| Also known as | E3887 |
| Diagram | Fig. 3 — OIL PUMP AND RELEASE VALVE · ref 11 |
| Subsystem | engine bottom |
| Listed in parts books | 1964–1971, 1974, 1976–1980, 1983 |
Serrated washer
Serrated lock washer for the oil pump mounting stud on Triumph twins, PN 70-3887.
70-3887 is the serrated lock washer used on the oil pump mounting stud, also seen in the parts books under the earlier E3887 designation. It sits under the special conical nut that clamps the oil pump to the timing chest, and its job is to keep that nut from working loose over time.
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This one shows up across a long run of oil pump and release valve figures in the catalog, spanning decades of production, which tells you it's a part that stayed consistent through a lot of engine changes. It's a small item but it's specific to this fastening job on the oil pump stud, so it's worth ordering by part number rather than substituting a generic washer.
Because it's a serrated/lock washer meant to bite into the nut and stud faces to resist loosening, treat it as a one-time-use item at each reassembly rather than something to reuse indefinitely.
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