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1929 626 Oil Pressure


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Hi Guys, I have a quick question. The oil pressure on my 1929 626 is between 30-40 PSI on start-up but once the engine is fully hot the pressure drops down to 12-15 PSI. The engine seems to run well, is this normal for the pressure to be so low?

Thanks!

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Hi Dave, I do not believe the engine was ever rebuilt. I purchased the car about 2 years ago and last year had a local restoration shop go through all the mechanicals. At the time (among other things) the mechanic replained the head and replaced the gasket, did a valve job, dropped the oil pan and removed any visible sludge and installed a reproduction oil filter. He assured me that he believes it is running properly but I agree that pressure is way too low. Is it possible the gauge may not be reading properly? Assuming the reading is correct and the pressure is that low should I not drive/run it until it is corrected? Thanks!

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Well, you didn't say anything about the shop doing anything with the rod bearings - did they take off the caps and check the bearings and measure the crank when they had the oil pan off? This would be where I would look if you have a low oil pressure problem as wear there would result in low oil pressure. Worn cam bearings can be a problem too, but that isn't easily checked. Since they had the head off, and it would have been easy to replace the rings with both the head and pan off, I am guessing that you don't have excessive taper (wear) in the cylinders or bad rings. You do mention that they put on a repro filter - perhaps there is a restrictor fitting missing also. You can simply fit a modern oil pressure gauge temporarily to check the accuracy of the original guage. I would be very careful driving it with oil pressure that low, keep your engine speed down and don't put a high load on it. If you destroy a rod bearing it can tear up the crankshaft and that will get expensive, or worse yet, can put a rod through the crankcase.

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I agree. Worn rod AND main bearings lower the oil resistance. (Cam bearings usually last much longer.) Remember, pressure comes from resistance to flow. When you start your cold engine, the oil is thick, more viscous (resistant to flow). Engine heat thins it out, and of course, oil flow takes the path of least resistance. I would believe your gauge. It isn't lying at one point, and telling the truth, later.

While you're at it, do a compression check. Let us know what the spread is (the difference between the highest and lowest pressures). If your mechanic is going to open the bottom end for bearings, you may want to replace your rings at the same time (based on your compression readings).

Usually, by the time oil pressure drops, it's time to do rings as well as bearings. Another indicator is, oil burning. Smooth bores cause piston rings to hydroplane and burn oil. A honed 45* cross-hatch gives the oil a place to go, aids ring lubrication, and stops oil burning.

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Right, the mains may be worn too, and may well need to be redone, but the rods will probably show more wear. I took it forgranted that if a shop takes the piston and rod assembly out, they will put in new rings, but I should have said that. Honestly, if the engine hasn't been rebuilt, it probably needs to come out, and be cleaned and bored, at which point, if the main and cam bearings are worn, I would have them rebabbited and align bored, put in a new timing chain, etc. The odd thing is that if the shop had the pan and head off, they should know what needs to be done. Giving them the benefit of the doubt, maybe everything else is ok and they just screwed up the oil restrictor, ok, well, I doubt it, but it could be. I assume that if they did a valve job and not rings, the compression should be ok, but you are right, a compression check takes very little time.

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Hi guys, thanks for all the great information and things to look into. I will have to call the mechanic to get more specific answers to your questions and get back to you (I may not be able to get him until after the holiday). What I can tell you now is that he did do a compression check and the pressure was good, not great but acceptable and was fairly consistent across all cylinders. I don't know if he checked the rings. He pulled one of the rods or bearings? and said that it looked ok, again not great but acceptable. The car doesn't seem to be burning oil, I never have to add any (although I have only driven it about 100 miles). There is white smoke (steam) at start up but that goes away when the car warms up which is the same as my modern car. I will also ask him about the possibility that an oil restrictor is needed with the oil filter. Thanks again for the help and I will post more specifics after I speak to the mechanic.

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There's also a mechanical-oil-valve that is in carburator-choke-linkage, opened when choke is closed, that puts extra oil in cylinders at start up, thru holes in cylinder walls below rings.

When valve is open, oil-pressure will be lower. Oil pressure should go back up when choke is opened.

The valve is located at right-rear of engine-block.

The 2 linkage rods can be connected to valve incorrectly,

And the L shaped arm can be installed backwards,

causing valve to operate backwards, as choke is opened and closed.

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Thanks Speedster. I have the original Detroit Lubricator carb removed until it can be rebuilt and have a Stromberg carb on the car. The original linkage is also temporarily removed since I have a custom linkage built for the Stromberg. I still pull the original choke knob at start-up so that the mechanical-oil-valve that you mentioned would operate until the engine warms up. I will check it to see if the remaining linkage was somehow reversed when the carb was changed. Do you know how I can tell if it is connected backwards other than watching the pressure gauge as I open and close it? Thanks for your help!

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<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Dave Mitchell</div><div class="ubbcode-body"> You do mention that they put on a repro filter - perhaps there is a restrictor fitting missing also. </div></div>

I've got a question about the restrictor. What does it look like, where is it located and how hard is it to find one if your missing one?

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jjohnb —

For whatever it is worth, attached is a snippet from the '28 Information Book on the Packard Sixes. I know your car is an eight, but the same sort of instructions might apply. It is worth checking out in the manual for your car.

In the same manual there is verbiage about the oil filter and its connector. An illustration of the connector used on the sixes accompanies the text. If you are interested I can supply both the text and illustration, but I need to rescan it to make it a bit easier to read and see. Let me know if this would help.

Pete P.

post-50405-143138021995_thumb.jpg

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