TR6 TR6 Oil Pressure

[TheSearcherMan]

I see it over and over again in discussions. Low oil pressure, inexperienced rebuilder/owner or high milege TR recently purchased. I don't know if I have ever seen a relief valve failure. This is checked first out of hope and ignorance. You measure the spring length, make sure the pistion moves freely, and that's that. It does not have anything to do with idle, unless it is extremly cold, or you are using to thick a motor oil, and it mite pop off when the engine is cold at idle, however, I doubt it. Hot idle is running down the interstate at least 20 miles, and then checking what you have at about 850 rpm. The low oil pressure is almost always caused by rod/main bearing clearance. You need to mic. your parts before/after you get them back from the machine shop, and I'm sorry, to do this properly you need experience, and a decent set of mic.s. Also, check the oil pump clearences as per Bentley manual. Yes, you will have to fork out the bucks and buy a book, I know it hurts terribly, and I'll shed tears for you. And, if you use the not necessary external oil feed, you will see a slight drop in hot idle oil pressure. Hot idle is not sitting in the garage for 10 minutes at idle, you have to go at least 20 miles at highway speeds. I'm not lookin to debate this thread, I don't have the time for it.

 

[tdskip]

This is a great/helpful post, but the tone of it doesn't really fit the forum. Experience is awesome, goodness knows I need lots of help, but is the attitude really necessary?

 

[TheSearcherMan]

Yes

 

[Tinster]

but is the attitude really necessary?

<span style="color: #660000">As a point of fact -
Attitude is NEITHER necessary NOR appreciated.

imho

d</span>

 

[14dna]

Maybe an explanation of why we are getting attitude would be helpful.
As for experience, I have about 44 years in garages as a mechanic and , therefore, do have a working knowledge of cars.
Even I can make mistakes and forget routine problems, so lets not point fingers or belittle anyone on this forum.

Dave

 

[mrv8q]

I hate to say it, but I kinda like the "Grump" factor....

 

[TRDejaVu]

I am just glad to see that we finally have a maven amongst all of us amateurs.

Licensed aircraft maintenance engineer, UK, Canadian and FAA licenses. Boeing 747s to small puddle jumpers. Basic line servicing through full D-checks of airframes and powerplants; speciality in major airframe structural repairs. There are others on this forum with specialized knowledge and yet we still don't pretend to know everything, which is why we are here. Why are you here?

 

[poolboy]

The voice of experience here. Don't play into this guy's hand. He's certainly not the only one here that knows a thing or two.

 

[TR3driver]

Well, while we're on the topic, IMO oil pressure is vastly overrated, too. I've seen engines last a long, long time with basically no oil pressure at hot idle. Really the critical issue is oil flow through the bearings; as long as there is sufficient flow to keep the bearings cool (which doesn't take much), there won't be a problem.

I've even driven engines where the oil light stayed on at hot cruise; but they still last for years that way.

So, low oil pressure is an indicator of overall engine condition, and specifically bearing wear (including cam bearings, seen a lot of 'rebuilt' engines that didn't carry much pressure because the rebuilder didn't do the cam bearings); but not necessarily a big deal beyond that.

I have seen an oil relief valve failure : the piston literally got stuck (open) in it's bore due to some sort of clear gummy deposit. (Just one of the bad experiences I've had with Castrol.) Cleaned the piston, switched to Valvoline, never happened again.

 

[Andrew Mace]

...I've even driven engines where the oil light stayed on at hot cruise; but they still last for years that way....

I may have told this before, but I had a Mk3 Spitfire (1296cc) that...uh...lasted well beyond it's sell-by date. It got to the point where I literally could only get about 30 mi./qt. of motor oil, at which point I began to buy straight 30wt nondetergent oil in 2-gallon cans (those were the days). There were any number of times that I'd end up running at highway speeds for many miles with the little green light glowing merrily away, but that 1296 turned out to be THE ENGINE THAT WOULD NOT DIE. Honest! I'd get home, add 2-3 qts, and I'd be ready to go again.

