One For The Gearheads

EXAIR Application Engineers are geeky about compressed air, but there’s a few gearheads at heart among us, too.  I’m one of them.  Read through my blog below for a dive into my most recent gear-driven fun!

1998 A4

Recently I took on a new project at home.  One of my friends called me to tell me about an A4 with a potentially blown motor that might find a happy new home for the right (low) price.  Seeing as how I’ve procured many a vehicle in just the same way, I’m always optimistic about these kind of things.

So, I made the trip to look at the A4 and found a clean interior, 80k on the clock, and a no-start condition.  After sitting at the dealer for over a month without an accurate diagnosis, the owner had it towed to his house where he put it on the market as-is.  Unsure of the problem, but confident I could find and fix whatever is needed, I bought the car.

AHA DOHC

Cranking the engine (2.8 AHA code) over, I could hear a lack of compression, so I pulled the plugs and confirmed with a gauge.  Bank one (cylinders 1-3) had virtually zero compression on any cylinder, and bank two (cylinders 4-6) was perfect.  Interesting…  My first thought was that there was a timing belt failure and valves were bent when getting readings on bank one.  But the perfect readings on bank two made me second guess.  Nevertheless, I pulled the front carrier/core support and tore down to the timing belt.  Sure enough, the teeth of the belt were chewed off at the crank!  But, the story goes on…

The repair in a case like this is to pull the cylinder heads, check all the intake and exhaust valves for leakage, and replace those that are faulty (or all the valves depending on their condition).  Some people call this a rebuild of the top half of the engine, which is pretty accurate.

When I removed the cylinder heads and began to disassemble them, I could tell something wasn’t right.  There’s a camshaft adjustment unit used to advance or retard valve timing that has a special landing and thread for a service tool.  On the bank one cylinder head, this landing was missing (see the photo below).  Strange!  And, normally, the camshafts can be removed fairly easily once their bearing caps are removed.  But, on this cylinder head, no dice.

VVT Unit

Ultimately I found that the landing for the camshaft adjustment unit broke off and wedged on the exhaust cam of bank one.  See the photos below for the gouge mark on the casting.  This cam seized, locked everything on the head, and forced the crank to chew the teeth off the timing belt.  Miraculously, the valves on bank two avoided any damage and triple checked out when disassembled.

Head Gouge 1

Head Gouge 2

This failure led to the damage of (5) valves.  Some of them are visible to the naked eye as seen below.

Bent Valves

Now comes the fun part of getting the engine back together, knowing that there’s a “new” car at the end of all the work.

Lee Evans

Application Engineer

LeeEvans@EXAIR.com

@EXAIR_LE

One Response to “One For The Gearheads”

  1. I’m Back! But My A4 Isn’t…Commence Troubleshooting | EXAIR Blog Says:

    […] I dug into a project at home that I’ve been working on here-and-there; my 98 Audi A4.  In an earlier blog post I showed the damage done to the cylinder head when a valve-train component failed and a few […]


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