Old Bus Photos

PMT – Daimler Roadliner – 6000 EH – SN1000

PMT - Daimler Roadliner - 6000 EH - SN1000
Copyright Ian Wild

Potteries Motor Traction
Daimler Roadliner SRC6
Marshall B50F

This is one of the prototype Daimler Roadliners which originally had the Clayton COMPAS heating and ventilation system fitted. There were two radiators, one each side of the bus just in front of the rear wheels which had the twin function of engine cooling and saloon heating. Sounds good in concept but like a lot of things at that time didn’t work reliably in practice. In January 1969 it reappeared with a front mounted radiator and conventional heating, the only PMT Roadliner so fitted. The radiator is hidden behind the front grille, which may look familiar to some as it was the grill fitted to the contemporary Ford Transit van. I cannot remember now why PMT fitted a front radiator to SN1000 and not a rear mounted one in the engine bay like the rest of the fleet. Incidentally the last 6 of the Marshall bodied Roadliners fleet numbers S1086-S1091 also had the COMPAS system – and they were no more reliable than SN1000!!
This was the only PMT Roadliner with air suspension, all the others had Metalastik toggle link suspension. The photo was taken on a test run near Clayton Schools on 20th January 1969.

Photograph and Copy contributed by Ian Wild

I have driven these buses and they were a total disaster, PMT only kept them for about 7 years.

Michael Crofts

I remember the PMT Roadliners. Some of them had home made looking slits in the panels behind the back wheels to improve engine cooling. They were very noisy.


Yes very noisy but sounding totally unlike a bus. It was a sort of deep "Ewwww" muffled roar. When North Western Fleetline 189 was fitted with the same Cummins V6 you could hear it descending Rassbottom St in Stalybridge (On the joint route 90 to Marple) long before it turned into the bus station.
I now regret that I never did take a ride on a Roadliner when I had the chance. A Potteries mate says they were just as deafening from the inside, and that the later Perkins engined ones whilst marginally more reliable, used to waggle their tails dramatically when driven at high revs.
Darlington and Chesterfield Corporations got long service lives out of theirs, whether that suggests they overcame many of the problems, or that the local councillors refused to give up on them for the costs and red faces involved in replacing them early?

Keith Jackson

When I was a boy the PMT Roadliners operated on route 13 to Bentilee. Apart from the noise the bodywork rattled fit to disintegrate! There was an emergency exit window half way along the off side the locking mechanism for which used to jiggle about when the bus was stationary. A big disappointment after the AEC Reliance 590s.

John Tinsley

Our problem at PMT was that we just had too many of the things!! The largest fleet of Roadliners anywhere in the world. The Plaxton bodied ones (timber framed bodies)could possibly have gone on to nearer normal service lives if re engined with Perkins V8s – but at what cost? The Marshall bodied ones (steel framed bodies)were disastrous and although we rebuilt a few at enormous cost in man hours they weren’t a right lot better. By 1972 failures of the Metalastik toggle link suspension units were becoming prevalent. These were expensive to buy and a nightmare to replace. Panhard rod bushes were a recurrent failure – again taking much longer to replace than a leaf spring on a conventional vehicle. We used saloon seats from withdrawn Marshall vehicles to replace the worn out high backed seats in some of Reliances SN801-810 making them more suitable for urban work and less susceptible to vandalism. Happy days!!

Ian Wild

Just a bit of clarification about the ‘home made looking slits’ (ref JT). They were fibreglass corner panels made in house in the fibreglass shop at Stoke and as JT says, the idea was to provide additional engine bay cooling. To the best of my recollection, they were fitted to the 47 Cummins engined Plaxton and Marshall bodied buses. I don’t think they were fitted to the later batch of 10 Plaxtons with Perkins V8 engines.

Ian Wild

08/02/17 – 16:55

I worked with Cummins at that time and spent a year or so carrying out a series of engine changes and modifications for Belfast Corporation. As it was the time of the troubles, suspect much of my efforts ended up as bonfires.
V6 engine wet liners incredibly sensitive to both corrosion and erosion/electrolysis if water filters maintenance neglected. Becoming porous within months.

Mike Hyde


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Demonstrator – Daimler Roadliner – CVC 124C

Halifax Corporation - Daimler Roadliner - CVC 124C

With – Halifax Corporation Transport and Joint Omnibus Committee
Daimler Roadliner
Marshall B50F

I have listed this under Halifax Corporation has that is who the Roadliner was on loan to at the time the photo was taken. I went on this bus to Brighouse on the 49 route which was normally serviced by double deckers maybe the intention was to replace them with high capacity single deckers. Halifax didn’t buy any Roadliners or any similar single deckers so the route must of carried on being serviced by double deckers.
I have tried to research which operator the Roadliner finally ended up with but to no avail, if you know, let me know, leave a comment.

