Mystery oil leak in back of 40 hp motor

[pdb27]

After restoring a 65 Beetle, one mechanical gremlin I have been unable to fix is a mystery oil leak in the back of the engine. I'm bound and determined to get this car up to daily driver status, which includes a periodic interstate commute of 50-60 miles one way. The picture below was taken this morning after the drive down, traveling between 60-65 mph the whole way.

Engine runs great, but popping the decklid on arrival reveals a bay that is baptized in fresh oil. Shouldn't it stay dry after a 1-hour cruise at highway speeds? Or do these old bugs simply leak after traveling that fast for that long?

So far I have replaced the generator stand metal plate (twice), added paper gaskets around the metal plate (twice), and changed the fuel pump gaskets (once). The metal deflector plate was installed as recommended in a bunch of samba posts, with the curvy part of the half-moon openings facing driver side, flat part facing passenger side, and indentations facing down. I used a liberal amount of engine gasket maker on all paper gaskets the last time, in case there was a non-uniformity on the metal sealing surfaces (you can see this in the photo). A couple weeks ago I changed the oil pressure control valve. I took off the fan shroud to look at the oil cooler, which was dry as a bone.

It looks like the oil is coming from somewhere on the right side of the engine (passenger side), but it's hard to tell after oil has been slung all around. Any ideas on how to trouble-shoot or fix this leak? (Or whether it can be fixed?)

[matthew henricks]

Possibly is it coming out the pulley? That would fling oil for sure. I had a 40HP that did the same thing. Had to install a sand seal to solve it. The gap between the pulley and case was too worn and oil would seep out.
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[pdb27]

[74 Thing]

It looks like it is coming from behind the pulley.

Make sure your breathers are open and your oil level is not overfilled.

Try a different pulley with good grooves. If that does not work then look into a bolt in sand seal pulley.

[kreemoweet]

How's your crankcase venting? A kinked breather hose can cause case pressure that pushes oil up and out
the dipstick tube, and past the crank pulley. Aftermarket pulleys can be undersize, and have ineffective
oil return threads. which will cause oil leak past pulley. Make sure you have the oil slinger in place between
pulley and crank.
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[pdb27]

OK, new direction. Pulley is my next focus. I just put on that aluminum one with the timing marks, but the leak was also present with the old stock black one. Oil slinger between pulley and crank ... I'll have to check. No idea what's in there. I bought the engine rebuilt, but it wouldn't amaze me if there was something missing; it has had consistent problems from day 1.

Crankcase level is OK. I just put in an 83 mm kit so the level is constantly checked between oil changes. (BTW, the oil leak was also present with the old stock pistons, so it's not related to blow-by. A leak behind the crankcase pulley is a possibility I haven't looked at.)

Here's a photo of the breather setup I'm currently using; it's new and (I believe) should be breathing freely. Are there other vents I should check to ensure they're clear?

Thanks for the feedback so far; thesamba.com forums can't be beat.

[Zwitterkafer]

If it is the pulley, there should be a "racing stripe" of oil under the back of the decklid. Swapping in a stock pulley with clean return grooves would be a good experiment. Another possibility is that excess case sealant has restricted or blocked the small oil return passage fed by the pulley oil return threads......I've seen 2 engines with this problem, and one was straight from the VW exchange program. If it is not the pulley, and looks like a generator stand leak, I would make sure that the bottom flange is dead flat, and not warped at the 4 nuts due to overtightening. Good luck....
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[1960vw]

Check the gasket on the oil fill cap. I would also clamp the bypass hose at both from oil neck to air cleaner. Nice looking engine!

[Eric&Barb]

Check that the oil groove in the pulley is not full of dirt or is even there. Some pulleys are are made for sand seal only.

Better to get the stock dog house crankshaft pulley that is bigger for more gen and cooling fan RPMs. That in turn will make the engine run cooler, and last longer.
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[pdb27]

[RWK]

Also check that the gen tower to breather/oil filler nut is tight and a gasket is ok.
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[pdb27]

Took the day off to begin trouble-shooting, with no clear smoking gun yet (that i can tell). Pictures below.

