|» Index Page
||Introduction, About the BMW M70 V12
|» Page 1
|» Page 2
||Fault finding, condition checking
|» Page 3
||Stripping and cleaning
|» Page 4
||Re-assmebly, Timing chain & heads
|» This Page
Most of the ancillaries are installed now.
The alternator and belt tensioner as well as the water pump
are now all installed. The two coolant pipes that deliver
water to and from the heads have been repainted, and new 'o'
ring seals have also been installed. These seals come with
the kit and are simple to fit.
Use some light oil to ease assembly of the pipes into the
water pump and other components. They should slip into place
The crankshaft vibational damper is installed using a large
bolt that cannot be reused. It is torqued once and then must
The power steering pump will not be used in this installation.
This presents a problem with regards to the alternator drive
belt as it loops past this item. An idler will need to be
constructed or an alternative method of tensioning the belt
will be required.
The bracket on the left of the engine is the air-conditioning
compressor bracket. I have not started to clean this item
at this point, hence why it is not installed now.
The sump and oil pump has also been installed. I decided to
fit the oil level sensor after all as it was easier than making
a plate up. I cleaned the sensor up and mounted it using a
new sealant ring as supplied in the lower engine gasket set.
|Here the belt, tensioner and air conditioning
pump have been installed. The air-con pump can be re-used.
When cleaning the air-con pump, make sure the ports remain free
of cleaning fluids and debris. The pump must remain clear of
any contaminants if it is to work correctly. Some oil may leak
from the pump as it is turned over for cleaning, this is normal.
A measured amount of oil is introduced to the system when it
is charged with refrigerant. It is this oil that lubricates
the pump during operation. As there is no pump or filter, the
oil must be clean.
|Inlet manifolds, fuel rails and injectors have
now been installed. All that it is required to complete the
engine is to install the HT leads and spark plugs. An idler
to replace the power steering pump will also need to be fabricated
as I will not be using power steering.
The throttle bodies are installed at the right end for the original
installation, but are not correct for the original Diablo engine
configuration. If I want to move them to the other end of the
inlet manifolds I will need to make spacers to clear the oil
filler pipe. Other implementations of this engine in replicas
have done away with the oil filler entirely so I presume they
fill the oil through the oil filter instead.
|The power steering pump would normally hang below
the alternator. The belt goes around the power steering pump,
the alternator to the crank pulley via an automatic tensioner.
If the pulley is not installed you cannot simply install a smaller
belt as the belt tensioning equipment gets in the way. The alternator
is not on an adjustable bracket so you cant simply do away with
tensioner and fit a smaller belt.
Three options present themselves. I can either fit the pump
with a pipe circulating a small quantity of oil, manufacture
a pulley system to replace the power steering pump, or use an
alternate system to tension the belt and use a much smaller
|I included this picture to show how well the
inlet manifolds came out. The discolouration on the surface
of the manifolds is dust from my mechanics latex gloves.
On reflection, I think this sort of treatment to the manifolds
looks much better than bolting panels on. It was practical considerations
that made me take this route, as well as finacial ones.
The inlet manifolds are a mare to fit. You must fit the manifold
(closest one in this photo) holding the fuel return lines before
moving on to fitting the other one. I used an 1/8 inch drive
socket, a UJ, small ratchet and various extensions to reach
the bolts. Stiffen the UJ with grease, a blob in the socket
helps prevents the bolt dropping off when you route the nut
onto its thread. I found an LED penlight useful in illuminating
the area I was working on, and a screwdriver to help guide the
nut onto its thread is useful too.
Remember to use a smear of sealant on the inlet manifolds mating
surface where they join with the rubber isoltaing gaskets. These
gaskets crack and harden with age, and are expensive to replace.
Sealant is a valid method of extending their life and preventing
idling problems due to air leaks.
|This is the alternate tensioning arrangement
I came up for the alternator drive belt. You need to remove
the power steering pump because it will foul the handbrake cable
lines. Also as I do not have a power steering rack its pointless
Parallel Designs offer a belt that is exactly the right size
to go between the two pulleys. I prefer the way I have done
it, as I can adjust the belt easily if it starts to slip.
The strap is made from a piece to 2mm thick steel originally
used to hold a fire extinguisher to the wall. I machined two
bushes from mild steel so the strap will clear the belt across
the top, and welded them to the strap before giving the whole
thing a good coating of paint.
|The flywheel end of the engine needs a little
preparation before you can reinstall the new flywheel and pilot
bearing. First the crank will probably have rust on its surface,
this must be removed if the flywheel is to sit square on it.
