Aston Martin DB4 Oil Pump Advise, Yeah I know its not Porsche (Long)

[Hugh R]

On another post on 911s about my shifter, yes, it only needed an adjustment, I made reference to the great support here on Pelican and zip on the Aston Martin site (I posted a question on the Aston site two weeks ago and have yet to get a useful response). A few kind souls ( AERKULD and Dentist 930 suggested I post about my oil pump problems, and so here it is.


I'm rebuilding my Aston Martin DB4, its a 1961 and its the first aluminum block engine that Aston made for the street. The big problem with these cars was that the aluminum blocks expanded under heat and the main bearing clearances grew dramatically. As a result, the oil pressure went south rapidly. The company set the main bearing clearances at 3/4 to 1-1/2 thousand of an inch, because when hot the main bearing clearances grew, due to expansion of the aluminum block by three or four times!. My crankshaft has been turned 0.020" on the mains and rods, and the rod clearances are fine so I'm looking at hard chroming the mains back to standard and going for that one thou or so main bearing clearance. The key issue with these engines is oil pressure, oil pressure, especially with a resale potential, not that I'm going to sell the car, but it doesn't matter how much you spent on pistons, valve jobs, etc., its oil pressure.

After all the background, here's the issue. I took my oil pump and inspected it and found that I couldn't pull a 2 thou feeler gauge between the vanes of the pump, which is great. But I have a machined grove of about 55 thou in the oilite bushings on the front and rear of the oil pump shaft that is there (I believe) to make sure that plenty of oil gets through the bushings. I bench tested the oil pump with a blanking plate so that I could use a drill motor (about 500 RPM, I guess) and suck parts cleaning fluid from my parts cleaner into the pump and back out again, and under minimal back pressure (I stuck my finger on the discharge) I got a constant pressure out the back of the oil pump shaft through the machined groove that shot fluid out about five feet. It was discharging the fluid out of the shaft into what would have been the area of the inside of the timig case. To me, when I'm dealing with trying to get LOTS of oil pressure to the mains and I get this huge discharge of oil/fluid out the back of the oil pump shaft under minimal restriction (my finger on the discharge) I see this as a major loss of oil going to the mains. The discharge of oil through the machined oilite bushing grove I don't think is necessary to lubricate the oil pump gear and chain since they're washed in oil anyway.


My thought is to solder the groove shut and at the end of the bushing, and let the oil go towards pressurizing the main bearings. The oilite bushings are no longer available, and I think I get enough oil through the old bushings to lubricate the bushings. This will increase my oil pressure to the main bearings dramatically. Here's a pic of the bushing. I hope I've made sense.

[TimT]

I would press that bushing out, and make another one.

Im not sure you can solder oil-lite, its impregnated with graphite I believe.

You can buy oil-lite bronze stock from a number of places. If you dont have your own lathe, any machine shop could replicate that bushing easily.

[Aerkuld]

I agree with TimT. It isn't difficult to get new bushings made and I would think that you'd be better off doing that. You wont need the spiral groove as, when under pressure, the pump will force sufficient oil through those bushes to provide lubrication.
Incidentally, with new bushings I would advise you to get the bushing machined with slight interference in the oil pump bore and leave the bore in the bushing under size by a couple of thousanths, insert the bushing to the oil pump by heating the pump and cooling the bushing, and then finish boring the bushing to the correct size with it in place in the pump. You sound as though you know what you're doing so you probably know this, but if you do want any more information on this, post or PM me for help with sizing/tolerances etc.

[masraum]

I'd try to find someone or documentation from someone who raced these things. They'd have surely done any easy/possible mod to improve oil pressure. Find out what the racers did about oil pressure. Maybe there's someone in Merry Old England that you could contact.

[Rot 911]

Hugh you have already received some good advice in the above posts. I agree with replacing the bushing. I would do some further investigation to insure you don't need the groove for lubrication. Or perhaps just have a smaller groove cut in the new bushing. One question I have is how many miles did you get out of the original engine or last rebuild using the standard bushing and oil pump?

[RickM]

I'm with Kurt on this one.

Perhaps the viscosity difference between parts cleaner and motor oil has some influence.

[Aerkuld]

Hugh,
I have been thinking about this and have a couple of questions.
Were the spiral grooves added to the bushings, or were they already there?
The reason I ask, there is a possibility that the groove is there to feed the oil into the timing case, but you do suggest that the timing case has oil in it anyway.

[Joeaksa]

We have the same style pump in the older Jags. Please inspect and check the outer part of the rotating pump assy for cracks at the top of the web.

If even a small part of debris gets there it will crack the ring and you will lose oil pressure there. Might even get some crack checking solution and make sure, or heat the puppy up in an oven and check then. I have seen pumps where a cotter pin (they use them on the rod nuts) has gone through the pump assy and cracked it but you cannot tell unless inspected closely.

[Jim Bremner]

dry-sunp!

[Hugh R]

I am getting new oilite bushings, they're cheap. They still have that groove in them however. The groove is there to make sure that oil get through the entire bushing, and is factory original. The squirt of oil that I get hits the oil pump gear and chain. But lots and lots of oil dumps from the openings in the front end of the cams into the timing case. I did speak with one very seasoned Aston guy and he said he'd never thought of the issue, but that he could see closing up the very end with solder on the new bushings and opening a small groove. I may call one of the Aston racing groups in the East Coast. Thanks for all the thoughts, and feedback. BTW, I dropped off the crank at the hard chromers today. I should get it back in two weeks, I'm taking it back to standard diameter and shooting for 1.1 to about 1.6 thou on the main bearing clearances.

[Aerkuld]

If the grooves are original I wouldn't touch them. The factory probably put there for a good reason.

Although you get a high pressure jet squirting out of that groove, the actual flow is probably very small as a percentage of the pump flow and the effect on the overall oil pressure from that will be minimal.

However, for the oil to get to that groove it has to be finding a path from from the high side to the low side of the pump. You will get some leakage here anyway as the rotor has to have face clearance to the pump housing and cover plate of course. If the clearance is too high or if the faces are badly scored this could have a more dramatic effect on the oil pressure. That might be worth looking into.

[Hugh R]

Thanks Aerkuld:

The problem that I had was I built a blanking plate for the suction and discharge side of the pump, and put a pickup port to suck oil/cleaning solvent into the pump, and when I spun it with a drill motor just finger pressure on the pump discharge caused me to get a large squirt out the groove that must have shot 4-5 feet. I just can't believe it needs that much oil going out the back of the pump. And yes, I'm sure it was put in for lubrication. Again, I'm going to call the Aston racing guys on the East Coast on Monday and see what they think. Also, I have two bushings, one at the impeller vane, and one several inches away at the end of the shaft where the chain and gear attach, both have the same groove.

[masraum]

Keep us updated. Besides the fact that I think your car is one of the coolest to come out of the UK, I'm curious to see how this turns out.

Awesome car, glad you've still got it.