Monday, 4 April 2016

The BRM H16 engine – part 4: The quest for reliability and conclusions


It is fair to say that the development of the BRM H16 suffered due to numerous reliability issues. Vibration and resonance issue was by far the biggest cause of these issues.

First engine test bed runs resulted in broken inlet camshafts at the shoulder for the driving gear. Initially this failure was attributed to the high loads in the camshaft. In order to try to cure the problem, a temporary additional camshaft bearing was added for both inlet camshaft drive gears to prevent the gear being over-hung. With this arrangement the engine could be revved up to approximately 6000rpm, when it started to vibrate violently, especially at the fuel injection units.

Further investigation by BRM highlighted that the 0.75” diameter torsion shafts that drove the output gears were bright blue in their centres. This unusual observation confirmed that the natural frequency of the torsion shaft coincided with certain modes of vibration of the whole engine. A torsion shaft with a diameter of 1.15” was required to increase its natural frequency above the exciting range. Unfortunately packing space would not allow such large shaft diameters; instead the maximum diameter allowed was 0.95” which allowed the engine to rev up to 10,000rpm for short periods.
Output gear pack with steel 'spectacle' plate


With this running, failure of the gears or their bearings that connected the two crankshafts would then occur. In order to cure this issue the diametrical pitch of the gears was changed (from 8 d.p. to 6 d.p.) as were the arrangement of the bearings to increase stiffness (by four times). This redesign would then allow an engine to run for up to 4 hours; just an adequate duration for racing. With this design re-work the torsion shafts were now further increased in diameter to 1.05”. The shafts were also made of maraging steel to try to increase their working life. The next difficulty came due to the bearings for the centre gear which connecting the output shafts working loose in their magnesium case within about 2 hours. The bearing location was therefore reinforced with steel ‘spectacle’ plates. By now, it was however apparent that the vibration would need curing at the source.


A pair of eight-pin type crankshafts were manufactured. The extra balance weights of this crankshaft caused the offset between cylinders to increase by 0.4” to 1.05”. This in-turn meant new crankcase castings were required. It was also necessary to increase the crankpin diameter to 1.875” from 1.5”. Since this modification would take considerable time due to re-tooling, the decision was made to prove off the theory by welding and bolting steel rings onto the balance weights of the original design crankshaft. It was possible to add only four additional weights could be added to each crankshaft, but as each pair weighed 2lbs, there was still a substantial increase in inertia. This crude modification proved successful to the extent that the engine could now be used in a car. In fact for the majority of the 1966 racing season the H16 ran in this form; even winning the US Grand Prix in a Lotus.

The downside of these modifications was a weight increase of the engine, which now tipped the scales at 520lbs. When the mk2 engines were available (with correct 8 pin cranks), problems with connecting rod failures resulted in destruction of all the engines. The connecting rod failures were attributed to a machining mistake which caused a stress concentration point in the con-rod bolt bore.

BRM kept experimenting with the engine, for example chrome plated steel and then chrome plated aluminium cylinders. The latter items were reasonably successful, however an increase in oil consumption was noted with their use. Camshafts and tappets by now were now made of case-hardened En-39 steel. This modification along with the new crankshafts allowed the removal of an additional steady bearing on the engine which reduced mass by 10lbs.

The biggest gain in engine reliability came as a result of BRM’s greater understanding of the working life of each component. BRM introduced a “ruthless scrapping” policy, for example; output gear bearings were changed every race, output gears, camshaft driving gear bolts and dowels every 10 hours. Although the engine reliability was now far improved, the vibration characteristics caused by it resulted in a spate of gearbox failures.

As well as the H16 being heavier than anticipated, low engine speed torque was below what was expected. For example at 7000 rpm the 1.5 litre V8 produced 140 hp, whereas the 3 litre H16 produced only 240 hp. The specific fuel consumption of the H16 was also high which further increased the required car mass due to higher fuel loads. In order to improve both these items, the intake ports were reduced in diameter by 0.1in and the valve lift to 0.35in. This resulted in 4-5% more power at 7500 rpm and a 3% reduction in fuel consumption. Conversion to upstream fuel injectors also gave a considerable improvement in power and fuel consumption at lower engine speeds.

