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Pelican Technical Article:

Rebuilding Your Engine

Time:

50 hr

Tab:

$2,500 to $6,000

Talent:

*****

Tools:

Cam shaft removal tool, cam shaft holder, snap ring pliers, heat exchanger removal tool, head stud removal tool, dial indicator tool, valve adjustment tool, torque wrenches, ring compressor

Applicable Models:

Porsche 911 (1965-89)
Porsche 930 Turbo (1976-89)

Parts Required:

Engine gasket set, o-rings, valve covers, piston rings, sealant, pistons and cylinders (if required), rod bearings, main bearings, intermediate shaft bearings, rod bushings, timing chains, head studs

Hot Tip:

Buy your favorite mechanic a six-pack of beer right before you start, so you can flood him with questions later on.

Performance Gain:

More horsepower, longer lasting engine

Complementary Modification:

Turbo valve covers, carrera chain tensioners, larger pistons, carrera oil pump upgrade
101 Projects for Your Porsche 911

This article is one in a series that have been released in conjunction with Wayne's book, 101 Projects for Your Porsche 911. The book contains 240 pages of full color projects detailing everything from performance mods to changing your brake pads. With more than 650+ full-color glossy photos accompanying extensive step-by-step procedures, this book is required reading in any Porsche 911 owner's collection. See The Official Book Website for more details.

One of the most talked about and most revered jobs on a Porsche 911 is a complete engine rebuild. Many mechanics will chatter all day about the mysteries of the design of the 911 motor that make it a very difficult beast to rebuild. In all honesty, it's just another engine that's slightly different in design than most of the other ones out there. To rebuild a 911 motor takes plenty of time, patience, and a little bit of know-how. This project is not designed to be a tutorial on the process of rebuilding your motor, but is organized to give you a broad overview of the tasks involved, and the steps required. At the very least, this section will provide you with enough information to ask your engine rebuilder questions about what he is doing to rebuild your engine.

The rebuilding process starts with the engine case. Depending upon what size and year engine you have, you may want to make some modifications to the case in order to make it more durable. The earlier cases, as well as the magnesium cases will require the greatest amount of modifications. The earlier cases can modified to later specifications by adding piston squirters for better lubrication, boat-tailing the main bearing ribs for better oil circulation, and align boring the intermediate shaft to accept the later bearing shells. As the 911 engine grew and additional smog restrictions were imposed, the magnesium cases became taxed beyond their ability. This weakness often resulted in the case yielding and becoming warped under the pressures of operation. These shortcomings in the case construction were especially profound in the 1974-77 2.7 liter models, when the added stresses of increased displacement and stricter smog restrictions caused the cases to weaken considerably. There are quite a few modifications that should be performed to the magnesium cases in order to strengthen them, but a detailed explanation of these is beyond the scope of this article.

The case should be taken to your local machine shop and checked for straightness. If a bearing has spun previously inside the case, or some other destructive event has happened inside there, then the bearing surfaces may need to be align-bored. This is the process of aligning all the bearing bores together as well as squaring them relative to the case. As a result, you may then need to use an oversized bearing set. It's quite common for this procedure to be used, and the oversized bearing sets are readily available. Have your shop thoroughly clean the case as well. Do not have the case sand blasted, as you do not want to get any particles of sand lodged in the fine oil passages within the case.

The case should be mounted on an engine stand that is designed for the 911 engine. There are general-purpose engine stands that will work, however, they will not be able to give you the support that you need when the engine gets significantly heavier. If you are rebuilding your own motor, make sure that you borrow a 911-specific engine stand, or invest in one for yourself.

If you are installing new head studs, make sure that you install them before your put the case together. It's a bit too easy later on to drop small items and/or shavings into the case if you need to redress some threads on the holes. I recommend that you use the older style steel studs instead of the Dilavar or late-style 993 head studs. Polling many years of research and testing by mechanics around the world has resulted in me coming to this consensus.

