|» Index Page
||Introduction, About the BMW M70 V12
|» Page 1
|» Page 2
||Fault finding, condition checking
|» Page 3
||Stripping and cleaning
|» This Page
||Re-assmebly, Timing chain & heads
|» Page 5
|First stage of a cylinder head rebuild is to
remove the camshaft and all the followers. Make sure you make
a note of exactly where each part came from so you can reinstall
them exactly in the same place. The reason for this is that
the parts wear against each other, and mixing these parts up
will cause excessive wear.
The old valve stem seals are still installed at this point.
These have gone all hard and are doing a very poor job of sealing
the valve stems. I had to worry the old ones off with a pair
of pliers, making sure not to damage the actual valve guide
or the washers that surround them.
The exhaust valves were in the worst shape, and needed to be
cleaned up on a wire wheel to remove carbon build up. The seats
showed pitting and discoloration. You can have the valves and
the seats reground at a machine shop, but some elbow grease
and time soon shaped them up.
|Here you can see all the valves, spring and collets
all laid out in order. The valves at this point have not been
cleaned up. They have a film of carbon covering the valves which
will need to be removed to prevent hot spots forming on the
valve which will eventually damage it. I used a wire wheel to
remove the carbon, the valves are tough and you need to be pretty
stupid with a wire wheel to damage them. Once clean, examine
the valves for burnt sections or cracks.
The valves are then lapped back into their seats using a two
stage grinding process. A coarse grinding paste is applied,
followed by a finer grade final stage. Make sure you don't get
the paste into the valve guide, and clean the whole working
area down when you are finished. You do not want this grinding
paste traversing your oil ways or combustion chamber after you
have put the engine back together again.
|Here you can see one complete head here. The
one behind has not been started yet and will be finished next
The mating surface of the head has yet to be cleaned yet. The
head gaskets on some engines come away with very little effort
on most engines, but not this one. Significant deposits have
been left on both the block and the heads, which will need to
be carefully removed to avoid damaging the mating surface. Both
the block and the heads are made of very soft material so a
gasket scraper would be a bad idea.
The ideal tool to remove this unwanted head gasket material
is patience and a soft nubbed nylon brush that fits to a die
grinder. The surface of both the block and the heads must be
scrupulously clean before re-assembly or overheating and blown
heads will result. As the heads have been removed for rebuilding
and not due to head gasket failure, there is no need to have
the head skimmed. If the heads have been skimmed, this has a
bearing on the head gasket and front engine gasket kit required.
These heads can be skimmed a total of once!
|The engine is shown upside down. The piston rings
have been installed and the engine is awaiting new bearing shells
before the sump and oil pump can be reinstalled.
The big end bearing shells were in generally good condition
but a few had worn areas where inclusions were present in the
soft surface. One of the bearings had a few worn patches. This
is caused by racing the engine when cold or low on oil. The
lower part of the timing cover has been installed on the engine.
At this point, none of the bolts have been torqued. They will
be marked to show they have been tightened correctly to make
sure I have not missed any.
|This view is of the top of the engine. You can
see the de-coked pistons and the cleaned head gasket mating
surface. The material of the block is easily damaged and so
the mating surface has been cleaned with a nylon nubbed cleaning
pad mounted in a die grinder. The pad removes gaskets and only
leaves swirls in the metal.
The engine is ready to have the heads refitted now. The head
bolts extend into the water jacket of the main block, and I
found it not necessary to re tap the head mounting holes.
The back part of the lower timing cover can be seen here. A
gasket is installed between the block and this cover and has
a special surface treatment to prevent leaks. You do not need
to use any instant gasket or mating compound here.
|Here the sump pan and baffles have been re-installed.
The torque settings for the sump seem to be too high. I stripped
two bolts, requiring longer bolts to be fitted, so care is required
when fitting the sump back on. You need to install the sump
before you can fit the heads so that the flywheel can be locked
in place. You can just see the hole for the timing pin on the
top right of this image next to the flywheel inspection hole.
The big-end bearing shells have been installed here. They come
in two colour's, blue and red. The red shells are for the bearing
cap, the blue for the con-rod. They have different BMW part
numbers but have identical part numbers stamped on the shells.
I do not think it would make too much difference if you mixed
them up, but it makes sense to install them as the manufacturer
intended just to be on the safe side.
Remember when installing bearing shells that you cannot use
too much oil. Make sure every moving part is doused in it as
you bolt it all together. This lubrication is all the engine
receives until it runs under its own steam, so be generous.
The towel on the floor below the engine is to catch spillage,
which just goes to show how much oil I was using.
|First head has been installed and torqued down.