So what could be concluded about the 2 valve 3 litre H16 engine. It was not the success that was hoped. This was due to initial reliability issues stalling development, an engine that was both heavier and with less low speed power performance than anticipated, an engine that required high levels maintenance and the final death-nail was that even when engine reliability was acceptable, gearbox reliability became a problem due to engine vibration.

Saturday, 2 April 2016

The BRM H16 engine – part 3: Performance and development


Given that the H16 utilised effectively 16 cylinders from their 1.5 litre V8 engine, BRM had anticipated that the H16 would produce approximately twice the power of their 1.5 litre V8 (i.e. 420 to 440 BHP). In practice this was not the case. Many of the initial investigations into this related to the suspected increase in oil churning and mechanical friction. In practice after analysing the heat rejection to both the oil and coolant, BRM concluded that this could not be the full cause. During this work BRM did note that early engines tended to overheat due to water flow stalling. A redesigned water pump impeller cured this issue and a smaller water pump also reduced friction and caused an unexpectedly large increase in engine power. Based on the last observation, BRM concluded that the combustion chambers had previously being over-cooled.
BRM H16 power curves compared to 1.5 litre V8


The volumetric efficiency of the H16 was very good. By using fuel flow and exhaust air-to-fuel ratio measurements, the volumetric efficiency of the H16 was determined to be 104% at 8000 and 9000 rpm, rising to 110% at 10,000 rpm. These measurements were confirmed by compression pressures, which showed the engine’s breathing performance was better than BRM’s 1.5 litre V8. This was attributed to the narrower valve angle and tangential inlet ports.

Initial running on the H16 highlighted a variation in cylinder-to-cylinder air to fuel ratio (AFR) of 5% with ideal mixtures and up to 10% with richer mixtures. As a result the cylinder-to-cylinder combustion speed varied by up to 10%. Following the calibration of the fuel injection equipment, the cylinder-to-cylinder AFR imbalance reduced to 0.5%.

The H16 used BRM’s ‘three-hemisphere’ combustion chamber that had been developed on the later 1.5 litre V8. On the V8, this combustion chamber had caused a 15-20% increase in combustion speed above 10,500rpm. This in turn caused engine power to keep increasing with engine speed up to 11,750 rpm.

Wednesday, 9 March 2016

The BRM H16 engine – part 2: Engine layout

The H16 was a clear descendent of BRM’s 1.5 litre V8 engine. The H16 utilised the same valves, springs, tappets and cam forms. It was originally planned that the H16 would use the same pistons, liners and connecting rods as the V8.



BRM H16 layout

The crankcase of the H16 was a spacious unit based on the practices of the earlier V16 unit in order to prevent oil churning issues.


An essential feature of the H16 engine was to employ a central inlet port between the pairs of camshafts, as utilised on the later form of BRM’s 1.5 litre V8. It was also intended to use a common inlet camshaft (on each engine side); this could be achieved by reversing the offset of the pairs of connecting rods on the upper and lower crankshafts. There would be no issues with the exhaust ports as they could exit at the top and bottom of the engine. In practice BRM realised that this arrangement brought each crankshaft too close together, which could have been solved by widening the included angle between the valves, however this latter item would have been undesirable for combustion and as such the single inlet camshaft design was deemed not acceptable. Instead twin inlet camshafts were utilised on each side of the engine, which meant the valve included angle could be reduced. The penalty of this was an increase in engine bore size, weight, bulk and centre of gravity.
BRM H16 layout
As mentioned previously, the H16 used the combustion chamber from the 1.5 litre V8, but with a slightly narrower included valve angle and a tangential inlet port. With the narrower included valve engine on the H16, it became apparent that there was not enough space for the upstream fuel injection system which the V8 utilised. Previous research by BRM had shown that upstream fuel injection resulted in better specific fuel consumption and a wider range of mixture tolerance. The H16 was therefore to use downstream fuel injection which was anticipated would result in a slight performance loss and a poorer idle.


BRM swirl rig
BRM’s work on the V8 engine had showed that some port induced swirl was beneficial to ensure a more homogeneous charge, however a penthouse piston crown tended to kill this swirl motion as it entered the cylinder. Flow tests showed some disadvantages of high levels of swirl in the intake port; for example lower cylinder filling (port flow) and also in extreme cases to centrifuge heavy fuel onto the cylinder walls.


