Someone we (Johan and I) know through our website contacted us that he had started an interesting project. He was planning to build a Cobra replica. Not powered by the average cast-iron Mouse or Rat V8, nor or a slainth six or obscure 4-banger. He (Cor Verlinde) decided to use a REAL engine, that mighty alloy hightec short-stroke 5 liter beloved & trusty BMW V12 (we are not biased ;-). So he bought himself a tired '90 750i and used it as a donor for his project. The idea was to pull the engine, give it some cleaning and painting, replace common seals and shoe-horn it into the engine bay of the Cobra.
BUT: the former owner of the 750i was at a certain point where he could barely afford to pay the fuel. When he couldn't spend even that money anymore, he decided to sell the car. Now the v12 is a forgiving engine, but not when it comes to neglecting and lack of maintenance. Cor faced some unpleasant surprises when disassembling his engine...
This is the story about partially rebuilding a tired v12 with 270.000 km and getting a second life in a cobra. The photo's are taken by Cor, some additional comments (based on what I saw on the photo's and Q&A's with Cor) are made by Sean. Cor, thank you very much for this contribution.
Pulling
the engine:
The engine of the
old 750i. You can tell that the engine hadn't been running for
quite a while by the slightly corroded alloy parts. One
distributor cap looked like its been replaced, the coolant
reservoir seemed somewhat contaimed. It's the first model v12,
with the oil filler cap at the right. Someone messed around with
the plugged vacuum hose connections of DK motors (the bolt with a
hose and 2 hose clamps are not original):
Cor about the car: 'the car had not been running for half a year. After that, it wouldn't run on 12 cylinders anymore. After replacing some leads and spark plugs it fired up and blew lots of dirt and water right out of the exhaust. After that, it was running smooth(!). A 300km trip with the car showed no problems whatsoever and my intention was to remove the engine, clean it and bolt it into the Cobra. Oh boy, did I make a mistake.'
Dismantling the front of the
car, to make removal easier. At last there is some easy access to
the ABS pump:
And from the right. The 2 loose
alumium pipes right in front of the engine are from the a/c
condensor connection. Notice the heavy shock absorpers of the
front bumper:
Actual pulling of the engine,
together with the transmission. Now you can see how unreachable
that alternator is. The oil filter canister is still attached to
the engine, I personally wouldn't do that. A part of the exhaust
(probably just the downpipe) is still connected:
Notice the absolute lack of rust
behind the left fender:
The engine and transmission.
Wiring loom already removed. Notice the engine hoist brackets
(not original):
Empty engine bay:
The removed wiring harness/loom.
You wouldn't say it, but this is the complete wiring harness of
the engine shaped like its more or less attached in the engine
room:
A removed (more or less)
fuse/relay box:
Unbolting the hydraulic pump
from the engine. Notice the hose connection next to the right of
the pump, that gave me some thinking. This is actually the hose
connection for the drain hose from the oil filter canister to the
upper oil sump. Usually impossible to reach:
Removed cover of the oil supply
and return connections to the oil filter canister:
Disconnected leads to the
starter. The starter is located behind the heat shield at the
bottom-right. Behind the leads the fill-tube for the tranny:
Removed airco pump. Lower and
upper oil pan still attached:
Cor about this: 'When I pulled the engine, I was shocked to see how full of oil and debris the outside of the engine was. There was a good chance the engine suffered in the past from a small engine fire because of some small melted parts. Probably because the thick battery terminal wire from the alternator shorted within his metal housing.'
Unbolting the intake manifolds.
Here you see you have excellent acces if you remove the noise
supressors (located underneath each manifold) first. At that
point you don't need to use swivels, just some extensions
(1/4"):
Removed and probably cleaned
intake manifold in all his beauty. Did you know that left and
right are 1:1 identical (and thus interchangable)? Excellent
castings:
This is where the trouble began
after removing the valve covers. A sheared off head bolt laying
around at the bottom of the picture. The empty hole just above it
is the place where it originally was located. Notice that these
are torque-to-yield head bolts, recognizable to the
windings from top to bottom:
Cor about this: 'it never was my intention to pull the heads. I just removed the valve covers to clean the engine. I was really worried and disappointed when I saw the contaminated inside of the engine, worn cams and the sheared head bolt laying around. The broken bolt surprised me, because I never experienced symptoms of a blown headgasket (also engine temperature during testrun was normal). After I saw this mess, I decided to tear the engine apart.'
Also both cams where in bad
shape, probably due to insufficent oil supply (loose banjo bolts
of the oil spraying bar) or inferior oil quality:
Upper timing covers removed,
revealing the camshaft sprockets and timing chain:
Definately sludge/crud buildup
and deposits in this engine. Probably the previous owner used
el-cheapo oil or didn't bother to change the oil at all. I just
hate it when people f*ck up their engine this way. This is the
reason why you should use a good brand oil and change the oil
frequently:
The removed waterpump. Luckily
the PO used coolant and not plain water, considering the overall
condition of the engine. The unbolting of the lower timing case
cover has started:
Removal of the exhaust manifolds
with an air wrench, behind the air wrench is the oil filler tube.
Notice that the upper timing case cover leaked severly, a common
problem with early V12's (there is actually a BMW service
bulletin about this problem):
Removed exhaust manifolds. At
the right, the big bolt sticking out next to the lower timing
chain cover, is the timing chain tensioner (also infamous for oil
leakage). Notice that 1 stud stayed in the cilinder head:
The other side with removed
exhaust manifolds. If you look closely, you'll see the actual
exhaust valves. Again, 1 stud stayed in the cilinder head (by
accident). The central bolt below exhaust port number #10 (third
from right) is the coolant drain plug of the engine itself:
Old versus bead blasted exhaust
manifolds (more on bead blasting later):
Starter removed, but torque
convertor is still attached to the flywheel:
You don't see the back of the
engine very often. The intake manifold gaskets are still
attached. Between them is the plumbing of the coolant system. Now
you have a good look at the coolant cross-over pipe (aka coolant
collector) between the cilinder heads. Normally very hard to
reach. Also you can see the 3 coolant sensors (from left to
right: 1 for both DME's, 1 for EML and 1 for your temp gauge)
All bolts of the lower timing
chain cover removed, crankshaft pulley and damper removed. You
now see that it isn't necessary to remove the big crankshaft bolt
to remove the crank pulley. And that is a good thing. The upper
crankshaft position sensor is removed, the lower one still
attached:
But this was a tough one, the
big crankshaft bolt. Its bolted on with a staggering 440 Nm and
you can't reuse this bolt, it's torque-to-yield and a beast to
remove. Cor about this 'even an air impact wrench didn't do the job.
Only the largest hammer I could find in combination with an
incredible whack did it. Normally we use these kind of brute
force for agriculture machines, not lightweight alloy v12's':
Draining the engine oil, black as
the night:
For removing the upper oil pan
you need to remove tranmission, torque convertor and flywheel:
If you would like to add any comments, remarks and/or corrections to this procedure, feel free to email Mike Oswald and we'll put it on our site. Share your experiences with us so others may benefit from it.