Vacuum Pump & Oil Pressure Problem

[chetbrz]

It appears that my car doesn't want to pump up oil pressure after sitting for a period.  I have to rev the engine to have the oil pressure pump up to normal.  Never had this issue with the vacuum fuel pump line plugged.  At start up, the car will not pump up to pressure at a slow idle.   I can't find any leaks.  I am using two oil gauges but they are in a closed system I don't believe that they would cause this.  After 90 years maybe my oil pump is a little on the weak side.  To be on the safe side I might have to revert back to the electric fuel pump.  Maybe try the Steward pump.  Don't know.

Any suggestions,  Chet...

[Russ T. Fender]

What is the oil pressure before it gets up to normal?  As long as you have some pressure I am not sure it is something to worry about. On my very tired engine oil pressure dropped to 5 at an idle after warm up and made it back to 30 at running speed.  Never seemed to bother it; ran like that for many years before I took it off the road for a restoration.  I wonder if your situation is just the nature of the beast.  What weight oil are you using?  I always ran straight SAE 30.  if you are using multi-viscosity oil could that possibly account for the difference at start up? 

[chetbrz]

I am using 1 Gal of 30 weight single grade Rotella with 16 oz. of Lucas TB Zinc-Plus.  Actually just changed the oil yesterday.

At startup, Zero psi after revving the engine it rises to 40 psi.  After warm up, 30 low rpm and 40 average to high rpm.  If I just let it run at slow idle it probably would never pump up to run pressure.  Don't know for sure didn't want to test that theory.  $$

I believe that the oil in the intake tube going to the oil pump is draining back into the pan.  I believe that if the Vacuum fuel line was plugged this doesn't happen.  When it was plugged it would instantly come up to run pressure even at very slow idle.

I am very leery of burning out another bearing.  I am not sure if having to rev the engine may do damage to the engine over time ??

This is the first time I used the Rotella do you think it is to heavy.  It says Heavy Duty SAE 30

Plymouth book calls for 35 - 40 psi at driving speeds

Maybe I am getting a little punch drunk with this motor.  I let it cool down and fired it up.  Oil pressure came up with my first rev.  I guess that maybe I might be getting to critical ??

[racertb]

Chet, for what it's worth, my Plymouth has been running QS 10w-30 since the motor was rebuilt in the mid-80's.

Ted

[Crazydave]

For what its worth mine does the same thing (low or no pressure on cold start) but I consider it wore out. Can't vouch for how accurate the pressure gauge is either. When I plug the vacuum tank fitting my oil pressure spikes and the motor actually sounds worse (like I'm starving the lifters or something) Pressure vs. volume?

I don't what is normal.

[chetbrz]

Ted, Thanks for the info.  The Plymouth book says for winter temperatures below freezing and above Zero to use SAE 20.  For temperatures below Zero to use SAE 10.  For Summer SAE 30 and for high speed conditions SAE 40.  I was told by the Builder to use SAE 30 and add Zink to every oil change.  Maybe 20w 40 for Florida.  Since below Zero is not happening and high speed or high temperatures is more likely.

I think the issue is viscosity especially with the vacuum fuel pump.  With the vacuum pump connected the oil pump is sucking both air and oil.  If the oil is to heavy it is hard for the pump to get the initial flow up the intake tube.  Once this is done it is easy for the pump to maintain pressure. 

Any changes to the vacuum side of the oil pump will affect the engine oil pressure.  If you plug an open vacuum line it will drive your pressure up.  It could drive it up very high depending how the relief valve is set.  If you open a plugged vacuum line it will drive your pressure down or eliminate it entirely.  Of course this will depend on the vacuum opening which should not be bigger than 1/8 copper tubing. 

Dave, In your case plugging the vacuum line to the pump might be driving your pressure way to high.  This isn't good for the bearings because it will eventually wash out some of the softer Babbitt metal.   

FYI.., you can add a modern oil pressure gauge to any of the three Oil ports on the drivers side of the engine.  I used the center port since the front port was blocked by the radiator hose and the rear port is blocked by the starter motor.  I added a column gauge holder and installed the modern oil gauge on the steering column.  Looks and functions great with no holes drilled or Plymouth parts damaged.



In my case I think this Rotella oil which I put in yesterday might be a little heavier than the Castrol HD30 I was using.., and which the builder recommended.  It was colder this morning and maybe that's why I had issues with the initial start up.  It seems to be working OK now but something I will keep a close eye on.   Based on previous issues I am extremely gun shy when it comes to engine lubrication.  I have a little over 10 runtime hours on the engine and can't wait to get it on the road.

Chet...

