry cylinder liners, chain-driven overhead valve gear, and a three-bearing crankshaft. The fundamental casting remained largely unchanged across the TD and TF, but significant production changes, particularly the water passage hole revision in June 1952 and the bore size increase for the TF 1500, created distinct specifications critical for parts selection.
Block Casting Changes
The original TD block used oval water passage holes between the cylinders and the coolant jacket. From engine XPAG/TD2/17969 in June 1952, a revised block with round water passage holes was introduced, five months before the corresponding head revision at engine XPAG/TD2/22735 in November 1952. The round-hole block is the more common specification today, covering the final year of TD production and all TF 1250 cars. The TF 1500 block is a further revision with siamesed bores increased from 66.5mm to 72mm to accommodate the larger XPEG pistons.
Gasket Sets and Block Sealing
The bottom-end gasket set is common across all TD and TF engines. The top-end set exists in three specifications matching the head gasket: TD to engine 22734 (oval coolant hole), TD from engine 22735 and TF 1250 (round coolant hole), and TF 1500 (enlarged bore). The block uses six small and two large core plugs, universal across the XPAG and XPEG and best renewed during any rebuild. Oil gallery plugs, oil feed and by-pass plugs, water pump studs, cylinder head studs, manifold studs, and water drain tap are all available individually.
Crankshaft Oil Seals
The original front crankshaft seal was a rope-type design in two halves. An improved modern lip-type seal is available as a direct replacement and is strongly recommended for any rebuild. The rear oil seal, oil thrower, thrower gasket, and fixings are universal across all XPAG and XPEG engines. Rear seal effectiveness depends on a true crankshaft journal and a correctly positioned thrower, so cleanliness and correct fitting technique are essential.
Cylinder Liners and Pistons
The XPAG and XPEG engines use dry cylinder liners pressed into the block. The TD and TF 1250 share a common liner with a 66.5mm bore, whilst the TF 1500 uses a larger liner with a 72mm bore. These liners are not interchangeable, the block machining differs to accommodate the larger XPEG bore and its siamesed arrangement. Pistons are available in multiple specifications and oversize options.
For the XPAG, the original three-ring solid skirt piston is available in standard through to +80 thousandths, with a 1,348cc overbore option at +100 and +120 thousandths for a modest capacity increase. A four-ring split skirt Hepolite piston is also available up to +60. For the XPEG, both pattern types are available with a more limited oversize range, up to +60 on the original three-ring and up to +40 on the Hepolite. Piston rings must be ordered to match engine type, piston specification, and required oversize.
Connecting Rods
The connecting rods differ between the XPAG and XPEG. The TD and TF 1250 share a common rod, whilst the TF 1500 uses a different rod designed for the higher loads of the larger capacity. Connecting rod bolts and nuts are shared across both engine types, and the gudgeon pin pinch bolts and spring washers are universal.
Timing Cover and Front Plate
The engine front plate and timing chain cover are shared across all XPAG and XPEG engines. The front plate gasket, timing cover gasket, cover bolts in three lengths (long, medium, and short), and the TDC indicator used for ignition timing are universal components. The tappet chest cover plate, available in either the original pressed steel or a cast aluminium alternative, provides access to the cam followers. Its gasket, studs, nuts, and fibre washers are universal across TD and TF.
Engine Breather and Ancillaries
The engine breather pipe runs from the tappet chest area, secured by upper and lower clamps with associated bolts, pinch bolt, and nuts; a carburettor overflow pipe clip completes the hardware. Engine paints, black, MG Red, BMC Green, and MGC Green synthetic enamel, are available for refinishing the block, head, and ancillaries. Wellseal jointing compound and Blue Hylomar are available for reassembly where a flexible, non-hardening sealant is required.
Engine Identification Hardware
Engine identification hardware, a blank engine number plate, the engine type button (XPAG for TD and TF 1250, XPEG for TF 1500), and the rivets securing both to the block, is available for engines being rebuilt or re-identified after overhaul.