TR2/3/3A Oil pressure gauge readings?

[karls59tr]

Seems to me that after a hard run I recall seeing the oil pressure around 30 psi at idle. Lately I've noticed that the oil pressure never seems to go below 50 psi? Is it possible for air to get in the line and cause a different reading. I checked the other posts about that leather washer or nitrile O ring having to be there so I'll check that. Is there any way to test the gauge to see if it's working properly?

 

[TR3driver]

Air could possibly cause the needle to move slower, but shouldn't change the final reading.

If the joint isn't leaking, I'd leave it alone. The leather washer (I use nylon) is just to seal the joint.

To test the gauge, either hook it up to a known pressure source; or hook up a known good gauge to the engine.

Pressure at idle will depend on a lot of things, including engine state of wear, idle rpm, and oil viscosity (which in turn depends on oil grade and temperature). Plus, each oil grade allows for considerable variation, so even two different 30 weight oils may give different results.

 

[TomMull]

Agree, of course, with Randall. The shop where I did a brief stint as a grease monkey/ mechanics helper 50 years ago had an oil gauge and box of fittings in the tool crib. We'd plug it right into the block.
If it turns out to be the grade of oil that took it from 30 t 50, tell us what you're using.
Tom

 

[sp53]

You will know when the leather washer is out because you will have hot oil all over your leg. Like suggest leave the fitting on the gauge alone if it is not leaking. If there was air in the line that would mean you are probably running out of oil and the gauge would bounce and fluctuate rather than gain pressure. If you are concerned, plumb in a new gauge in at the firewall were you have good access because working under the dash is difficult, and it is easy to do more harm than good. My experience has been those stock gauges give faulty readings after time. I have taken many apart and cleaned them. The unit is basically this little brass bladder looking dealie that rolls and expands with the oil and transfers that to a calibrated reading on the dial. They are pretty cool really. Buy one on eBay for 30.00 and see, but be carefully when you take it apart-- make sure to leave the nut on the fitting on the back of the until you have the glass off and are ready to dumb the guts into your hand or you will bend the needle.
Pease out

 

[CJD]

The washer could have an errant "flap" that is acting as a valve...letting pressure to the gage, but restricting the back pressure. Or, most likely, there is dust or corrosion on the internal brass mechanism that is sticking the needle so the hair spring is having trouble returning towards the low indication. Significant oil pressure drives the needle to the right...but a hair spring is all that returns it left.

 

[TR3driver]

The washer fits over a hollow spigot, so it's not likely to be blocking the flow. And the hair spring is only to remove backlash in the gears (keeping the needle from vibrating); the Bourdon tube supplies the force to return the needle to zero. You can even cut the spring and the gauge will still work.

But dirt and corrosion can definitely be problems. Another common problem on these old gauges is that the copper alloy used in the Bourdon tube eventually work hardens and doesn't move as much as it did originally. Overpressure can also permanently distort the tube, causing the gauge to not return to zero.

 

[CJD]

The washer fits over a hollow spigot, so it's not likely to be blocking the flow. And the hair spring is only to remove backlash in the gears (keeping the needle from vibrating); the Bourdon tube supplies the force to return the needle to zero. You can even cut the spring and the gauge will still work.

o.

Not true with all versions. This one has a positive connection from the bellows to the needle

This version does not. The spring holds the needle against the bellows wire. The needle can be swung right without moving the bellows.

 

[TR3driver]

Interesting, I've never seen one like that! Is that from an early TR2?

 

[6TTR3A]

Yes, early TR2, when the Smiths part number was X80516/** The later PL2561/** did away with the
positive connector. (Makes sense; went from 5(?) parts to one to accomplish the same result)
Frank

 

[CJD]

Yes, early TR2, when the Smiths part number was X80516/** The later PL2561/** did away with the
positive connector. (Makes sense; went from 5(?) parts to one to accomplish the same result)
Frank

That's what I was thinking, but I rebuilt so many last year I couldn't remember for sure which was which. The top pic is my TR2 gage...it not only has the positive connection, but also an adjustment screw. I found one that was between the two, having the connection, but no adjustment other than bending the link. Just shows...older is often better!