At a recent PCA driving event I witnessed an early 944 exiting the track being
followed closely by a trail of oil smoke. After the car came to a stop, the
hood was raised for inspection and a handful of people came over to inspect
the situation. After a few minutes, one of the people inspecting the car uttered
these words of wisdom to the vehicle owner: "The wafting trail of smoke,
the unmistakable smell of oil on the exhaust…now that’s a real Porsche!"
It is true that certain model Porsches have had a history of oil leaks from time to time. It is also true that virtually all Porsches are created equal in terms of leak probability. However, the oil leak that will instantly take the pleasure out of driving a 944, is the dreaded cam-housing leak. This is due to the fact that the oil will leak right onto the exhaust manifold causing an extremely foul odor and the possibility, although slim, of creating an oil fire.
The reason for a cam-housing leak is usually two fold. The first part of the failure is caused by poor design and the second part by poor execution of a previous repair.
(See Figure #1 for reference)
Figure 1.
944 Engine - Reference Engine Exploded View.
Refer to Figure #1 for a pictorial representation for the following:
First, let us start with design. During the fabrication of the cam housing, (item #31), it is machined at various locations, as well as the ends, to receive the cam. At the assembly stage, the front side is sealed off with the cam belt sprocket housing (Item #18). There are a series of high-grade seals and o-rings to keep this end dry, and this works quite well. The back end is a completely different story. The rear cam housing cover (Item #38) is held in place with three 6mm bolts. Between the housing and cover is a soft cork gasket (Item #39). When new, the gasket works fine, but as time and heat take their toll, the gasket will shrink and become hard. This allows the bolts to become loose, which then leads to that smelly, smoky oil leak. In some extreme instances, the bolts will even fall out.
The second problem is how the cam housing is bolted onto the head. Each time the cam housing bolts (Item #30) are tightened, they stretch. When they are loosened they stretch, and this changes the amount of clamping force that is exerted onto the cam-housing gasket. (Item #32) If even one bolt has less clamping force than the bolts on either side of it, there will be a leak.
Now that we know the problems, lets concentrate on the remedies. The biggest
part of this job is the clean up. The old cam-housing gasket will be stuck to
the cylinder head like a 2 billion year old fossil. Be very careful not to scratch
any of the sealing surfaces during clean up or you’ll have another leak
(see “poor execution of a previous repair”, stated above). The clean
up on average is a 2-hour job. For our purposes, we’re going to start with
a cam housing that’s been removed and disassembled, with all of the parts
and pieces already being cleaned and dried. When removing the cam housing, you
will quickly notice that all the lifters will fall out. Try your best to keep
them in order, and mark the faces with a permanent ink felt pen. Start with
#1 at the front of the engine and end with #8 at the back of the engine.
-For the rear cam housing cover, we simply eliminate the problem entirely by
eliminating the gasket. Surprisingly, it doesn’t even need to be there!
To seal the cover on the back of the cam housing, use Locktite 574 flange sealant.
(Porsche part number 000.043.101.00, costing $30.35) This is the same sealant
used on 911 engine cases, and it works like a charm. Replace the bolts, (Item
#35) use lock washers and torque all three 6mm bolts to 6 ft.lbs (8Nm).
-Check your clean camshaft and make sure there are no remnants of the old membrane
washer on the front nose of the cam (Item #21). To make sure, scrape it clean
with a razor blade.
-Coat the camshaft with a light layer of oil and slide it gently into the cam
housing.
-Install a new membrane washer (Item #21) on the end of the camshaft.
-Take the front cover (Item #18), install the large O-ring (Item #22) and the
small seal (Item #23) to the backside. Dip the small seal in silicone paste
to keep it in place and use the same paste on the large O-ring to help it slide
into the cam housing without becoming torn or damaged. Push the front housing
into position and tighten the three 6mm bolts to 6 ft.lbs. (8Nm).
-Install a new membrane washer (Item #21) on the end of the camshaft. Slide
the seal spacer on (Item #20) right after the membrane washer.
-Install (Item #19) the new front cam seal, part #999.113.282.40 at a cost
of $15.00.
-Install the woodruff key (Item #15), followed by the cam gear and rotor spacer
(Item #13-14).
-Install a new bolt, (Item #12) and torque to 50 ft. pounds. At $2.66 this
is cheap insurance to keep everything together. (Part # 999.510.022.08)
-Line up the TDC mark on the cam gear and flip the cam housing upside down
on the workbench. Install the lifters in order from one to eight using some
thick grease or assembly lube. This will keep the lifters from falling out when
you install the cam housing.
We are now ready to install our cam housing onto our perfectly clean and dry
cylinder head surface.
-Place the cam gasket (Item #32) on the cylinder head so it’s held in
place by the two locating dowel pins.
-Gently place the cam housing on the cylinder head making sure the camshaft
and crankshaft are both on TDC #1. If the are not, and you tighten themdown,
you will bend some valves!
-After making sure the gasket is still in place, install 4 new cam-housing
bolts. (Part #900.067.214.02) I have found that starting them in the holes one
space in from the outer most position works best. (This can be seen in the position
of Item #30) Tighten them in an even criss-crossing pattern until they are almost
seated. Then install the remainder of the new bolts and tighten them all down
lightly in the same alternating pattern. Before the final tightening, install
the bolts that hold down the heater tube.
The new mounting bolts are really the key to keeping this gasket from leaking.
It’s also critical to make sure that they are tightened properly. Once
again, see “poor execution of a previous repair”, stated above. I
use a special tool to assure proper torque of these bolts, since getting a non-flexing
allen socket inside the cam housing is nearly impossible. If you use a standard,
short 3/8 drive allen socket, it will not fit inside the cam housing. If you
use a standard 6-inch long 3/8 drive allen tool, it will flex while tightening
and give you a false torque reading.
The solution for this problem is to take a high quality 3/8 drive, 6mm allen socket, and cut the allen drive down to 5mm in length. Then take the drive section and machine it down to 15.5 mm so it will fit into the cam housing. Now the tool will fit into the interior of the cam housing, (using a standard 3 inch extension), yet have zero torsional twist due to the extremely short length of the allen drive, see figure 2 for a comparison of these tools.
Figure 2. Tool Comparison.
The top tool is the standard long extension, and will flex under heavy torque.
The middle tool is the standard short tool and will eliminate flex, but is too
large to fit inside the cam housing. The bottom tool is the same type as the
middle but has been machined down to fit inside the cam housing.
Using the special 6mm allen tool and 3-inch extension, torque the cam housing
down to 14 ft.lbs. Be sure to use the same crossing pattern as we mentioned
above. At a grand total cost of $13.50 for the fifteen bolts, it’s not
even an issue as to whether you should replace them or not.
Finally, you can re-install the six sealing plugs and washers (Item # 28-29),
tightening them to 30 ft.lbs each.
Our cam housing reseal is now complete, and after we re-install and adjust the
cam belt, we’ll be able to drive our 944 knowing that not all real Porsches’
have to smell of oil.
Good Luck!
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