T140E Oil Pressure

[Dashfixer]

This is my first post and I'm hoping that someone can help.
I have just finished a complete rebuild of a 1979 T140E. I have fitted an oil pressure gauge to the oil pressure switch outlet. The bike is running well after a few minor niggles, and I've just completed the first 50 miles since rebuild. The only issue that I have is the oil pressure when the engine is warm. When the bike is started from cold the pressure gauge indicates a fluctuating 45 to 60 psi at tick-over. As soon as the revs are up the pressure steadies at 60psi. After 12 to 15 minutes of riding the pressure starts to drop, which is expected as the engine and oil are heating up. After 20 minutes the pressure is still dropping down to an indicated 25 to 30 psi. It seems to stay steady at that. I'm using 20W50 oil and have a paper filter in the bottom of the reservoir. It has a new oil pump. There are no apparent leaks and the bike feels good with the engine very responsive.
Am I being paranoid or have I got a real problem? The manual says 65 to 80psi at normal running, but as the relief valve operates at 60psi I'm not sure if that's correct.

 

[atomsplitter]

When dealing with positive displacement pumps, like a gear oil pump, pressure and flow regulation is obtained by either pump speed or use of a relief valve. When the oil is cold viscosity (resistance to flow) causes the pressure rise to the relief valve setpoint and as it warms oil flow resistance drops and the relief can close if total flow is low enough. The pump's speed in your Triumph is regulated by engine RPM (unlike an electric motor driven single speed pump) so with warm oil pressure and flow will vary some. If it's a concern, a new relief valve may be the answer since the relief may be affected by temperature. Most reliefs operate with a spring and springs are notorious for changing behavior under different temps. Relief valve operation is based on pressure against a spring, so as pressure rises above the lift setpoint the valve opens further, increasing flow thru the valve, limiting the pressure rise to the relief's setpoint. A 60 psi relief will never get to 85 psi unless the valve is full open and total flow thru the valve is inadequate to relieve the pressure (highly unlikely). So too temperature can affect the pressure guage you're looking at. Most of the simple pressure guages are Bourdon tube types. The temperature of the oil in the tube can also affect the reading.

 

[Rudie]

oil pressure when the engine is warm.
The manual says 65 to 80psi at normal running

Above 3,500 rpm.

The manual says 65 to 80psi at normal running, but as the relief valve operates at 60psi I'm not sure if that's correct.

A 60 psi relief will never get to 85 psi

You might want to check what the manual says with a long time Triumph dealer like TMS, Triumph manuals are infamous for misprints that were not corrected year after year.

complete rebuild
new oil pump.

Oval port pump?

Did you check to ensure the gasket between the pump and crankcase did not not cover any part of the ports in either pump or crankcase?

Did you measure the end of the crankshaft where the oil seal runs with a micrometer to ascertain whether the crank was good for a standard seal or required an undersize seal?

Did you fit specifically a Pioneer Weston seal?

positive displacement pumps, like a gear oil pump

Plunger pump on Meriden twins.

 

[atomsplitter]

Thanks for the clarification Rudie. Plunger (piston) PDP's work with a set volume for each stroke (just like a gear oil pump with a set volume between gear teeth), so total system flow is still regulated by pump speed and a relief bypass valve (usually) in both cases. The principal is the same, the major difference is in a plunger type you get more pulsing than with a gear driven pump so sometimes a pulsation dampener will be employed to smooth the flow of fluid to reduce fatigue stress on passages and pipes. But with each plunger stroke a set volume of fluid is discharged, so the faster the pump goes the higher the total flow rate (volumetric increase of flow). To limit the total system flow to a desired maximum flow rate a relief bypass valve at a set pressure lifts and returns some of the system flow to a sump or oil tank (reservoir). By bypassing some of the fluid flow back to a reservoir total system presssure and flow is regulated. If a relief valve (or similar equipment) isn't used the oil presssure upper limit is set by maximum pump speed only, because the pump discharge flow is set by the volume of the plunger stroke. If the pump can be spun fast enough to achieve the breaking stress of the material it's flowing in, it will. The only way to stop a PDP is stalling it with back pressure (not desirable unless it's being used in a hydraulic system, and those sytems are usually air driven PDP's that use differential piston size between air and hydraulic pressure). That is simply basic system operating theory with a PDP to limit maximium pressure rise. How Meriden engineered their system I'll bow to your experience Rudie, I was only trying to provide some basic pump operating principles applicable to a lot of systems.

