Oil Pressure

[DaveR]

The best point to start from is Standards Triumph's spec on this family of engines. This gives a hot idle pressure of 10 to 20 lbs and a hot running (2000 rpm) pressure of 40 to 60 lbs. It also stated that the oil pressure relief valve should limit the pressure to 60 lbs. If we are saying an engine is showing 80 lbs when hot then there is a problem with the relief valve. Also hot pressure is measured after a good run.

 

The above is true for all Standard Triumph SC four cylinder engines and 1.6, 2.0 & 2.5 Litre six cylinder engines.

 

Just my thoughts

[john.r.davies]

Hogie,

A sudden increase in a low oil pressure couldn't be due to the release of a blockage downstream from the oil pressure take-off, clearing that would reduce the pressure.

The take-off is on the main oil gallery, just below the dizzy. Upstream from there are the oilways to the rear crank main journal, the rear camshaft bearing and thence the rocker shaft, the oil filter, the pressure releif valve and the pump. A blockage release in the bearing oilways would also reduce pressure, so in your case, the problem is isolated to the oil filter or the relief valve, presuming the pump is good.

 

Oil filter. I don't know if a filter problem could partly block flow. I wonder if a non-drain valve, just a rubber flap, in an aftermarket disposable filter, could be faulty?

 

Relief valve. The valve is not a needle valve, but a 'pin' with a half inch (?) wide face that bears on a machined face in the block. I've seen valves whose removeable 'pin' face is extremely and assymetrically worn. This might be okay, if the block face has worn in concert with it, but in renovation the pin will be removed. Assembly with the faces now out of register would lead to a permanent leak, a by-pass through the valve back into the sump. If, eventually, the pin rotated back into register, the pressure would suddenly rise, as the by-pass ceased.

Such a worn valve really needs the block face to be remachined, not something that can be done without a complete strip down. Examination of the 'pin' face, and with a probe the block face, might tell you if you have a problem.

Hope that helps!

John

[peter moffatt]

peter, those pressures are NOT low.

 

the recorded pressure is simply the resistance to forward oil flow. If you want high oil pressure put gearbox oil in the sump, the pressure will be high but the flow low (and hence the lubrication)

 

the lubricity of an oil in a plain bearing is INDEPENDANT of the supply presssure, it all rests on the film strenght between the journal and the shell.

 

yes knackered engines have low oil pressure, ie less than 5 lbs at hot idle (oil press light comes on) and 20-25 lbs at 3-4000 rpm

 

repeat 50 lbs squinch hot at 2500 rpm is exactly where it should be with oil from 0-30 to 20-50

 

have you thought about taking out health insurance? you probably won't need that either...

 

spikius maximus lateralis

Jbinnington

 

Your first point recorded pressure

----------------------- You dont have to have a degree in rocket science to know that increased resistance equals more pressure.

Your second point lubricity

---------- No oil in the world will stay on a given surface indefinitely so it requires pressure from the pump to give a constant flow.

Your last point Health insurance

-------------------- Yes I have insurance. But do you have a degree in spelling?

 

Peter.

[jdbinnington]

Peter, if you can't understand the answers, don't ask the questions.

 

Try reading a tribology starter.

 

I use the third degree when spelling, it also gives me pleasure

 

j

[peter moffatt]

Peter, if you can't understand the answers, don't ask the questions.

 

Try reading a tribology starter.

 

I use the third degree when spelling, it also gives me pleasure

 

j

 

JB

 

I think that the word you are looking for is garbology

 

Peter

[Richard Crawley]

Oh dear I think this one is going off the rails a little! Peter, I really don’t think you have a problem with your oil pressure & I think you’re giving yourself & some other forum contributors who are trying to help some unjustified grief.

 

Your pressure readings aren’t low enough to worry about, run the car but if they drop significantly lower then you may need to look further.

[jdbinnington]

see: http://www.roymech.co.uk./Useful_Tables/Tr...Lubrication.htm

[stuart]

I dont know what you lot are worried about. The Bentleys that ran at Le Mans in the twenties had approximately 8 PSI oil pressure and none of them ran a bearing!

 

Stuart.

[DaveR]

I agree with Alex re the oil pressure and the effects on the engine.