By 1975 this bus was with the Transport and Road Research Laboratory at Crowthorne Berks, and was used for "Guided Bus" experiments involving the bus being guided by a wire buried in the road.

Derek Lucas


It was the Daimler demonstrator, a deal was struck with Bob Crouch at Daimler to keep the bus in Halifax but it would be released back to Daimler when needed for demonstration purposes, it usually worked the 5/6 circulars and later had a green roof.
The Cummins VIM V6 engine was a poor unit and lead to the early demise of these buses.
In Halifax the poor roads lead to chassis body flexing and the long chassis severely restricted route availability, also with long routes such as 48/9 it meant too many unhappy passengers standing up.
Finally at this time – it had to have a Gardner 6LX – or it was out!


08/03/11 – 15:44

I believe this bus was sold in the late 70’s through the Gov auction sales at the OSDD at Ruddington, Nottm., I was a fitter at the time, my apprentice and I had a drive around the perimeter, it still had the mountings for the experimental equipment and only about 4 seats were installed.

Roger Broughton

29/08/11 – 08:14

We had a number of batches with V6/V8 engines, with Plaxton Coach Bodies for express services, FAST/GOOD HILL EATERS, but required one driver-one coach, to keep them on the road.
The engine sound going through a urban area at 02.00 hrs. was out of this world!!!! Went back to LEOPARDS, after the 4th batch, that or buy a 2nd towing unit. [mind you all top management had Daimler cars by then, buy 9 get a free car?????]

Mike 9

29/08/11 – 16:31

Halifax Corporation - Daimler Roadliner - CVC 124C No2

Here is another picture of the Roadliner under evaluation in Halifax, taken, if my memory serves me correctly, near King Cross. Personally, I doubt that GGH seriously considered this vehicle as a contender for the Halifax bus orders. Knowing his fascination with all things in the bus world, I suspect that he wanted to try it out through curiosity alone.

Roger Cox

04/01/12 – 06:56

I well remember the Roadliner from my time with Eastbourne Corporation in the 1960’s. The demonstrator CVC 124C arrived in Churchdale Road depot one Sunday afternoon, I can’t remember when, it was not used in service only inspected and must have had an impression on Mr R R Davies the manager as one was ordered duly arriving in mid 1967 as No 86 (DHC 786E). I was the first driver to take it out on service as a additional bus on service 6, the seafront route, the first one man operated bus for the Corporation which I must say did not go down too well with the residents of the Meads section of the route. Two more similar vehicles arrived the following year as No’s 90/91 (EJK 890/91) all three having two door East Lancs bodies and fitted with the Metalastik suspension. As many others have commented they were very raucous both inside and out the suspension also I seem to remember chattered quite a lot but their performance was a revelation. I believe all three had to have new engines before they had covered 30,000 miles. I recall that when selecting 1st gear when stationary the N/S front corner dipped quite noticeably. My lasting memory of these buses is of stopping on the seafront to pick up passengers when the engine cut out for no obvious reason and would not restart I then noticed in the N/S mirror smoke coming from the engine bay upon investigation I found the main electrical control box and master switch had broken loose and was swinging on it’s cables with terminals shorting on the exhaust pipe after very carefully switching off the master switch I found the short circuit had burnt a hole in the exhaust pipe. Meanwhile orders had been placed for Leyland Panthers, I left the Corporation in 1969 and the Roadliners quite soon after, it has to be said the Panthers were only marginally better.

Diesel Dave


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West Riding – Daimler Roadliner – FHL 826D – 133

West Riding Daimler Roadliner

West Riding Automobile
Daimler Roadliner
Plaxton B50F

I always thought the single deck version of the ‘Fleetline’ was called a ‘Freeline’ but it appears I was wrong, it was called a ‘Roadliner’. It as come to light whilst researching this bus that the ‘Roadliner’ was not the most reliable chassis in fact it was quite the opposite. That I find strange as the ‘Fleetline’ the double deck chassis was very reliable if you know what the problem was please leave a comment? Another interesting thing about this bus is that the body was built by Plaxton who were better known at that time for coach bodies rather than bus bodies although having looked at there website today they do four very impressive bus bodies at the moment.

