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TR2/3/3A TR3A Low Oil Pressure Solved

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rlandrum

rlandrum

Jedi Trainee
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Since we first fired up the TR3A a few months back, the oil pressure has been dropping steadily. At first, it was near 50, then 20, then, at idle, nearly zero (yikes).

Despite our best efforts to remedy the problem without doing anything drastic (like pulling the oil pan off), we were unable to solve the low pressure issue.

It just had to be the oil pump.

So we ordered a new pump, new pan gasket, and pump packing, and decided to do the swap to see if that would help.

Mother Nature decided that rain was in order. For the past 3 weekends, anyway.

Finally, we had a weekend without any rain. My Father drove the TR3A over and we managed to get it up on the lift. We got the pan off, and swapped out the old oil pump for the new one. It was almost too easy. We changed the filter too, since it was near enough to the break-in period replacement anyway. Luckily, the pan was clear of any debris, despite our low oil pressure problems.

We got it off the lift, and filled with oil. It fired right up. No leaks. The oil pressure read 25 PSI, at 1250 idle. 50 PSI near 2500.

For three or four weeks we'd been wondering exactly what we could have missed that would have caused the oil pressure to be so low and to fall off like it did. What a relief to finally see 25 PSI at idle. :smile:

00004.jpg


Lots more here:
https://xjguy.com/triumph/2009may26/800x600/
 
So, what was wrong with the old pump? Cracked outer rotor? Severe wear? Defective aftermarket part?
 
In 1988 when I was restoring my 1958 TR3A, I bought a new repro pump in England. I later heard about rotors slipping on the drive shaft of the pump. Original pumps had a pin right through to make sure the rotor would not slip on the shaft. But the repro units were failing because the "new" method of "securing" the rotor to the pump shaft was by means of some knurling about 0.001" deep embossed into the steel shaft and then the rotor was pressed onto this knurling. When the knurling failed to "secure" these parts together, many of these pumps failed. Some lost pressure slowly as in this case. Most failed drastically. Suddenly no oil pressure!

So I took my pump out and found it was the knurled type. Knurling cannot be pressed into a hardened steel shaft so the repro pumps used a soft mild steel shaft. In 20,000 miles or so, this mild steel shaft had worn about 0.005" and this caused the lobes on the rotor to become sloped or tapered from top to bottom. This explins why my pressure was dropping. The hardness of an original pump shaft measured Rockwell C 60 (hardened) while the hardness for the mild steel shaft on the repro worn pump would not even read on the C scale. It read something on the B scale, but that is normally used to measure the hardness of much softer items - maybe like plastics or hard rubber.

Check if your pump shaft had a pin across it as shown in the S-T Spare Parts Catalog- or if it was knurled. Has the knurling permitted the rotor to slip ? Measure the diameter of the pump shaft and if it has worn, what are the measurements ? Are the lobes of the former pump rotor still straight or are they tapered from top to bottom ? A quick look will tell you this.

If your new pump you just put in has a cross pin, then it should be good for 100,000 miles. If not - well - GOOD LUCK !
 
Your car is looking great and I am very impressed at how quickly you completed the rebuild.
 
Not exactly sure why the old one is bad. It feels "looser" just in my playing around with it, which might just be due to wear.

If it has as many miles on it as the car (88000), then perhaps it was just the combination of new bearings and rings with the heavy weight 20w50 VR1 that led to it's failure.
 
Could be, but seems unlikely to me. I've always reused the original pump, after dressing the housing if needed (per the book) and never had a problem like you describe. And that includes an engine where I used to run straight 40 weight even in winter time; after the rebuild it would literally peg the oil pressure gauge at cold start.
 
No clue if the old one was original on the car or not. We simply brute forced the solution - swap out the pump and hope it fixes the problem. Since this was one of the few items we did not replace on the car during the restoration, we figured it was a good candidate to be the culprit in our low pressure scenario. Replacing the pump certainly raised the oil pressure to acceptable levels - even if there is something else hiding in the background we haven't seen yet - and getting that pressure up was our primary concern. When you're out of oil pressure, your out of beer, so to speak, and I didn't want my son's engine rebuild to get trashed so soon after we got it on the road.

Next time I'm over at my son's house, I'll take the old pump apart (looks like 4 small bolts will do it) and see what I can see.

After the swap and after running for an hour, the oil level stayed constant, so I'll assume I'm not dumping oil out of some opening that is critical :smile:

Man, this car is fun to drive!

Eventually, we'll get around to fixing all the bodywork boo-boos that I'm sure you pros spotted, but considering it was our first ever bodywork effort, we're happy with the result.
 
