Main Menu

Leaky 1990 911 oil return tubes o-ring


Vehicle Information: Year: 1990; Body Type: Coupe;

I've had with the diameter of the oil return tubes that was installed in my rebuild. Let me recap:The engine is an ordinary '79 SC. The oil return tubes that were installed by my builder is part no. 930 107 040 01. During the break in period (1000 miles), two of the tubes were leaking at the forward end of the engine, both sides. After observing the leaking over a period of time, hoping it would work itself in and staying in touch with the builder, we decided to replace them. I did the replacement. The actual task is not a big deal as I've done it before. Upon receiving the replacement parts, I began to take measurements of the dia. of the groove in the tube at both ends. The diameter of the rings as they sat in the groove, and the diameter of the holes in the case and the cam tower. Here's what I learned: The o-ring (green was the color and was told it is the latest part for the o-ring) slipped on the case end of the tube nice and snug. I got a reading of 1.53" + - diameter I could not rotate the ring around the groove. On the opposite end, the ring could easily be rotated while in the groove. I took a measurement of 1.438" + - diameter. When installed in the case end, it fit nice and snug using a light grease/oil mixture. No problem. When I installed it in the cam tower, it slid in without any resistance. In fact, I could wiggle it around and see a gap. I took it out again and measured the holes in both ends. The case hole measured enough to allow a tight fit. (I didn't write down that measurement). However, the cam tower hole measured the same as the o-ring as it sat in the groove loosely. So I tried the installation again. Snug at the case hole, loose at the cam tower. At this point I carfully seated it as best as eye and feel would allow and put everything back together. Same issue on the opposite side of the engine. After topping off the oil level, I fired the engine and observed what would happen. The leaking seemed to have stopped.Later after a drive and a cool down, I checked again and wiggled the cam tower end of the tube and a bit of oil would gush out. At this point I left it alone and hoped time would help expand the rings. After 6k miles, the leak never came back.My point is, no one has checked what I have found out or cares to, and have not gotten a satisfactory answer from anyone. I have other aftemarket tubes that don't have that problem that I installed in my 914-6. They are snug. When the weather turns for the better, I will again check the condition of the tubes after sitting a cold garage for the last 3 months. The only answer I'm looking for is whether this is a common problem with the current tubes and has anyone else experienced the same problem.

You must log in to view answers associated with technical questions. Join PCA to participate in our community.
No votes yet