Editor's note: This article is a representation of Leland's experiences with rebuilding his motor. There are some points in here that are specific only to the 3.0L and CIS cars other engines may require slightly different procedures. Be sure to refer to the factory manuals for more information. I also don't recommend using any engine stand other than one made specifically for the Porsche case. Using a general-purpose one can both be dangerous (especially if you're trying to support a full-weight Turbo motor, and it may damage your case. The 'factory' ones have a unique lip that holds and supports the case in addition to the large bolts.
The purpose of this Tech article is not to provide a step-by-step guide to rebuilding a 911 motor. There are complete volumes of Factory manuals on this subject as well as a multitude of books and other written material that cover the specifics of engine rebuilding. This article is simply a collection of my own personal experiences and tips meant to aid in understanding various aspects of a rebuild. It is my hope that this article will become one of many tools used by the determined DIY'er as he/she prepares to rebuild a 911 motor.
I am going to assume that the decision has been made that the motor in question is in need of a total rebuild. In my mind, the first thing to do is to collect as many 911 books and manuals as you can get your hands on. There are many good books available including Bruce Anderson's "Performance Handbook", Bentley Publishing's "Porsche 911 Service manual", the Haynes "Porsche 911 manual", Wayne Dempsey's "101 Projects for your Porsche 911" (Link) and of course the applicable volumes of the Porsche "Factory Repair manuals". Reading books will only get you so far. I found that it was almost impossible to completely understand how some things worked until I actually had the pieces in my hands.
If you aren't scared away from what you have read in all those books you bought than it is time to start gathering the proper tools that will be needed to remove, teardown, and reassemble the motor. In Bruce Andersons' "Performance Handbook" there is a good list of required and specialty tools that will be needed to rebuild an engine. I am going to assume that the person attempting to rebuild his/her motor is at least a competent weekend mechanic with a good workspace and common hand tools.
Next, I suggest you start buying the parts that you "know for a fact" will need to be replaced during your rebuild. This includes, above all things, a quality Rebuild kit (available from Pelican). Don't go the cheap route on this; you'll need a good kit. Plus, you need to be aware there will inevitably be many parts that will need to be replaced and that some of these things you will not be aware of until you have cleaned and inspected the parts. (Such as burnt valves, worn guides or intermediate shaft gears) Ã¢Â Budget for this!
This article will be broken down into 5 main sections:
Removal, Teardown, Inspection, Reassembly and Break-in.
Removal of the engine is covered in detail in Pelican Parts Tech Article on Engine Removal.
Personal Note #1: it is a good thing when you DON'T drop your engine when trying to remove it from the car. Trust me.
Once the engine is out of the car (hopefully via "Controlled descent") you need to get it off the floor and onto an engine stand. Before you can fit the engine to a stand, you will most likely have to remove the clutch and flywheel. Removal of these components are covered in Pelican Parts Tech Article on Clutch Replacement.
You can buy the Factory Engine stand (very expensive) or get a generic engine stand from your local NAPA store and modify it to fit the studs on your engine. I managed to modify a cheap $75 dollar stand by cutting the mounting tubes down on the arms to fit the shorter studs on my engine. With a bit of imagination it is possible. I was lucky enough to have access to an engine hoist, which I used to lift the motor off the floor and onto the stand. I found it much easier to mount the face of the engine stand to the motor then lift the engine up with the hoist and slip the yoke into the stand. If you get this far in one day it's time to stand back and drink a beer.
Now that you have the motor on a stand it's time to get started with the real fun stuff.
Have a collection of assorted size Ziploc bags and boxes of all shapes and sizes in a holding pattern next to your work area. I suggest using a small notepad and disposable camera for taking notes and photographing pieces and parts as they are removed. Be absolutely sure to group, label and separate all parts removed.
Personal Note #2 One thing most books don't mention is the fact that when you receive your new Rebuild kit, it comes as a box full of gaskets, o-rings, washers, seals, chains, piston rings and other misc. items. On the one I bought, nothing was labeled. It is not fun trying to figure out where two- dozen different sized o-rings go to unless you saved the old o-rings as you removed the parts. So, my suggestion is to keep all of the old gaskets, o-rings and other seals with the parts as you remove them. That way, when it comes to reassembly, you can take an old o-ring and dig through the rebuild kit until you find it's new counterpart. If I had thought of this ahead of time, it would have saved me a lot of trouble.
