OIL PRESSURE SWITCH CONFUSION

In 1968 Triumph twins and triples were supplied with a low pressure oil warning light in the head lamp shell. This was supplied power by a single wire from an engine mounted switch. The warning light would remain lite till oil pressure exceeded 7 lbs. On twins the switch was on the forward facing edge of the engine timing gear cover. On triples the switch was under the engine. BSA twins also had this switch from 1968 till end of production.

The confusion regarding this switch lies with the factory changing the case thread in 1969. One could speculate as to why this was done. Most like it was done to save money. In 1968 the switch had an American tapered pipe thread (1/8x27NPT). Tapered threads require a bit more attention to machining and installation. This is due to the sealing being done by the taper with the aid of some sealing compound. A straight pipe thread is much easier to machine and install. Requiring just a sealing washer. Generally it is accepted that the American straight pipe thread switch (1/8x27NPS) was introduced in early 1969. In the factory notes Triples started coming with the straight thread switch commencing engine number AC01629 (Jan 1969). I have not been able to find records of the changes on Triumph or BSA twin machines.

After the switch was changed the factory manual should have been updated. This was over looked and only added to the confusion. For example the tapered switch part number 60-2133 continued to appear in the Triumph twin parts manuals up until 1973. Books from 1974 reflect the updated straight thread switch part number 60-3719. Some have suggested that there was some over lap, of the tapered switch, into 1969 where the factories were using up existing stocks. Hard to say for sure.

When it comes time to replace the oil pressure switch we suggest threading the switch in by hand first. That way you can ensure you have the correct thread pattern. Threading the early taper switch into a later cover can cause case damage. This would be due to the taper dimensions of the switch (major diameter .383-.412 inch over the length of the thread). A later switch (major diameter .380 inch) could thread into and early cover but due to the taper may only catch on the lower threads. Tightening in both cases can result in stripped threads or a cracked switch boss.