The Roadliner was a different beast to the Fleetline, it was a 36 foot long, and for it’s time, a low floor chassis, incorporating air or metalistic toggle link suspension.
In the days before one man operation of double deckers was permissible, the high seating capacity Roadliner like it’s contemporaries the AEC Swift, Leyland Panther, and Bristol RE, was after a piece of the action.
The Bristol RE proved to be the only reliable model of the bunch, enjoying large orders and long service lives. The Roadliner sadly proved to be just about the worst, due largely to it’s weird and unreliable Cummins V6-200 engine.
Later models were instead equipped with the Perkins V8 engine, but it seems the damage had already been done, with braking and suspension problems meantime manifesting themselves.
West Riding really didn’t need these problems, with their hands already full of the woes presented by their large fleet of Guy Wulfrunians.
PMT Ltd (Potteries Motor Traction Ltd) however got their hands burnt the worst as the biggest operator of Roadliners, with 62 buses and 6 coaches (?). Despite strenuous efforts to keep their Roadliners on the road, by 1970 PMT’s problems were such that they finally threw in the towel, and withdrawals started soon after. Their last left the fleet in 1976.

Keith Jackson

You’re right about PMT’s 6 Roadliner coaches. They were fleet nos. C1097-C1099 (KVT 197-199E) and C1100-C1102 (PVT 100-102F). The first three had Plaxton bodies and the last three Duple.
All the early PMT Roadliners had Cummins engines. The Perkins alternative was trialled in the rebuilt PMT prototype S1000 (6000 EH) and then the last 10 examples (built in 1968; 130-139 (WEH 130-139G)) also had the Perkins unit.
I remember going round the PMT depots on my bike in about 1975 and seeing huge quantities of Roadliners dumped around the back of Cheadle depot prior to disposal. There weren’t any Roadliners at any other depot so I suppose this was either the last depot to operate them or it was a convenient place to collect them.
As you say, long before then the writing had been on the wall for the Roadliner and PMT tried several different alternatives; a batch of 21 Fleetline single decks in 1970 with unusual Alexander ‘W’ type bodies was followed by several batches of Bristol REs. Even these didn’t survive long, however, as the Leyland National revolution gathered pace.

Mel Harwood

The plus points with the 9.6 litre Cummins VIM V6 200 engine were its compactness and potential to deliver a hitherto un-heard of 192 bhp (hence the 200). Tragically, the engine failed to live up to its promise, maybe because it was fundamentally a marine unit designed for totally different working cycles. Result? Mechanical mayhem.
By the time the slightly less-powerful V8 unit from Perkins was offered, the Roadliner’s reputation was irretrievably damaged. Sad, really, because in other respects, it wasn’t a bad vehicle.

Chris Hebbron

Thank you for your comment on the Roadliner I did not know that the Cummins engine was based on a marine engine no wonder it was a disaster. When you think about it a marine engine is set at a steady rev rate and stays there for hours which couldn’t be more opposite to a bus engine.


Early diesel locos in the UK were powered by modified versions of marine engines and seemed to do surprisingly well in general. However, there was a stage well into the lives of the High Speed Trains, when they suffered overheating problems one hot summer. The engines in a couple of power cars were strapped up with sensors and the results were a revelation to the engineers. One was that that these engines never spent much more that 10 seconds on one power setting! Your point precisely! They had to redesign the cylinder heads and radiators which cured the problem and made them more reliable and efficient. Some might argue that this survey was well-overdue! Most have been re-engined with ML (German) engines which are probably far superior to the old Ruston ones.
We know that Cummins nowadays produces some superb diesel engines, renowned for their high-revving abilities. However, I do recall that about 10 years ago, a class of diesel train here in the UK was fitted with one type of their engines and was a disaster after about three years! After mutterings about legal action, they changed all of the offending engines at great cost them themselves, better than at a cost to their reputation, I suppose!

Chris Hebbron

Let’s not be too unkind about marine engines: after all, the Gardner 5LW & 6LW were essentially marine engines, and they had a strong claim to be the most economical, reliable and altogether unbreakable engines ever installed in a bus.
Ironic really that as the Bristol Ks and Lodekkas went to the scrapyards in the 60s & 70s, a huge proportion of their engines were shipped to the Far East to be fitted in junks, where they are probably still puttering about at that legendary 1700 rpm governed speed!

David Jones

Just to correct the details of the PMT Roadliners: There were 64 in total, 58 buses and 6 coaches. The prototype SN1000 never had a Perkins V8 engine fitted. The first Perkins V8 was trialled in fleet number S1078 in 1968 – just before I joined the Company as Technical Assistant. Later (about 1970) Fleet number S1065 was also fitted with a Perkins V8 but that was a far as the conversions went. We had horrendous problems with the Marshall bodied buses (S1069-S1091) with the bodies literally breaking their backs requiring major rebuilds as early as 1970. Some were exported to Australia in 1972 by a Cranes and Commercials (Dealer), Southampton.