The first thing to come off will be the induction system. Whether it be Carburetors, MFI, CIS, or DME, they all basically come off the same way. The intake ports on each cylinder have two 13mm nuts on them. Some of these nuts were almost impossible to get at with a wrench! On my SC, there were a few that required some pretty ridiculous combinations of drive extenders and universal attachments as well as stubby open-ended wrenches. Best advice I can give you is: "Good luck... It isn't fun." My injection system experience is limited to that of my '79 SC so I can only give specific information applicable to the K-Jetronic cars. I removed the entire fuel system from the motor as one unit. I unbolted the intake runners, disconnected and marked all fuel lines and wiring harnesses and pulled it off.
The removal of the engine mounts, tin, fan/alternator and ancillaries is pretty straightforward. Just make darn sure you take pictures and mark the alternator wires!
The exhaust system turned out to be a bigger job than I originally anticipated. When people say: "Yup, those exhaust studs normally rust up and freeze solid they aren't lying. I squirted the nuts with WD-40 and let them sit for a couple hours while I ate lunch.
Personal Note #3 I found that instead of buying the "Super Special Porsche Factory tool" to remove the exhaust nuts, that an 8mm T-handled Allen wrench with a breaker bar fitted onto one end for leverage worked like a champ.
Some people suggest using a torch to heat cycle the exhaust nuts several times before trying to remove them. I didn't have the luxury of having one available so I just let them soak in WD-40 and gently tried backing them off. I was successful at getting them all off without incident except for one, which snapped. It really didn't matter though because all of them were severely corroded and pitted so I decided from the get go that they would need to be replaced when the cylinder head work was performed.
With the engine shroud removed, you now have a long block! (Time for the next beer)
No more kiddie stuff, now we're getting into the Meat and Potatoes of this baby!
Everybody knows that taking apart an engine isn't exactly brain surgery! It's puttin' it back together and having it run which is the tricky part. I won't get too specific about what comes off next and in what sequence. There are obviously several ways to do the same thing.
The next parts that must to come off are the cam chain housings. (Image) Once you get the tensioners out and the cam gears taken apart (special attention is needed here to keep all the tiny parts organized) you can sit down and remove all 12 rocker arms and shafts from the cam housings. These little suckers can be a pain in the butt. Calling them stubborn would be too nice. Let them soak in WD-40 for a couple hours; I found that it helped a bit. (Remember to properly label each rocker arm with its shaft,- i.e. #3 Intake) Once the rocker arms are removed than you can slide the cams out of the cam housings. Be careful when doing this, the cam housing is made of aluminum, the camshafts are steel, if one of them binds as you are removing it don't be too rough, you could damage the softer aluminum housing.
With the cam chains out of your way you can now remove the cylinder heads and cam housings from each bank as one unit. I found that this was the easiest way to do it.
Personal Note #4 I discovered that you don't have to buy the Super Special 10mm Porsche tool for removing the head stud nuts. A common Allen head socket on a drive extension worked like a champ.
When you remove the head stud bolts, do it in an even, progressive manner. You don't want to possibly warp the cam housing. Once the cylinder heads have been removed you should be staring at the tops of your pistons! (By now you should be very excited). Remove the air deflectors and oil return tubes and bag 'em up.
Using a soft mallet, gently tap on the base of the cylinders and they should slide right off without too much of a fight. I put rags underneath the exposed pistons to keep them from flopping around against the head studs and possibly damaging them.
If you have an early engine, remove the oil sump plate cover, thermostat, breather housing and engine mounted oil cooler. (treat the oil cooler as if it were made of gold.. it's almost worth its weight in it!) Now you should have an engine block with pistons sticking out of it.
Personal note #5 I found out the HARD way that you MUST remove the pistons from the connecting rods before you attempt to split the case. "DO'H!!" At this point it is easy to get a little ahead of yourself with anticipation. Remember to take it slow and steady.
As far as removing the pistons goes, the most important thing to remember is that when the piston wrist pin cir-clips come out of their groove, they can do so at Mach 6.5. Be careful!
Use a hardwood dowel to drive the wrist pins out. You don't want to put a heck of allot of cross load on the connecting rods so don't spank them too hard!
Mark the location of each piston and bag them. Now you can spit the case!
