The XPAG and XPEG oil system comprises a gear-type oil pump, an external canister oil filter mounted on the right-hand side of the engine, and a system of internal oil galleries feeding the crankshaft bearings, camshaft bearings, and rocker assembly. Adequate oil pressure and effective filtration are essential to the longevity of the three-bearing crankshaft, making this one of the most important systems to address thoroughly during any engine rebuild.
Oil Filter History
The oil filtration system underwent multiple changes during TD production. The earliest TDs used a Wilmot Breeden oil filter, which was replaced by a Purolator canister type at engine number XPAG/TD/2985 in July 1950, one of the earliest production changes on the TD, affecting the filter housing, mounting straps, and element specification. The filter mounting strap kit exists in two early specifications: TDs to engine number 2984 use one strap design, with a revised strap kit from engine number 2985 to 14223. A further significant change occurred at engine number XPAG/TD2/14224 in February 1952, when a modified oil filter element and new casing were introduced alongside a simplified by-pass valve arrangement.
A modern replaceable-element filter assembly is available as an improvement over the disposable original, with replacement paper elements, sealing rings, and centre bolt seals.
The Oil Pump
The gear-type oil pump is mounted externally on the right-hand side of the block and is driven from the camshaft via the distributor drive shaft. The pump body, gear set, and bush set are common across all XPAG and XPEG engines, but the mounting bolt specification changed at the same engine number 14224 breakpoint, the quantity of short bolts was reduced and the quantity of medium bolts increased. A complete oil pump rebuild kit is available, and the gear set and three-bush set can be ordered separately. The oil pump end plate was further revised at engine number XPAG/TD2/20972 in October 1952 to incorporate a priming plug, and a new type of oil pump body was introduced at engine number XPAG/TD2/26635 in March 1953. The pump should always be stripped and assessed during an engine overhaul, wear in the pump gears or bushes is one of the primary causes of low oil pressure on rebuilt engines.
By-Pass Valve and Pressure Relief
Early TDs to engine number 14223 used an oil filter by-pass valve comprising separate components, a ball seat, ball, guide, and spring. From engine number XPAG/TD2/14224, this was simplified to a single by-pass valve unit.
This distinction is critical when ordering, as the components are not interchangeable between early and late specifications. The by-pass valve ensures that oil continues to flow to the bearings even if the filter becomes blocked, a vital safety function on any engine, but particularly important on the XPAG with its three-bearing crankshaft, where any interruption in oil supply can be catastrophic. The oil pressure relief valve, separate from the filter by-pass, comprises its own ball, guide, spring, cap, and copper sealing washer, and controls the maximum oil pressure in the main gallery.
Oil Pressure and Gallery Maintenance
The oil gallery plugs, five oil feed plugs, one oil by-pass plug, and the front and rear oil gallery plugs, should all be removed, the galleries thoroughly cleaned, and the plugs refitted during any engine rebuild. Blocked oil galleries are a common cause of bearing failure on rebuilt engines where the block has not been properly cleaned before reassembly. As a general guide, a running engine showing less than 40 psi oil pressure when hot indicates that a rebuild is likely to be needed. For Stage 3 competition-tuned TF engines, MG's Special Tuning guidance recommended increasing oil pressure to 80 psi.
The internal banjo oil coupling and oil pipe from gallery to cylinder head were revised during TF production at engine number XPAG/TF/31943.