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Bristol 405
2 Litre
This is one of the most unusual and iconic British cars ever made. Bristol used to be an aircraft manufacturer and this vehicle is designed and build in the same vein. Working on it is a delightful experience, all the nuts and bolts are British Standard threads, and the whole design of the car is similar to that of its aviation ancestors.
However, there is a small design fault, in as much as the wall of the block in the main water passage is only 3/16" thick (4.5mm) and seeing as the car is now 70 years old, the metal has gradually wasted away over the years. Add to that, the heating and cooling that the block undergoes, means that eventually the cast iron metal fractures. There are various methods that can be employed to repair the damage and this can be seen later in the story. The car itself is in remarkable condition and apart from a bit of tidying up here and there, is nigh on concours.
So, let's start with the plan of what's to happen. The engine is to be removed from the car, completely dismantled until the block is stripped. All the parts will be measured and checked for wear or damage, and then everything will be refurbished or renewed. The customer wants the engine bay to be as impressive as the rest of the car, so a lot of attention to detail will take place.
The two pictures above show the engine once it had been removed from the car. You can certainly see the aircraft influence with the cover plates on the block. The engine was then systematically dismantled checking all the parts as they were removed. The picture on the right makes for grim viewing, this is inside the block where the coolant flows around the cylinders. It is very badly corroded which undoubtedly has contributed to the wasting of the block wall and the inevitable fracture of the metal. Below shows the fracture in the side wall of the block. If you look below the large brass nut shape, you can see where the coolant has started to leak from the water passage.
The photo below is of the flywheel, the area where there is scoring, is the part where the clutch fits. It looks like it has had a hard life, the flywheel has got hot and the surface isn't smooth anymore. The pressure plate and friction plate were also in poor condition, and will be replaced. The flywheel will be ground until the surface is restored back to as new. Although it looks bad, only a small amount of metal will need to be removed before it is perfect again
The photo above is the oil filler with a somewhat dubious repair. The brass tube is supposed to locate into a brass housing which is pressed into the alloy rocker cover. Over the years, the housing has vibrated loose and leaks when the engine runs. In an attempt to stop the leak, a sealant has been applied. This will all be removed and a new housing piece fitted, restoring it back to original.
Below is the block having been repaired, and new camshaft bearings installed. The top of the block has been lightly cleaned up and the bores honed. It has also been painted in the correct colour that Bristol painted their engines, and is now ready for assembly.
The photo on the left is the block after it has been acid dipped. It can clearly be seen, that the block has been repaired before at some point. The small black circle is the area where the coolant is leaking out of it. If you look to the left and right of the circle, you can see further cracks in the metal which will be repaired. Below is the flywheel after having been ground, all the damage has now been removed.
The photo below shows the block and some of the components that have been painted. All the alloy castings have been vapour blasted to remove years of corrosion and dirt. You can also see the new water pump that has been modified to include a ceramic seal and a new anodised pulley. The camshaft on the top of the block is an uprated "sports" cam which should improve the mid range torque.
The two plates that can be seen below, fit at the front and rear of the block, to seal the water passages. Both of the plates have been vapour blasted to remove the corrosion, but neither of the plates sat flat on the block. The was some degree of distortion, possibly caused by heat over the years, so they were set up on the mill and machined until they were perfectly flat, and all the corrosion and pitting removed. They now fit nicely on the block and should create a good seal..
The pistons in this engine are made by Cosworth and are really nicely made. Unusally the conrods have an oil feed through the centre of the rod, which supplies oil to the gudgeon pin, you can see the holes in the shells which are the feeds. You can also see on the top edges of the cylinders, small areas that have been cut away to allow the valve heads clearance. The picture on the right clearly shows the new camshaft bearings
The next two shots show the crankshaft and flywheel installed, and all the conrods and main bearing caps fitted. New shells and piston rings have been fitted along with the camshaft. Another interesting feature of this engine is it doesn't have a rear crankshaft seal like most conventional designs. Instead it has a reverse Archemides screw on the end of the crankshaft, so that as the oil seeps from the rear bearing, it is forced back into the bearing cap and then back into the sump. You can see the screw in the right hand picture, and the tube from the bearing cap in the left hand one.
Bristol being an aircraft manufacturer, applied quite a few aviation techniques to their cars. One of which is wire locking to prevent fasteners coming loose. Below you can see the oil pump, which has been refurbished, and the bolts that secure the top cover and the strainer being wire locked. One of the common problems with this engine is the strainer bolts coming loose. Originally there was a tab washer which wasn't very satisfactory, so I drilled the bolt heads and wire locked them for added security.
The cylinder head has been meticulously cleaned with various chemicals, until all dirt and gasket material has been removed. The mating surfaces have been dressed and any damage corrected. All traces of carbon were removed from the valves, and then each one was lightly ground so that the seat of the valve made a perfect seal with the valve seat in the cylinder head.
The valves were then refitted to the head along with the springs, but alas, the collets weren't in the best shape. I ordered a new set, but it seems that a road going engine has 8mm valve stems, whereas the ones in this engine were 7mm. It seems that 7mm valves were only fitted to race prepared engines, so some investigation is being done towards the pedigree and history of this particular car. There is a strong possibility that this car was used by the factory in a race capacity.
The photo on the right shows the cylinder head with the valves installed ready to be fitted to the block. The tubes across the top of the cylinder head are for the pushrods that operate the exhaust valves. A very unusual design, in so much as the pushrod is moved by the camshaft on the side of the engine, then is turned across the head with a bell crank arrangement to a rocker that moves the exhaust valve. I have only seen this previously on a radial aero engine, quite unique. Below is the block with the new head studs fitted, ready for the cylinder head to be installed.
The next task was to modify the front timing cover which originally had a felt seal that the crankshaft pulley ran in. This doesn't work very well and oil would inevitably seep from the cover. A new seal is available to correct this problem but involves machining the cover in order to accommodate it. The video on the right shows the cover set up on the milling machine being bored until the correct size is created for the seal to be fitted. Below shows the new seal fitted to the cover which is now ready to be bolted to the engine.
On the left is the engine with the cylinder head installed, the clutch fitted and the carburettor bases bolted to the top of the intakes. The oil filler cover has been repaired and all the covers have been painted which will make a big difference to the appearance of the engine when it is back in the car. The next task is to install and time up the camshaft, which is new and boasts a much more aggressive profile from the one that was taken out. It should give the car a much stronger mid range performance and make it more enjoyable to drive. All the camshaft bearings have been replaced as they were on the limit of serviceability.
To the right and below shows the inlet and exhaust valve train installed. The original set up had springs to tension the rockers, but this has been upgraded to brass spacers, which will keep the rockers in position at higher RPM's, and will also help to keep the geometry correct. You can clearly see the pushrods that run across the head from the inlet side to the exhaust rockers. The rocker shafts are new ones as the original ones were worn. They are a few thou larger in diameter and the bushes in the rockers have been reamed to achieve a perfect fit.
Above shows the new water pump installed along with the new pulley. On the left you can see the rocker covers with the polished brass plaque, and the alloy "button" retainers. The next task is to install new carburettor spindles and bushes as they were worn, letting in air which upset the mixture and running of the engine. New PTFE seals will also be installed which involves some very delicate machining. The exhaust manifolds are to be Zircotec coated matt black which is a very robust finish and totally heat proof.