engine and drivetrain New Engine Rebuild Oil Pressure Problems

[FB73tii]

A novel and innovative solution! Would not have thought to do a manually controlled pressure relief valve. very creative. Glad you figured something out so you can work on other aspects of the car and enjoy it. So I take it that you never tried a different oil pump? Thanks for posting your solution.

 

Best, Fred

[sl0ride]

Why not use a regulator instead of the valve? I wish we had these problems, with our car it was low pressure. 90 at startup then 10-18 at operating speed and temp. We swapped the pump with high hopes.

Edited February 28, 2014 by sl0ride

[Preyupy]

I'm sorry I have not seen this thread before. If you have made sure the pressure relief valve is assembled correctly it sounds to me like you may have an obstruction in the pressure relief tube that runs down the front of the engine and plugs into the pump. I once saw someone that thought there needed to be a gasket between the block and the pipe and that just closed it off completly. There may be something stuck in the pipe.

Just to make sure it is assembled correctly: the pressure relief valve is installed from the bottom of the pump with the closed end of the plunger pointing up, then the spring , the long tube is installed with the short end up with the spring sitting on the shoulder, then the washer, this is all held in place with a snap ring from the bottom. Completly assembled there should be no load on the spring and you should be able to wiggle the tube. I worry about taking very much material off the piston or the bore, if it gets loose enough the piston can cock in the bore and stick.

The system is very simple, I have never had a problem with a correctly assembled pump. If you know FOR SURE it is correct it just about has to be the bypass tube. With the pump off the engine you should be able to blow air backwards through that tube with very little resistance ( the air will go backwards through the filter and come out the pump feed hole in the block and also every bearing and cam spray bar hole, be careful you will spray oil everywhere). You can also blow air into the feed hole in the block and see if you get air out of the bypass tube with the pump off.

[kbmb02]

Long shot: While assembling an M10 block yesterday, I noted the ID of the oil galley where the tube/pipe attaches is threaded (I wondered, "Why?" and then moved on).

 

If some imaginative-yet-unknowing individual decided to install a plug in that end of the galley, the pressure relief system would not function (it would act as blocked, just like preyupy described above). -KB

[Preyupy]

I was thinking the same thing KB, if it is an early block that used the early gear type oil pump it would not have the bypass tube and would have had a plug in the end of the oil galley in the block.  If someone put a plug in it then put the bypass tube over it you would have this exact problem. 

[felix_666]

I'm sorry I have not seen this thread before. If you have made sure the pressure relief valve is assembled correctly it sounds to me like you may have an obstruction in the pressure relief tube that runs down the front of the engine and plugs into the pump. I once saw someone that thought there needed to be a gasket between the block and the pipe and that just closed it off completly. There may be something stuck in the pipe.

Just to make sure it is assembled correctly: the pressure relief valve is installed from the bottom of the pump with the closed end of the plunger pointing up, then the spring , the long tube is installed with the short end up with the spring sitting on the shoulder, then the washer, this is all held in place with a snap ring from the bottom. Completly assembled there should be no load on the spring and you should be able to wiggle the tube. I worry about taking very much material off the piston or the bore, if it gets loose enough the piston can cock in the bore and stick.

The system is very simple, I have never had a problem with a correctly assembled pump. If you know FOR SURE it is correct it just about has to be the bypass tube. With the pump off the engine you should be able to blow air backwards through that tube with very little resistance ( the air will go backwards through the filter and come out the pump feed hole in the block and also every bearing and cam spray bar hole, be careful you will spray oil everywhere). You can also blow air into the feed hole in the block and see if you get air out of the bypass tube with the pump off.

 

 

Long shot: While assembling an M10 block yesterday, I noted the ID of the oil galley where the tube/pipe attaches is threaded (I wondered, "Why?" and then moved on).

 

If some imaginative-yet-unknowing individual decided to install a plug in that end of the galley, the pressure relief system would not function (it would act as blocked, just like preyupy described above). -KB

 

 

I was thinking the same thing KB, if it is an early block that used the early gear type oil pump it would not have the bypass tube and would have had a plug in the end of the oil galley in the block.  If someone put a plug in it then put the bypass tube over it you would have this exact problem. 

 

I'm open to any ideas, but please read through the whole thread before posting, thanks.

 

The block and head are from a late 74' model.

 

1. I rebuilt the engine from scratch.

 

2. I've had the pan off twice, pulled the pump twice, and checked the pressure pipe as i thought that perhaps an o-ring might have gotten stuck after reaching such high pressures. The first time I was checking the orientation of the relief valve, it was correct, I even wet sanded the piston and bore - see earlier in the thread as I took photos. The second time I pulled the pump and inspected the pressure hose pipe.

 

3. Most importantly - pressure is around 30psi once warmed up. How could the system manage this if something were blocked?

 

I understand a liquids' viscosity changes with temperature, but if an orifice is blocked... its blocked?!?

 

My theory is that the block was assembled (by my builder) a little tight (although it turned over by hand no worries), the pump is a new febi unit (which are known to stick - pressure relief valve that is), and it simply needs a little time to bed in.

 

I've come to this conclusion after pulling the pan off twice and speaking to a plethora of people. If the needle valve didn't work then I would have pulled the pan again.

[felix_666]

A novel and innovative solution! Would not have thought to do a manually controlled pressure relief valve. very creative. Glad you figured something out so you can work on other aspects of the car and enjoy it. So I take it that you never tried a different oil pump? Thanks for posting your solution.