I'd have gladly rebuilt the bottom end (I'd already had the head done), but the poor Spit's body tub was almost completely gone...and I found a nice GT6+ to replace it! But it kept running around the yard until I finally disassembled it several years later!

 

[TRDejaVu]

I have seen an oil relief valve failure : the piston literally got stuck (open) in it's bore due to some sort of clear gummy deposit. (Just one of the bad experiences I've had with Castrol.) Cleaned the piston, switched to Valvoline, never happened again.

I had that happen and I think that it was you who advised me where to look. That was Castrol as well; since changed to Valvoline.

 

[Tinster]

Well, I see it like this:

Dale knows just about nothing about auto mechanics and
I am happy to share my lack of knowledge with everyone.

I don't even look down upon you poor amateur LBC owners
who have not yet mastered powder coating- in colors other
than black.

d

 

[prb51]

All gear heads, experienced or inexperienced, are gauge watchers. We can't help it and we like to commiserate when something 'just doesn't look right' (see my old threads).....much good advice and experience here and that's why I come back time and time again.
BTW, I love to talk about this oil, that oil, viscosity and wear factors...you name it.
I've learned a great deal from the guys/gals here and appreciate it when everyone takes the time to state/restate old experiences and issues.
We all get 'attitude' a time or two, but I have to say, this is the most gentlemanly site I've been associated with and I appreciate those with great knowlegde taking the time to share it with those with just a tad (myself).
I've actually learned to live with my less than perfect oil pressure as the TR3 runs like a Bat outa Hades....thanks to the info here.

 

[TR3driver]

It got to the point where I literally could only get about 30 mi./qt. of motor oil, at which point I began to buy straight 30wt nondetergent oil in 2-gallon cans (those were the days).

That sounds a lot like my first car, a non-LBC that had a habit of burning holes in pistons. The third time it did so, I took the pushrods out of that cylinder and kept driving it on the other 5.

But in my neighborhood, you could buy motor oil in 5 gallon cans ...

Alas, the swarf from the broken piston took out all the bearings until it wouldn't run faster than maybe 45 mph; so we donated it to the fire department to set on fire.

 

[2wrench]

I see it over and over again in discussions. Low oil pressure, inexperienced rebuilder/owner or high milege TR recently purchased. I don't know if I have ever seen a relief valve failure. This is checked first out of hope and ignorance. You measure the spring length, make sure the pistion moves freely, and that's that. It does not have anything to do with idle, unless it is extremly cold, or you are using to thick a motor oil, and it mite pop off when the engine is cold at idle, however, I doubt it. Hot idle is running down the interstate at least 20 miles, and then checking what you have at about 850 rpm. The low oil pressure is almost always caused by rod/main bearing clearance. You need to mic. your parts before/after you get them back from the machine shop, and I'm sorry, to do this properly you need experience, and a decent set of mic.s. Also, check the oil pump clearences as per Bentley manual. Yes, you will have to fork out the bucks and buy a book, I know it hurts terribly, and I'll shed tears for you. And, if you use the not necessary external oil feed, you will see a slight drop in hot idle oil pressure. Hot idle is not sitting in the garage for 10 minutes at idle, you have to go at least 20 miles at highway speeds. I'm not lookin to debate this thread, I don't have the time for it.

Searcher: Thank you for caring enough to be honest. As for me, I am ignorant and I am
hopeful that I will learn something from my rebuild experience. That's why I'm here.

Please clarify a question I have about the pressure relief valve.

It seems to me that the spring provides a static pressure on the piston and that once
pressure builds high enough, the piston is pushed back allowing "excess" oil pressure
built up in the engine to be relieved.

That is my suppostion. If correct, I suppose that, conversely, as oil pressure begins
to drop (say, because of lower rpm's,) that the spring will push the piston more to a
closed position, allowing oil pressure to slowly build up again.

I am not here to argue. I am here to learn.

I did plastigauge the crank and bearings. Seemed to be correct.

