A4 head rebuild, Part 3

[Igor Kessel]

PART 3 - head cleanup.

*WARNING*
My notes below are NOT meant to be a substitute for not reading your
Bentley! They are only a supplement, ought to share some tricks and
hidden obstacles with you.

12. Relieve the pressure on the chain tensioner using the Audi tool
#3366. Make sure that you don't over tighten it or you will damage the
tensioner.

13. Using a Torx #30 bit carefully relieve the pressure from both
camshafts in a diagonal sequence: caps #2 and #4 first, then the rest.
Remove the caps, the camshafts and the chain tensioner. Note that for
some mysterious reason Audi has decided to mark the camshaft bearing
caps in an unusual manner: their numbering starts from the back of the
head.

14. Using some Lacquer Thinner on a rag carefully wipe off oil residue
from the 8 Exhaust valve lifter tops and mark them 1 through 8 starting
from the head's front (my personal convention). Repeat for the 12 Intake
lifters. The idea is to place the lifters back in their respective wells
after you will have finished rebuilding the head.

15. Using a suitable magnet remove all 20 valve lifters from their
respective wells and store them upside down while rebuilding the head.
You don't want the oil to leak out of the lifters.

16. Using the special Audi valve spring removal tool compress the valve
springs and remove the valve keepers. The long nose curved tweezers work
very well. Sometimes the keepers are jammed in the top washer and don't
want to budge. In this case just whack the top of the spring compressor
with a hammer, while holding the handle in the compressed position.
Watch out for the keepers jumping out and all over the floor. You don't
want to lose any of those tiny wedges. Now remove the springs and their
top washers.

17. Using the valve stem oil seal removal pliers remove the oil seals
from the valve stems. Remove the spark plugs.

18. Flip the head upside down. Watch out for the valves. You don't want
them to fall out of the head! Pull the valves out one by one by a few cm
at a time, but not completely out and wiggle them radially. Or better
yet use a machinist's indicator to measure the wear on the stems against
the spec in your Bentley. If the wear limit is exceeded, the bronze
valve guides will have to be replaced. Which in turn will necessitate
the replacement of all the valves, coz it is pointless to put old valves
into new guides.

19. Using a straight edge and a feeler gauge measure the flatness of the
head's working surface. If it is warped you are looking at a re-plaining
job in a machine shop, possibly even replacing the casting.

20. Remove the first exhaust valve counting from the head's front and
clean it up with a Dremel and the soft pad that I have listed in the
previous paragraph. Once you are done, carefully degrease it with
Lacquer Thinner on a rag and mark it #1. Repeat for the rest of the
exhaust valves, marking them #2 through #8.
Repeat the whole procedure for the Intake valves, marking them #1
through #12. if you will be reusing the valves and their guides you
really want each valve stay with its respective guide.

20. Mount the valves one by one in a chuck of a good stationery drill
press and spin them. I personally prefer to use a milling machine with a
collet for accuracy. Look for any wobbling. If a valve wobbles replace
it with a new one. In my particular case all 8 exhaust valves were bent;
all 12 intake valves were intact.

21. Now it is time to lap the valves. Do not use the Valve Lapping
Compound that Sears (Craftsman) sells. It contains Silicon Carbide grit,
which likes to embed itself into work. Use only the good professional
stuff from McMaster-Carr http://www.mcmaster.com (Lapping Powders for
Bearing Surfaces, Hard-metal grade (green label), McMaster p/n 4781A6).
Add a few droplets of motor oil to it, mix to a sour cream consistency,
carefully apply the resulting paste to the working circumference of the
valve/seat and using a reciprocal back and fourth movements lap the
valves. A cheap lapping tool, made like an old hand drill with a manual
crank, will expedite the job dramatically. Keep on lapping the valves
until the working surface is consistent and even in width (~1.5mm for
the intake and ~1.8mm for the exhaust MAX) and is matte in colour. Audi
explicitly forbids grinding the valves (including the 3-angle jobs).
Only hand lapping is permitted.
After you are done lapping, carefully wipe the valves and the valve
seats with Lacquer Thinner. Pay close attention to the valve guides. You
don't want any of the abrasive compound find its way into their
precision ground bores.

22. By now the head should not have any plastic or rubber or moving
detachable parts on it. It prolly looks like shit, with the carbon
buildup and burnt oil residue all over. My head was almost factory
clean, thanks to 30kmi on Mobil-1 syntectic with its excellent detergent
capabilities, but the carbon buildup was none the less quite
substantial. If you are a slob, don't do anything and skip to paragraph
. For the rest of us some heavy duty cleaning is in order. There are
several ways to clean the head.

23. Professional cleaning. If you know of a GOOD professional shop, that
SPECIALISES in VW/Audi all-aluminium heads, you can ask them to clean it
up. They will most likely "glass bead" (sandblast) the surfaces and "hot
tank" (dip the head in a boiling base) it afterwards. The results of
such a treatment are usually quite spectacular.
However! I would strongly recommend that you don't do that. Firstly, the
oil galleys in the 1.8T 20v head are so narrow and convoluted that if
heaven forbid they fail to clean the galleys perfectly, an oil blockage
of a camshaft journal lubrication jet may result. In which case you will
get a melted Aluminium cam bearing in no time at all, with the
disastrous consequences.
Secondly, should they use a wrong solution, or accidentally keep the
head in the base for a longer period of time, the Aluminium will become
spongy. In which case you might as well trash the head casting.

24. DIY cleaning - my preferred way. Yes it is messy, smelly but it is
safe and reliable. Firstly, use the previously mentioned Dremel/pad
combo and clean up the combustion chambers. Do not use the wire brush
bits with the Dremel. The trouble with them is the fast spinning Dremel
makes them shed wire bristles, which will get everywhere, including the
oil passages, the valve guides and so on.
Secondly, liberally spray the head with the Engine Bright or whatever
the engine degrease happens to be you favourite when you pressure wash
your engine each Spring. You DO pressure wash your engine each Spring,
don't you? ;)
Let the degreaser soak in, then brush off the stubborn oils spots and
hose the head off. Repeat until the head is looking nice and shiny. Call
me a snob, but I do hate working with greasy oily and dirty car parts.

(to be continued)

--
Igor Kessel
two turbo quattros