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Politically Incorrect
Join Date: Aug 2005
Location: Hoover, Alabama
Posts: 1,494
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4th hole myth BUSTED (with pictures!)
Since I had to change the gasket again anyway (I over torqued it), I thought I would investigate the 4th hole on the cam tower rear cover and dispel the rumor about what it is for.
 Here you see the bottom two CT cover mounting holes that are about 18mm apart. The bottom right hole in this picture is not used for anything. Some people say to install them dry, but I always prep cork gaskets with a transparent coating of red Permatex on both sides. If you do this you absolutely MUST let it cure for 24 hours before you install it or it will squish out if you install it wet. I found the trick to keeping this leakproof is to use split lock washers and tighten the bolts evenly until you feel a noticible rise in torque. STOP THERE. You don't want to squish the gasket out. Let the lock washers maintain compression of the CT cover to the CT.  Hard to get a good picture of this directly with the engine in the car, but it does show where I added a dedicated ground wire for the cylinder head.  This is a much better picture, done with mirrors, that clearly shows the mystery unthreaded hole on the back of the CT. The bottom CT cover threaded mounting hole and the unthreaded mystery hole are about 30mm apart. You can see in the first shot that the mystery hole lines up with one of the "wells" inside the cover. Since the mystery hole is included within the sealing perimeter of the cork gasket, there should be NO oil leak from this hole if the gasket is properly installed. Oil does come out of that hole, but it stays inside the CT cover. OK, so there is nothing special about the 4th hole. Just install the gasket properly and no leaks. Myth busted.
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Edek '87 924S '91 535i Last edited by onZedge; 05-19-2007 at 07:09 PM.. |
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05-19-2007, 07:06 PM
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Job well done! I would why it exists. Any torque values?
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John '87 944 N/A (first Porsche) '95 E-350 Diesel '03 S-Type Jag 3.0 '03 Taurus SES '06 Eddie Bauer Explorer RIP SoCal |
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05-19-2007, 07:16 PM
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Politically Incorrect
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Location: Hoover, Alabama
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Of course Haynes didn't have torque values and I couldn't find any in the FSM either. Just don't make it so tight that the gasket squishes out. It is well worth spending a few extra minutes with a mirror to monitor your progress to insure a leak free CT cover. BTW that hole is to let the oil drain back into the crankcase after it is done lubricating the camshaft.
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Edek '87 924S '91 535i Last edited by onZedge; 05-19-2007 at 07:27 PM.. |
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05-19-2007, 07:23 PM
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ok, good to know. I am doing the cam and the tower gasket next week. Waiting for the flywheel lock to get here. The tower should be easier to reach with the cam off.
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John '87 944 N/A (first Porsche) '95 E-350 Diesel '03 S-Type Jag 3.0 '03 Taurus SES '06 Eddie Bauer Explorer RIP SoCal |
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05-19-2007, 07:30 PM
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Could be that these parts were used on some of the 928 motors.
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05-20-2007, 03:08 PM
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Could be.
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John '87 944 N/A (first Porsche) '95 E-350 Diesel '03 S-Type Jag 3.0 '03 Taurus SES '06 Eddie Bauer Explorer RIP SoCal |
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05-20-2007, 03:10 PM
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Politically Incorrect
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Location: Hoover, Alabama
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These are the exact same CT covers and gaskets used on the SOHC V8. SOHC V8 CT covers use one or the other bottom mounting hole depending on which cylinder head bank it is. The SOHC V8 and L4 CT cover and CT cover gaskets are all the same part numbers. Starts to make sense, no?
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Edek '87 924S '91 535i Last edited by onZedge; 05-20-2007 at 03:50 PM.. |
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05-20-2007, 03:46 PM
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I found the same problem when I did the top end on my car a few months ago. I was amazed to see that the "mystery" hole went right into an oil passage in the head. I don't think that the one fastener on the bottom is adequate enough to seal the cap and prevent oil from seeping out. I took preventative measures by tapping the hole 5/16-18 and installing a piece of threaded stock into the hole with some Permatex to keep the oil from working it's way out to the cover. My engine is still leak-free and clean and I think it will stay that way.
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1988 944 Turbo Guards Red - Black Leather Autothority Stage 2 Chip Set Weltmeister Strut Tower Brace 1984 944 - Sold to rcecale |
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10-17-2007, 04:18 PM
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Politically Incorrect
Join Date: Aug 2005
Location: Hoover, Alabama
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You're kidding. Right?
Quote:
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Edek '87 924S '91 535i |
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10-17-2007, 09:31 PM
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This means that once the cover fills up with oil and if it can't drain back with the hole plugged, the last cam journal will not be very well lubed. Don't block the hole!
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Art '75 911 US Carrera #390 '74 MGB, AH 3000 BN7 V8, '65 Mustang Fastback, 66 bronco U13 |
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10-18-2007, 09:42 AM
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Politically Incorrect
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Location: Hoover, Alabama
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Quote:
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Edek '87 924S '91 535i |
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10-18-2007, 11:19 AM
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