Current progress so far
Links to parts and information websites
Where I will be building my diablo
Where most of the important bits come from
The stuff it all bolts to
What makes it go
What makes it pretty
The cars nervous system
Where you sit
The gubberment bit
Who really cares?
Stuff that will not fit anywhere else
Other diablo replica websites


Due to the size of these pages, I have split them over a number pages for quicker loading. You can click on some of the images to link to a larger version:

» Index Page Introduction, About the BMW M70 V12
» Page 1 Engine removal
» Page 2 Fault finding, condition checking
» Page 3 Stripping and cleaning
» Page 4 Re-assmebly, Timing chain & heads
» This Page Ancillaries


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 fairly easily.

The crankshaft vibational damper is installed using a large bolt that cannot be reused. It is torqued once and then must be replaced.

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 belt.

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 anyhow.
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 on.

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 was using.

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 it again.

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.