VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1929-1932 Normal oil pressure

I'm sure you guys are tried of talking about this,but I think I may have trouble on the way. I've been hearing a slight knock on start-up and noticed the oil pressure at 5psi after the motor warms up.The knock goes away in seconds and the pressure is 15psi on start-up.The motor has about 250 miles since rebuild but it's been 15 years ago.I pulled the oil pan tonight and inspected the main bearings.The bearings are in mint condition.I still need to check the rods.I inspected the oil pump for weak springs or a vane problem but it looks just fine. I know the bearing clearance doesn't control oil pressure but I know the mains and rods get oil from the cooper lines.I'm not sure what the oil distributor does,could it be the problem or is my car normal and I'm wasting my time? Any help would be great! Thanks,Stan

In my opinion your oil pressure is a bit low both when starting and running. If the oil pump is not working properly and needs a replacement, I suggest you change to a pump from 1934. It is the same size, but far more effective, so if you change, let the engine run idle for some minutes before driving.

Hope you have joined or will join VCCA. This is a great club.

:vcca:

First - what year is your engine? The 1929 had no pressure to any of the main bearings, the 1930-31 has pressure to the center main only. 1932 and up has pressure to all three mains. On the 1929-31 engines main bearing clearence would have little affect on the oil pressure....a bit more in 1939-31. I will agree that the pressure sounds low. The 1929-31 often have about 7 pounds at speed when hot.
I would suggest adjusting the bearings as per shop manual, that is removing shims till drag is felt and then adding one shim. If it is a rod or main noise this should eleminate it.
The change to a gear type pump will give a boost in presure but first I would want to determine why its low.

Hot at idle, depending upon the type of oil pump you have, 5 pounds of pressure is normal. The first design factory pump put out just a couple of pounds pressure at idle when hot. However, if you are only getting 5 pounds of pressure at speed then the pressure is low.

:) :grin:

About 5 years ago I remember this nice sunday that I was driving the 31 with my grandpa and when I checked the oil gauge it was almost at 0, so we hurried home, turned of the car and removed the oil line from the gauge turn it on and there was no oil coming so we new the 74 year old pump was gone, I was able to get my hands on a new one from ebay for 75 bucks, talked with my grandpas friend that has been the car mechanic since 1968 installed the new pump and I remeber the first readings close to 15psi and in normal driving its at 10psi

Thanks for all the help gang! I have tightened the mains and going to the rods next. The pump still looks new inside so I'm going reuse it.Stay tuned for the final update! Thanks again,Stan

I have been battling my oil pump off and on for about a month now. My problem was a little different than Oniz. When I went around a corner to the right it would start to knock, straight was fine and going left was fine. Over the past year many people have given their opinions as to what the problem was, even as to saying the center main bearing was it. We have not driven the car (a '29 coupe) much this summer since I was concerened about damaging the engine. Finally I took it apart about a month ago. Inside there wasn't anything that SCREAMED fix me. A lot of little things but nothing major. I used plastigauge on all of the bearings and got them as close as I could. The oil pump was the old style with the ball of screen around it. One of the fellows in our region suggested a pump out of a '34 - sounded like a good idea. Unfortunately I did not know there is a difference in the length, and the shaft connection between the Master and the Standard. After modifying the shaft to fit I bolted it in. Since I didn't have a similar one to compare it to I tightened up the pan. Did I mention there is a 1/2" difference in length? Perhaps the fellow who sold it to me didn't know either or maybe he just wanted to finally sell that old rusty pump he's been holding on to for the last forty years. You know I'll be buying more stuff from him right?
Bear in mind that this pump has to push oil through the same tiny little 1/4" hole that a gear pump would so at a savings of $250 it seemed worth a shot. Now when I go around a corner to the right the oil pump still looses siphon and consequently the oil pressure. So far the only solution has been to take the distributor out and run the pump with my cordless drill and the oil distributer loosened up. Next I'm going to overfill the oil pan and if it runs out the rear o-well. The technical advisor I called from the G & D wasn't a lot of help saying "You can expect to pay $7,000 to $8,000 for a good rebuild now" Boy you know I'll be calling him with a lot more questions in the future. With helpful advice like that I'm suprised people are still actually trying to fix these things instead of hot rodding them all. It was almost like he was saying - Give it up now guy, you aren't rich enough to have and enjoy an old car like that. We as a club ought to be trying to actually be helpful instead of condescending and holyier than thow.
My latest thought is that the baffles are letting the oil move around in the bottom of the pan fast enough that the pump draws in a bubble of air and then can't pass it out through the outlet. It holds 15 psi sitting at idle now and 20 plus at speed going straight. I was very thankful of Rays reminder to properly install the pan gasket. I have had it off five times in the past month and have not had any problems with that aspect at least. If any one has any truely helpful suggestions I would appreciate it.