You must use new head bolts when reinstalling the heads as they
are stretch bolts and cannot be re-used. Missing from this image
is the timing clamp. Once you have the heads in the correct
position, you can remove the clamp. You would not be able to
do this with a four cylinder engine as the camshaft would 'cog'
round to another position. You must have both timing clamps
and the flywheel locking pin installed before attempting to
fit the timing chain.
DO NOT turn the engine over at this point. If you do, you will
damage the valves. Once the timing chain has been installed,
you can turn the engine over to make sure the valves do not
interfere with the pistons. Try not to turn over the engine
too much as there is no lubricant flowing through the engine
at this point.
Here the second head has been installed, and
the upper timing cover rear has also been fitted. The gaskets
that join the upper and lower timing covers have holes punched
in them to indicate what thickness they are. The head gaskets
you have installed determine which set you fit (You get both
in the upper engine gasket set). The sets are divided into
single hole and double hole types. The marking holes on the
head gasket are at the flywheel end.
It soon became apparent that the timing clamps I carefully
manufactured are only required to make sure the valves do
not interfere with the pistons when you assemble the heads.
To time the valves you require a long straight edge. The camshafts
have two holes which should face each other. If you use the
straight edge, you should be able to draw a line through the
center of each camshaft, and through the centers of the facing
holes. The flywheel should be locked with piston one at TDC.
|The timing chain has been installed and tensioned
at this point. The procedure is fairly complicated for timing
the engine. Suffice to say that you should be aiming for six
millimeters of travel on the adjustable tensioner.
If the timing chain has been installed correctly, the engine
should turn over easily and still be 'in time' if you lock the
flywheel and check with your long edge again. If it does not,
time to start again. I had to jog the left camshaft sprocket
over one tooth to make sure everything timed up correctly.
|The bottom front timing cover has now been installed.
The oil seal on the this cover has been changed. The best method
to fit this is to use plenty of oil and a socket about the same
size as seal. Use a small hammer and support the cover carefully.
Take your time and tap it lightly to ensure it goes in straight.
You can use the same method to fit the oil seals to the distributors
later on, after you fit the upper front timing cover.
|Here the upper timing cover has been installed.
You will notice that where various pieces of the gaskets join
up with the various parts of the covers, that some may be too
big or even just a touch too small. Use a razor blade to trim,
and a small blob of instant gasket to fill in the gaps. Be careful
torquing the various bolts. I stripped two threads in getting
to this stage, Luckily I was able to get away with simply installing
longer bolts to over come the problem.
Its starting to look more and more like an
engine now. The Distributors are now installed, and the timing
covers installed. I forgot to install the oil spray rails
at this point, so I had to take them back off. I installed
replacement banjo bolts from BMW, they have a small blob of
'magic' goo on them which will stop the bolts from undoing.
In the upper engine gasket set you will find a set of aluminium
crush washers to use with these bolts. Once you have torqued
these bolts down, they cannot be re-used.
I managed to shear one off. I have no idea how, but still
had one of the old ones which I used a new crush washer and
a blob of thread locker to secure. If you decide to re-use
the old bolts, make sure you use some sort of thread locker
or take precautions to prevent the bolts from coming undone.
Significant damage can occur to your heads if you do not follow
|This is a nice view of the engine. It gives you
a good idea of how clean the engine is. The key to engine rebuilding
is cleanliness and clean oil. Make sure everything is clean,
and use plenty of oil on reassembly. If the engine is going
to remain in this state for a long period of time, you can use
a graphite based grease for bearings and camshafts. This does
not run off components and so they can be stored for long periods
of time without worry when it comes to turning them over for
the first time.
I intend to turn the engine over as soon as I have it reassembled
to check I have good oil pressure and compression.
|I have started installing the ancillary brackets.
Here you can see the alternator and power steering pump bracket.
The oil filter is fed through this bracket through two thick
braided hoses. Make sure you don't get any crud in these inlets!
|The inlet manifold gaskets and engine hoist brackets
have been re-installed. The inlet manifolds mount to these rubber
gaskets to isolate engine vibrations from DKM motors.
These gaskets are notorious for going hard, cracking and causing
air leaks. These leaks are a bear to trace and can be diagnosed
by disabling each computer bank in turn. If the idle improves,
you have found the faulty bank.
You can simply purchase new inlet manifold gaskets, but at £130
a pop (you need four), its easier to just use a silicone sealant
on the mating surfaces as 'belt and braces'. Gaskets that need
this treatment are often hard and cracked. The silicone extends
their life and is an accepted method of extending their life