You have made it to the last lesson on the 911 Air-Cooled Cylinder Head, reassembly. As we built these lessons we showed you all of the processes involved. Often we tried to show you how to work with the old components and bring them back to life, or at the least test them. For our assembly, we are working with new parts, new valves, new springs, and new valve stem seals. The shims and collets have been reused, and of course the refurbished heads.
Take your time and get the heads perfect. If your engine is ready, pop them straight on. If not, you can store the heads well oiled till the time comes to join them to the block.
Cylinder Head Reassembly
In lesson 7 the heads got very dirty for the last time. Cylinder heads should be washed to remove all traces of machining chips and cutting fluids. Degrease the heads, wash down with hot water, and blow-dry with compressed air is the best way to prepare the heads for reassembly
The first thing to do is to pull the assembly specifications for the head you are working on. Cylinder head installed valve spring heights will vary depending on the model.
Valve Spring Height
To set valve spring height, start with 3 shims followed by the lower valve spring seat. Install the Porsche special tool P 10 b/c, or Sir Tools P288, followed by the upper spring retainer and collets. Read off the currently installed height and compare it to factory specifications. To adjust valve spring heights, add or remove shims as required. Shims are available in .5 mm and .25 mm thickness.
Valve Stem Seal
After setting the valve spring height, remove the height tool and leave the lower spring seat in place. Lubricate the valve stem seal and install it onto the guide by pushing it down using your fingers. Make sure that the seal seats all the way onto the guide and that it is straight. Before installing the valve make sure to lubricate the lip of the valve stem seal.
To install the valve first lubricate the stem using a heavy assembly lube or light grease. Install the valve into the guide and slowly push it up towards the seal. Be careful as the valve passes through the seal that it does not get caught on the collet grooves causing the seal to become damaged.
Assembly Lubricants we use.
Valve Spring Reassembly
Next, install the valve springs over the valves. Take notice of the outer spring, the closer coils on the spring need to be installed against the lower valve spring seat. Install the upper spring retainer and using a valve spring compressor, compress the spring, and install the collets. After installing the collets lightly tap the back of the valve a couple of times with a ball-peen hammer to seat the collets and the valve.
Reassemble all six cylinder heads
Repeat the above steps on all valves until all cylinder heads are assembled. Now you have rebuilt your cylinder heads you can put them directly on to the case. If the rest of your build is not ready it is best to wrap up the heads and store them. Make sure they are well oiled for storage.
Thank you for following along with our air-cooled cylinder head restoration. A lot of the work is the cleaning and measuring. Remember, being precise in your measurements is super important in Porsche motors.
If you did any machine work to the cylinder heads, you will need to recalculate your engine compression. Head over to our engine math course to see how to calculate chamber volume.