Assembly of the crank and rods should be performed on a workbench. Bolt the crank to the flywheel in order to make a handy stand for assembly. Make sure that you test fit all the rods, and don't ever recycle the rod nuts or bolts. Use red Loctite on the rod nuts, and also apply plenty of assembly lube to the bearing surfaces. The assembly lube allows the parts of the engine to be turned and rotated during assembly, and also provides lubrication during the first few moments when the engine is started and no oil pressure is available. Apply it in an even pattern covering the entire surface, but don't lay it on too thick.

Each rod consists of two parts that are numbered and matched together. Make sure when you take your rods to the machine shop that they machine them to be round again (see Pelican Technical Article: Machine Shop 101). Also make sure that you have the wrist pin bushings replaced.

When placing the crank and rods in the case, make sure that you fully lubricate the main bearings with assembly lube. Also make sure that the oil pump and intermediate shaft are properly installed and that you have also installed the two timing chains. The backlash alignment between the aluminum gear on the intermediate shaft and the drive gear on the crankshaft should be checked as well. It's also a wise idea to pour a little bit of motor oil into the oil pump prior to installing it.

Closing up the case is an important step of course. Use an appropriate case sealer (the orange Loctite 571 case sealer is preferred) and apply it evenly with an acid brush. The Loctite sealer doesn't cure with contact with air - it cures with metal-to-metal contact, so don't be concerned if the excess that drips out when the case is sealed never hardens. The long through bolts that hold the case together need to have small o-rings placed on each end. This is because oil flows through these passages, and will leak out if not properly sealed. It's also wise to put some high-temp silicone around the o-rings as an added measure. Make sure that you torque all the fasteners to the required torque, and don't forget the one or two hidden fasteners in the recesses of the case.

Once the case is together, you will be feeling a bit proud of yourself, as it will look like it's coming together. The next step is to assemble the pistons and cylinders. This is perhaps the trickiest part of the process. It is very easy to break a piston ring here. Work slowly and carefully, and assemble the pistons and cylinders on a workbench. Some people recommend putting the cylinders on after the pistons are attached to the rods. However, it's easier to break a ring during this process because you don't have a really good angle on the pistons, and you also don't have plenty of working room.

The installation of the pistons/cylinders to the rods is a bit tricky. In order to get the snap ring that holds the wrist pins in place, you will need to plan out your assembly procedure. Don't forget the copper sealing gasket (wet it on both sides with some case sealer). Also don't forget to install the cylinders with the large cooling fins facing down, and the pistons with the dimple facing up (if so equipped with CIS pistons). These are important details that will wreck your engine rebuild if not closely watched.

Once the pistons and cylinders are installed, assemble the heads to the cam towers. Using the same Loctite case sealer and an acid brush, liberally coat the mating surface of the cam tower. When finished, bolt the heads to the cam tower. Now, mount the cam towers and heads to the engine. Don't forget to install the cooling tin in its proper orientation. Make sure that you also remember the cylinder head gasket that sits on the top of the cylinders. Also don't forget the large washers that go under each of the head stud nuts.

With the cam towers installed, you can install the cam into the cam towers. The chain housing and chain tensioner equipment is next. The assembly here is pretty straightforward: see Project 16 for more details on installing the chain tensioners and associated oil lines. Now, install the rocker arms and set the adjustment screw for the intake valves on cylinders one and four. The rocker arms have a compression-type fit that prevents oil from seeping past the interface, but it doesn't always work. There is a secret fix for this problem: a little seal that goes in the groove of the rocker arm and prevents nasty oil leaks. For some reason, these only seem to leak on the exhaust side of the engine. Make sure when you are tightening down the rocker arms that you don't over tighten them, as you can create excess friction that will cause the rocker arm to not turn smoothly. Check each of the rocker arms after you tighten them down to make sure that they move freely.

The cam timing should be performed with only the two intake rockers installed on cylinders one and four. Without going into extensive detail, the cams are set by measuring the amount of valve lift with respect to the orientation of the crankshaft. Small adjustments are required in the camshaft sprocket in order to achieve the desired results. It is in this step that you can choose to advance your timing to a setting that is a bit more aggressive than the stock factory setting. See Project 15 for more details. When the timing is complete, install the remainder of the rockers. Leaving most of the rockers uninstalled while adjusting the cam timing reduces the chances that your valves may accidentally hit the tops of your pistons when setting the cam timing.

