1931 Chrysler CM6

[Rick Marsh]

I've got a 1931 Chrysler CM6 sedan that runs well with good compression. It starts the morning at 40 Lbs or better of oil pressure and deteriorates as engine temp comes up. After a few miles, I'm down to 5 lbs on the gauge.   1. I swapped the gauge and confirmed the pressure drop. 2. I'm told the pressure is adjustable.  The owners manual says the adjustment is via a spring change.  3. Two "experts" have told me I need to drop the pan and change out the crankshaft bearings.        I have no maintenance manual ( only a detailed owners manual) and feel some questions need answering before I dive in.  This is the first year for this engine design. Did Chrysler use inserts this far back? Are the bearing clearances .001, .002 or what?  What are the torque specs for the bolts in the bearing caps?

 

Thanks in advance,

Rick Marsh

 

 

[Guest]

Torque wenches were not available until the mid thirties.  Many manuals said to tighten enough.  I am attaching two torque charts that will give you some guidance.  The standard bearing clearance unless otherwise stated is .001" per inch of diameter of the journal.

Some WPC fan will probably answer soon.

Good Luck

[Spinneyhill]

What oil are you running?

 

Is the oil pan clean inside?

 

There should be a dome shaped cover on the side of the engine, beside the oil filler tube. The oil pressure adjustment is in there. It may be stuck, gummed up. Follow the red arrow below:

Edited April 20, 2019 by Spinneyhill (see edit history)

[keiser31]

I know my 1931 Dodge Brothers coupe have babbit bearings and I am fairly certain the Chrysler CM6 does, too.

Edited April 20, 2019 by keiser31 (see edit history)

[Guest]

Even insert bearing surfaces are babbit, just thinner and easier to replace.

Edited April 20, 2019 by Guest (see edit history)

[keiser31]

19 minutes ago, Tinindian said:

Even insert bearing surfaces are babbit, just thinner and easier to replace.

The babbit on mine is part of the connecting rod, so they would definitely have to be completely re-configured or machined in order to use inserts.

Edited April 20, 2019 by keiser31 (see edit history)

[Rick Marsh]

Gentlemen,

 

Thanks for getting back to me.

 

I'm running straight 30 weight HD oil.    I have previously dropped the pan, cleaned out what was less than 1/2 cup of junk in the bottom of the pan and replaced the pan gasket.

 

I pulled the adjuster out of the side of the block at that time, it looked clean and I put it back in.

 

 

I've had this oil pressure issue since.  I'll start knocking on doors as to who can do a babbit job for me.

[Spinneyhill]

 

2 hours ago, Rick Marsh said:

I've had this oil pressure issue since.

 

So before you pulled the oil pressure relief valve, the pressure was OK?

 

What is "HD" oil? I am in a different market and it may not be something I see here.

Edited April 22, 2019 by Spinneyhill (see edit history)

[maok]

Has the oil filter been deleted? If so, how has the plumbing been re-routed?

[hwellens]

5 hours ago, Rick Marsh said:

Gentlemen,

 

Thanks for getting back to me.

 

I'm running straight 30 weight HD oil.    I have previously dropped the pan, cleaned out what was less than 1/2 cup of junk in the bottom of the pan and replaced the pan gasket.

 

I pulled the adjuster out of the side of the block at that time, it looked clean and I put it back in.

 

 

I've had this oil pressure issue since.  I'll start knocking on doors as to who can do a babbit job for me.

Your owners manual has some of the answers on bearing clearance and normal oil pressure. see below:

 

[Rick Marsh]

Thanks for the .002" clearance statement. Know I know what the clearance should be. It still leaves the question of inserts or babbits.