A method to improve mixture homogeneity on the H16 was therefore sought. The solution settled on was to give the stainless steel tube supplying to the central injection nozzle an aerofoil section and a 2° angle of incidence. Flow tests were conducted to help determine where this aerofoil should be positioned radially relative to the inlet valve stem. This was done to try to send charge around the back of the stem to reduce flow losses due to the valve stem. BRM’s flow rig showed a gain in airflow from 112 to 115 ft3/min.


BRM H16 induction trumpet showing aerofoil section fuel feed tube


In order to promote good coolant flow from lower to upper cylinder head, prevent leaks and also increase stiffness, the pair of heads on each side was cast in one. This made for a very complex casting and the resulting foundry issues caused a 6 month delay to the project.


Cast iron cylinder liners were utilised on the H16. During BRM’s earlier V8 development it was noted that cast iron liners as well as costing a quarter of a steel equivalent, also resulted in a slight increase in power. The disadvantage of cast iron liners noted by BRM was that any valve to piston contact experienced during development testing also tended to result in a shattered liner which led to total engine destruction due to the uncontrolled piston. With steel liners valve to piston contact typically only resulted in a bent valve. This was especially problematic on the H16 as on early engines torsional vibration issues were noted which could produce dramatic changes in valve timing. These valve timing variations could then lead to the total destruction of an engine, which made it very difficult to determine the initial cause of the torsional vibration.


Each cylinder on the H16 had a bore and stroke of 69.85 and 48.89 mm respectively. The crankcase was vertically split with the split being offset 2.5 inches from the engine centreline. The crankcase was cast in LM8. At the lower front of the crankcase, a triple-gear scavenge oil pump was installed. A ribbed magnesium sump was utilised.


The connecting rods for the H16 used BRM’s existing V8 forgings. The crankshaft was a nitrided fully balanced affair in EN40 using 2.25 inch Vandervell VP1 main bearings and 1.5 inch diameter crankpins. The rear journal of the crankshaft contained serrations which were used to drive a torsion shaft which passed through the output gear to serrations at the end of the gear which were carried in a pair of roller and ball bearings. The forward end of the crankshaft drove a disc carrying four lobes which triggered the Lucas transistor ignition system. The shaft driving this disc also carried a skew gear which drove a pair of distributors at half engine speed.




Saturday, 5 March 2016

The BRM H16 engine – part 1: Concept


New rules for Formula 1 engines were introduced for 1966 which stipulated that normal pump petrol was to be utilised in either 3 litre naturally aspirated or 1.5 litre supercharged engines. This blog post details some aspects about BRM’s choice for this new formula.

BRM had much experience with supercharging due to their development of the 1.5 litre V16 unit in the late 1940’s and early 50’s. The new engine formula specified using pump petrol, which meant that intercoolers would be necessary. A 1.5 litre supercharged engine was therefore dismissed as it was believed that the powertrain would be complex, awkward in shape and heavy.

With a 3.0 litre naturally aspirated decided on, the next call for BRM would be the number of cylinders to utilise; 8, 12, 16 or even 24. BRM considered the V8 layout to be very attractive for packaging reasons in a racing car. BRM concluded that whilst the V8 engine would produce excellent torque and be relatively light, engine speeds of over 10,00rpm would be required to produce a power to make a car competitive. BRM therefore decided to dismiss the V8 layout due to mechanical limitations of operating such an engine at these speeds.


The 24 cylinder engine was also dismissed, as it would allow only a very small engine speed increase over a 16 cylinder unit. BRM then decided to let two separate teams carry out design studies on a 12 cylinder and 16 cylinder engine.
Prototype BRM H16 engine

The 12 cylinder unit would be arranged in a V formation and was based on the successful BRM 1.5 litre V8 engine, but using 4 valves per cylinder with a very narrow valve angle. It was estimated that the V12 could produce 475 HP from an engine 30 inches long and weighing 360lbs.


The 16 cylinder unit was based on a H-16 layout. A flat 16 was dismissed on engine length, whilst a W16 was dismissed on engine width. It was deemed that a H16 layout would give a very compact engine with a low centre of gravity, which would fit well into a racing car chassis. The cylinder head joint faces would run vertically fore and aft and could be used to carry the car’s rear suspension. The H16 was estimated to produce 500 HP from an engine 24 inches long and weighing 380lb. Another interesting aspect of the H16 layout was that initially it was planned to use only 2 valves per cylinder. This meant that the cylinder size and number of valves were as BRM’s already very successful V8 1.5 litre unit.