Turn the engine on its side and remove the butt-load of nuts securing the case halves together, including the crankcase through-bolts. Don't forget the ones that sit behind the flywheel, they could be covered with gunk and overlooked. This next part is tricky to say the least! I used a soft mallet and a large screwdriver to "coax" the halves apart. I did not force the screwdriver into the seam and "drive" it open. That will definitely damage the sealing surface. Rather, I used the mallet to get the case to start to separate and once I had a small gap going, I used the screwdriver to gently spread the halves. It takes quite a bit of jostling. Once it comes free, lift it away and take a beer break--you'll need it.
Now the crankshaft and connecting rods may be lifted away. To remove the oil pump and lay shaft you need to break or bend the small Lock-tabs that secure the pump to the case. Pull it all apart, bag and label everything. Mark all of the main components with their respective numbers.
Congratulations! You have just completely torn apart a 911 motor! Now you have to put it back together--oh boy.
Inspection of components is where the expensive manuals you bought will come in handy. Understand that there are some parts that require special tools or professional equipment and expertise to properly inspect for wear and serviceability. Clean everything thoroughly. (A solvent tank is very nice to have.) I knew that some of the parts would be waiting a while before I got to refit them, so I put a thin coat of oil on things like the cams to keep them from rusting and wrapped them up in rags. Depending on what you have discovered up to this point you can determine what work needs to be completed and which parts will need to be replaced. For instance, I found that the intermediate gear on my motor was quite worn. (Image) It was still in spec, but just barely. I decided it didn't make much sense to reinstall a part that was just marginal so I bought a new one. I did the same for the chain gears.
There are many good Machine shops out there who specialize in Porsches. They can handle all of your cylinder head and balancing work. The bottom end of 3.0-liter engines are amazingly tough. My main bearings looked almost brand new (With 220,000 miles on them). Some people use the 3.0 liters reputation of being very sturdy to avoid tearing apart the bottom end. I personally disagree with that because although the main bearings looked great and the rod bearings looked ok, the lay shaft bearings were almost totally shot. They were worn into the bronze. Second point, by the time you've got the motor out of the car, disassemble and clean the top end, you've already done 80% of the work. Why not split the case and throw a new set of bearings in there. It's really not that much more work!
I had my crankcase, cylinder heads, and cam housings Hot Tanked by the local NAPA store. If you take your parts somewhere to be hot tanked, just make sure they have a separate Hot Tank for aluminium parts. The Hot Tanks used for cast iron blocks will melt or damage aluminium parts.
Personal Note #6: Make sure you remove the two Oil pressure relief valve pistons and springs located on the lower left and bottom sides of the crank case. I would also strongly suggest you replace the springs. They only cost a couple of bucks apiece.
I sent my crankshaft out to be checked for cracks, inspected for wear, and micro polished to finely polish the wear surfaces. I had my connecting rods checked over, new wrist pin bushings installed in the small end and had the big ends machined back to their proper size. The rods were precision balanced with their respective pistons. I also sent the machine shop my new flywheel and pressure plate so that they could be balanced with the crankshaft. Next I sent them my old rocker arms. The bushings were pretty worn and I was lucky enough to find a supplier who got a shipment of rocker arm bushings so I had new bushings installed and honed to fit new rocker arm shafts. Porsche builds some pretty good little engines. The machine shop I used was fairly impressed with how close the parts were (from the factory) in terms of tolerances and wear.
I sent my Cylinder heads to another machine shop who specializes in Cylinder head work. They disassembled and cleaned the heads, installed the new valve guides, valves, springs and keepers I bought and shipped me back a set of shiny new looking heads. I also sent my engine mounted oil cooler out to be ultrasonically cleaned.
This stage is a good time to replace the head studs if any are broken. Almost everybody has a different opinion about the head stud issue. On my engine, I was rebuilding it due to a broken bottom stud on the #6 cylinder. From what I have been able to tell, on 3.0-Liter engines, the bottom studs are prone to breaking. The bottom studs are made from a material called Dilvar while the top row of studs are made of steel. Most people seem to think that years of exposure to the elements and countless heat cycles make the Dilvar studs weak and brittle.
