Porsche Cam Boxes
The cam box for air-cooled Porsche is a cast and machined part. Its job is to hold the camshafts and let the lobes of the cam act on the rockers to open and close the valves. When you are restoring a cam box you must first clean and measure to see if it is within specifications. If a cam box has damage on key surfaces it is usually replaced. I have never bought a new cam box from Porsche? Unless they become impossible to find, replacement with a good used unit is normal.
Prep for Cleaning
The first thing we are going to do on this cam box is to remove the oil plugs. You need a 17mm wrench to remove the oil fill and Oil blanking plugs. Notice that the crush washers underneath the plugs showed signs of over-tightening. These washers are one-time use and need to be replaced. The plugs and studs can be put in your plating bucket. We already have replated parts for this restoration.
Removing the Cam Box Plugs
Using a socket head sized to fit the plug and a long extension, carefully run the extension through the cam box. Tap the plug out from the inside. The plugs will be cleaned up and sent to plating to be replated in yellow cadmium. Note that the cam boxes are reversible so care needs to be taken when re-installing the plugs. Now we are ready for cleaning
Cleaning the Cam Box
We do not show you the extensive cleaning process we go through on these parts. Magically, the cam box is super clean and polished. We show more of this cleaning on the Cylinder Head Series episode one. Basically, the cam box is first degreased then sandblasted, in our wet blaster with a glass bead and aluminum oxide mix, then polished. The polisher closes the pores in the aluminum that were opened by blasting.
At this stage, we are going to look for any obvious signs of damage. The valve cover gasket surfaces can get beat up from poor shop practices. Some amount of damage can be spot dressed, but if it is really bad you can machine these gasket surfaces lightly.
Next, we are going to take a look at where the rocker shafts run. This surface is an oil sealing surface and damage here will mean oil leaks. Mechanics can slip when removing shafts, so take a look at each one to confirm no gouging.
Cam Box Bearing Surfaces
Cam boxes in early Porsche, 1965 to 1977, have three bearings. Later engines have four bearing cam boxes. Perform a visual inspection, again, any damage will mean cam box replacement. Camshafts do not come with oversize bearing journals.
The last surface to check before the measurement is the gasket to head sealing surface. The surface does not wear in use but heavy-handed disassembly or poor storage can cause damage to this surface. You can only lightly dress this surface, any machining will change the engine mathematics and is not recommended.
Measuring the Bearings
Now that we have completed the visual inspection, and your cam box has passed, we can confirm the bearings. The tolerance for the cam box bearing is 46.967mm to 46.992mm, with a wear limit of .1mm.
Using a bore gauge that is set within the tolerance range, measure the bearing surface in a few different places. I have set my gauge up to the max setting 46.992mm and so a reading of zero means we are that size.
Bore Gauge Measurement Tools
Servicing the Spray Bar Tube
Porsche put out a TSB, technical service bulletin about the oil spray tube. The spay tube supplies oil to the cam and the valves. The cam box oil spray tube is the end of the line for your oil system. Any debris in the system may end up in the spray tube. To clean out this spray tube you will need to remove the tapered plugs at the ends.
Removing the Oil Spray Tube Plugs.
Set your cam box up in the mill. We drill out the plug with a 5mm drill because we are going to tap the hole with an m6 x 1 thread. Use eye protection when machining. Do not drill too deep, just through the plug, then tap the hole. To remove the plug use a spacer that is big enough so that it does not touch the plug. Install a bolt and tighten to pop out the plug.
Push a bronze wire brush through the oil spray tube in one direction all the way through. Any debris will push out the end. It is time to clean with solvent, brake clean, and spray down all the tubes and check feed holes. If you do not have good flow through the feed holes you may need to remove the spray tube.
Removing the Oil Spray Tube
The oil spray tube is fragile aluminum and great care needs to be taken when knocking it out. Using long punches we gently knock out the oil spray tube. With it out you can clean some more where it was blocked by the tube. With the tube, you can clean out any blocked holes and give it an all-over clean as well.
Reinstalling the Oil Spray Tube
It is very important to orientate the oil spray tube correctly in the cam box when you reinstall it. The oil holes need to be in the correct place to lubricate the can bearings and intake side. In a three bearing cam box, there is a short end and a long end on the tube. This will cover direction, then you need to aim the holes down. The is held in place by the specialty bolt at the plug end which has a pin to hold the tube. Don’t forget a new washer.
Install the new plugs at the end of the feed line. The plugs are a tapered fit but we like to be sure and add a small amount of Loctite 574 when re-installing. Drive the plug in with a hammer then use a small punch till it is just below the gasket surface.
Cam Shaft Plugs
Before you push in the cam box plugs you should clean up the gasket surfaces. We use 320 grit wet and dry on a machined block. At this point, you will need to make a left and a right from the two cam boxes. Place the cam boxes on the bench like the engine. The intake side will be on top, the exhaust side on the bottom, and they will face each other. For MFI and Turbo make sure you install the cam plug on the right side bank, cylinders 1,2,3.
You should be doing your inspection and cleaning of all your engine components. While your engine case is at the machine shop, you have time to work on various systems. Get a jump on the heads, and timing chain tensioners.