 

[TR3driver]

It seems to me that the spring provides a static pressure on the piston and that once pressure builds high enough, the piston is pushed back allowing "excess" oil pressure built up in the engine to be relieved.

That is my suppostion. If correct, I suppose that, conversely, as oil pressure begins to drop (say, because of lower rpm's,) that the spring will push the piston more to a closed position, allowing oil pressure to slowly build up again.

That's basically right, except the 'slowly' part. Since oil is non-compressible, and the passageways do not expand and the pump is positive displacement; the changes in pressure are basically instantaneous (even though the gauge is a little slow to respond).

Also, the spring force on the valve is not constant, but rises as the valve opens (and the spring is compressed). Thus the valve does not snap full open, but instead opens just enough to regulate the pressure; moving smoothly in response to changes in pressure.

So, as rpm drops off (reducing flow from the pump), the relief valve piston (or ball in the case of the TR2-4) is what moves slowly. The pressure will drop only slightly, until the valve is fully closed. Below that, the pressure will vary much more with rpm.

 

[dklawson]

Owning both Triumphs and the Mini, I'd like to add a non-Triumph comment that in the A-series engines the pressure relief valve is very active and prone to problems. This is particularly true in the Mini where the engine's sump is the gearbox. Debris is routed through the system and swarf can cause the relief valve to jam open or closed. There are multiple upgrades to the A-series pressure relief valve available to address this. However, no amount of adjustment or tinkering will compensate for worn bearings or a worn oil pump.

2Wrench, you said you checked the bearing clearances. How did the rocker gear look and did you replace the oil pump?

 

[TRDejaVu]

Is there any good way to set a TR4 relief valve or is it just trial and error. I recently changed to a spin on adapter with a Wix 51516. My oil pressure is now showing about 10PSI higher at speed and during a sustained run yesterday it got to about 85PSI @ ~4K RPM after being well warmed up. This caused me to back off the RPMs as I started thinking about oil seals etc. The previous week it was OK as the temps were in the low 70s, but this weekend I was out in the mid 50s (top down of course).

 

[poolboy]

I wish I had a TR4 to see your relief valve. I thought my OP was too high,too, at start-up in the Winter. I'd sit in the driveway at idle way past the time it took for the coolant to get warm, waiting for the oil to catch up.
I ended up putting a spacer in the form of a nylon oil drain plug washer between the plug and the block. This was in addition to the standard steel washer. It helped, at least according to the oil pressure gauge.

 

[2wrench]

Owning both Triumphs and the Mini, I'd like to add a non-Triumph comment that in the A-series engines the pressure relief valve is very active and prone to problems. This is particularly true in the Mini where the engine's sump is the gearbox. Debris is routed through the system and swarf can cause the relief valve to jam open or closed. There are multiple upgrades to the A-series pressure relief valve available to address this. However, no amount of adjustment or tinkering will compensate for worn bearings or a worn oil pump.

2Wrench, you said you checked the bearing clearances. How did the rocker gear look and did you replace the oil pump?

Head rebuilt at/by machine shop; entire rocker assembly rebuilt by Rocker Arm Specialists
out of Anderson, CA., and lastly, yes, I did fit a new oil pump.

My plan is to eliminate the relief valve piston and spring from the equation; then look
at electronics and then proceed to verify the other hardware in the rebuild itself.

Hope and ignorance says to do the small, easy and inexpensive stuff prior to ripping
into the bearings and the like. Wouldn't I feel beyond ignorant...more like flat out dumb
to tear into the bowels of my newly rebuilt engine, only to then discover it was a bad/scored/
otherwise non-functioning few dollar piston in the relief valve??? I just ain't that
sophisticated, you know, and I'm the first to admit it.

My present problem is: I don't have the parts (but they are on order,) nor do I have the
time to mess with it much at all at the present.

All Forum friends: My time is not allowing me to jump on every possible attack on
the problem. But I am planning on a thorough review of all threads re oil pressure, etc,
and will attack each possible diagnosis one at a time with the last thing to look at being the
bearing clearances.