B7 S4 Overhaul
I went against all my better judgment and became the owner of an early 2000's Audi. I violated my own morals in the pursuit of knowledge and skill. I want to be able to work on cars just like these, but theres no way someones going to give me theirs and let me start tearing into it. If I wanted to learn how to work on these cars it was gonna have to be on my own dime.
1.1
Potential Damage
For some context here I should fill you in on what exactly ails this here Audi. To put it simply it has a gnarly misfire, camshaft correlation faults, and according to the previous owner low compression on the whole second bank of cylinders. Which would indicate bent valves, but I'm not gonna use the dots collected through a Facebook marketplace description decide my next move. Instead I'll implement some diagnosis into the motor...
1.2
Checking Vital Signs
The first thing I wanted to do was inspect the cylinder walls for any major scoring. Little did I know scoring would be the least of my worries. Unfortunately foreshadowing wasn't available for me than so I scoped the cylinders and got promising results. Minor scoring on the cylinders walls built up my confidence in this motor just enough to get crushed by the compression and leak down results. Which were horrible, as the listing said it had no compression on bank two. Bank one wasn't much better either. Despite what the correlation faults would lead you to believe the valves were sealing just fine. Pressurizing the cylinders at tdc no air was heard coming from the intake or exhaust. Upon removal of the dipstick though 20% of that air was found in the crankcase. Either the rings were toast or that scoring was more than just minimal, regardless a tear down would be my only way of knowing for sure. While the exact demise of this motor interests me, all an autopsy would do is waste time. While I plan on one in the future my present plan is to get this car moving again. Sleeving a 4.2 isn't cheap either.
1.3
Another 4.2
My main concern with this build was to avoid re sleeving a block. The high price and lack of qualified machine shops makes it very unrealistic for me. So I went to the junkyard with some compressed air and a leak down tester and found a motor that had lower miles and a decent leak down. This motor isn't perfect though, with 130k on the chain guides along with every other seal, its definitely worse for wear. My intangible is satisfied though, this motor shouldn't have to be re sleeved (knock on wood). If all goes to plan that should be about the only thing that goes unattended too on this motor. While its on an engine stand it would be ignorant to not do some diligence and rebuild it.
2.1
Tear down
When I began my tear down the biggest thing I was looking for was obvious smoking guns. Why wasn't this engine good enough to keep the car it came out of on the road? Visibly the car wasn't damaged and the trans was up for sale too so that couldn't have failed. The owner of the business told me the car probably needed chains and obvious oil leaks taken care of. It supposedly ran with a lumpy idle. He also said a quick scan showed correlation codes which plague any BHF or BBK S4. After tearing into the motor most of what I was told seemed true. The main timing guide was trashed which would've definitely caused some correlation codes. The main and rod bearings all looked to be in good condition along with the cylinder walls.
2.2
Checking tolerances
Visual inspection can only go so far, so I broke out the micrometer and t gauge. Using these fine and precise instruments I was able to really double check whether everything was within specification. This also made any plasti gauging redundant, which was good because despite Audi’s repair manual recommending the use of it, the procedure to measure it is flawed. The torque specs for plastigauge measurements were too low to correctly squish the plastic. I trusted my measurements and bought my specialized yellow bearings. I knew my crank required yellow bearings because of the markings on the counter weight.
2.3
Reassembly
As far as double checking goes from here all I can really do is lay my RTV correctly (this engine uses a lot) and torque my fasteners. From there my first start will dictate my accuracy. Which seems like an unnerving gamble to say the least, which is why I try to double check in the few ways possible. For instance turning over the motor to make sure the crank feels good, or water testing my valves after lapping them. With or without anxiety, reassembly must continue. With the heads going on I'm nearing where I thought i'd be starting when I first devised the plan of buying an s4, and that's timing.
2.4
This stinks
As much of a priority as my engine is I can't neglect the car it will be going in. When the window regulator unexpectedly decided to fail I had to rearrange my priorities. Luckily I seem to have caught it soon enough and was able to take care of some light mold and moisture.