I decided to only replace the bottom 12 studs. I ordered a set of the factory steel studs and installed them myself. In order to get the old ones out of the case you need to borrow your beefy neighbor for a bit. Some people suggest gently using a torch to heat the base of the stud in the case to melt the Loctite that was used when they were installed at the factory. I didn't like the idea of putting a torch to my precious case so I just went with careful, brute force. You can either use Vice grips, double locked nuts, or a special built stud remover available at most specialty stores. Since I didn't remove the top row, I was able to install the bottom studs to the same HEIGHT, measuring off of the top stud. I used a high strength Loctite to secure the studs in the case.
Once all the rotating parts have been cleaned, measured, machined, repaired or replaced, it is time to begin reassembly. The bottom end is actually quite simple to reassemble. The biggest hurdle is having everything laid out in a neat, logical order. You need to have all the tools, parts, and other items set out in a way that you can work things methodically and quickly at the same time. (I say quickly because you only have a set amount of time to seal the case before the Loctite used between the crankcase halves begins to harden.)
When I assembled the connecting rods to the crankshaft, I lightly oiled the rod bolts and evenly torqued the bolts in steps to their proper torque. Some manuals say to torque the bolts to a certain torque, and then turn the wrench 90 degrees. I didn't like that idea; it just didn't make sense to me. But as with almost anything automotive, there are several methods that can be used which achieve the same goal. I also installed my crankshaft with the flywheel main seal installed.
Once the crank and rods are assembled, you can install your new main bearings in the right crankcase half and lightly oil them with assembly lube/motor oil. Gently lower the crank into place with its nose bearing and new o-ring installed. Make absolutely sure that the nose bearing is aligned with the dowel pin on the crankcase. If it is not, then it will not seat and you'll have one big mess on your hands. After I had my case hot tanked, I noticed that the dowel pin was missing on my case half. I called around to see what I should do and a very reputable source who shall remain anonymous, (John Walker) suggested that I take an old drill bit of equal size, cut off a short length at the base and use it as a makeshift dowel pin. I used a mallet it set it in the hole and it worked like a champ!
Once the crank is correctly seated in the case half, then it is time to install the lay shaft and oil pump (as one assembly). (Image) Don't forget to put the new timing chains around the gears before lowering it into place! You will need 3 new lock tabs to secure it to the case. My rebuild kit didn't come with any and it set me back a week waiting for three little dinky lock tabs to arrive before I could proceed. Remember to lube and carefully install the o-rings that seal the oil pump into place.
Now with the crank, lay shaft and oil pump in place it is time to begin preparation to lower the other half of the case onto the first. This represents several small problems to overcome. First, you have three connecting rods that are flopping all over that need to stand straight up to go through the cylinder spigots on the left crankcase half. And you also now have one of the timing chains dangling about. This is one of those steps where it is almost as if you need six pairs of hands to hold everything. I used a stiff piece of cardboard cut into a strip to support the chain straight up in the air (Image). And as for the connecting rods, I used masking tape to hold them up (Image). (This is where the methodical, neurosurgeon attitude comes into play.) Now that you have everything secured and out of the way, it is time to place the other half of the case into position. Install the main bearing shells (correctly) and lightly lube them. Gather up all of the nuts needed for the case perimeter and the socket wrench to tighten them with. Pre-assemble the crankcase through-bolts with their new o-rings and lube them up with Dow Corning 111. Have your trusty Torque wrench set to the proper torque standing by. The next step is to put a bead of sealant, whether it be Loctite 574 or an equivalent, around the sealing surface of the case. I must say, I thought this was pretty straight forward and not hard at all. I do however have an oil leak on my rebuilt engine coming from the area immediately around the crankshaft nose bearing, behind the fan pulley. I don't now if it is because I used too much Loctite, or too little, or if there was a slight burr in the surface that I didn't notice. At any rate, there is nothing I can do about it, but I want to stress the importance of closely inspecting the sealing surfaces for any gouges or burrs, or anything at all that could lead to a poor seal.
Immediately after you get a thin, even coat of sealant around the sealing surface it is time to lower the left case half into place. It is really handy to have a helper at this point. I had a friend help me lower the half into place, all the while making sure that the timing chain and connecting rods weren't hung or fallen out of place. I used a mallet to gently tap the case halves together and immediately started hand tightening the multitude of 13mm. Perimeter (crankcase flange) loc-nuts. As my friend was busy fumbling with the loc-nuts, I was busy installing the crankcase through-bolts, complete with lubed o-rings, in their respective places. The through-bolts are the first to be torqued. I torqued them in stages and in a criss-cross pattern. Once you are satisfied that all of these have been torqued (including the two behind the engine mounted oil cooler and one in the left chain opening) then you can proceed to torque the crankcase flange bolts. Once all of this is done it is definitely time for another beer. Congratulations you now have a completed Bottom end!