Oil level OK, right under the top line. Took the breather off and ensured it was clear by blowing through it; cut a new gasket and cinched it back on tightly. Popped off the air cleaner top and took a photo of the oil condensate; there wasn't much, but it does appear to be breathing fine. Removed pulley and compared to the stock version - both were the same size and had clean grooves (and both experienced the same leak, so those grooves aren't a likely contributor). Gasket on the cap was very oily, but sealed up fine.

It was difficult to get a good photo of the crankshaft area with the engine still in, but I attached the best one of the bunch. I could not tell whether there was an oil slinger in place, but there was a washer-like thing in there that I could move with a long screwdriver. It looked flat to me, so I can't say whether it's cupping in or out. It is rusty, like many of the old parts my engine builder put on the bug (separate story).

Anybody have ideas based on these pictures? Sand seal is the next step?

[1960vw]

Another spot , though rare, is from base of distributor, O-ring on shaft going into case. You've checked the common culprits. Hope you find it!

[Eric&Barb]

Clean up the stock pulley, and you can sand the inner bore so it just slides onto the crankshaft. Then install it to see if the oil leak goes away.
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[pdb27]

[Eric&Barb]

[pdb27]

Quick update on this thread: I haven't yet driven it on the Interstate for an hour, which is typically when the oil leak is most obvious, but I've been watching it closely enough for the last 2 weeks in mixed driving around town to say that the leak is still there. Very low level, but definitely present.

Crankcase oil level does seem to play a role. During troubleshooting I changed the oil and refilled to between the low and high marks on the dipstick, and at that level there was very little leaking. A few days ago I poured in an oil additive that brought it up to the high mark on the dipstick, and afterwards I could see evidence of more oil coming from behind the pulley. I'll drain a bit back out and see if the leak abates.

My intention to try a stock air cleaner with better negative pressure is on pause, because the one I have has the breather port pinched shut and sealed. Not sure why anybody would do that, but I'll try to bang it back open at some point when I have the time.

I haven't put the stock pulley back on because the leak was present with both pulleys, and a visual inspection showed them to both have clean grooves. Maybe later.

Final comment is that the oil appears to be most noticeable on the tin to the right of the pulley near the dipstick, and I've read in other threads that some owners will put string up there to help seal in oil splashing up from the crankcase. I'll give that a go and see what happens.

So maybe this wasn't such a quick update, but the quick summary is that the oil leak persists and I'm learning bit by bit. When the oil leak is addressed I'll add a closing write-up to the post. Thanks again to all commenters for your help.

[cyclehobby]

All the responses from the Samba are excellent possibilities for the cause of your oil leak. But your last post has me intrigued. You said you changed the oil and added oil to put it in the proper spot on the dipstick, but not all the way to the top.

Is it possible you have an incorrect dipstick and you're overfilling the crankcase each time? Too much oil can cause leaks in certain ways. Your oil breather, the crank pulley, the main seal. All can spew oil if there's too much volume and associated pressure. I would think that at high speeds, extra oil slinging around could find it's way out in a number of places.

In my car, I found that filling the crankcase until the highest mark on the dipstick was way too much oil. During an oil change, I put in EXACTLY the 2.5 quarts needed and the dipstick showed oil right in the middle of the low and high marks. I filed a mark right there so I know the right amount of oil is on that spot and I've been very leak free for years.

The rather low oil capacity of these motors also means that when you have a full crankcase and add some sort of oil additive, you're potentially raising the oil level too high. Not sure what to tell you about additives (that may be a separate discussion), but if you've had issues with some of the parts used on your engine rebuild, the dipstick could be the culprit.
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[pdb27]

[pdb27]

This morning I finally had the chance to run the bug down the interstate for an hour, and after popping the decklid to take a look ... (drumroll) ... it was dry! Mostly. Dry enough for my expectations. It looks like the culprit was an overfilled crankcase due to relying on an uncalibrated dipstick to tell me when to stop adding oil. Lesson: only dipsticks rely on just the dipstick.

The engine even sounded better while purring down the interstate. I think I'll change the generator stand and fuel pump gaskets one last time to clean those up, and then call it good. Many thanks to the commenters on this thread!