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Oil Pumps and Oil Pressure - A survey question

Started by 29UJohn, January 16, 2011, 11:15:15 PM

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29UJohn

 :P   I am rebuilding my 29 Plymouth engine (SN U50105).  My car was manufactured approximately May 15, 1929. On this engine, the line to the oil pressure gage comes off an oil galley port on the left rear of the engine under the starter, near the rear main bearing.  I obtained a 1929 parts engine (SN U29287) that was manufactured earlier than my engine.  On this earlier engine the oil line to the oil pressure gage comes directly off the oil pump. I am using oil pump from the parts engine on my rebuilt engine.  This has allowed me to place a second after-market oil pressure gage in my car, with the "new gage" showing the pressure at the pump, and the original gage showing the pressure at the other end of the oil gallery.  When I run the engine, the difference in oil pressure between the two is 5-10 lbs when running at operating speeds (30-40 mph).  At warm idle the two register about the same (~20 psi).  Also, the gage measuring the oil pressure at the pump fluctuates quite a lot, while the oil pressure measured downstream on the original gage is much more steady.  
   Now - I am trying to set the engine oil pressure.  The "May 1929" manual states the oil pressure should be 35-40 psi at normal operating temperature.   I have set it so the oil pressure at the original downstream gage is 32 psi when warm, and the pressure at the gage is about 38 psi. When the engine is cold and run at 30-40 mph, the pressure at the pump is about 45 psi - until the engine warms up.  I hope this is OK?
???    My survey question is:
1) What year is your car?
2) Where is the oil pressure line connected - to the oil pump or to the oil gallery under the starter?
3) What is the max oil pressure when run at operating speeds - cold and hot?

John

   
John
1929U 4 Dr

Rusty

on my 29, the oil pressure comes off the driver side of the block below the starter.  I have a fresh rebuild (bored 40 and rebabbited mains and rods) and with 30 straight rolleta oil, it starts at 38 psi cold and drops to 35 running hot.  This is the orginial gauge and may or may not be that accurate.  I did install a aftermarket once and it read the same at idle.  My gauge does not read dead steady but boucnes around 5 psi, some days higher, some days lower. May be the gauge.

I did take a look at glens (south dakota) last weekend and his is like your set up.  He has alot of crud on the black but I could not feel a  connection for a fitting below the starter but I also did not look that hard.

rusty


chetbrz

John,

Great Questions !!

My car was manufactured around the March time frame.  The oil pressure gauge is hooked up to the oil pump as displayed in your pictures. 

I believe we had a lengthy discussion of this topic on the POC site back in June of 2008.

Here is the link to the posts in case you want to stroll down memory lane.

http://plymouthbulletin.com/smf/index.php?topic=1719.msg8285#msg8285

I hope you come up with something definitive in your research !

Chet...
http://www.1948Plymouth.info           Web Master - Forum Administrator - AACA member

29UJohn

#3
Thanks Chet - that helps!

As for the location of the oil port behind the starter, it is a screw plug where the oli port was drilled to connect the mail galley to the rear main and rear cam bearings.

If you look on the front left side of the engine, there is a plug with a square drive where the main oil gallery was drilled from front to the rear of the engine.  If you look just above the oil pressure relief valve, there is a slotted screw plug.  This plugs the hole where the oil port was drilled to the center cam bearing and center main bearing.  If you go forward and aft from this oil plug, you will find two smaller slotted oil plugs, one at the front (behind the water pipe), and one at the rear (underneath the starter).  You may be able to feel the one under the starter with you hand.  This oil port plug is where my oil pressure gage line is connected.  

John
1929U 4 Dr

29UJohn

#4
Thanks again Chet!

After rebuilding  my engine and cam shaft, I adjusted my 29U pressure relief valve and now get the following:

Cold:  45 psi at pump, 40 psi downstream

Hot:   40 psi at pump, 35 psi downstream

Hot idle:  20 psi at both locations

I think this should be fine now.   My 29 Manual states the pressure should be 35-40 psi at normal operating speed, and my factory gagae was set up to read from the downstream port, so it seems to be right on target.

After ths experience, I am convinced that he main bearing wear that most effecs oil pressure is the center cam bearing.

PS - If anyone has a 28Q manual, I would be interested to know what it states the normal oil presure should be, since those engines took the reading from the pump.
John
1929U 4 Dr