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)

[Cap'n Krusty]

How is a larger oil pump, which will definitely increase flow, going to increase oil pressure. I agree with the previous post. I may be wrong but, IMO, low oil pressure is a result of insufficient restriction somewhere in the system. That means something out of tolerance, like an OP relief valve, bearing clearance too great, or damage to an oil passage resulting in a leak.

The Cap'n

[worn]

How is a larger oil pump, which will definitely increase flow, going to increase oil pressure. I agree with the previous post. I may be wrong but, IMO, low oil pressure is a result of insufficient restriction somewhere in the system. That means something out of tolerance, like an OP relief valve, bearing clearance too great, or damage to an oil passage resulting in a leak.

The Cap'n

I found a wonderful post on the Samba in which they tested 100 newly rebuilt VW engines at different temperatures, monitoring oil pressure and flow using both a 26 and 30 mm pump. It is worth reading for most of us:

http://www.thesamba.com/vw/forum/viewtopic.php?t=280293

For me, several parts were of interest. For one thing it shows what happens when you change pump size. So they answer the Capn's question. I am regretting the Melling already, but it was enough work to get in that I am giving it a try. Car is almost buttoned up. Maybe I will end up with lower viscosity oil in the end.

The second part was in a warm engine, they uniformly found low oil pressure at idle - about 10 psi. 100 engines, very low variance.

For me the most interesting part was the design of the pressure relief valve. These were two valve engines, although not type 4. The VW engineers were very careful about how these should be made, and a very clever bevel modulates opening pressure to make it higher than closing pressure. I can say for certain - mine ain't shaped like it is supposed to be! It is either completely worn out, or more likely, never made right to begin with.

I understand there were design changes between the motors described in the article and the ones we run, but read the post, it is completely worth it. (IMG:style_emoticons/default/pray.gif)