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)

[r_towle]

Please post some pics of what you are doing.

[worn]

Please post some pics of what you are doing.

OK, I am making some progress. If the bearings are loose, this will be a bit of an extra, but that hasn't been tested yet.

It is hard to show, but here is what I found:

The first image shows a comparison between the Prussian blue rub off in my old worn out 2.0 and the new 2056. The pistons are identical.


You can see a clear seat in the old, but you can hardly see contact with the new. In fact, there is a small rim around the chamfer where dye has transferred.

OK, getting a photo of the cylinder was tough. Here is my best and it shows the problem:


The green arrow shows the offending ridge running all round the circumference of the cylinder. A slightly smaller final bore perhaps? At any rate, that is what stops the piston a couple of mm short of the seat. the line between the pressure bevel and what is supposed to be the seat is shown with the other arrow.

What I did was to get a piece of scrap iron. It should have been steel - I made a bad choice based on what was lying around and made a cutter at 15.9 mm. It is shown below with a before and after prussian blue test. I used grease to catch the swarf, which in my case was a very fine powder - like anti seize. At first I thought this would go quick, but it took quite a lot of turning the tool because basically the tool I made is not at all aggressive - it dulls fast and there was purposely no relief cut for the cutters.



I have to rinse well, clean like the dickens and get it back off the stands to find out how things go. Since I changed two variables at once with the new pump, I will never know. What I can say is any oil that gets by the piston is back to the sump. The bores tend to wear and there is nothing to stop it but viscosity at the valve. So if as I suspect the valve wasn't sealing, I would expect what I found. Low pressure with hot oil.

[nathansnathan]

aircooled.net used to rent out a 5/8" end mill to dress the seat as you have done there. Pretty bold, making your own cutter!

It's weird the poor attention to detail the factory had for this mechanism. I have seen pics where there is a stamped VW logo on the face of the piston, right on the edge interfering with the seal.

-Seems like cleaning the bore up though, might let oil get by when it is off idle. I've been tempted to use a reamer to oversize the bore, but would want to turn a new piston. Shoptalkforums awhile back, we came to the conclusion the best thing to turn a new piston out of would be "Torlon" which is a high temp lubricating plastic, like high temp teflon. Pricey, but it would never wear a ridge in that bore again.

[worn]

aircooled.net used to rent out a 5/8" end mill to dress the seat as you have done there. Pretty bold, making your own cutter!

It's weird the poor attention to detail the factory had for this mechanism. I have seen pics where there is a stamped VW logo on the face of the piston, right on the edge interfering with the seal.

-Seems like cleaning the bore up though, might let oil get by when it is off idle. I've been tempted to use a reamer to oversize the bore, but would want to turn a new piston. Shoptalkforums awhile back, we came to the conclusion the best thing to turn a new piston out of would be "Torlon" which is a high temp lubricating plastic, like high temp teflon. Pricey, but it would never wear a ridge in that bore again.

That's funny - both of the pistons shown have a small VW stamped on the mating face, but very small. Also they used a bench grinder to dress away the piston cutoff nub from the lathe. The system is brilliant, but vulnerable to wear and I think in my case poor construction. You may get something you like, but you won't get the sophistication with a ball valve. Might solve the headache though, I dunno. Can't wait to get it back on the ground. The turbo tie rods will have to wait.