It's good to have all these definitions listed on the ‘Abbreviations’ page - but I see the Bristol SC is described as "underfloor engine". I always though it was fitted with a front vertical engine, and that it was the replacement SU series (SUS, SUL) that had an underfloor engine (amidships). Also, the usual designation was "SC4LK", presumably because the standard fitment was the Gardner 4LK engine. I believe that Gardner also produced a 4LW series (I guess in the same mode as a 5LW and 6LW), and I think Eastern Counties or Eastern National had a few saloons fitted with a 4LW, (designated Bristol L4G) or re-engined older vehicles - maybe a Dennis Ace or two? Not being a technical person, I have no idea of the difference between a 4LK and a 4LW (except that logic says they are both 4 cylinder jobs). No doubt knowledgeable people out there will contribute some good information.
Michael Hampton
04/02/11
You're quite right, Michael: the SC4LK had a vertical engine, the Gardner 3.8-litre 4LK, which gives 57 bhp at 2100 rpm. The 5.6-litre Gardner 4LW (two-thirds of a 6LW) yields 75 bhp at 1700 rpm, though I imagine that when Gardners uprated the 5LW and 6LW to 20 bhp per cylinder they probably did the same to the 4LW. As for the SUL4A, I had always assumed that it was powered by the Albion-designed 4.88-litre unit, but I've since been told that the engine is two-thirds of a Leyland 350: 3.84 litres turning out about 60 bhp at 2200 rpm. Can anyone give the definitive answer? Many thanks in advance!
Ian Thompson
05/02/11
The underfloor replacements did indeed have a Leyland/Albion unit. It was a cut down Leyland Comet engine - as Ian stated - and was the self-same unit as fitted to the Albion Nimbus.
David Oldfield
06/02/11
Some Bristol SU chassis were also fitted with Perkins engines West Yorkshire classified these SMP Saloon Medium Perkins rather than SMA Saloon Medium Albion in their letter numerical fleet numbering system
Chris Hough
06/02/11
According to the PSV Circle publication CXB1405, the engine in all Bristol SUS and SUL chassis was the Albion EN250, 4.1 litres, four cylinders, giving 72bhp at 2200 rpm. A few years ago, I had a ride on the preserved ex West Yorkshire SUL4A 811BWR - the performance was amazing!
Bob Gell
08/02/11
Michael, you are right about Eastern Counties O.C. having some L4Gs powered (or perhaps underpowered) by 4LW Gardners, and they also operated a handful of LS4Gs, including the second prototype, which used the horizontal version (4HLW). ECOC also ran some Dennis Aces fitted with 4LK engines, and in the 'fifties ran a small fleet of Bedford SBO/Duple coaches powered by 4LKs, which I believe were unique to the company. Gardner introduced the 4LK in the mid-thirties and it was aimed at the 3-5 ton lorry/small PSV market. Unlike the LW, available with any number of cylinders from 2-6, the LK was not part of a range and was only available as a four-cylinder unit. (The first one built did have six cylinders (6LK), but never went into production). However, the major difference between the LW and LK was that of construction. The LW used aluminium alloy for the crankcase and sump, with the cylinder blocks and heads being of cast iron. The LK utilised magnesium alloy for the crankcase and sump, and aluminium alloy for the block and head assemblies, making it lighter for the intended applications. Engine capacity was 3.8 litres, with a bore of 3.75" and stroke of 5.25". Early 4LKs developed 52bhp @ 2000rpm, but this was soon upped to 57bhp @ 2100rpm - a heady speed by Gardner standards! Production of the 4LK ended in the mid-sixties around the time the Gardner 6LXB was coming into being. As other manufacturers were by then mass-produce reliable, small-capacity diesels more cheaply, the 4LK was phased out. As an aside, the humble little 4LK played an important role during World War II, including being fitted into the midget submarine responsible for crippling the German battleship 'Tirpitz'. The 4LKs not only powered the submarines, but also generated the electricity for them. The first 4LK was installed in a Lagonda for experimental purposes, and is said to have had a top speed of over 80mph, and recorded an average fuel consumption of 42mpg on a test run around North Wales. (This engine was rated at 85bhp @ 3000rpm). The aforementioned 6LK had been fitted to an Invicta sports car, and this it was claimed had a top speed of 90mph and averaged 35mpg on a tour of the Scottish Highlands (nice scenario!). Regarding Chris and Bob's comments, the standard engine as fitted to the Bristol SU was indeed the Albion EN250H, but West Yorkshire Road Car converted one of their 1965 batch of SUL4As to six-cylinder Perkins P6.354 power in 1966. Originally numbered SMA17 (EWT 386C), it then became SMP17 to denote the Perkins transplant. Performance was said to be impressive - the speedo needle being capable of resting on the 'H' of MPH by all accounts! - but no more were converted, and so it remained unique.
Brendan Smith
09/02/11
Thanks to Brendon for clarifying the engines in the West Yorkshire SULs - isn't EWT386C the one in preservation with Thornes?
Bob Gell
10/02/11
Thank you to all who have contributed information about both the Bristol SC4LK and the SUS/SUL series. It was fascinating to read about the development of the 4LK (and original 6LK) and some of the various engine installations that have happened. The use in a Lagonda car must have been quite spectacular. Although Dennis Aces were known as "Flying Pigs" regardless of their engine, more because of the front end design, those ECOC ones fitted with 4LKs must have truly lived up to their nickname.
Michael Hampton
12/02/11
One of the ECOC Bristol L4Gs is preserved, and a ride on it is quite an experience, believe me! I call it the Spirit Level, because if it will go along the same road in both directions in 4th gear without losing speed, the road must be perfectly flat. Surprisingly it has an ovedrive 5th, and given long enough, can achieve quite a creditable turn of speed. One of the LS4Gs is also preserved and is said to be much better. I don't know if it's lighter, but certainly by the time it was built the LW series would have had a fuel pump modification which increased the engine's output by 10 per cent.
Peter Williamson
13/02/11
Bob and Michael, thank you for your comments. The SU fortunately preserved by Thornes is indeed the unique SMP17 (EWT 386C). I believe it operated with them for quite a few years after its withdrawal by West Yorkshire. Peter's comments about the performance of the ECOC L4G and LS4G were also most interesting - especially the one about the L4G actually having a fifth gear. (Bet that brought the revs down!). Now for an apology - in my ramblings I meant to write that the LW-series could be had with any number of cylinders from TWO to EIGHT, and not TWO to SIX as I have typed. I could have blamed the computer, or one of our cats for having walked across the keyboard, but no - 'twas I to blame and nobody else!
Brendan Smith
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