Pistons and Cylinders
Here is another topic of great debate. Porsche used two suppliers for its pistons and cylinders, Mahle and Kolbenschmitt (KS). The Mahles cylinders use a plating process in the bores lined with a material called Nikasil. While the KS cylinder bores are impregnated with a substance called Alusil. The Mahles have a rock hard nickel-plating while the KS cylinders are impregnated with a kind of silicon. In my opinion both are well made but most people tend to think that the Mahles are the superior brand. You can tell if you have the Nikasil cylinders if the bores are very shiny and reflective. They also have "MAHLE" cast into the base. The KS cylinders are not near as shiny and have almost a yellowish tint to the bores. As of yet, no one has ever been able to tell me if there is some sort of rhyme or reason to the way Porsche chose to use the different types of pistons and cylinders (P/Cs). My personal guess is that Porsche used whichever pistons and cylinders they could get their hands on at the time so that is why you never know which type you might find on your car.
On horizontally opposed engines such as the 911, the cylinder bores have a tendency to wear in an oval, making them out of round. If you try to re-ring the pistons and slap it all back together with even slightly out of round cylinders, I have been told that you run the risk of having the new piston rings dig into your cylinder bores and you could end up with broken rings very quickly. If you are lucky and your piston skirts and cylinder bores are still within factory tolerances, you may still be able to use them. After asking many shops, Porsche-gurus and one certain pillar of the Porsche community, most of them seem to think that you can get away with roughing up the bores a bit using a scotch-brite pad to help the rings seat and put it all back together. But others have told me that they have tried this method and although they said to have had some success, one in particular said that if a customer wanted him to do that then he asked them to sign a statement saying that the motor may smoke more than usual. Well, I didn't like the idea of my brand new motor smoking as I drove down the road so I looked for other options.
One of the other options includes, buying a set of new pistons and cylinders. Obviously this would be the best route to go but I simply could not afford to spend $2500 on pistons and cylinders. So, I kept looking for other alternatives. I found a place in Reno, Nevada who offered a "reconditioning service". They have the ability to re-size and re-plate the Mahles and re-impregnate the KS cylinder barrels using some pretty advanced methods. Both of these services are much cheaper than buying new pistons and cylinders.
My car originally had Mahles installed but I ended up putting a reconditioned set of 9.3:1 CR, KS pistons and cylinders in my motor.
Bottom line is that there are many different options out there, but you must decide how much you're willing to spend and what risks you find acceptable.
When it is time to install the pistons and cylinders onto the assembled bottom end, there are a couple ways to do it. I, being a novice, did what most novices probably do, which was mount the pistons to the rods then try to slide the cylinders over them. This proved to be the biggest pain in the rear of the entire rebuild. What I now suggest, is to take a piston and cylinder on a workbench, install the piston rings, compress the rings, slide a barrel over the piston just enough to cover the rings, then take the whole thing and slide it over the head studs on the case, drive the wrist pin into the piston and then squarely tap the cylinder into place. (Do not forget to install a new cylinder base gasket before installing the cylinders!) For some odd reason, I have read that some books tell you to make sure to only use new wrist pin cir-clips and to ensure that they are facing (open end) either towards or away from the connecting rod. I can't imagine why, but I did it anyway. Also, before pressing the cylinder to the case Double check that you didn't forget to install a cir-clip on both sides of the wrist pins.
Personal Note #7 In order to get to all of the connecting rods you must spin the crank over to get each rod at TDC (Top Dead Center). When you do this, the cylinders might try to move away from the case due to the resistance from the piston rings. You can buy the Super Special Porsche Cylinder Holding Tool, or you can take two head stud nuts, thread one all the way past the threads, up against the cylinder and tighten the other one down right behind it. Worked like a champ. I can't even believe they" made" a special tool for this job! Remember that when you try to rotate the crank that the two timing chains can bind on themselves really easily. You might think that there is a problem because your engine won't turn over but it's most likely just one of the chains or one of the loose connecting rods catching on something because they are loose.
