T140 Oil Pump

The '80s T140s came with a four valve oil pump. The oil pumps that served Triumphs well in all the years previously were two valve.
Most other makes of British Iron’s oil were pumped round by geared oil pumps, vintage Triumphs use a twin piston type pump.
Vintage bikes are mostly dry sump, that is, oil is kept in a seperate tank away from the sump.
There are two pistons in the pump, both driven by an off set gear on the inlet cam. One piston draws the oil from the tank and forces it into the crankshaft big ends, it then runs down into the sump and splashes around, some finding it’s way into the primary side lubricating the primary chain and the clutch.
The other piston draws the oil from the sump and pushes it back to the oil tank. There’s a narrow off shoot on the return oil line that takes some oil up and into the rocker boxes, that then trickles back down into the sump.
The pump’s delivery piston has a smaller diameter than the return piston. The return therefore pumps more than the delivery. This ensures that the oil in the sump remains at the level of the scavenge pipe on the return side.
The oil pressure is controlled by a pressure relief valve (basically a piston held by a spring) that lets oil pass by the big ends and directly into the sump if the oil pressure rises too much. (This sometimes operates when the engine is cold while the oil is thick - so don’t rev the bollox off of the bike to warm it up).

A basic diagram of how the oil system operates on nearly all vintage Triumphs.

Here’s a couple of l;ater type 4 valve pumps. New one on the left :stuck_out_tongue_closed_eyes:

I think most people have heard of wet sumping. This is when too much oil is sitting in the sump - on BSAs and Nortons the oil can dribble passed the geared oil pumps if left standing (some owners resort to fitting a one way reed valve or a turned or automatic valve into the oil feed pipe).
On Triumphs this doesn’t happen due to the design of the pump being piston driven.
Triumphs do wet sump but it’s mostly caused by the weenie ball bearings not sealing in the pump - a clean and it’s usually sorted. There’s a whole list of causes of wet sumping in all British Iron but at least Triumphs don’t drain oil into the sump overnight.

Here’s the old pump dismantled. Earlier pumps only had two valves but to alleviate the ball bearings getting dirt under them and not doing their job, another valve was introduced on each side of the pump.

And here it is after a good clean.

And reassembled next to the new one. It all tests fine. No by passing no leaks. But I wont use it.
It should be fine but I’ve had wet sumping a lot and I’d rather not risk a used pump. If I rebuild an engine it’ll get a new pump and a new pressure relief valve.
Just to be sure, to be sure. :slightly_smiling_face: