The 1500cc lower engine uses entirely different components from the A-Series. The Triumph crankshaft runs in three main bearings but is a completely different forging, and all bearing shells, thrust washers, and seals are specific to this engine.
Engine Detail
The most significant difference is the timing chain arrangement. Where the 1275cc uses a duplex chain without a tensioner, the 1500 uses a single-row chain with a separate chain tensioner. Chain stretch on the 1500 is a known wear characteristic, as the chain elongates with use, the valve timing retards progressively, causing a gradual loss of power and increasingly rough idle. The chain tensioner compensates for moderate stretch, but once the tensioner reaches the limit of its travel, the chain and sprockets must be renewed.
This should be inspected at each major service interval.
1500 Lower Engine
The 1500 oil pump is a different design from the A-Series, bolted to the block with three bolts rather than being driven from the camshaft. The camshaft is secured by a lockplate rather than a thrust plate. The sump and sump gasket are specific to the 1500. At the rear of the engine, the 1500 uses a conventional lip seal in a separate housing, whereas the A-Series originally used a scroll-type seal. Pistons are available in standard and oversizes (typically 0.020", 0.030", 0.040", and 0.060" over standard).