 

Best, Fred

 

 

Never tried another pump. I know a fella with a new OEM and he wanted US$550, so it seemed too expensive for an experiment. I could find one if need be, but thought I'd try the valve first. If I'm still having problems later I'll pull the pan again and try another pump.

Cheers.

[Preyupy]

I'm sorry but I missed the fact you know it is a 74 block. 

 

As for the drop in pressure when it warms up:  Once the engine warms up clearances change, the oil gets thinner this is normal.  The pressure relief valve is just that, a relief valve!  It is set (normally) to open at around 60 psi below that it is closed and the pressure change you see is just from the change in pump output volume/time.  The amount of oil that flows through the engine does not change significantly with engine speed (a certain amount of centrifugal pumping goes on from the crankshaft and if you are running a center oiled camshaft)  the volume of oil moved by the pump is controlled by the engine speed because it is driven by the crank  (double the crankshaft speed=double the pump speed and output volume)

 

Oil pressure is strictly the resistance to flow,  the pump does not really care what the oil temperature is it is a positive displacement pump and for every revolution it tries to move a known amount of oil, if that is more than can easily flow through the various clearances in the engine then you will have pressure.   The pressure relief valve is designed to control the pressure at a safe limit.  The problem with most pressure relief systems is they have small passageways also and even fully open with cold oil you very likely will have enough restriction to make more than the 60 psi the valve is set for.  As the engine warms up and the oil gets thinner the PRV can handle the excess volume the pump is delivering and when the engine slows down enough so the pump is not putting out more volume than is needed to hold that 60 psi the pressure will drop (most of these engines idle at 15psi with hot oil) 

 

IF your machinist cut every clearance in half at every bearing surface and your pressure relief system was working correctly you should not see more than 120psi @ 2000 rpm on a cold start up.  You have a restriction somewhere between the front of the engine oil galley and the outlet of the pressure relief valve.  It is possible that the oil pump housing is not machined correctly on the outlet side of the PRV (I've never seen it but that is one possibility) 

[felix_666]

The correct oil pressure at idle, 4000 rpm or whatever else is highly contested if you look back over old threads, so I'm not sure what to think. I know the blue manual says 11-17 psi at idle and 57 psi at 4000 rpm, for a stock engine.

 

Until I get a more accurate gauge I can't say for sure (I only have a 0-500psi gauge at the minute).

 

This is how the engine looked beforehand. I installed a new style Febi pump on rebuild.

 

 

I'm trying to find a pic of the rebuilt engine...

 

The below picture is an oil filter housing for cartridge type filters, not screw on, right? Can't see any threads on the spindle.

 

[AlanM]

I had the same thing happen with an M10 I built with and M3 head.    I had replaced the oil pump and had massive oil pressure over 150 psi with 10/40 oil, I took out the pump checking the relief valve, and the route for relief oil.  I have and M3 oil filter housing with no thermostat fitted, only a blanking piece in place so the oil flows through the cooler at all times.  I refitted the pump, same problem, fitted another new pump, still same problem.

 

 I did a similar thing as above, by fitting a Peterson relief valve in the line to the oil cooler, and welded a fitting to the side of the sump for the relief oil to go. This of course fixed the oil pressure problem, but should not have been necessary.

 

I did wonder whether the pump got some sort of twist or strain on it because I had removed the brace that supported it at the main bearing to accomodate  the windage tray and baffle, and this caused the relief valve to jam.  I still do not know.

[classicman]

I had a similar problem after my engine rebuild. Fitted a new pump at the time. Turns out the new pump had a massive spacer in behind the pressure relief valve. Took the spacer out and problem solved. Might be that replacement pumps may be for later E30/46 cars that may need a higher oil pressure?

[Preyupy]

The pressure relief valve in the oil filter housing ( yes that is a cartridge style housing) is only for differential pressure across the filter. If the filter gets plugged for some reason that valve opens and allows oil to bypass the filter so you don't 1)blow the housing up 2)starve the engine of oil pressure it does not control oil pressure to the engine.

[felix_666]

 

I did wonder whether the pump got some sort of twist or strain on it because I had removed the brace that supported it at the main bearing to accomodate  the windage tray and baffle, and this caused the relief valve to jam.  I still do not know.

 

Hey Alan, just wondering how you knew that the relief got jammed?

[felix_666]

Slightly old post now, but thought I should follow it up for anyone in the future having similar problems.

 

The car went on it's maiden voyage this week and aside from running like crap (carbs) the oil pressure seemed good. Maybe around 140psi on cold - 10 degrees ambient temp (50 fahren). Once the engine was warm after going for a drive the idle oil pressure was about 25 psi.

 

The engine has 15km, but my odometer seems to be stuffed, next project.

 

The manual valve will stay put for the next while.

 

Thanks for all those who chimed in on the thread.

 

 

Edited August 16, 2014 by felix_666

[AlanM]

Hey Alan, just wondering how you knew that the relief got jammed?

The car is basically a road registered race car and has a 700 KPa VDO oil pressure gauge, which I didn't believe as it was hitting the end.  I then fitted a 1000Kpa gauge (150PSi) which also hit the end at revs, particularly when the 10W40 oil was cold.  I then tested the gauges against a master gauge at work, and were found to be within 40kpa of being correct at the top end.  I ended up "fixing" the problem by fitting an external adjustable pressure regulator in the oil cooler line and ran a relief line back to the sump.  So I fixed the resultant high oil pressure, but still don't know why this engine did this.