| Also known as | E3903 |
| Diagram | Fig. 1 — CRANKSHAFT AND CONNECTING RODS · ref 3 |
| Subsystem | engine bottom |
| Listed in parts books | 1960–1962, 1964–1965, 1967–1968, 1970–1971, 1974, 1976–1980, 1985 |
SLUDGE TUBE 650/750
Steel sludge trap tube fitted inside the crankshaft on 650/750 Triumph twins to catch debris before it reaches the big-end bearings.
The sludge tube, also called the sludge trap tube, is the steel sleeve that fits inside the crankshaft on 650 and 750 Triumph twins. It sits down in the crank where the connecting rod journals are drilled, and it's there to catch grit and heavy particles flung around by centrifugal force before that debris can reach the big-end bearings. Triumph parts books list this under the crankshaft and connecting rods section, which tells you exactly where it lives - inside the crank assembly, not something you see from outside the engine.
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This one carries the legacy number E3903 alongside the modern 70-3903, so if you're working from an older parts book and see E3903 called out, that's the same physical piece. It shows up across a wide span of catalog years for the 650/750 twins, so it's a part that stayed consistent through a lot of production changes.
Any time a crank comes apart for a rebuild or inspection, this is worth pulling and cleaning out - accumulated sludge in there defeats the whole purpose of the thing. If you're not sure which tube your particular crank takes, bring the crank in or give us a call before ordering.
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