100 Oil Pump--options and resources

[Michael Oritt]

Though I have not yet dropped the sump to remove and examine the oil pump signs are that it is up for replacement: 55-60 psi at 2500+rpm's/30 psi at 1000 rpm's on start-up, falling off to 35-40 psi at 2500+rpm's/10 psi at 1000 when oil gets hot.

Assuming the pump needs to be replaced what is available out there? Unless I am missing something Moss does not seem to supply one for my car, though I do see one on the VB site. I don't mind springing for a more expensive product from UK if there is a real advantage in quality, performance and/or reliability.

Thanks in advance for all advice and opinions.

 

[pan]

Check the oil pressure relief valve before tearing down. The spring may have weakened.

 

[Bob_Spidell]

Denis Welch sells them. You'll probably need a new shaft as well. But, I'm not convinced the pump is your problem (or only problem). Could be main and/or rod bearings, etc. but, before you do anything check against a known good pressure gauge (or have yours checked and 'calibrated'). My BJ8 showed similar symptoms, but after the gauge was overhauled and 'calibrated,' I got 15PSI more pressure at idle.

 

[Michael Oritt]

Pan--

If the spring were weak wouldn't it be yielding consistently low OP regardless of the oil's temperature? As said, OP is good on start up and falls off as the engine warms to normal operating temperature. I had thought of that--hope against hope department--but I think if that were the issue I would have the same OP regardless of temperature.

 

[roscoe]

Of course I don't always follow my own advice but fwiw, do the easy and inexpensive stuff first is what I always say. My scheme would be to put a known ( new or calibrated) gauge on the oil press line and drive it first. If still bad, I would suggest replacing both the oil press relief plunger and spring (both pretty cheap and why disassemble it twice), or simply add a washer or two to give more spring compression and see if that helps. If somehow you can get high enough pressure at low revs or idle without too much at high revs you could just watch it to see if it starts to get worse with time. Oil pump would be next in my book, and then bottom end bearings, although once you are into the pump you might as well at least look at the mains and rod bearings.
On the other hand we all love new stuff and a new pump would make anyone feel good. Did the idle pressure just creep down over a long period of time or did it happen all at once?

 

[Michael Oritt]

Jon--

The hot OP has dropped gradually over the last year or so.

Though I always like an easy solution I still do not see how the pressure relief spring can be the culprit as to my understanding the problem would be there on start up as well as once the engine reaches running temps which is NOT the case.

In any case I agree with your recommendation re the main/rod bearings and will certainly check them if the sump comes down. I probably have 50-55K on the engine since it was overhauled. It has served me well and deserves the care and attention.

 

[roscoe]

I understand what you are saying but I would still replace the spring and plunger and fiddle with a couple of washers behind the spring in that perhaps the pump output is not linear with RPM or maybe there is some other non-intuitive hokus-pokus going on. I am a firm believer in hokus-pokus. You might replace those two parts when you put the new pump and bearings in anyway. That being said, a slow decline in op in a 50k mile engine does tend to make one think of bearings or a pump.

 

[red57]

I haven't had a 4 cyl for a lotta years but in the 6 cyl, the rocker shaft and rockers are one of the biggest culprits for oil pressure loss.
I agree with Roscoe, I would much rather play with the relief spring & plunger first (it doesn't cost much in parts or labor).... And it is not just the spring, the plunger can wear too. It tends to bounce against the end of the bore and I have found some with serious grooves worn into them.
As far as the pressure dropping when warmed up, I figure that is because the oil gets thinner (less viscous) when hot and more is "leaking" out around bearings and things (cam, crank, rods, rocker shaft, etc.) resulting in a drop in pressure - why would you discount the oil being able to "leak" out from the plunger where it seats in the bore? I guess I am just confused as to why you seem so confidant it is not the pressure relief valve?
Dave

 

[Michael Oritt]

Dave--

I am certainly ready for an easier and less expensive solution and I will inspect the relief valve before dropping the pan, etc. but as Roscoe points out it is reasonable to suspect the oil pump in view of the car's mileage.

Several years ago I removed and inspected the plunger/spring and as I remember it was not an easy task getting it back into place. If memory serves I had to use one hand to lever the cap into place with a large screw driver against the spring's pressure while having a wrench in the other hand situated to start it into the threads. Is anyone aware of any neat tricks to make reinstallation simpler?

 

[red57]

Mike,
Again, my last 4 was about 1970... But, with the 6 cyl. it's not too bad - at least there is good access. I do use both hands together - thumb of one pushing in the center of the cap and the other hand pushing in and turning at the same time to get the threads started. Part of my questioning is that I think a well treated motor should be good for at least 100k so I wouldn't expect the pump to be that far out of spec yet. Actually, now that I'm thinking about it, your pressure numbers are still well within the old saw of '10psi for every 1000rpm' - 10psi at hot idle may be a bit light but 35-40psi at 2500rpm is a good number. So, I am guessing you are reacting to the 'change' more than the numbers themselves?
Dave

 

[Randy Forbes]

Dave, My first inclination was the rockershaft too! Oil squirting out past the rocker bushes can really sap the oil pressure; saved many owners from a total engine rebuild by just replacing the rockershaft__back in the late 70s, best we could do is get the worn ones welded up, turned and hard-chromed__and fitting/reaming new bushes to size.

That was especially true of the 6-cylinder cars, but I don't have the same amount of expose to the big four jobs, but Mike, it still falls into the easy to determine category.

When I worked at Austin-Healey West, San Francisco, the replacement spares situation was pretty bleak, for example, the Moss catalog__for Big Healeys__was only about twelve (12) pages. Compare that to a currently printed Moss catalog

 

[Michael Oritt]

Dave/Randy--

I checked the rocker shaft and fortunately or unfortunately it is not the source and it dribbles oil in the appropriate manner.

Dave, your comment about "change" is not inappropriate. Prior to my initial post I searched "Oil Pumps" in the archives and ran across a very similar observation made by the late and sorely missed Dave Russell, and yes I do miss seeing the OP needle up around 60 at speed and never below 25-30 at warm idle.

While my readings may be presently borderline acceptable they have been trending down for the last year or so and will likely soon fall below the 10 psi/1000 rpm rule. I am simply trying to stay ahead of the repair curve and do not mind doing what needs to be done.

 

[pan]

I only suggested the relief valve as something to eliminate before major engine work. It would be a nuisance to find that after the major work the op was still low and caused by a worn valve. My 100 engine holds good op now after a major rebuild some years ago, but before that it ran at never more than 40psi for many years. The relief valve and spring were replaced during the last rebuild.
Dave is right, the valve piston also wears, and I have heard of them sticking.
Speaking of the oil pump, I once owned a Jaguar which lost its op. At idle on a warm motor the gauge said zero. When the thing was dismantled we found that the oil pump rotor was in two pieces! Different from a 100 though which has a gear type pump.
Alwyn