VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1912-1928 1925 No Oil Pressure Again

So I finally got a replacement rear in the car,new aluminum radiator that has solved cooling problem but now have lost oil pressure on a basically new pump. The pump maybe has a couple hours on it. I call the guy I got it from and he said he has not had one issue with them in eight years but if returned and inspected and found defective he could get it replaced. But we left it as I will play with it quick first and see if there is something stupid going on. Oil pan was removed and cleaned prior to new pump so no sludge or blockages, I even sucked on the bottom elbow and drew oil. I opened the pump up and it looked ok. I did not check for depth of bores in case they might be too deep but again it did have great oi pressure after initial installation. I reprimed it with a drill and got it to suck/shoot oil. I tightened the bottom (draw) elbow a whole turn on the oil pan so there would be no loss of suction. Reinstalled pump and it took a few seconds till it built pressure again, maybe slightly lower but engine was slightly warm. Took it for a ride and it may have dropped pressure just as I got home but it built back up. After two hours went and tried it again and I had to rev the heck out of it to get it to build pressure. Before any issue cool or cold it would shoot right up as soon as it started. Any thoughts before I return it for inspection? Oil is prob 10-30. I added a half quart the other day from lifter loss.

A couple questions for you:

1) Is this a 1925 engine/oil pump or a different year?

2) Is the pump you're using a vane or gear style pump?

3) Have you bled the oil lines up to your pressure gauge?


My guess is that the pump is actually pumping but you may have too much air in the oil lines which is causing the gauge to read incorrectly. I had this issue with my 1928 engine, I ended up bleeding the oil line up to the gauge, by eliminating excess air and have not had the issue since.

When I first start up, it usually spikes the oil pressure right away however, if it has been sitting for an expended period of time, I usually have to rev the engine for ~10 seconds or so before it registers on the gauge (I'm assuming that is due to some air working its way into the lines again).

Also, I have noticed that the lack of oil pressure on startup tends to be worse with 10w30 vs. straight 30wt which tends to support my hypothesis.

-Tyler

Hi Tyler, it is a 25 engine with gear pump on back of generator. I even took the line off for the gauge and nothing came out while reving the engine. All was good till recently. I could try the heavier oil. I did get it to build pressure today but stopped for gas and it took a long time to rebuild pressure. I got home shut it off retightened connections and it would not build pressure,even at a high rev.

Strange, I'm not super familiar with the '25 pump but I thought it was a little "external" gear pump like this animation:

https://en.wikipedia.org/wiki/Gear_pump#/media/File:Gear_pump_animation.gif

Is that the case? If so, you definitely have a head scratcher, there's not a whole lot to go wrong except for wear over time.

Is it possible that the generator shaft or coupling has sheared off/stripped? Can you verify that the gears are rotating?

-Tyler

Yup thats it. It is mounted to the back of the generator and it is definitely turning as there is an open window in the side of the housing where you can see the shaft. I had it apart and shaft is fine.

I agree that gears pumps are pretty simple. About all that can go wrong is wear between the gears and on the end plate.

I would check the clearance between the gear teeth and housing as well as the face of the gears to end plate. If the gasket on the end plate is too thick the extra clearance allows oil to bypass around the gears and just circulate in the housing.

Is the pump an original diecast type?Is it missing the "pressure relief spring & ball,both brass"?Have you tried tightening up the gland packing nut at the front of the pump?,it could be sucking air past the shaft packing,which will prevent it from drawing oil from the sump.The gear to housing clearance should be no more the 0.004" on the gear diameter(0.002" maximum between the teeth & the gear bore),and the gasket should be cut exactly to the shape of the internal machining of the pump,and no more than 0.002" thick(brown paper is ideal for this),otherwise the gear to cover plate will be excessive and the oil will just cavitate within the pump as Rusty 37 Master says.

It was a brand new billet pump,no packing around the shaft,sealed bearing.
i was in a hurry to get the pump back to seller and did not have a chance to go over it properly. I did open it quickly again and I am thinking there was a little too much gap in the way the gears meshed. Hopefully I will have some word back soon.

The billet type aluminium pumps use a neoprene type oil seal in place of the original gland nut & packing,and the way the seal is installed with the seal lip facing inwards,it will stop oil leaking out but could allow air to be drawn past the seal lip.The pump doesn't have any type of bearing for the shaft to run in,the shaft just runs straight in the body of the pump,and a steel shaft running in aluminium requires constant lubrication otherwise the steel shaft will pick up or gall the housing.
I used to make those pumps in bronze as per the original style and no problems.

Just figured I would post an update. After installing the replacement all has been good. I did not even change the oil to make sure it was not some kind of viscosity breakdown. I have used the car several times a day around town on most days for the past week and a half with no issues. Takes several second then pressure comes right up. Cold 6-8lbs at idle. hot 4-6 driving. I did measure gear to back of pump housing and it does have more clearance than CJP'S 29 suggests. .009 without gasket and about .017 with. As there is no issues I will leave it but if any occur I will start with thinner gasket and maybe then dust the back of the housing but I see no reason for it to change(hopefully)

The rear faces of the drive & driven gears should be just level with the pump housing,or barely below it,and not have 0.009" clearance gear face to housing.And 0.017" clearance is way too much,which is probably why the pump is a bit slow to draw the oil out of the sump.The gauge readings are fine,as it's only an indicator that the pump is pushing oil around,the gauge is more like a mechanical warning light.

Thanx for the input, I finally got around to playing tithe the pump itself. I found some thin brown paper,about .0025 and sanded the the back of housing on a disc sander removing about .004 or 5 and so far does seem to make a great difference on startup when it is warm,much quicker oil pressure. If anything happens again I guess I will just bring it down flush and let the paper gasket be the clearance ( I did not want to push my luck on first try).

Glad you got good results. I totally agree with your cautious approach. You can always remove material but it is hard to put it back on!

Cheers, Dean