[rwollman]

Chet - following these posts with interest and I have some thoughts to share... I would be looking at oil pump first.  This pump is centrifugal pump with 4 movable vanes.  As pump shaft rotates vanes move outward to form seal creating pressure.  Vacuum is created secondary to pressure due to vanes moving past vacuum port.  If vanes cannot move freely or body or vane ends are scored then more rpm would be required to create adequate seal to work. 
Changing relief valve setting should not effect amount of vacuum signal as you are not changing the volume of oil going thru the pump but rather the amount of pressure bypassing the relief valve spring. If pump internals look ok then I would check vacuum signal at the pump then at the vacuum tank.  If u have even a small leak this could cause your problem.  The 28 I work runs about 5 seconds on  initial startup at idle before oil pressure starts building. As far as oil draining back down pickup tube don't think this would bother as pump body and cam lines will hold enough oil to start working.  Good luck       

[chetbrz]

Chet - following these posts with interest and I have some thoughts to share... I would be looking at oil pump first.  This pump is centrifugal pump with 4 movable vanes. 

This is very interesting.  I haven't taken the top cover off this pump for a number of years but I don't recall any moving parts other than a single eccentric solid metal center.  I could be wrong and if so this would explain a lot.  I would be interested in seeing any pictures you might have. 

I agree with what you said about the relief valve.  Changing this setting has no effect on vacuum if I said this I definitely miss-spoke.  Although opening the vacuum port will have an affect on oil pressure.  At least this is what I have observed by doing and some others have reported in the past.  But I am open to new theories.   I find I am constantly learning new things about this car.

As for right now, I think it is working OK.  I will keep a good eye on the oil pressure at startup.  It pumps right up with a rev.  When starting the engine with the timing retarded, the engine runs very, very slow, maybe too slow to get the pressure up.  If what you are saying about the pump is correct this would explain everything.   My only issue is startup.  Once up to run pressure no issues not even at very low rpm.

I think you have put my mind at ease, Thanks,  Chet...

[racertb]

Hey Chet, just a comment and side note to this conversation. I usually leave my spark advance all the way in when starting, and I believe the instruction book says to do so as well if I recall. I do realize that retarding the spark during startup should make it easier to start. Just have never done it that way.  Upgrading to the 00 cables a while back fixed my starting issues.

Ted

[chetbrz]

Hay Ted, Thanks for the comment.

When setup properly retarding the timing makes it very easy to start the engine.  I generally just pull the knob slightly out and only after the engine has been sitting for a long period.  If set properly.., with the spark advance all the way in the cylinder is firing just before TDC (top dead center).  This increases your power.  Also with the spark advance all the way in, if you were hand cranking the car you risk kick back and serious injury.  When pulled out, the spark will fire after TDC.  This decreases your chances for kickback and serious injury.  It also makes starting the engine extremely easy and is less of a strain on the starter motor.  Downside is low power. 

Like you for many years I kept the distributor set in one position that worked well for both Run & Start.  If setup properly being able to retard the timing for start and push in for run works extremely well.  It gives you the best power setting for driving.  A setting that basically might make it hard to start the engine.

My 2 cents

[Russ T. Fender]

As the owner of several stem winders I would never try to start with timing set before TDC.  The chances of a kick back and the attending consequences are just too great.  If you have a starter,  instead of breaking your arm or wrist,  you can damage the starter Bendix or the starter itself.  In my estimation, the best way to start is with the timing retarded and then immediately advance the timing.
Chet, as an aside, I think you mentioned that you are running 4 quarts of oil.  My 30-U calls for 6 quarts.

[chetbrz]

Many thanks, The 29 is 4 quarts and the 30u is 6 quarts.  That would make a difference. For sure.

Do you have an oil filter?

[Russ T. Fender]

No oil filter.  I believe the PA or PB were the first ones with an oil filter.  I just change the oil every 500 miles or once a year whichever occurs first.

[rwollman]

Chet- that is correct on the solid eccentric.  In this eccentric are the 4 vanes that slide out under centrifugal force when turning.  They must be able to move freely and create a good seal - hence the check for scoring.  Another place for scoring is the cover plate.  I have some knowledge in this area as I work on hydraulics and this is the same theory.  Should be a paper thin gasket under the plate.  Don't know where you can get replacement so be careful...good luck

[chetbrz]

Should be a paper thin gasket under the plate.  Don't know where you can get replacement so be careful...good luck

Great info. Everything makes sense now.  I think the pump is working properly. Like I said I'll keep a good eye on pressure at start up.   Just a little gun shy with this rebuild.

BTW... The oil pump gasket comes in the complete engine gasket kit for the 29U 175.4 engine. I'm not sure about the Maxwell engine in the 28Q

Thanks again. Chet