Heads and Cam housings
I am not going to get into too much detail about the actual assembly of the heads. When you send them out to most machine shops they reassemble them for you as part of the job. Again, there are several ways to go about doing this and everyone has their preference. You can bolt the individual heads to the cam housing on a workbench then mount the whole assembly on the engine, or you can loosely bolt each individual head to its cylinder, place the cam housing on top of it and bolt everything down. The most important thing to remember is that whatever you do, you want everything to be evenly tightened to prevent any warping of the cam towers. The best way to check for warping that might be occurring as you tighten the cam housing and head bolts is to temporarily install a cam shaft and constantly turn it while you tighten the bolts. If any resistance is felt in the rotation of the cam then stop, back off and try tightening it in a different order.
With the heads, cam towers, crankcase breather housing, thermostat, cam chain housings and oil cooler installed you almost have a completed long block! (Don't forget to fit new oil return tubes into the case before attaching the cam housings!)
The dreaded Cam Timing - Yes, we are finally there!
I was just as confused and worried about the cam timing as every other 911 rebuild virgin. I must say right now that even though it is a tedious task that must be done right, it is not that hard at all once you understand what you are trying to accomplish. Trust me, if I can do it than you can do it too!
Before the cams can be timed it is necessary to install the intake rocker arms on the #1 and #4 cylinders. Refer to the Pelican Parts Technical Article on 911 Valve Adjustment for complete details.
First off you must understand the basic idea of how a 4-stroke internal combustion engine operates. Hopefully you already understand this before you completely rip apart your engine! Bruce Andersons "Performance Handbook" has a very good section, which gives a detailed description of how and why valve timing is so important. For sanity's sake I will not go into a step-by-step detail about the cam timing because it is covered in such detail in every manual out there. I would like to give an explanation of "what your trying to do" in normal language to hopefully clear up a bit of what the manuals don't get across too clearly in my mind.
First it is necessary to "Rough time" the engine. Rough timing of the engine is accomplished by eyeballing the position of the camshafts in relationship to the crankshaft. First thing to do is to turn the crank to TDC. That means (in theory) that the #1 and #4 cylinders both have pistons at their full extension. So, how do you get the #1 cylinder to TDC? Simple, first Install the crankshaft pulley on the crankshaft. Notice that there is a dowel pin that dictates how the pulley goes on the end of the crankshaft. You can't mess it up; it'll only go on one way. Now, on the face of the pulley there are 3 marks, one of them has "Z1" marked next to it, that is your TDC mark. So, simply rotate the crank until the Z1 mark is matched up with the seam in the crankcase. (There is also a notch in the bottom of the fan shroud if you have it installed.) Once these are lined up your crankshaft and pistons #1 and #4 are now at TDC.
I found that the best way to figure out which stroke the cylinder is on (compression or firing) during this whole process is to install the distributor and use the rotor as a guide. To set the distributor to #1 firing stroke is easy. Simply set the crank to TDC, get the distributor shaft started in the hole (with new o-ring installed of course) and roughly point the rotor where the #1 spark plug wire would normally go into the distributor cap (if it were installed). The rotor should be pointing at something like a 45 deg. angle up and away from the engine. When you seat the distributor fully into the case, the worm gear on the crankshaft meshes with the gears on the distributor. It takes a bit of playing with it to get the rotor to point in the proper direction. The Pelican Parts Tech Article on Setting Static Timing gives a detailed description of how to set the distributor.
With the distributor rotor pointing as described, the engine is now at #1 TDC firing stroke. If you were to rotate the engine 360 deg. at the crankshaft, from this point, the rotor would now be pointing 180 deg. from where it was. And now the engine is on #4 TDC firing stroke and #1 in at TDC compression stroke. If you understand these two things than you can time an engine.
Once the cams are installed and have been sealed to the cam chain housing you need to get them roughly pointed in the right direction. (Image) On each cam there is either a number or a dot stamped on the face. This number or dot must point up. With the cams pointed up (chains not attached) and the crankshaft at TDC, your engine is now rough timed.
Now that the motor is rough timed, assemble the gear flanges with the woodruff keys on the cams and install the gears on the cams with the chains.
The cam gears are kept in position by the use of the little dowel pin that locks the gear flange with the gear. There are 17 holes around the circumference of the gear. When you are timing the cams, you are doing so using a method that measures the amount of overlap of one valve on each bank of cylinders. These measurements are taken with the use of a dial indicator on a special "Z" mount. (Fortunately you can pick up a dial indicator for around $30 or so and I believe Pelican carries the indicators and the Z mount. I would suggest buying a Metric dial indicator; it makes the process much easier without having to do conversions.)
