David Brown Engine Development

David Brown tractors always had a reputation for having hard working engines, engines that were not only reliable but also showed very little wear after many thousands of hours of service and also gave excellent fuel economy. Obviously there were few exceptions to the rule but generally the DB engine was known as one of the best available in any tractor, and it was used in some other applications as well.

The sale of DB engines to other manufacturers will be well known to some readers, but a complete mystery to others. Known in the factory a ’Skid units’ these engine were made for numerous power unit applications, including pumps, compressors, combine harvesters, and forklift trucks. In the latter field, the name of Bonser was well known to the staff at Meltham Mills.

Initially wet liners were used on DB engines, and, according to Herbert Ashfield, this was due to the higher temperatures encountered with gasoline fuel. Also a wet liner could be pressed out and replaced in those third-world countries where re-boring machinery was not available locally or in other areas where it proved to be too expensive for the poorer farmer.

The late Tom Lazenby wrote: ’This was a distinct advantage over our competitors, and I know that Ford in particular were very envious of our system.’ Starting in the early 1950s the standard production diesel engines always had direct injection, but there was some pressure to introduce indirect injection and a few were built experimentally. Also an experiment was undertaken with Perkins Diesel Engines, and one of their power units was mounted in a Cropmaster and sent on trials in Scotland. It is said that Sir David wanted nothing to do with this tractor, and was furious when he saw pictures of how the main frame had been cut down to accommodate the Perkins engine. As a result the concept went no further, but the tractor survived and is now preserved by Joe Thirwall in Carlisle.

At this time Herbert Ashfield was running a Mercedes car that had an indirect injection diesel engine, so this was removed for inspection and ran on a dynamometer in the Engine Development Department. The fuel consumption results in Pts/BHP/hr were almost 25% higher than a similar DB direct-injection engine and the exhaust smoke samples very dark in comparison. The conclusion was that direct injection was the way to go. Another digression – but never installed in a tractor – was an engine based on a Tilling-Stevens’ design. This was a three-cylinder supercharged two-stroke diesel, which produced nearly 100hp when it was put on the test bed. With the introduction of the cylinder bores integral with the block, the maximum wet liner bore size of 3 5/8 in was increased to 3 13/16 then to 3 15/16 diameter. These increases in bore gave more potential for a higher output but prior to production worries were expressed about potential bore wear.

As a consequence, a small liner of more durable material was pressed in the top three inches of the bore and machined in situ. Fears were unjustified though and even old David Brown Tractors never have the bigger steps in the bore that you would find in an old Ford engine for instance. Most importantly to David Brown, the integral bores were cheaper to produce and there were more advantages over wet liners. For example, a wet liner distorts slightly when pressed into the block. Dispensing with the liner meant there were no water leaks into the sump, whilst the bores were truer and there were no real problems with wear. Integral cylinder bores were first introduced on the three-cylinder engine, fitted to the 880 lmplematic in 1964 and the 770 Selectamatic in 1965, but it was 1968 before they were seen in production models of the popular 990 (4/49 engine).

The three-cylinder engine changed very little over the years and its final home was in the 1194 giving 48hp output. initially the vertically-mounted distributor pump ’a’ size (dpa) pump drive from the camshaft had been seen to be a potential weak point. However, according to Eric Turner, of Engine Development, ‘it was so well over-engineered that it gave no real problems.’

The three-cylinder engine never had specific fuel consumption or power output as good as the four-cylinder engine, because with a three-cylinder engine a dpa pump could never be as efficient due to its method of fuel delivery. Turbo-charging was tried on the three-cylinder engine, but this was not cost-effective when a four-cylinder engine was available. A three-branch inlet manifold was also experimentally fitted but it caused too much upset in the airflow. Eric Turner relates: ’The volume box manifold was found to be the best compromise in absorbing the pulse from the closing inlet valve and supplying the engine with air.’

When the Selectamatic range was introduced, the largest tractor – the 990 – got 55hp from the four-cylinder engine. The late Tom Lazenby recalled that this placed the company at a disadvantage to both Ford and Massey Ferguson saying ’we desperately needed something with a bit more life in it, and as a result Bert Ashfield’s department was asked to come up with a tractor that could deliver 65hp. He said that they could happen to do a bit better if he was allowed but I was sceptical. in my opinion the sales team were badly let down because farmers wanted at least 6th, and we had nothing really new to offer.

’On the face of it the 990 had done too well, and certain people at senior level thought it would go on for a long time. In all probability a block on development into a higher power range may well have been introduced because a potential merger with BMC Nuffield was on the cards. There was quite a lot of joint experimental work going on, but the troops at Meltham knew nothing at all about this until years later. i kicked up such a fuss that Ashfield was given the nod and allowed to uprate the 990 engine.’

Another former member of staff involved in the experimental side, who we will just call John, writes. ’What Mr Ashfield said about the experimental 100hp eight-cylinder crawler in the first book is quite correct as far as it goes, but his design wasn’t quite the white elephant he might have thought it to be. Sir David had seen the way the big American tractors were performing, and he was convinced that this was the way the British agricultural market would go in the long term. There was certainly an existing demand for 80hp-100hp tractors in the industrial market, and Caterpillar was doing very nicely in meeting the demand. But you have to remember that this was a time when American dollars were in short supply in Britain, and our balance of payments were not too hot.’