Once the timing is set and the cam nuts tightened, you can adjust the valves. With the engine out of the car, this typical four-hour job takes only about a half-hour. After you seal up the valve covers and the timing covers, your long block is completed!

The final steps of course, are the reinstallation of the fuel injection, the addition of the exhaust system, and the reinstallation of the motor back into the car. Break in procedures are very important, and should be followed very carefully. Use non-detergent oil if possible, as this will help the chances that the rings will seat properly. When first starting the car, make sure that you disconnect the CD box and let the engine turn over until the oil pressure light in the dashboard goes out. This should take about a minute or less. When you finally start the engine, let it run at about 2000 RPM for 20 minutes. Take a stopwatch with you, because as 10 minutes pass, it will seem like it was running for a half-hour. Check under the car for major oil leaks, and shut it off if you see oil pouring out from underneath. Before driving the car any significant distance, take it to your mechanic and have him check the mixture. If the car is set to run rich, then it might prevent the rings from seating properly. Expect lots of smoke and a bit of a sulfur smell as the rings go through the seating process. The best thing that you can do for the car to break it in is to just drive it. In general, do not take the motor past 4000 RPM during the first 500 miles. It's also a wise idea to change your oil every few hundreds miles until you reach about 1000 miles on your new engine.

Hopefully when you are done you will have a strong running motor. The rebuilding process is not difficult if you have the right tools and the right instructions. For more information on rebuilding your 911 engine, see my upcoming book when it is released.

It all begins with your checked and/or line-bored case.
Figure 1

It all begins with your checked and/or line-bored case. The aluminum 2.0 liter, 3.0 liter, and 3.2 liter cases make excellent rebuild candidates. If you have a 2.2L, 2.4L, or 2.7L case, there are a few modifications that you will certainly want to do to the case in order to make it stronger. Most important is the addition of time-certs in the cylinder head stud mounting holes. This will decrease the likelihood that the studs will pull out of the relatively soft magnesium. You also want to make sure that all three mounting surfaces for the cylinders are flat and level. The magnesium cases have a tendency to warp over time, and rebuilding the motor without machining the case will most likely result in an oil leak. It's also wise to reinforce one of the center engine case studs that has a tendency to pull out from the case.

Assemble the rods and crank away from the case.
Figure 2

Assemble the rods and crank away from the case. It's a good idea to mount the crank to the flywheel and use it as a stable base for tightening up the rods. Use plenty of assembly lube here, and red Loctite on the rod nuts. The rod nuts and bolts should always be used only once. They are designed to stretch, and deform when torqued up to their final specifications. Make sure that the two rod halves match each other: the numbers stamped on both sides should always be kept together.

The crankshaft, intermediate shaft, and oil pump are all shown installed in this photo.
Figure 3

The crankshaft, intermediate shaft, and oil pump are all shown installed in this photo. Use a new bend-up lock tab when installing the oil pump. Make sure that you properly install the timing chains before you go too far in the process. Even if you forget to install the chains, you can always install a master link chain later on. The master link chain allows you to disconnect the chain and remove it from the intermediate shaft without reopening the case. Everything that is a moving bearing surface should be coated with assembly lube: no need to be shy about spreading it on there. Make sure that you don't get the assembly lube on the case mating surfaces though. Don't forget the two thick o-rings on the oil pump and the one that seals the lower oil passages within the case (not shown).

The two case halves are together, and the new head studs are installed in this photo.
Figure 4

The two case halves are together, and the new head studs are installed in this photo. The consensus of the Porsche experts is that the Dilavar studs are to be avoided, and original style steel head studs should be used instead. Make sure that all the studs are at identical heights (133-134mm), and use some red Loctite when installing them. Remember when installing the through bolts on the case to insert the small o-rings that stop oil leaks. I recommend that you use silicone sealant under the washers as an added precaution.