 

[Dashfixer]

Above 3,500 rpm.

Yes this is happening above 3500 rpm.

Did you check to ensure the gasket between the pump and crankcase did not not cover any part of the ports in either pump or crankcase?

Did you measure the end of the crankshaft where the oil seal runs with a micrometer to ascertain whether the crank was good for a standard seal or required an undersize seal?

Did you fit specifically a Pioneer Weston seal?

Yes to all these.

 

[Dashfixer]

I've taken the bike out for a few more rides with exactly the same thing happening. It starts with an oil pressure of 60psi and then slowly decreases to 25-30 psi at 3500 or above rpm, and stays there. I'm beginning to think that that's where it is happy to be and if there was a problem wouldn't it continue to decrease in pressure.
I would like to know what readings other owners of T140Es fitted with an oil pressure gauge get.

 

[sikatri]

So the engine warms up the oil pressure drops. What’s the spec for the operating oil pressure on this motorcycle? Ok, 65 to 80 from previous post. I think you definitely have issues.

 

[atomsplitter]

There could be other factors involved, such as scavenging, which puts air into the equation. Air being compressible mixed with oil will not develop the same pressure as a solid fluid system would. Where the oil pump pickup is located is it fully submerged in a continous solid liquid sump? My old '05 Rocket III had a oil tank on the side of the engine and the oil pump was just a scavenging pump that returned the oil in the sump to the oil tank. So on startup the oil pressure was high but as you rode it around it dropped because it was also pulling some air with the oil.

 

[Rudie]

There could be other factors involved, such as scavenging, which puts air into the equation. Air being compressible mixed with oil will not develop the same pressure as a solid fluid system would. Where the oil pump pickup is located is it fully submerged in a continous solid liquid sump?

All pre-Hinckley Triumph engines are "dry sump" - the engine oil is stored in a separate compartment outside the engine; o.p.'s bike, the separate compartment is the large diameter frame tube above and behind the engine. Primary oil storage is the vertical part of the tube behind the engine, the feed side of the oil pump is fed from the bottom of the tube. The pump is behind the (heart shaped) timing cover on the right hand side of the crankcase so the 'head' of oil in the vertical frame tube uses gravity to pressurise the oil into the pump.

The only place to connect an oil pressure gauge on any 69 onwards Triumph twin engine is the the oil pressure switch port in the front edge of the timing cover. As that area is pressurised by the feed side of the pump primarily for the timing end of the crank for the plain bigend bearings, there should not be any air in the oil there, would be a major fault in the pump or its connection to the crankcase if there was ...

My old '05 Rocket III had a oil tank on the side of the engine and the oil pump was just a scavenging pump that returned the oil in the sump to the oil tank. So on startup the oil pressure was high but as you rode it around it dropped because it was also pulling some air with the oil.

Unless Hinckley Rocket 3 engines do not have any plain bearings, I highly doubt it, for the above reason. Air in plain bearings would terminate them in short order. The reason oil pressure is high on start up but drops as you ride is: on start up, the oil is cold, thicker; engine running, oil circulation under pressure and combustion heat warms the oil, it thins.

That is also why engine oils are multigrades, lower viscosity when cold so the (feed) pump can pressurise plain bearings, viscosity increases with temperature so pressure to plain bearings is maintained.

 

[atomsplitter]

So based on what Rudie is saying, as long as oil pressure is maintained, the bearings are being fed.

Rudie, Hinckley Rocket's (pre-2500cc models for sure) have two oil pumps. A main pump to supply pressurized oil (part T1210092) to bearings and journals and a twin rotor scavenging pump (part T1210002) to return oil to the tank from the sump. (Service Manual page 9.12) Sorry for any confusion.

 

[sikatri]

How is the the running oil pressure difference from the manual explained? Curious? Does it mean anything? I understand Rudie’s explanation just don’t understand why the manual would indicate such a high running pressure and not account for an expected drop once the engine is warms up.

 

[atomsplitter]

If it's an issue, replace the oil pump and see if the problem persists. Another possibility is back pressure drops as engine temps rise and internal moving parts expand. I doubt it accounts for a 40 psi drop but it does have an effect.

 

[Rudie]

How is the the running oil pressure difference from the manual explained? Curious? Does it mean anything?
don’t understand why the manual would indicate such a high running pressure and not account for an expected drop once the engine is warms up.