3.1
Its time
Timing the engine wasn't exactly one linear process. Before I even got the heads on I timed the accessory chain and crank to the intermediate gears that drive the cam chain. Which really just meant throwing in the crank lock pin, than the two chains and upgraded main guides. I did this because draping the chain over the intermediate gears while the heads are on is impossible. With the gears already torqued down and loctite applied to the threads I didn't want to have to pull them off again if I didn't have to. Then before I did anything else timing related I rebuilt my cam adjusters. Some people say this is a necessary part of the timing service and I'd have to agree. There's a small pin that locks the actuator when there's no oil pressure and over time the hole that pin sits in will wear out and cause a rattle during cold starts. If a timing service has been done recently any sort of clacking is the last thing you'd wanna hear. With that done I got the heads on so I could proceed with cam timing. Which on most engines is pretty straight forward, what makes this engine's timing different than the average engine is the hall effect “transmitters” that spin independently from the cam for whatever reason. VR6’s have these style “transmitters” too but they don't spin freely on the adjuster, rather they're a part of the adjuster. All this means is that a special lock has to be put into place to ensure this sender is locked at TDC when you torque down the adjuster. Which means you need effectively three hands to torque down the cam bolts. One for ensure the lock stays in the correct orientation, one to counter hold the cam, and another to turn the torque wrench for multiple high torque stages. After all that you can turn the engine over, double check your marks, than start laying mad rtv.
3.2
Tying up loose ends
There were a few loose ends I wanted to tie up before I was ready to drop the motor into the car. The clutch and flywheel had to be installed, Intake and exhaust manifolds. If this sounds like a laundry list that's kind of because it was. Loose ends aren't especially interesting, they're just things that need to be tied. Deleting the combi valves was really the only modification besides the timing guides that I did this whole build. Deleting the secondary air injection system and the plastic vacuum lines that go with it should add some much needed simplicity to this engine.
3.3
She lives
With the engine all put together I strapped it into the back of my dads truck and brought it to the car which has been waiting months on me. When I pulled the old engine out I was met with some surprises, for instance the ac compressor clutch exploded, which caused some minor carnage. Not all the surprises were bad ones though, for instance I found some 034, goodies and punched out primary cats. Once I had everything swapped over to the new motor I installed the engine and trans back into the car. Unfortunately a few plastic coolant pipes met a timely fate so I wasn't able to get the car driving but I was at least able to hear it run for the first time after the rebuild. Which was exciting to say the least.
4.1
Do it nice, or do it twice
With all the excitement of a running vehicle powering me; I began installing everything that would be needed for the car to drive. Axles, slave cylinder, and the whole core support. After I managed to finish all that up I went to pull the car out under its own power for the first time. Which exposed a fatal mistake I made, the flywheel was toast. I couldn't fully let off the clutch without the whole driveline shuddering from the warped/damaged flywheel. For context I didn't decide to install a faulty flywheel, the flywheel I had installed was the one that the engine came with when I bought it from the pick and pull. I decided to use it because the one in the S4 was original to it and had almost 200k miles, although it was known good I didn't want to install that high mile of a flywheel. So instead I used the one that came with the engine I bought. It had 130k miles, and was free (technically), with my only other options being around $1,000 I figured I’d save the money and roll the dice. Which was a theme that didn’t really fit the script of this whole build. Straying from that and partaking in my frugal experiment is forcing me to pull the transmission and buy that expensive flywheel anyway (i'm still not putting in that other flywheel with 200k) A frustrating endeavor to say the least, but it was self induced.
4.2
What is diagnosis?
Despite the frustrating task of removing a recently installed transmission ahead of me I was excited. All I had to do was swap out the flywheel then I’d get to drive my car. Inspired by the oversimplified prospect I tore the trans out and swapped the flywheel. With the old flywheel out I examined it with suspicion, it wasn’t much different than the new one I had. I was already deep and this had to be it so I continued on. About halfway through the reassembly I was threatened by a dangerous epiphany. The front axles just looked wrong, one of the cv’s was almost completely compressed and the other axle was completely extended. Were these axles on the right sides? A now troublesome flashback of me reinstalling the axles after installing the new engine made my worries even more valid. Blinded by a days worth of ignorance and a flywheel sized hole in my wallet I continued to reassemble the car leaving the axles where they were. When all was said and done I turned the car over, put it in gear, than released the clutch and was greeted with the same exact issue.