Ian Wild

Interesting to hear the problem with the Roadliner breaking it’s back because the 36′ Fleetline with the panoramic windowed Alexander W body did the same, no doubt the effect of sticking a ton and a half of engine and gearbox across the end of a long rear overhang. One of the Scottish operators of the type (Dundee?) rebuilt some of theirs with a traditional Fleetline bustle and rear bulkhead – not sure whether it was a success in engineering terms – it was certainly an oddball in looks!. The 33′ version of the Fleetline single decker escaped these problems.
The Freeline was a mid underfloor engine.
While we are on the subject of Marine diesels – what about the Deltic, that engine came from a marine ancestry.


I am out of my depth here, but was always told that the Deltic appeared so that English Electric could find a use for its Napier marine diesels which were intended to run more consistently. Some say it was prone to the same problems, but I think it was diesel electric and so was driving electric motors, possibly a more consistent task.


I once heard that there was another issue with marine diesel engines in railway locos (I believe that all the relevant ones, by the way, were diesel-electrics). In addition to the constant engine speed issue, there was a big difference between the natural "secondary resilient mounting" provided by the sea water under the hull of a ship, and the fairly rigid track bed on which a loco rode. The relevant engines preferred the former, and tended to protest at the latter.

Stephen Ford

As Stephen says, the locos were diesel-electrics and their "marine" engines were supplying a constant output rather than a variable. My family event last weekend including a trip on the canal from Sheffield Victoria Quays towards Rotherham. I was surprised to learn of the existence of the Gardner 2LW – very popular on narrow boats. Once the beast was underway, no need for anything bigger, no need for acceleration! John Deere, of tractor fame, are also involved in marine engine supply these days – using another "trade" name (Lugger I believe). Diesels have many applications but there are definitely horses for courses. Dare I suggest that, in their day, Gardners were so good that the design could cope with marine, road and generation applications whereas others didn’t quite get their act together!

David Oldfield

According to Alan Townsin, one of the problems with the Cummins V6 was that, for production reasons, Cummins used the same "V" angle as on their V8s. As a result the engine was inherently unbalanced and prone to vibration problems. This may have contributed to its well-known tendency to run hot, tighten-up so that it wouldn’t re-start, and smoke badly as well. Shame about the Roadliner, as the overall design concept was brilliant and well ahead of its time.
The body problems were not unique to the Roadliner: many rear-engined buses tended to have problems with chassis flexing, and many coachbuilders struggled to cope with it. Even AN68s can exhibit symptoms: just look for all the popping rivets above the rear axle on a well-worn Roe example!

David Jones

27/01/15 – 13:52

I’ve just seen David Oldfields comment about Gardner LW-series engines in narrow boats (two comments above). As he says, acceleration is not important in that context; however, deceleration most certainly is. The propeller is shaped specifically to push the boat forwards. It is much less efficient when running in reverse, and that’s where Gardner torque comes into its own. Stopping power is everything on canals and rivers, and Gardner engines are even more revered there than they are on the road.

Peter Williamson

28/01/15 – 06:33

You have reminded me of a vehicle much closer to home with Cummins problems in miniature. The Hillman Imp was an excellent car, the first hatch- well, notch- back with luggage space at each end and a wonderfully smoothly revving aluminium engine and precise steering and gear change. Does distance lend enchantment to the view? I did have three, not all at once. The engine, it is said, all 875cc of it, came from a Coventry Climax fire pump (is this true?) and, yes was not used to revving, especially like that. So, apart from the water pump, you could go through cylinder head gaskets, especially with the twin choke Sunbeam version which had an oil cooler. The benefits of this became apparent when the "boiling" light came on: go faster, force more air through and the light would gently fade. Are we a bit off-thread? Memories…


