In my last article, I discussed how my newly rebuilt engine strangely lost oil pressure. The story continues here …
So after many minutes of idling I decided the loss of oil pressure was for real. I will note in all this time, I heard no strange noises. No lifter clatter, no knocking, no ticking. Just no pressure.
Swapping in a different pressure sending unit did not help. I took off the oil filter. It was dry. Once upon a time, I had a car with a new oil filter with a blockage so I put on another filter. No pressure. Next I started the car briefly with the oil filter removed. No oil. I reviewed Rennlist forums extensively for ideas. One idea was priming the oil pump by pouring oil down the filter bracket. I did this multiple times, including spinning the engine by hand both forwards and backwards. No improvement. Some threads pointed toward the pressure relief valve as being a potential culprit. I took the small screwed cover off the valve and withdrew the spring and the valve plunger. Everything seemed to be in order. Although it is very hard to get to with the engine installed, I took off the oil/water heat exchanger. I cranked the engine a little more. No oil came gushing out.
Becoming desperate and very confused, I dropped the oil pan looking for issues like an oil pick-up tube that had come loose. Everything looked shipshape. I checked the torque on the crankshaft bolt. No issues there. I took the crankshaft bolt out and inspected the spacers that drive the oil pump. Everything looked good. Eventually I took off the oil pump. I set up a rig with a drill motor to bench test the pump. It would suck and exhaust a stream of oil when spun by the drill motor.
At some point, I decided to use a Mighty Vac to draw a vacuum on the intake port to the oil pump, with the pickup tube screen setting in a pan of oil. The first sign of a tangible problem was that I could not get oil to draw up into the tube. I didn’t know what kind of vacuum it took to prime the pump but a Mighty Vac will generate a pretty good suction. I had made a temporary blanking plate to go over the oil pump inlet area on the block, with a fitting for a vacuum line. I inspected everything carefully but could see no fault.
Up to this point all the work had been done with the car on a lift but with the engine in the car. Due to all of the time spent with the engine at idle and no oil flow, I was pretty sure that the various bearings were now suspect. I decided to pull the engine.
Once I had the engine out I put it on my engine stand. I decided to remove the crank. Of course the first step is to remove the crank girdle. Finally, I found the proverbial smoking gun. Remember that JB Weld job I did in the area where the balance shaft bearing had blown out? (Link to JB Weld article) I couldn’t believe my eyes but there were obvious signs of a leak path from the oil pump supply gallery back into the sump. In effect, the pump was sucking air through this leak path rather than pulling oil through the pickup tube. Even more exasperating was that the leak path was not through the JB Weld repair area but rather on the opposite side of the gallery, where my file had roughened up the contact surface of the block to the girdle. It’s hard to see but here are some photos I took.
Some of you will surely wonder if I prepped and sealed this surface correctly. I also wonder about this point. I followed the directions of the shop manual and used the required Locktite sealant. It is hard to believe that this sealant was so sensitive to the file marks. It does make some sort of sense that the failure could occur after several hours of running the engine. But what a strange failure mode!
I was anxious to get on with life so I checked around and decided to buy a used engine from DC Auto, which is fortunately about 1 1/2 hours drive from my house. They fixed me up with a used engine out of a 1984 944.
The used engine had leaks at the various timing and balance belt seals so I did a R&R on the belts and seals. I also decided to put in a new set of rod bearings. I put on my cleaned up oil pan with the sump baffle and my cleaned up cam tower. So in effect, I installed a “short block” and put on all of my existing ancillary parts. Being my 2nd engine effort in a few months, this effort went much faster due to my new found experience. Once again, I struggled with getting the engine to mate with the torque tube shaft but finally everything was together and in good shape.
I had great trepidation as I fired this new engine up for the first time but there were no issues this time. Except for noisy lifters, which I now understood to be normal. The noise subsided in a short while.
So I was back on the road again, so to speak. Not a very happy experience but an educational one. I was thankful that the oil pressure problem occurred at home and not at some expensive track weekend. I looked forward to getting the 944 on the track.