Relief, Oiling system in a type 4 Options

[worn]

If anyone has read my previous threads my two week vacation turned from driving to lying on the creeper under the new engine and transmission. Low oil pressure after warm up. I ordered a new Melling 30 mm pump and we shall see, but at the same time I looked into the pressure relief system - especially where it shunts oil away from the cooler because it is easier to see in the car.

What I found surprised me. First, looking at two different cases (72 1.7 and 76 2.0) I found that the piston seats on a shoulder in the bore that is at most a mm wide, and is not at all uniform in width across the piston face. OK, maybe it isn't supposed to seal.

Second I found that by the time you have opened the valve to shunt past the cooler, you are also dumping into the sump. That is there is a small overlap between the outlet to the oil gallery and the grooves cut in the bore leading to the sump exit.

Finally, the piston is simply loose in the bore. I can understand a fear of seizing, but there is no way that with my system oil isn't streaming into the sump, and it will stream faster as it thins - much faster.

I also spent a long time cruising the Samba - they ought to know whats up. What I found is a recurrent theme of new engines built in a variety of ways making low oil pressure. Many people were happy with what I ended up with - 10 psi at idle. On a new engine.

It is steel against untreated aluminum, so wear would be expected, but mine do not look worn - just poorly made. Maybe they are worn and I cannot tell. I got a face full of oil on one attempt at examination, so I may have missed things.

It seems an ideal situation for machining or sleeving during the rebuild, and I actually found a manufacturer of a sleeving kit with a ball bearing valve.

Thoughts ladies and gentlemen? (IMG:style_emoticons/default/idea.gif)

[reharvey]

I've been following your posts about the oil pressure problem because I went through this very same thing many years ago after a rebuild. I tried to find a solution in the way you have but the bottom line was to much bearing clearance. As soon as the oil heated up the pressure dropped off. Hate to be the bearer of bad news but my only solution was to take the motor back apart. You'll find that if you use 20w50 oil along with a can of STP it'll keep the pressure up and you may be able to just drive it for a while. I did for over a year with no problems. Good luck.

[worn]

I've been following your posts about the oil pressure problem because I went through this very same thing many years ago after a rebuild. I tried to find a solution in the way you have but the bottom line was to much bearing clearance. As soon as the oil heated up the pressure dropped off. Hate to be the bearer of bad news but my only solution was to take the motor back apart. You'll find that if you use 20w50 oil along with a can of STP it'll keep the pressure up and you may be able to just drive it for a while. I did for over a year with no problems. Good luck.

I am not ruling out the bearings. They are new, I measured the case lots of different ways - Pawn shops have micrometers that even include calibration standards.

As the Capn says there is oil leaking out somewhere. And while it might be the bearings, it might also be something else. My initial idea was that the pressure relief couldn't possibly be the problem, but I am looking at a valve that has tons of clearances all over - at the non-existent seat, and with at least ten fold more side clearance than any of my bearings. I was shocked at how the thing was made after I looked at it closely. I figured that the idea of the relief system letting out pressure was simply wishful thinking (cannot say I'm not wishful) - but now I am really not so sure.

In answer to the capn. Given some leak of pressure, a larger pump will bring a higher equilibrium pressure for a given size escape hole. So the oil pressure should go up in a system that is below the rated delivery pressure of the pump. If the bearings are loose, this is probably just making the gauge feel better because the oil film depends on close tolerances.

If someone has a shot case, I would love to cut it apart to have a better look at the relief and other parts of the oiling system.

Capn - have you ever seen a case with an inadequate relief bore?