BRM believed that the increased length of the V12 unit would mean that the fuel tanks had to be placed alongside the crankcase, which would mean that engine could not be used as part of the car’s structure, as was intended with the H16 unit. This would therefore negate some of the weight advantages of the V12 unit. BRM therefore settled on the H16 unit.





Thursday, 3 March 2016

A Living Legend: Huddersfield and the Aston Martin DB6




Sir David Brown and DB6
 
When most people think about Aston Martin, they think about a hand-made English sports car produced at Newport Pagnell. The more knowledgeable would know of their origins as Bamford & Martin in Kensington, followed by a period in Feltham. Others may know of the firm's association with Touring of Milan and of the wonderful and stylish cars that were produced as a consequence. Few however could imagine that without the small Yorkshire town of Huddersfield, none of this would have happened.

This is a blog relating to a Northern Powerhouse nestling in the Pennines.

In February 1947 the Huddersfield industrialist David Brown bought Aston Martin Ltd. from Gordon Sutherland and Claude Hill for the sum of £20,000. Later that year he also purchased Lagonda for the sum of £52,500, as he was interested in a new engine that had been designed for the company by W.O. Bentley.  He felt that this 2.6 litre DOHC engine would be ideal in his new sports car the DB2.  

In 1955 he bought Tickford, the coachbuilding company started by Salmons & Sons and based at Tickford Street, Newport Pagnell. David Brown was not just a wealthy and astute industrialist; he had both an appreciation of engineering in general and a keen eye for motor cars. It was his wish to produce the finest sports-car in the world.

His purchase of Aston Martin in 1947 heralded the dawning of a Golden Age for the marque and their continuing association until 1972 resulted in the finest hand-made cars to have ever passed through the factory gates. He also turned AM in to a winner on the race tracks, with a LeMans victory and the World Sports Car Championships in 1959.

In 1961 David Brown Industries employed a work-force of over 7000, with factories in Huddersfield, Coventry, Manchester, Salford and London. The company also bought a controlling share in shipbuilders Vosper Thorneycroft in 1964 and had factories and business interests throughout the world.

However Huddersfield was David Brown and David Brown was Huddersfield.



The Company badge of DB with a white and red rose says it all. This was a town at the sumit of the Pennines, with Lancashire to the west and Yorkshire to the east. From Farsley in the north to Peniston in the south, virtually the whole of the town and surrounding area came under his influence.

To list but a few:-
                 Lockwood                                            Head Office
                 Park Works – Swan Lane                 Heavy gears/boxes/heat treatment
                 Keighley Gears – Howarth Lane     Radicon/reduction units
                 Meltham Mills                                    Tractors
                 Peniston – Green Road                     Foundry/pumps
                 Aspley - St. Andrews Road               Forge/fabrication/chassis shop
                 Scholes                                                 TrainingSchool/AdvanceTraining/R&D              
                 Newlands Works – Farsley              Tractor/LB6 engines/DB2/4 assembly line

Forward thinking as ever, he also had his own private airfield at Crossland Moor, one of the slightly less hilly parts of the town from which he would fly his De Havilland Dove to business operations further afield. Invariably he would be accompanied by at least one glamorous assistant and this was well before the advent of the PA.

So to Huddersfield



Lockwood Head Office


I came across a very nice brochure relating to the DB6 the other day entitled ‘A Living Legend’.




I would like to share with you the contents of this publication, partly because it is a great period piece from Aston Martin but mostly because it shows just how much they cared about their product.







It was very pleasing to note that the chassis were transported to Newport Pagnell by road from David Brown Industries in Huddersfield. Indeed they were fabricated in the chassis shop at St. Andrews Road, Aspley situated between Broad Canal and the river Colne.


St. Andrews Road Works


 If you accept that the chassis is the bones of a car, it is certainly nice to know that it was made in Yorkshire. It also shows how committed Aston Martin was under David Brown to make the ‘complete car’. Even their great rivals Ferrari at that time had their chassis made by Vaccari in Modena.








