The lower engine category encompasses the components below the cylinder head, the crankshaft assembly, connecting rods, pistons, cylinder liners, sump, and associated sealing and hardware. These are the components addressed during a bottom-end rebuild, and several carry critical distinctions between the TD, TD2, TF 1250, and TF 1500 specifications. The Engine Block and Components section and the Crank and Camshaft section cover the individual component groups in detail; this overview sets out the lower engine assembly as a whole and the relationships between its constituent parts.
Bottom End Rebuild Scope
A lower engine rebuild on the XPAG or XPEG typically involves removing the sump, withdrawing the pistons, removing the crankshaft, and assessing all components for wear. Compression testing and oil pressure assessment will indicate the likely scope of work. On the XPAG in particular, crankshaft condition is the single most critical factor: it must be crack-tested by a specialist, and its journal diameters measured before the main and big end bearing sizes can be established. A reground exchange crankshaft is often the most economical route provided the original unit is within regrinding limits.
Sump and Sump Changes
The sump gasket set, comprising two gaskets for the sump-to-block joint, is universal across all TD and TF engines. The sump drain plug and its copper washer are similarly common. The sump casting itself was revised at the TD2 breakpoint at engine number XPAG/TD2/9408 in July 1951 to accompany the revised bellhousing, larger flywheel, and 8-inch clutch assembly. The dipstick tube and dipstick were revised at engine number XPAG/TD2/10900 in September 1951, when a shorter dipstick tube with a new dipstick was introduced.
The oil suction filter within the sump was moved to a central position at engine number XPAG/TD/7576 in April 1951, and a new type of suction filter was introduced at engine number XPAG/TD2/24489 in January 1953. These changes mean that the internal sump arrangement differs between early, mid, and late TD production as well as the TF.
Bearing Assessment
The three main bearings and four big end bearings run in replaceable shell-type bearing sets. Both main and big end bearing sets are available in standard and a range of undersizes to suit reground crankshaft journals, and must be matched to the measured journal diameters after regrinding, ordering bearings to a standard size when the crankshaft has been reground will result in excessive clearances and oil pressure loss. The bearing sets are universal across the XPAG and XPEG, as the crankshaft journal dimensions are common to both engine types.
The Sump and Oil System Interface
The sump provides the oil reservoir for the gear-type oil pump. The oil pump pick-up pipe draws oil through a gauze strainer, and the bolt quantity securing the pick-up to the sump changed during TF production at engine number XPAG/TF/33024, from two bolts to four, reflecting a factory improvement to the pick-up security. The pick-up gasket also changed at this point, from a two-bolt to a four-bolt fixing pattern. The sump bolts comprise three distinct types by length, two short front bolts, ten medium side bolts, and two rear bolts, all of which should be checked for thread condition during reassembly.
Identifying Your Lower Engine Specification
The sump, bellhousing, and flywheel are the components most affected by the TD-to-TD2 change at engine number 9408. The key question when ordering lower engine components is whether the engine is pre-TD2 (7¼-inch clutch, original sump and bellhousing) or TD2 and later (8-inch clutch, revised sump and bellhousing). All TF engines use the TD2-specification lower end. The cylinder liners and pistons then split between XPAG (66.5mm bore) and XPEG (72mm bore) as covered in the Engine Block and Components section.