The operative word with Triumph Workshop Manuals is "Workshop", they were written for franchised dealer mechanics, who were usually externally qualified plus had been on courses run by either Triumph at Meriden (British dealers) or by a given country's importer appointed by Meriden. Fwiw, ime this is true of all workshop manuals by manufacturers, whether they make motorcycles, cars or supersonic planes. So, like any manufacturer's workshop manuals ime, ones for Triumph motorcycles do not contain "baby steps".

I am not qualified as a mechanic but I have been around motorcycles long enough to have met designers and builders who worked at Meriden and Small Heath. Specifically oil pressure, I bought a pressure gauge kit for my T160 from Les Williams - after being made redundant by Norton Villiers Triumph, Les set up a business (L.P. Williams) making Triumphs (primarily triples) go better, based on his and his two partners' extensive firsthand experience of them. It was from Les I learned that "Normal running" oil pressure range in a Triumph workshop manual applied to oil at normal working temperature above 3,500 rpm.

Any engine with plain bearings, it is the tiny clearance between the moving and fixed part of the bearings that causes the pressure; oil is (usually) fed to the middle of a plain bearing, escapes at the sides. The thinner the oil, the more easily it passes through plain bearings, the lower the oil pressure; the larger the clearance between the moving and fixed parts of plain bearings, the more easily any oil passes through the bearings, the lower the oil pressure.

 

[atomsplitter]

So if I get the gist of what you're saying Rudie, (paraphrasing) as the oil temp gets to normal operating range and oil flow resistance drops, as well as backpressure from increasing clearances between journals, the pressure hot could be significantly lower than when the oil is cold and the tolerances are closer (i.e. more backpressure).

 

[sikatri]

Ok, so the 65-80psi normal running above 3500rpms and dropping to 25-30psi after it’s warm is normal or not?

Hopefully I’ll learn something. LoL. Reading the conversation again….

 

[Rudie]

65-80psi normal running above 3500rpms and dropping to 25-30psi after it’s warm is normal or not?

oil pressure when the engine is warm.
The manual says 65 to 80psi at normal running

Above 3,500 rpm.

Yes this is happening above 3500 rpm.

If @Dashfixer's "this" is:-

When the bike is started from cold the pressure gauge indicates a fluctuating 45 to 60 psi at tick-over. As soon as the revs are up the pressure steadies at 60psi. After 12 to 15 minutes of riding the pressure starts to drop, which is expected as the engine and oil are heating up. After 20 minutes the pressure is still dropping down to an indicated 25 to 30 psi.

... and "After 20 minutes the pressure is still dropping down to an indicated 25 to 30 psi" is "Above 3,500 rpm", not "normal" afaik.

"Ten psi per thousand rpm" is another measure of hot oil pressure favoured by some people as a reason for not stripping an engine - ; however, equals 35 psi @ 3,500 rpm ...

 

[Rudie]

If it's an issue, replace the oil pump and see if the problem persists.

While it is not impossible for a pressure problem to be caused by the plunger pump, it runs in oil and the correct 4 valve pump on a 79 twin was designed to negate a problem in any one valve. So simply replacing the pump without testing the existing one - stripping and inspecting its components if desired - could be an expensive solution for something that rarely causes a problem ...

 

[sikatri]

Thanks for the in-depth answers @Rudie . Following.

 

[RobinV]

Thanks for the in-depth answers @Rudie . Following.

Just a thought here from an interested reader. The air cooled motors I have been building for years, VW, Have shell bearings that run a clearance of a thou and a half. They follow the same pattern. Run up to 60-80 cold, then settle down to 25-35lbs. Different oil pump obviously, but a similar relief valve.
My thought is, what pressure causes the stock oil light to come on.? I'm sure this is listed somewhere and would indicate what the factory thought might be a low pressure imminent failure danger zone. VWs are 6 lbs. The light will flicker at 6lbs. That means too hot of an engine or mains going out. Just my thought.

 

[Rudie]

what pressure causes the stock oil light to come on.?

The three different switches Triumph fitted 69 to the last have different on/off pressures. Part number on your bike: original 74 to 78 Smiths turned on the light between 3 psi and 7 psi; original on your bike was Veglia, you hope the Co-op specified and tested to the same psi range; current pattern, who knows.