 

I'll answer the other comments with a little history. When I bought the car, it ran and was in need of some TLC. Oil pressure was about 35 to 40 LBs.  I went through the brakes and the cooling system first. I then focused on the engine and the oil was very black. Rather than just changing it, I dropped the pan, cleaned it out and replaced the old pan gasket. I also pulled the pressure valve out of the side, inspected it for debris buildup of which there was none and put it back in the side of the crankcase. I did not change the oil filter because there is not one on the engine. (I anticipate putting on an oil filter from a 1950 Chrysler at a later date).

I filled the crankcase with  straight 30 weight heavy duty detergent oil and started it back up.  I've had this oil pressure problem ever since. Obviously, cleaning things up uncovered something and it could well be the bearings or, perhaps, something simpler.

[ArticiferTom]

How did you reset the adjusting spring after you cleaned . Did you count number of turns on removal  ?

[Spinneyhill]

What Tom Said. Did you put it back in exactly the same place it was before you took it out?

 

The Instruction Book for both Dodge Brothers Eight and Six say the same thing, word for word. It is in a section headed "Oil Pressures" and is under a larger section called "ENGINE LUBRICATION". It is probably fairly similar in your Instruction Book.

 

"If it becomes necessary to adjust the oil pressure relief valve, the cap nut adjacent to the oil filler should be removed and the locking wire withdrawn. The slotted plug should be turned clockwise to increase the pressure or anticlockwise to decrease the pressure."

Edited April 23, 2019 by Spinneyhill (see edit history)

[Stude17]

Rick in your  original post you state, "The owners manual says the adjustment is via a spring change."  I take from this statement that there is no adjustment of the oil pressure other than changing the spring to a different one for various pressure settings ie there is no mechanism to screw in or out to adjust the pressure.  If it has been re-installed correctly and it is all clean this should not be an issue in my opinion.  I also note that in a later post you state, "I pulled the adjuster out of the side of the block at that time, it looked clean and I put it back in."  Could explain what you mean by "adjuster"

 

Before taking any drastic steps to replace the bearings perhaps you could consider  draining  the oil and refilling with 15W40 oil and see what effect this has on oil pressure.

 

 

 

[Alfa]

I agree with Stude17. Unless you can hear rumbling noises from the crankshaft main bearings, or knocking from a big-end bearing, I would not rush to strip the bottom-end. Try a 15W40 oil, or even a 20W50. It doesn`t cost much to try and those oils will maintain greater viscosity at 100 degrees centigrade than the SAE 30HD will.

 

I would expect oil pressure to reduce with temperature, but is your 5lb reading taken at speed or at idle? If at Idle, I would not be too worried.  

[edinmass]

Nothing has changed if you only cleaned the pan, and didn't change the regulator adjustment. Was the oil pressure perfect before you cleaned the pan? Low oil pressure just isn't bad lower end bearings, cam bearings and an open oil gallery or leaking oil line internally are other possibilities. Are the rods pressure fed or splash? While 5 lbs at idle is low, its not the end of the world.....rule of thumb is 5 psi for every 1000 rpm. Is it possible the regulator was installed up side down? Missing a shim that was dropped? If things were fine before, it shouldn't be too difficult to get thing back to square one. Also, if the engine is clean inside consider a 100 percent synthetic oil........with low pressure it will stop gauling and overheating on the bearing surface. Something just doesn't sound right about the whole problem here. Either an engine has good pressure, or it doesn't. If things have changed, you need to figure out the regulator.......or, adjust it so it will not dump pressure under any circumstance.......then you will really know what the condition of the system is. 

Edited April 24, 2019 by edinmass (see edit history)

[Rusty_OToole]

Babbit bearings can be adjusted by removing shims. They can also be scraped for better fit. It is not always necessary to replace them.

 

What oil does the manufacturer recommend? 30 seems pretty thick and was only used in very hot conditions. Something like a 15W40 might work better for you. Is the oil pressure 5 pounds at idle or at speed? 5 pounds hot idle could be perfectly ok.

[Spinneyhill]

5 hours ago, Rusty_OToole said:

30 seems pretty thick and was only used in very hot conditions. Something like a 15W40 might work better for you.