I have had similar problems with a small block chevy under hard braking conditions and such (the oil pickup becomes uncovered).

My suggestions are not any kind of new revelation or any thing and you know some of these things from your statement above. The oil pump is loosing siphon or oil is not where it is supposed to be. This is due to several possibilities. 1st the oil pump pick up is biased toward the right side of the engine so going around a right hand corner uncovers the pickup screen allowing air and thus loss of pressure. This could be due to the screen not being located low enough in the oil pan athough it seems you investigated this possibility even going as far as installing a 1/2" longer pump by choice or by folly. I have only seen a few pickup tube assemblies in these older engines but mine has a round looking kitchen sieve appearance and is spring loaded so that it can actually touch the bottom of the pan. I kind of worry about the connection of this spring loaded pickup which brings me to the 2nd possible problem you might have.

If you have ever tried to drink through a straw with a crack in it you know where I am going here. If my spring loaded slide where to develope a air leak I would loose siphon anytime the oil would uncover this joint. Other pickups I have only seen in pictures look more oval in design and are stationary by design. If there is a leak in this assembly (especially on the right hand side) either in a gasket between the oil pump and tube or the tube and screen or a small crack in the tube or any kind of leak this is going to cause a problem similar to the one you are seeing. It would be a very good idea to inspect this assembly very carefully. Next this will be a little more difficult to check and I personally have never done it, but the alignment of the oil tubes to the oil pan troughs could be your problem. If these are not aligned properly both in placement over the trough and placement above the trough(Too High above) this might cause your problem (there is a tool made to check this). Do you remember the old rule of the universe "Mass that is in motion tends to stay in motion centrifugal force those kinds of things". So it is with oil. The oil may be missing your troughs on right hand turns if they are about off the edge of the trough or too high above the trough.

Also a couple of things thrown in here just because they can be a problem, even though you have probably looked at them. Dippers need to be the correct direction (opening toward the the camshaft I believe)and the correct depth 15/64" into the trough.

I don't know if the oil distributor can cause this type of problem or not. Looking at the description of its function and from your particular problem I wouldn't think so but never totally rule anything out until it is ruled out.

I am sure you are putting in 5 quarts of oil and not relying on the dipstick to tell you when your oil level is correct. I have seen situations, believe it or not, where an incorrect length dipstick was installed in an engine by a previous owner and an unknowing later owner did not know this and overfilled an engine causing it to liquid lock.

As a final suggestion, here again I have not had a lot of experience with these particular vane pumps but have had some with industrial vane pumps they can do some strange things as they wear. If you have not checked the condition of the vanes this could be a possible problem again don't rule it out until you rule it out.

Hope some of these suggestions help. And ease up on the G&D guy maybe he just had a bad day. They are usually very helpful.

Please don't overfill your engine with oil you could cause bad results. Find your problem. Don't see it as frustration but as an investigation. :eek: :confused:

beachbum,
I would suspect that the pump is drawing in air when this happens. I assume that you are filling the pan with 5 Qts. of oil....my simple suggestion would be to add another Qt. and see what happens. There is a gear type pump conversion that was made for a 1929. It included the gear pump, screen and housing around the screen and the necessary tube and fittings to amke it work correctly. I would guess either you present plumbing is drawing in air when the oil sloshes to one side or the pick-up is too high.

yes I forgot that I add 6 quarts of oil to my car instead of the regular 5 and until know it keeps working ok

That for sure indicates that the pump plumbing is drawing air when oil moves to one side.

well I always tought our cars used 6 quarts instead of 5 and the car has been with my family since 1968 and we always put 6 and even the mechanic told me to use 6 and my pump its about 4 years old right now

6 cylinder Chevrolet cars from 1929-1962 used 5 Qts....+ 1 for filter if so equipped. They will show pressure and get along fine with less than 3 Qts.

good to know ChevNut and one question would you recommend installing one of those fram vintage oil kits that I have seen in ebay to our cars thanks