Perhaps the ‘most dangerous' part of rebuilding the engine is installing and compressing the new piston rings.
Figure 5

Perhaps the 'most dangerous' part of rebuilding the engine is installing and compressing the new piston rings. Make sure that you stagger the gaps on the rings, and also be very careful that you don't break one. If you do, the entire top end of the engine will need to be removed and the engine will need to be re-ringed. If you are in doubt, pull the cylinder out and check.

A tricky process is the actual installation of the piston/cylinder assembly onto the rods.
Figure 6

A tricky process is the actual installation of the piston/cylinder assembly onto the rods. Some builders prefer to install the pistons and then place the cylinders over the pistons while the engine is on the stand. While this is easier, it's also much easier to break a ring this way. The cylinders must be installed in a particular order, or you will not be able to slide in the wrist pin for the last one. Make extra sure that you don't drop any of the small wrist pin snap rings down into the engine while you are installing the pistons.

The cylinders are all installed, and the air guide sheet metal is ready to be installed.
Figure 7

The cylinders are all installed, and the air guide sheet metal is ready to be installed. Make sure that the long fins on the pistons are installed on the exhaust side, or your pistons will overheat and seize. Also make sure that you install the sheet metal in the proper orientation. A seemingly minor mistake on the sheet metal can translate into serious heat problems for the motor later on.

Bolt the heads to the cam tower before attaching them to the engine block.
Figure 8

Bolt the heads to the cam tower before attaching them to the engine block. This avoids any alignment problems that may be caused by the case not being completely flat on the piston mounting surfaces. Liberally coat the mating surfaces of the cam tower with the Loctite 571 case sealer while using an acid brush. Use new seals and oil return tubes. Make sure that you wet the seals with a little bit of motor oil before you install them. Immediately after bolting the heads to the cam tower, bolt the cam tower and heads assembly to the motor, tightening down the head stud nuts to the proper torque. You want to make sure that you have the entire assembly torqued down before the sealant cures. This photo shows a dry-run test fit of the heads and cam towers that was made prior to the installation of the air guide sheet metal. It's a wise idea to make sure that you have all your fasteners, washers, and sealants lined up before you assemble the cam towers and the heads.

When attaching the valve train, don't over tighten the rocker arm shafts, as they tend to leak if stretched a bit too much.
Figure 9

When attaching the valve train, don't over tighten the rocker arm shafts, as they tend to leak if stretched a bit too much. On the older 911 engines, the rocker arms sometimes have a tendency to leak despite the design of this compression fit. The solution is to install a small seal in the groove of the rocker arm prior to installing it into the cam tower. See Project 21 for more details.

A very important step in the rebuild process is the setting of the cam timing.
Figure 10

A very important step in the rebuild process is the setting of the cam timing. This is measured by using a dial indicator gauge that is mounted to the top of the valve. When the valve lift reaches a certain height, the engine must be at top dead center. The procedure calls for adjustment of the cams until the valve lift reaches its require specification. See Project 15 for more details. With the timing set, the cam nuts can be tightened. Installing the chain tensioners is a snap when you have clear access to the front of the motor. This photo shows the newer style Carrera chain tensioners installed. For more information on this upgrade, see Pelican Technical Article: Upgrading to Late-Style 911 Carrera Chain Tensioners, Installing Carrera Chain Tensioners.

The completed long block, looking shiny and new! The majority of work is done, but to do the job right, there is still a lot of work to be performed on the fuel injection.
Figure 11

The completed long block, looking shiny and new! The majority of work is done, but to do the job right, there is still a lot of work to be performed on the fuel injection. Hoses, clamps, and seals should be replaced where necessary, and all parts should be cleaned as well as possible.

Sand-blasting or bead-blasting your intake manifolds really adds the finishing touches to the fuel injection.
Figure 12

Sand-blasting or bead-blasting your intake manifolds really adds the finishing touches to the fuel injection. It's also a wise idea to use new screws and washers for attaching the engine shroud to the block. Carefully reassemble the fuel injection according to the notes and pictures that you took when you removed it.

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