Um, more information please.

 

It is my understanding a 15W-40 would have a higher viscosity when hot (SAE 40 compared to SAE 30). The 15W would mean it behaves as a lower viscosity when cold (SAE 15 vs SAE 30)..

[C Carl]

Always factor in that in general these slow turning  low power old engines run cooler oil temperature than modern engines.   -   Carl 

[Rusty_OToole]

2 hours ago, Spinneyhill said:

Um, more information please.

 

It is my understanding a 15W-40 would have a higher viscosity when hot (SAE 40 compared to SAE 30). The 15W would mean it behaves as a lower viscosity when cold (SAE 15 vs SAE 30)..

That is the point. The multigrade should allow easier starting and circulate better when cold, but hold a higher pressure when hot.

[Rick Marsh]

Ok, I'm back in town and you all have given me much to think about.  One other observation I failed to share is that the engine starts right up when cold and the oil pressure reads high, often 60 Lbs. It slowly degrades as the engine warms up getting down to the 5 Lbs range and doesn't noticeably change when warm.

 

I think I should do the following in this order.

1. Take a closer look at the oil pressure adjustment on the side of the block.  One source tells me they are dependent on which of three available springs are installed. The other source suggests that it can be adjusted by turning (clockwise for more and counterclockwise for less)

2. If that doesn't work, then I should move on to dropping the pan and looking to a possible oil pump rebuild. I could also at that time drop a cap to see if I have inserts or babbits.

3. If I still have an oil pressure issue, I guess the bearings are next.

 

I'll precede all of this by draining and filling with a multiweight detergent oil and post any observed changes.  I'll probably use Pennzoil 10W30.

 

I'll be heading to Wilmington for the SE Divisional Tour this afternoon so it will be next Friday when I get back to the Chrysler.  My thanks to all of you for the feedback to date.

 

[Spinneyhill]

On 4/24/2019 at 12:55 AM, Rick Marsh said:

the oil was very black. Rather than just changing it, I dropped the pan, cleaned it out and replaced the old pan gasket.

 

So it had dirty oil and the pan wasn't very dirty. Was the dirty oil thick and sludgy?

 

It is hard to understand how it went from 35 to 40 psi pressure hot to 5 psi pressure hot at speed after just a clean out and oil change. 5 psi at idle is OK, even if it starts at 40 psi when cold. The oil viscosity is reducing as it warms. A multigrade should reduce that change.

[Rick Marsh]

OK, I'm back and the tour in Wilmington was a great outing. I went back out to the garage and the Chrysler decided to not start. After much aggravation there was some trash in the fuel line. Now that it starts and runs, I drained the oil and put in 4 1/2 quarts of 10W30. It runs about 60 Lbs when cold. I have not gotten it up to temperature yet and will do that in the next day or two.

The attached images are of the oil pressure valve. I'll want to see what my pressure is at normal engine temp before I pull any wire and start turning things.

[Spinneyhill]

1 hour ago, Rick Marsh said:

I'll want to see what my pressure is at normal engine temp before I pull any wire and start turning things.

Yes. Also, 60 when cold is a bit higher than I would expect, but lets see what you get after a 10 mile drive to warm it up properly. Is 4¹/₂ quarts all it takes?

Edited May 6, 2019 by Spinneyhill (see edit history)

[Mikefit]

Let'sthink out of the box if the oil pump is capable of 60 # cold I would rule out the pump. The pressure regulator only limits the maximum oil pressure similar to a pop off valve .   I would lean towards oil breaking down when warm .  What is the curb idle speed when warm. You should have about 8-10# pressure per each 1000 RPM.  So idle at 800 RPM= 8# road speed of 35MPH just a guess of 3000RPM would = 24 #  .   This just a common rule of thumb.  Mike

 

 

 

 

[Rich in Fla.]

I vote for 20W-50 oil.  Will hold it's viscosity better when hot.