4.3
Axle Autopsy
I may have been one flywheel poorer but atleast I knew for sure what had happened. The axle that was fully extended was basically pulled apart. Ultimate CV joint destruction was the culprit behind my noise. Which really really makes sense now. The torsion awd will send power to wherevers easiest. An axle flange that's spinning a knocking cv is a lot easier to turn than the wheel of a 3,800 pound vehicle. Initially the car still somehow moved but barely wanted to as I limped it out of the shop. The noise from what I thought was the flywheel got worse and worse until ultimately the car wouldn't move anymore. Those maybe 20 feet of movement I got out of the car were enough to completely separate the inner CV joint. 20 feet of luck because I don't know how the CV endured what it did.
4.4
The moment of truth
With yet another simple fix between me and a driving Audi S4; I worked with flat rate speed as I swapped the unfazed passenger side axle to its correct side and installed the new axle on the drivers side. With certainty and despair I again turned the key, put the car in gear, released the clutch, and began creeping back. My test drive was a crucial assessment of my vehicle (how hard could it pull in second gear). Jokes aside I was in a break in period because I rebuilt the whole motor, and installed a new clutch. Meaning my first drive was limited to a shake down and not a full fledged victory lap. The items I had touched felt fresh, but the ones I hadn't felt their age. The patina’d brake rotors humbled me, this car wasn't road worthy quite yet. Despite that I was happy with myself, and happy with the car.
5.1
Not there yet
They’re wasn’t much holding me back from being able to take this car on its maiden voyage back to my house. That was the case at least, until my friend took a look at it and pointed everything else out that I had chosen to forget. With the car being in the state of disrepair it was things like rear axle boots, or seized rear calipers that I had neglected to address. With all these odds and ends left untied I was discouraged from wiping my hands clean. 6 scrambled ball bearings later though, along with other basic work I was ready to mount my newly resuscitated steed for my trip down i93.
5.2
First drive on road
Some would say a car's main purpose is to drive you from point a, to point b. So all things considered my intentions of driving my car from work, to my house weren’t far fetched in the slightest. Despite my request being quite reasonable, I felt like I was boarding the titanic while I merged onto the highway. Despite this I was excited, who wouldn’t be?
5.3
The shakedown
My first few drives in the car were uneventful to say the least. Sticking to a break in period for the engine, and clutch kept me at or below the speed limit, and below 4k rpm. After about 4 oil changes, and a few hundred miles it was time for me to meet my hero. All the time, money, and axle boots felt worth it. 7,000 rpm is euphoric. This European V8 brought out a patriotism in me I didn't know I had.
5.4
Real automotive journalism
Getting to know this car has been just as fun as ringing it out. It’s not a peaky powerband like you would expect. There’s plenty of fun to be had in the mid range, and sufficient torque on the low end. The Jackal tune I got flashed with recently really put the car together. Being a naturally aspirated car the tune doesn’t give crazy before, and after numbers. What it does do is satisfy the intangibles; which I’ve come to learn is really this car's strong suit.
A means to the end of automotive masochism
I loved this car, I loved the way it sounded, the power, and what it represented of my workmanship. My enjoyment was bittersweet, I couldn't get over the nagging oil consumption. Its presence irked me, mostly because it was my own fault. Taking care of it would mean taking the engine apart. This presented an opportunity, I could put stronger rods in it, the engine's ceiling could be seriously raised. I wasn't interested in digging this deep again though. I already spent enough time and money putting this car together and getting it to drive. I had satisfied my learning and curiosity in the process. So even if the car wasn't perfect I was ready to part ways with it. In the end I’d gone further with this than I ever thought I would.