You also need to clean the flywheel and remove the flex plate
that would normally couple to the torque converter. This flex
plate simply spins off, although if its rusty it made need just
a little gentle persuasion.
|This picture shows the area of metal I have needed
to remove in order to fit my starter motor. The metal to be
removed is marked with black pen. The recess provided on the
left hand side of the engine (looking at the flywheel), is off
centre, and I can only assume this is to accomodate a smaller
starter motor than the one I have. A die grinder is all that
is required to remove the excess material, after which the starter
fitted with no further problems.
|The original flywheel is retained for the starter
motor to engage to, the second flywheel is bolted to this after
first installing the pilot bearing. This is simply tapped into
the crank with a soft rubber mallet. Make sure the hole is clean
and free of rust and debris before you do this.
The starter motor on my engine is on the same side as the alternator.
This may not be true for your engine. Handily both positions
are provided for with the engine adapter plate. The flywheel
is secured to the crank using bolts supplied with the flywheel
kit. They must be torqued to a seting of 105Nm. Proceed tightening
these bolts as you would do with a wheel, ie in a star pattern.
Check all the bolts after you have finished tightening to make
sure you have not missed any.
|Here I am measuring the flywheel runout. This
check makes sure that the flywheel is on straight, and has not
been damaged. Runout is measured at the extremity of the flywheel,
as you would for brake disk. The maximum permitted runout for
a BMW flywheel is 0.1mm. Mine came in at 0.09mm, so it is just
within the permitted amount. Although it should be noted that
this deflection only occurred near one of the bolt holes, the
actual run out over the rest of the flywheel was only 0.02mm.
If the runout of the flywheel is too high, the clutch will judder
and stick. Also you will get a lot of engine vibration which
will eventually cause things to fail.
|Engine to firewall clearance is visible here.
A good few inches of clearance make changing belts reasonably
easy. There is more space than I would have expected. An engine
of this size is always going to have tight clearances around
it, although its no where near as tight as some I have worked
|This image shows the routing of the coolant pipes.
They come in at a much more severe angle than would be the case
in a Rover V8 installation. The bottle for the coolant is installed
on the rear bulkhead and the clearance between the bottle and
the engine is fairly small. Careful placement is necessary to
make sure it does not foul the engine cover or the engine as
it vibrates. The multimeter on the air conditioning radiator
is connected to the oil pressure sender and was used to check
if sufficient pressure was being generated by the engines oil
pump. It took less than thirty seconds to reach pressure. I
used ten second bursts on the starter to ensure I didnt overheat
either the starter motor or the rather fragile jump leads I
|A close up image of the coolant bottle. I have
installed one of the distributor caps here to check the clearance.
The bottom hose coming out of the bottle will require rerouting
as it is too high at present. The water will fail to fill engine
at its current height. Its one of those things I absent mindedly
installed. Everthing at the moment is held together with cable
ties. In some instances this is perfectly acceptable, but any
components exposed to high heat or vibration should be secured
with something more durable.
|This image show the oil cooler and filter arrangement.
The blue wires are connected to the pressure sender located
on the side of the oil filter. The oil drain plug on the engine
is inaccessable once the engine is installed. Fortunately you
can still drain the sump oil through the oil level sensor. The
engine will require ten litres of oil to fill from empty. Its
probably a good idea to use a reasonable quality oil at this
stage, but dont go mad. You will only have this oil in for a
short time to clear out any residual crud in the engine. After
the engine has been run up for a few hours, dump the oil and
put your expensive stuff in. Change the filter at the same time.
|Here you can see the throttle body extension
piece installed. There are two of these, one for each bank.
They parts are made from stainless steel which was then TIG
welded together. Its quite difficult to weld stainless pipe
without it distorting. Stainless steel does not conduct heat
particuarly well, and so the extreme localised heating caused
by welding can ruin a part through excessive distortion. The
key to reduce this is to make lots of quick tack welds along
the edges to be joined, keeping the weld power down low and
performing the tacks as fast as possible. Ideally the part should
be quenched after each tack, but this can cause cracking. Once
you have a number of tack welds, you can then proceed to join
them all up as you would with a normal welder.
These pipes have been sandblasted, primed with acid etch primer
and then given a coat of satin black paint.
|Here is one half of the exhaust manifolds. They
exit from the rear of the vehicle in twin pipes, from a three
to two to one configuration. The pipes are highly polished so
I need to be pretty careful when I install them.
|Here you can see one bank of manifolds installed.
Installation instructions for the original manifolds specifies
studs and copper nuts tightened to a torque of 23Nm. This is
little more than hand tightness, and you will need much more
torque than this to get the manifolds to fit with no leaks.