Has everybody forgotten that the oil pressure relief valve must be re-set when you build/tinker with the old tr lump???????I once had a friend with a bad knock and O pressure at idle.When the set screw was cranked down to the max, it had 25 psi at 2500.It was latter found that the previous(dork) had put std bearings on a .010 crankshaft,then sold it quick. The book specs the oil at 55 to 60psi at 3000 hot,more is NOT better,but anytime you are on the low side of normal, just set it up a half turn while running and watch the gauge come up.
MD(mad dog)
PS real men just re-build their oil pumps!!!PHA on that AM junk!!!
 
MDCanaday said:
Has everybody forgotten that the oil pressure relief valve must be re-set when you build/tinker with the old tr lump???????
Click to expand...
No, I haven't forgotten it, because I don't believe it! The ONLY time you need mess with the PRV is when someone else has already messed with it, or it's actually broke.

And my book says the PRV should not open until 70-80 psi.
 
We played with the PRV. No change, so we reset it back to it's original location. I have no reason to suspect that it was fouled in some way.
 
Randal,you made me laugh out loud,do you really think that this set screw hasn't been monkeyed with on 99 out of 100 cars still on the road???That the factory service manual would go into detail on how to set it correctly if it were not important??? I have even seen a fresh set of bearings and a new pump blow the gauge right out of the dash on start-up!!(lord what a mess!)
MD(mad dog)
 
MDCanaday said:
Randal,you made me laugh out loud,do you really think that this set screw hasn't been monkeyed with on 99 out of 100 cars still on the road???
Click to expand...
Well, I'm about 10 for 10 that haven't, or at least have been reset properly.<div class="ubbcode-block"><div class="ubbcode-header">Quote:]That the factory service manual would go into detail on how to set it correctly if it were not important???[/QUOTE]Actually, my factory manual says specifically to leave it alone.
 
Considering the age of these cars it is hard to imagine that these pressure relief valves could maintain their intended set point. The hard steel ball usually corrodes, the spring force relaxes and the soft valve seat wears, thus allowing the oil to bypass it's intended path. It seems like a sensible place to look for the cause of lower than spec. oil pressure.
As an engineer I like to see adjustability (sp?) engineered into mechanisms. That said, not everyone is qualified to make said adjustments.
 
No doubt you are in the majority, Frank; like a red flag to a bull it seems that few can resist that big adjustment screw sticking out.

But in over 35 years of wrenching on these engines, I have yet to see that valve be the cause of low oil pressure.

And it seems odd to me that the same people who wouldn't consider twisting a tie rod without a $10,000 machine to tell them when it was right will happily crank down on that adjustment screw, without the faintest idea of what they are actually doing. This is what leads to scenes like what MD described above.
 
So what does the PRV do then? I thought that it would have no effect on low oil pressure at low revs. I thought that it was to prevent excess oil pressure at higher revs.
 
NickMorgan said:
So what does the PRV do then? I thought that it would have no effect on low oil pressure at low revs. I thought that it was to prevent excess oil pressure at higher revs.
Click to expand...
That's exactly right, Nick. It doesn't do a blessed thing until oil pressure exceeds 70-80 psi.

The oil pump basically delivers a fixed amount of oil per engine revolution (ignoring internal leaks), meaning it's output per second goes up with engine rpm. But the bearing gaps and so on that the oil flows through stay fixed; they don't increase with engine rpm. So as rpm goes up, the oil pressure also goes up (so it can force the increased amount of oil through the gaps). The PRV is what limits how much it can rise. Otherwise the excess pressure would do bad things, like blowing the filter canister off the head.

I was spectating once when a professional mechanic put a Japanese engine together with the PRV accidentally blocked off. Within seconds of initial startup, it literally blew the spin-on oil filter apart. He thought it had to be a defective filter, so he mopped up the lake of oil and put another gallon in along with different brand of filter. When the second gallon hit the floor, he decided I might be right ... turned out he had disassembled two almost-but-not-quite identical engines and hadn't noticed the difference in the timing covers. A little quick work with a die grinder fixed it up.
 
Mine says that too...


TR3driver said:
MDCanaday said:
Randal,you made me laugh out loud,do you really think that this set screw hasn't been monkeyed with on 99 out of 100 cars still on the road???
Click to expand...
Well, I'm about 10 for 10 that haven't, or at least have been reset properly.<div class="ubbcode-block"><div class="ubbcode-header">Quote:]That the factory service manual would go into detail on how to set it correctly if it were not important???
Click to expand...
Actually, my factory manual says specifically to leave it alone. [/QUOTE]
 
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