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)

[Jake Raby]

All these rules and myths change when bearing clearances are altered. I prefer to move a higher volume of oil through the engine and to do that requires a higher volume oil pump and altered internal clearances.

There are no rules, if there were I wouldn't enjoy it so damn much.

[worn]

All these rules and myths change when bearing clearances are altered. I prefer to move a higher volume of oil through the engine and to do that requires a higher volume oil pump and altered internal clearances.

There are no rules, if there were I wouldn't enjoy it so damn much.

Replying to Jake and Yeah.
I was worried that 10-15 psi at hot idle was too low for a new engine. That is what started it. I will find out tomorrow and if it worked will start tuning my mps - the horror.

What I think is interesting is we have numbers for bearing clearances, suggested tolerances for oil pump lapping and lash, but nada, zipperino, nothing when it comes to the system that is designed to actually control oil pressure. I had to hunt for diameters and spring constants and never found them.

So, I will post cylinder head and oil temps, rpms and hopefully oil pressure. And God willing I won't pop the cooler instead. This ruined my vacation and added stress when really, I wanted seat time with the world flying by my narp. (IMG:style_emoticons/default/driving.gif)

[nathansnathan]

What I think is interesting is we have numbers for bearing clearances, suggested tolerances for oil pump lapping and lash, but nada, zipperino, nothing when it comes to the system that is designed to actually control oil pressure. I had to hunt for diameters and spring constants and never found them.

The specs are as follows, from the Porsche 914 Technical Specs book
Spring for oil pressure relief valve length loaded: 39mm, on installation new 6.8-8.8 kg (15-19 3/8 lbs lbs)
Oil pressure switch opens at 6.6-8.8kg (2.1 -6 psi)

I don't see bore sizes anywhere, possibly 16mm bore?