 

With one engine I covered 125,000 miles from new with a hot pressure of 50 lb at 3,000 RPM and 60 lb at 4,500 RPM. When I stripped the engine the crank was still in tolerance only the bearing were worn.

 

I did change the oil every 3,000 miles which I am sure help to pre-long the life of the bearings.

[Andy Moltu]

I think your oil pressures are fine.

 

However you probably feel that they are lower than expected for a newly rebuilt engine. I'd tend to agree with that view too.

 

The most likely explaination is a ****, new oil pump. Many of the new oil pumps are poor to say the least both in terms of end float & rotor clearance. I had the same suprise at the worse oil pressure after I rebuilt my engine & even dropped the sump to check the bearings. In the end I swapped my old oil pump back on to the engine and hey presto the pressure was 10-15 psi higher at low revs (the same at high revs as the oil PRV was working fine)

 

Your oil pressures are fine so you don't immediately need to swap the pump but you are not alone in being dissapointed by the quality of parts!

[Eyetee]

Peter

Thanks for the help with the chasis and for being so patient with all the questions, no problems on return trip. Have read your low pressure thread after your mentioning and demonstrating the low pressure on UYM 790F, to recap the engine was rebuilt 2 years ago or so done 5000 miles and after an oil change this May the oil Pressure dropped (once at running temp). Am I right in thinking that the symptom was first noticed after a particular testing days driving or are my facts muddled.

 

The purpose of oil is to Lubricate, cool, clean, disperse, power transmissions, seals, prevent corrosion, absorb noise all pretty vital. Methods of lubrication are splash, pressure and jet. So a drop in oil pressure is worrying. Pump I believe is mechanically driven direct from crank but don't believe the pressure alters with rpms' due to the oil demand increasing in tandem, this might be incorrect.

 

Reasons for low oil pressure are pressure relief valve stuck open / broken spring, pump worn, leek e.g. broken pipe e.g. to gauge pump to gallery, faulty switch / gauge, low oil, oil to low viscosity e.g. diluted with fuel, main bearing wear, big end barings worn. Most of these have been considered and ticked off.

 

The passage of oil is pump, past a pressure relief valve (e.g. 60 psi/4 bar), filter, past gauge / switch, then fed to Crank gallery/barings, cam, rocker and then if fitted via oil cooler to sump.

 

Now the gauge is after the filter and reads good at low temp when oil is thicker, dropping when oil warms. Don't know what sort of filter is fitted (purolator or other) but the basic method is for the oil to enter the can through one way valve through filter paper, through perforated metal support and return back into engine, however there is also a filter bypass valve generally located at the base e.g. 7 psi/0.5 bar pressure difference between the sides of filter paper and perforated metal support.

 

All this information is from a diesel tractor engine basis but (apart from pressure release settings) shouldnt differ to much from a 6 pot pi. Cant really point to one thing or another, might suggest the filter, then gauges, the pumps been done but the recon could be knackered. Miss the relevance of the rocker shaft...

Does the engine temperature remain constant during a cruise / blat?

Looking forward to the remedy

John

[peter moffatt]

John,

 

Glad to hear you arrived home without problems,and it was very pleasing to have a cup of tea and a chat. The problem with the oil pressure I am still convinced is due to the repro oil pumps I have fitted.

The amount of replies to my thread is amazing and I am truly grateful for the comments received.

The lack of oil pressure first started towards the end of the previous year, and when I changed the oil & filter this year the problem I think worsened.The relief valve has been changed alas no difference in pressure.

Very shortly I will be taking The 5 off the road for the Winter, and will have further thoughts at a later time.

As you know I have much to keep me busy over the next few months particulary my next project being the restoration of my other 5.

 

Thanks for the business and please let me know about the Surrey I have for sale.

 

Regards Peter.

[Eyetee]

Peter

you never said wether or not the engine temp rises or remains constant, the reason for asking is that a rise would result from an insufficient oil circulation.

As for the surrey am in the market, just need to control the spending been going a little ott just recently.

John

[peter moffatt]

John you are absolutely right I must have had a Senior Moment in not writing on the engine temperature. the temperature is always quite normal and up to now never o/heated.

 

Regards Peter.