John continued: ’Eventually Harold Wilson devalued the pound, but in the meantime there was very strong political support to British industrialists who were willing to make ”home-grown” products to reduce the dependency on overseas suppliers. This had begun in the mid-1950s after the Suez crisis, and David Brown Tractors had already received assistance that not only helped the country reduce the dependency on imports, but actually earn foreign currency from exports as well. It was at this time that l was asked to head up a special unit, The Concept Department, which few DB employees ever knew about.

’Ostensibly based at Leigh, we worked at an old airfield a few miles distant, and we did all manner of things that were a complete mystery even to senior management.’ Some of the experimental work will be recorded elsewhere in this book, but, for the moment, John continues about engine development: ’The desire to produce a good crawler tractor saw more development of the 990, and a picture of this is shown in the first book, but we knew that the engine was just not up to the job the industrial market wanted it for. The concept of the 1010 tractor went a long way, and this would have been in the 75hp range had the engine been developed. As it stood we received a modified 990 engine with a longer crankshaft throw, but it was only delivering 65hp.

’Two 1010s were built and one was tested extensively in the Burscough and Southport area, whilst the other was used by the Mersey Docks & Harbour Board before going on to Liverpool Corporation’s Parks & Gardens Department. A crawler version was built in 1964-5 (I forget which), and it was used by Laings the contractors on a gas pipeline contract, but it still suffered from being under-powered and no match for the American-built crawlers. However, we did have more success with the experimental 65hp-70hp engine on a new frame that we tested on several farms in the Pennines. The contractor who tested the tractor had been buying David Brown tractors since the war, but few could effectively cope with the spreading work he did in steep-sided upland pastures. The new tractor, initially called the 999, took to the job like a duck to water. Our report was favourable and during 1966 further models were produced for evaluation and test. The 999 designation was rapidly dropped, as someone at Meltham decided we needed to have a tractor designation that sounded to be a significant step forward from the 990, so I expected that this super 990 would now become the 1010. However, it was clear that someone high up still had hopes for the 1010 in industrial applications, and so the new tractor became the 1200.’

The 1200 tractor was introduced in 1967 with the same basic engine as the 990 but with a longer throw on the crankshaft giving a 4.5in stroke as opposed to 4in. This engine was fitted with an inline injector pump that, although more costly due to the more complex construction than the rotary type, could be more easily tuned to give more power and a better specific fuel consumption. Eddie Herbert first drove the 67hp 1200 and reported back that a tractor of that size should have more power. Eric Turner takes up the story: ’ln 1968 the power was increased to 72hp; however, crankshaft failures started to occur. The manufacturers of the cranks, BRD and Ambrose Shardlow, suggested Nitriding the crank but we found it difficult to prevent distortion during the process and it was more expensive than the solution we finally used, which was to indent the fillet radii under extreme pressure. We built a test rig to break cranks and whereas a standard crank would break overnight, an indented crank would last for weeks. Broken crankshafts were never a serious problem after this.’

There was also a problem with the water pumps used on the 1200. Alan Earnshaw remembers that the episode cost Browns about 400 replacement engines, clue to a problem that existed in the pump housings supplied by the Ransome Hoffman Pollard’s Dick Bearing works in Blackburn. He writes: ’The problem began that summerjust as we were getting ready for the annual two-week shutdown, when l was working as a purchase progress-chaser. On the Thursday afternoon quite a row broke out, and l was called in to see Derek Mallinson our Purchasing Director and asked to explain what problems we had with RH P. Of course I looked a total fool because I didn’t know of any, but it transpired that not only had supplies been coming through much slower than normal, but serious complaints were coming from overseas customers who were suffering bad water pump leaks. On investigation our quality control engineer Stuart Wetherby discovered that the fault lay in the depth of the machining on the ”O ring” groove which, when the engine got hot, would allow the rubber ring to be compromised.

’When the engine got very hot, as it did in warmer countries, the whole thing would collapse and catastrophe ensued. As I hadn’t planned any holidays that summer, due to a serious lack of cash, l jumped at the chance of overtime to sort out the problem. On the Monday, the first day of the works’ holidays I caught a train from Huddersfield to Newcastle, where a sales engineer from George Angus Ltd collected me from the Central station. Once at their Wallsend works we looked at the offending pump housing, with its non-standard groove, and discussed ways of curing the problem. In the end an ”0 Ring” with an ovaloid section was produced, and when the works reopened two weeks later, we had sufficient stock to get production moving in engine assembly. The moral of this is that if any owner of a preserved 1200 has problems getting their water pump to seal, don’t try taking it to a warm country with a standard ”0 ring” making the seal. I also recall that we had another problem over the years with the original cast-iron timing gears giving no end of trouble, until my old manager, Alf Hurst, managed to find a supplier who could offer spheroidal graphite iron gears. Later I think they turned to hardened steel gears.’