Quote: 'The body is hand formed from 34 separate 16swg alloy panels, welded together to make the shell. A steel wire surround is lipped into the lower edges of all sections to give added strength. All dents and ripples are hand beaten out before being passed to the paint shop, where between 20 and 22 coats of primer and final colour are applied to each car'. Wonderful stuff.




Then we come to the engine.

Well if the chassis is the bones of the car, then the engine is its heart.
The wonderful thing about Aston Martin at this time is that they truly made their own engines. From raw castings and forgings, everything was machined and assembled in-house. After all, how could a car manufacturer that did not make his engine be taken seriously? This was the failing of Jensen and Bristol for example, well made and stylish cars but with a bought-in and mass produced engine.











What is apparent from the brochure is the level of care and pride that went into the building of these engines at Newport Pagnell.

The seven main bearing bores within the crankcase are line-bored on a DIXI/Le Locle jig-boring machine to a tolerance of 0.0006 of an inch, impressive stuff indeed when you consider the length of this crankcase. These machines were hand operated and reliant entirely on the skill of the operator. The crankshaft is balanced statically and dynamically, initially on its own then with the flywheel attached. The con-rods are weighed and selected to make up a perfectly matched set of six. The same is done with the pistons and gudgeon pins, all to ensure a perfect balance throughout.
The engine is solely built by one fitter, the attention to detail so great, that the tester can tell who this individual was by the performance on the brake. All engines are run at varying speed up to a limit of 5,500 rpm for 4 ½ - 5 ½ hours using a Hennan & Froude dynamometer.


 

HOTh
Of course David Brown had a long history of building engines at the Newlands Works, Farsley just north of Leeds. The tractor engines were built there as was the Lagonda designed LB6 fitted to the Aston Martin DB2 onwards. In fact a production line was introduced at the factory in 1953 for the new DB2/4 model. Almost all these cars were assembled in this factory before being driven to Feltham for final inspection. The factory closed in 1957 at the end of the model run and the car engine production with many of the engineers moved to Newport Pagnell.


DB2/4 assembly line Newlands Works


Not only did Aston Martin produce their engine in house, but David Brown Industries manufactured many of the machines and much of the tooling used in production. From gear planing machines to floating reamers, they made them all.


Newlands Works Farsley


Back to the brochure.

After the car is completed and has passed all its tests, it is driven for at least 100 miles of solid workout. It is then given a final coat of paint and the bumpers fitted, only then is it passed to Sales for distribution. A total of 1200 working hours or three months will have passed since the steel platform chassis arrived at the factory. This is how long it took to make an Aston Martin DB6.



So what have we learned from reading this period literature?

Well there was clearly no raiding of the corporate ‘parts bin’ here.  No use of a chassis/platform designed and used previously by another car maker. No use of an out-sourced engine produced in the factory of a mass car manufacturer. No these were hand made cars through and through.
That is not to say that specific parts were not sought elsewhere if they were considered to be the best available products of the time. Examples of this are the Salisbury back axle, 5 speed ZF gearbox and power steering components used on the DB6. Oh and the track-rod ends from a Coventry Climax fork lift truck.



As always perfection does not come cheap.

In 1965 the model was launched with a UK recommended retail price of £4,998, all Alternative Equipment being available within that cost. In July 1966 the Wilson government increased purchase tax and clamped down on hire-purchase tax concessions, which lifted the retail price to £5,085. This and the overall economic uncertainty of the time resulted in a distinct lack of orders. David Brown took the drastic decision to reduce the price of his cars and by 1967 a £1000 had been knocked off the original list price. There is an often repeated story that relates to the DB6, in that David Brown at a business lunch in London was approached by an old friend and asked if it would be possible as a favour, for him to purchase a car at cost. David Brown replied he would be delighted to oblige and several days later the friend received an invoice for a £1000 more than the published list price.
True or not, it is a lovely story and one any Yorkshireman would be proud of.




I would like to leave you with a few sentences from the front page of the brochure.

‘Each car is an individual achievement of dedicated men; hand-built with imagination, skill and superlative craftsmanship. The Aston Martin is a living legend – and the legend will continue as long as pride in workmanship, awareness of real distinction in design and appreciation of truly beautiful things persist’

What sentiment.
A living legend indeed.