Thank you all for the tips, unfortunately I have tried virtually all of them except for the six quarts - that is next. I tried to run it down to the local auto parts store with the oil at the add oil mark so that I could get a quart of the Lucas additive as recommended by Steve K from the Filling Station it lost all pressure. Towed it back to the garage. It is a brand new pump with less than five miles on it. It is a '34 Master pump and was too long for the pan. When I tightened the pan screws the first time it crushed the pickup screen so bad that it closed off the pickup tube. I had a second block at home that had a '32 pump in it. It was too worn out to use but gave me the proper length. I just can't help but feel that a gear pump would have the same problem. I have been mechanicing on '50s Chev six cylinders for over thirty years but this is my first early six. I put grease in the bottom of the pan after shortening it to the proper length and it misses by about 1/8". Seemed fine. I looked at the baffles on the other pan and they are spaced about the same from the bottom. It is too rusted out to use, must have had water in the oil when they took the engine out. I put it back together and have not started it after the latest adjustments but have no confidence that I have corrected the problem. If it doesn't work I thought I might try a piece of expanded metal shaped into a ring so as to keep the oil from actually making waves and troughs in the bottom of the pan. Five quarts usually brought it up to the top mark during an oil change. The book says to use 5-1/2 quarts on initial start up after having the pan off and five thereafter. Obviously I'm running out of things to try at this point. Has anyone ever had this much trouble with one before?

1931 chevy,
I am not familuar with the oil kits on ebay. My suggestion would be to have the original oiling system and make sure that it is working properly. The only modifiaction I would possible make is installing a gear type pump and it must be the proper one that CHEVROLET sold for replacement...that is the correct one for your year and all of the parts that came with it must be used (oil lines, screen, fittings, etc.

beach bum,
I still believe that you pump lines/connections are drawing air some where above the pump. When the oil drops below that point it is picking up the air. We have a member in our region with a 235 engine that has that problem. When the oil dropped down a 1/2 Qt he lost pressure. I suggested he run 6 qts until he fixed the actual problem. That was several years ago. He has never fixed the problem but continues to run the "extra court" and has never had a problem.

Again, thank you all for your tips and experiences. I put it together again last week and filled the crankcase to the top mark on the dipstick. My wife and I took it on a 100 mile regional tour last Sunday over some very winding and sometimes steep roads. Even included a trip across a suspension bridge over a gorgeous green lake. Never had a lick of problem. HOT it idles at 10 psi, and at 45 to 50 mph runs at 15 to 20 psi. Cold it almost pegs the gauge at 30 psi. Seems like the problem has been solved unfortunately just in time for winter. Had I not started down this path I would probably have been better off to install the replacement gear pump.

Hi all together, it's me from the other side of the ocean.
My 31 runs great, and since weeks I correct all problems made by previous owners without any experience. The last owner who bought it from africa was a doctor and all he did know about mechanic was: There at the wall is a knob and if I push it it will be bright in the room. If not, I call the housekeeper.
You can imagine he had to give up with this "bucket of bolts" completely frustrated.
Now I am sorting the bolts in my bucket since many weeks and have much fun.
As I understood the repair manual, the oil pump brings only the oil to different places and pans (oil troughs) inside the engine, from where it drops to the bearings and where ever it has to go without any forced pressure.
If I start the cold engine, I see at the dashbord-gauge about 5-8 pounds oil pressure, if the engine is hot, about 5 at idling speed and between 5 and 10 while driving.
Last monday I hat to drive to another town to pick up a correct special thick gearbox oil to have a try to fix the problems with my leaking gearbox only by using the correct oil following the manual, and I drove about 50 mls there and 50 back, and backways I didnt use the highway again because I was scared about the big trucks always under pressure of time and driving as fast as possible and I didnt want to have driving devils in my neck all the time with my "grandpa on 4 wheels" (remember I am from and in germany, I think we are the only one country around the world without speed limit on highways) so I did use a normal street and I did realise I can hear the connecting rod bearings knocking a little bit when the street goes left (???!!!) I did not understand this because the pump is on right side and if I go left, the oil goes on the right side and the pump should not suck air instead of oil.
OK, it was just a bit knocking (had not the suggestion it would be necessary to panic about) and I did know, the oil is at down level. I didnt refill any, because season is just over now, winter is coming, and I want to remove the oil-pan now to clean it because I did read in the manual it should be removed at every third oil changing to clean it and I found out nobody did it since more than 10 years...and it might also be the wrong oil, because it was a modern thin oil, completely dirty, and the correct oil should not cover any dirt, it should sink down in the oil pan and therefore it should be removed and cleaned time by time. Modern oils (as we know) should cover all dirt and it is filtered out later in the oil filter. Using that oil in an engine without filter means all the dirt circulates in the engine and can block oil tubes and anything else, very dangerous to use the wrong oil... ok, enough, this is another thing to talk about.
Ok, back: I can only say I have between 5 and 10 pressure and the engine goes smooth and silent normally.
I was just wondering, there is a video with two guys showing first run of an overhauled engine and the gauge shown there shows a very high pressure....I did contact the boys to ask about but got no reply unfortunately