| Also known as | E3858 |
| Diagram | Fig. 5 — CYLINDER BLOCK AND HEAD, T90 · ref 26 |
| Subsystem | engine top |
| Listed in parts books | 1964–1970 |
Rocker box stud, 500 (7/8 UA)
Rocker box stud for 500cc Triumph twins (3TA/5TA/T90/T100 family), also known by its earlier number E3858.
This is a rocker box stud, part number 70-3858, listed for the 500cc engine family (7/8 UA per the catalog note). It appears across cylinder block and head figures for the 3TA, 5TA, T90, and T100 series machines through the mid-to-late 1960s catalogs, holding the rocker box down onto the cylinder head. The older factory number for this same stud is E3858, so if you're working from an earlier parts book that's the number you'll see.
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Because this stud shows up across several different cylinder head figures for the 500 twins, it's worth checking your own head casting and rocker box against the parts book diagram before ordering, rather than going strictly by year. Studs like this take clamping load every time the rocker box is torqued down, so if the one you're pulling looks stretched, corroded, or the threads are chewed up, it's a good idea to replace it rather than reuse it.
We don't have extra dimensional specs beyond the 7/8 UA note in our records, so if you need exact thread pitch or length confirmed, give the shop a call before you order.
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