You are attempting to set timing on one bank of cylinders at a time. Starting with the left bank, position the dial indicator with about 10mm. of preload so that the indicator needle is resting on the cylinder #1 intake valve cap. When you have the crank at TDC and the left banks camshaft pointed up, and the dial indicator set on the valve cap, you are ready to time the cam on the left bank. (You can either install the tensioners at this stage, which is what I did, or you can use a long screwdriver to keep pressure on the idler arm, which will keep the chain tight.)
With everything ready to go on the left bank, insert the small dowel pin into whichever hole is lined up (It'll make sense when you see it) and hand tighten the large nut and washer. While you tighten the nut you don't want the cam to move even the slightest bit. Once you think you have it set as best you can by eye, you turn the crankshaft exactly 360 deg. while watching your dial indicator. (In your manuals it will give you a certain value of overlap in millimeters for your specific motor and camshafts; for my 3.0 it is 1.55mm.) That's what you are trying to get on the dial indicator. If, after spinning the motor exactly 360 deg., you get a reading higher or lower than what is called for, then the dowel pin will have to be removed and relocated to another hole. This is more less a trial and error process. It took me several times to get it down right. When you can rotate the crankshaft 360 deg. and get the exact value that is needed that bank is now timed properly! All you have to do is torque the nut and re-check to make sure nothing moved. Now you just move on to the right bank of cylinders and repeat the whole process.
(Remember that when the crank is set to "#1 TDC firing stroke", if you rotate the engine 360 deg., that now even though the crank has made one complete revolution, you still need to turn it another 360 deg. to get back to your starting point of "#1 TDC firing stroke". It takes 720 deg. (two complete revolutions of the crankshaft) to get from #1 firing stroke to #1 firing stroke again because it is alternating with the #4 cylinder.)
There is a little more to it but the repair manuals break it down pretty good. Just be absolutely sure to double-check your work before moving on. Next, it is time to install the rest of the rocker arms and shafts in the cam housings. This was a bit tricky because you have to center the rocker arm shafts in the camshaft housings. The rocker arm shafts are held in place by the use of a pinch bolt. There are cone shaped pieces that fit into each end of the shafts and when you tighten the bolt it draws these two cones towards each other causing the ends of the shafts to flare just a bit. This flaring action is what secures the shafts in the bores. I bought a set of RSR o-rings that were used by the factory on racing engines. These little o-rings sit in the grooves on the rocker arm shafts and provide a bit of extra sealing protection against oil leaks from around the shafts. I think they are a pretty good idea, especially for the price. After you torque each rocker shaft into place, wiggle the rocker arm back and forth to make sure that it moves freely. If it binds than the shaft is off center and must be corrected. I found that the shafts were pretty close to center when the flared nut was just about flush with the narrow side of the cam tower. The next order of business is to perform a precise valve adjustment. Again, this procedure is explained at length in pelican Parts Tech Article on 911 Valve Adjustment. (Link) Pat yourself on the back and go kill a six-pack because you have just completed a long block!
Injection System, Exhaust, Ancillaries
The majority of the remaining work is simply "reverse of removal". From this point on, everything should really speed up. The exhaust system is pretty simple, the only hard part is figuring out a way to get a wrench in some of the incredibly tight places under there! Remember to use only new gaskets and put a bit of anti-seize on all of the stud threads.
For CIS cars, refitting the injection system is not all that hard. I really didn't disassemble mine beyond the intake runners. I fitted new rubber boots, vacuum hoses, warm up regulator, cold start valve, thermo time switch, injectors and o-rings and cleaned up the air box and metering plate real well. It worked fine before I removed it so I figured it was better not to mess with it any more than I already had.
Those notes and photographs you took when you removed everything will be invaluable at this stage. Trying to remember where all those vacuum hoses, fuel lines and wiring harnesses go is not fun if you didn't label and take notes of their locations before hand.
Once you get the exhaust, intake, fan/alternator, plug wires, engine tin, engine mounts and cross bar re-installed you are on the home stretch.