Install the bottom bolts to hand tightness first as you will
be hard pressed to get them tight afterwards. The original studs
will have been installed with locking compound and this must
be cleaned out before installing the new bolts. In truth there
probably isnt much to clean out if your studs came out cleanly,
there wasnt on mine.
After you have tightened the bottom bolts, you can commence
to tighten the top bolts. Ensure the gaps have closed up, and
try not to overtighten them. You do not want to be drilling
and helicoiling a block at this stage. If there are any leaks
you can rectify them after you have started the engine.
The dip-stick is going to require a little rework as it fouls
the closest manifold at present.
|This image shows the tap I have cut into the
rear air inlet temperature plate. The tap connects the manifold
via a one way valve through to the brake servo.
The tap is a modified air hose fitting that I turned down and
retapped on my lathe. The air hose fitting is held tight using
a small amount of JB Weld as the material the cap is made of
is pretty thin.
|I finally got the last piece of the exhaust system
from Naz at the Stoneleigh 2006 kit car show. I was expecting
a simple and straightfoward installation. Alas as is the case
with most jobs on this car, this was not to be.
The link pipes from the manifolds up to the system foul the
engine adapter plate on the left hand side, a grinder quickly
relieved the situation. The other pipe fouled a mystery casting
on the gearbox that seems to serve no particular purpose. Again
my trusty grinder dealt with this. Even after this work, the
left hand pipe was not as far over to the centre of the car
as the right. A quick phone call to Naz revealed that he uses
a four by four fence post to tweak the pipe over an inch. Not
having a fence post to hand, I used a short scaffold pole wrapped
in towels to prevent damage to the chassis or pipe.
This is not the sort of thing you expect when you buy a quite
expensive stainless steel system, and its something I hope he
gets rectified for other builders.
||The system at present has a number of minor leaks
so its a little noisier than it should be. I will rectify this
when I get the trim pieces for the end of the exhaust system
as I do not want to apply exhaust sealant only to have to remove
The system gets suprisingly hot very fast when you start the
engine up, so I will be going to some length to insulate the
pipes around the fuel pumps, alternator and starter motor to
ensure these parts are not damaged by heat.
||I picked up some air filters from the 2007 Stoneligh kit car show and this is one bank fitted into position. I used a 90 degree 70mm elbow to which the air filter is attached. A coupler connects it to the hot wire air meter, this is the dusty box with the right angle connector going into it.
The brackets which hold the filter is bonded to the body, and the brackets are different each side due to the engine being offset inside the car.
Installed the second air filter and installed both engine bay trim panels that line either side of the engine. They take a suprisingly long time to fit, a lot of adjustment and installation/removal needs to take place to make sure everything fits correctly.
The engine bay is now more or less complete. A number of minor mechanical tasks, such as wrapping the manifolds with insulation and tidying some cables but now all the donkey work is complete.
||I had a problem with the way the exhaust was mounted. Using the parts supplied by PD to mount the exhaust, the back boxes were originally secured to the gearbox using flexible rubber mountings. This might have worked for PD's usual V8 and Renault gearbox setup but it pushed the tail pipe sections too far up inside the rear valance and made it impossible to mount the trim sections.
So in order to mount the exhaust correctly, I made two brackets from stainless steel and bolted them to the spreader bar along the top of the chassis. This bar stiffens up the section between the rear wheels and presented an ideal place to attach brackets.
||Heres the rear of the car with the exhaust and sections and trim pieces installed. This job was reasonably easy to complete, requiring just careful measurement and cutting to ensure the pieces all fit together correctly.
On an original Diablo, four pipes would emerge from under the vehicle and merge into two tail pipes, but the PD exhaust system consists of two separate banks instead of four, so you only have two pipes to contend with.
The tail section kit must be welded up yourself as each car is different for mounting of these components. It consists of two mounting plates, four walker 90 degree bends and two chrome trim pieces. The Parts are all mild steel, whereas the rest of the exhaust is made from stainless steel. I will try and paint the two tail pipe pieces with black high temperature paint and hope it stands up to the high temperatures its likely to experience.
||This is the almost completed engine bay, the centre panel has been installed although its still missing its bull emblem which I have not fitted yet.
There is a little bit of painting to be done at the rear of the engine bay, and some general cleaning and de-dusting to be done.
The last stage here is the application of the informational and warning stickers.
M70 Engine problems
Some people who are re-using the BMW M70 engine computers are encountering problems with limited revs and the car being stuck in limp-home mode. The problem does not seem to affect all makes so there may be differences in software for cars built in different territories. Regardless, If you are having problems, try connecting Pin 14 on connector X20 to ground, or through a ground interrupter speed sensor as this seems to fix the problem. Thanks to Mats Høkeli for this information.