In the early 1970s tests were carried out on a power unit that could give 90hp, and all manner of ideas were tried before the turbo-charged 91hp 4/55 engine was introduced in 1974. Before its mass production five units were built, and these were extensively run on a test bed before being put into tractors and handed over to the Field Test Department. William Noble remembers driving up Knowle Lane, a steep hill alongside the works, on his first trip with the experimental turbocharged tractor and specifically recalls being amazed at the increase in power. Turbocharging, the long held goal of Herbert Ashfield, was an excellent way of getting more power whilst the specific fuel consumption improved as well. This was achieved because the exhaust gases hitherto just waste were still expanding, and these could be used to drive the turbo.

However, a turbo was notjust bolted on to a Naturally Aspirated (NA) engine, as this would not prove reliable at the increased power outputs, so better engine specifications were required.

A higher capacity oil pump was fitted to supply oil for the turbo bearings, and the exhaust valves were made from better  – harder-wearing – material. I remember seeing a cylinder head removed from a well-used 1210 belonging to the contractor Hughie Cartwright, and even on this NA engine the exhaust valves had cupped over along a period of time. The compression ratio was reduced from 17: l to 16: I to cope with the increased volume of charge compressed into the cylinders. The valve overlap was altered on the camshaft and the clearance between ’top land’ of the piston and the bore was increased to cope with the extra heat. The top ring grove had a cast-Iron insert and an all-chrome top ring was tried but it would not bed in successfully so a cast-iron ring with a chrome insert was used. The big end and main bearing diameters on the crankshaft were also increased. Initially work was done with a CAY turbo unit, but for production a Holset turbo was used. Later Switzer supplied turbo units for a better price than Holset, despite their factory being just five miles down the road. The 1490, 1494 and 1394 models also used the turbocharged 4/55 engines but were fitted with the cheaper Dpa pump.

Browns even designed and produced an experimental long-stroke engine the stroke was Sin but this was never put into full production. However, in 1979 after a period of some 20 years, the company reintroduced a six-cylinder engine, which had last been used on the VAK6 or 50D. This engine had not been the success that the company had hoped for. To save on production costs the new six-cylinder engine shared a common bore of 3 15/16in with the three-and four-cylinder engines, and had a stroke of 4 1/2in. This gave it a capacity of 329cu in compared to 219cu in on the 4/55 engines, 195cu in on the 4/49s and 165cu in on the 3/55s.

The original six-cylinder engine in the 50D had experienced problems with a troublesome single cylinder head, but Herbert Ashfield had seen the obvious cure for the problem. He said: ’The real problem of the six-cylinder head was its tendency to warp once it became hot, and the materials we had then were not able to stand the heat and distortion occurred. I thought, if we could use two separate heads on a single block, we might cure the problem and we already had a three-cylinder head. Using two of these meant that achieving a new six-cylinder was simpler and cheaper, and it used standard parts that were proven to be reliable. We only had to make a few modifications notably the water jacket and exhaust manifolds and fit two three-cylinder heads.’

An inline injector pump was also used, as the dpa pump on this NA engine would not give 100hp without excessive smoke. When it was fitted with a turbo it was a very good engine, but this arrangement was never used on production models. The six-cylinder engine used in the 1690 tractor was rated at 103hp, and a number of these engines were built into experimental tractors in the mid-1970s. One of these was sent on loan to Viscount Ridley of Blagdon Estates, Northumberland, a DB customer who needed a tractor capable of producing more power than was then available from existing DB models. He had been considering purchasing a Ford but readily agreed to run our experimental six-cylinder – suitably disguised – on his estate. He kept a log of its work, fuel and oil used, etc, but Ken Jagger from Field Test, looked after the tractor. When any major work or modifications were needed, Ken went up to Northumberland with a fitter and carried out the work at local DB dealers, Reids of Shiremoor.

In 1984 the 94 series was introduced and, at the same time, the NA engine was down-rated to 95hp giving a better specific fuel consumption for the 1594. The 1694 engine was mildly turbocharged to provide 108hp, but it was actually capable of producing much more power and when fully turbocharged – and tuned – it delivered about 145hp. These engines ran for many hours on the test bed and in a Field Test tractor disguised as a 1410. When the six-cylinder engine was first introduced in 1979/80 there were some initial difficulties with the front pulleys damaging the crankshaft, and latterly many years after production of this six-cylinder engine operators have suffered oil-pump failure resulting in crank seizure. If you own one of these tractors, it may be wise to fit an oil pressure gauge and have the oil pump overhauled by a competent engineer.

VAK 1

(1939-1945)

VTK1 / VIG1

(1941-1949)

VAK 1A

(1945-1947)

VAK1C

(1947-1954)

Tracklayers

(1942-1963)

Taskmaster

(1948-1965)

VAD6 50D

(1953-1959)

900 Series

(1955-1957)

VAD12 2D

(1956-1961)

950 Series

(1958-1961)

850 Series

(1961-1965)

880 Series

(1961-1965)

990 Series

(1961-1968)