Getting the engine back in the car is a tricky bit as well. When you have the engine assembled to this point, you can't do anything further on the engine stand. I fabricated a wooden dolly mounted on casters to set the engine on. Now that you can roll it around and without the engine stand in the way, you can now install the flywheel and clutch. When installing the clutch and flywheel remember to properly center the friction pad with a centering tool (Image) before you tighten down the pressure plate. And, pack the pilot bearing on the flywheel with heavy grease to keep it well lubed.
It is now about time to prepare the car for installment of the new engine. A good cleaning of the engine bay will make things go smoother. I drained the gas tank since it had been sitting for almost 9 months. I then filled the tank up with premium Techron and charged the battery. Once the battery was charged I put a bucket under the fuel hoses in the engine bay and turned on the ignition to pump the old gas out of the fuel lines. Once new gas started coming out I was satisfied. I had the advantage of using a car lift to raise my car in the air. Then I rolled the engine on the dolly under it and v e r y slowly lowered it towards the engine. (Image) I had a helper who kept an eye on things and moved the motor around a bit while I lowered the car even lower. The biggest problem I encountered was the fact that there just wasn't enough room under there to try to mate the engine up to the gearbox, which was still in the car. If I have to ever do it again I will remove and install the engine and gearbox as one unit instead of shoehorning it like I did. It was next to impossible to squeeze myself under there and wiggle the day lights out of the engine while raising and lowering the car mere millimeters, countless times trying to get the studs on the engine to mate up with the gearbox and getting the throw-out bearing release fork to engage the TO bearing. I still think it was a miracle that we ever got it all together. I will never do it that way again.
Once we got the motor bolted to the transmission, I lowered the car until I could attach the engine mount bolts near the bumpers. From there it was simply a matter of reattaching the throttle linkage, clutch arm and cable, oil and fuel lines and wiring connectors. After topping it off with fresh oil and I was ready to try and start it.
The first few seconds that a rebuilt engine runs it has very little lubrication and no oil pressure. These first few minutes might very well be the most abusive moments your engine ever knows. When I was ready to start my engine I first, disconnected the fuel pump relay, (to keep gas from the engine) then pulled the ignition wire out of the Voltage transformer also known as a coil (to keep the engine from sparking). Then I hopped in the car, crossed my fingers and gave it a whirl. I cranked the engine with no gas or spark about 5 times at 6 or 7 second intervals; until I saw my oil pressure gauge move. When the gauge needle moved I knew that oil had been circulated throughout most of the passages in the motor. Next, I re-installed the fuel pump relay and cranked it several more times to get fuel into the fuel lines. After a few seconds of this I connected the plug wire and gave everything a once over, triple checking that I didn't miss anything I closed my eyes and turned the key.
I must have cranked on that thing for 15 minutes. I got nothing, not even a blip. I started pulling fuel injectors and found that they were all dry. I knew the fuel pump was running and that fuel was getting to the fuel distributor so I was puzzled as to why it wasn't getting past the injectors. After a bit of reading I discovered that CIS injectors are designed to open at a certain amount of pressure. I wasn't getting enough fuel pressure to open the fuel injectors and I couldn't figure out why. After another 10 minutes of periodic cranking the engine started showing signs of life. Every time I cranked it, the motor started sputtering a little longer and longer until finally, she roared to life! (After allot of discussion, we decided that there must have been air somewhere in the fuel system which was preventing it from building up enough pressure to open the injectors and it simply took some time to cycle it all out.)
I let it run for about 20 minutes at a high idle to bed down the drive train components then shut it down and drained the oil.
As far as actual break-in of the motor is concerned, I decided to drive the car real easy, revving up to 3500 rpm for the first 500 miles. After that I wanted to drive it a bit harder, allowing revs to reach 4500 rpm with the occasional burst to redline.
I say that I "wanted" to do this break-in procedure because I still have not had a chance to do it! As I write this article, I am sitting in the middle of the Persian Peninsula having been deployed over here with the USAF only days after my motor was put back in my car. I am writing this article from memory so I am sure that I have left some things out and have made some (hopefully) minor mistakes. If you find one or have any other ideas or tips please feel free Pelican Parts. I would never have attempted rebuilding my engine if it weren't for the countless people from Pelican Parts and the loyal PP Bulletin Board addicts who gave their time and energy to answering my many questions. A special thanks goes out to Wayne Dempsey who puts up with us Pelicanphilies on the 911 Tech Bulletin Boardand to the many members and contributors of the SCWDP. You know who you are!
Leland E. Pate, USAF