02/02/15 – 07:01

Part of the legacy of Gardner’s early Diesel engines, designed originally for marine and stationary use, was the continued use of its own design of all-speed governor on the fuel injection pump. Many other Diesel engines have utilised injection pumps fitted with 2-speed governors (eg: CAV N and NN types, Simms BPE type, and the Friedmann & Maier pumps fitted to Leyland National 2s and Tiger TRs). Such governors regulated only idling speed and maximum rpm as determined by the engine manufacturer. Without any load on the engine (for example when running the engine with the gearbox in neutral), if the accelerator was set to any given position, the engine would either steadily climb to maximum rpm, or rise slightly and then steadily fall back to idling speed. On the road, variables such as vehicle load, gradient, gear selected etc all influenced engine speed between idling and maximum rpm, keeping things much more predictable for the driver.
With Gardner engines having an all-speed governor, this meant that when the engine was running without load, the accelerator could be set to any given position, and the rpm would stay at a constant speed for that position (hope this is all making sense!). All-speed governors were particularly popular in marine and generator set applications, as when loads on the engine could vary, the engine speed would remain fairly constant. This could be heard on fairground generator sets (many of which tended to be Gardner-powered), when the load on the generator reduced, yet the engine speed remained more or less the same, albeit quietening as the load decreased. Conversely as generator demand increased, the engine could be heard to work harder, but the rpm would hardly change.
In road vehicles, as with the two-speed governor, vehicle load, gradient, gear selected etc still came into play, and drivers would probably be unaware of such differences in governor types, as the accelerator position would be constantly changing when driving. However, I have heard drivers say that with Gardner-engined vehicles the further the accelerator was pressed the more resistance could be felt, as more tension was placed on the governor spring via the various mechanical linkages. This ‘heavy throttle’ feel, as far as I’m aware, was peculiar to Gardner-powered vehicles due to the design of governor. Gardner’s injection pumps were very large, heavy affairs with a large strong governor spring, and the cambox, camshaft, governor assembly and casings were all of Gardner design and manufacture. The fuel injection equipment mounted on top of the cambox was manufactured by CAV (Charles A Vandervell), and the original design was by Bosch, with CAV having an agreement to build the equipment under licence at their works in Acton, London.

Brendan Smith

02/02/15 – 11:41

I agree entirely with your comprehensive comments about the Gardner all speed governor, Brendan, and I have remarked on this feature myself elsewhere on this site. When pressing the accelerator pedal, one felt a very strong initial resistance against the spring that then softened until the engine speeded up to the new governor setting. As the rpm built up, so one felt the resistance building up again under the pedal. When changing gear with a conventional gearbox, the best technique, having selected the required gear, was to blip the engine slightly before re-engaging the clutch, which reduced the resistance on the throttle pedal. This obviated the snatch in the transmission that resulted if the accelerator had to be pushed down against the governor resistance, which would give way suddenly. Gardner abandoned the all speed governor in favour of max/min CAV fuel pumps in late 6LX and all 6/8LXB production. I suspect the LW20 range also had CAV pumps. The Gardner/CAV pump could not provide the higher injection pressures required for the increased output of the later engines.

Roger Cox

03/02/15 – 09:17

I often wonder what contribution Edward Turner might have made to the Roadliner. Edward’s main strength was in engine design, most famously for taking his Ariel Square Four motor bike engine and splitting it down the middle to give us the Triumph 500 cc parallel twin – hence the Tiger 100, Bonnie etc.
When Jack Sangster brought Edward into the BSA owned Daimler fold in the mid fifties, Edward went on to design various ‘V’ formed petrol engines for Daimler cars. I am sure that, if anyone could, he would have designed the ‘V’ diesel to power their Roadliner. We would then have had ‘proper’ low floor buses decades before we actually got round to them.
One can only speculate why this was not done. Was it Daimler’s reluctance to invest in a new Daimler engine? Or did politics dictate that the US owned Cummins factory should be given work in the deprived north east of England? Or did Edward Turner simply retire?

Alan Johnson

06/02/15 – 06:39

The late 1960s can’t have been an easy time for WRAC’s engineers: on top of the Wulfrunians the Roadliners can’t have been exactly good news . . . and then there were some Panthers on top. Following on from Alan’s comment, it was my understanding that the Cummins V6 was imported from America, so Cummins’s Darlington factory didn’t benefit in any event. A quick Google has confirmed the latter, but suggests part of "the grand plan" was for the Cummins engine to be built in a joint-venture in the old Henry Meadows factory (which was adjacent to JDGs Guy factory). The same article also suggests that a batch of 12-metre Roadliners was ordered but later cancelled (by whom?), that the Panther Cub was produced for Manchester after it threatened to order 10-metre Roadliners, and that a Rolls-Royce-engined option was considered. Looking at the original picture, I’m surprised to see a Cyclops fog-light fitted as late as 1966: Cyclops fog-lights were surely a fad of the 1950s . . . perhaps it was felt a more conventional near-side fitting might have added to the "inherent imbalance" of the Cummins engine.

Philip Rushworth

07/02/15 – 06:09

Thank you for that fascinating information regarding smooth gearchanges Roger. The first Gardner Diesel engine to have a non-Gardner injection pump was the 6LXDT introduced in 1984, which as you mention had the CAV ‘Majormec’ pump, rather than the usual CAV ‘tops’ on a Gardner cambox and governor assembly. The fitting of CAV injectors, rather than Gardner’s own (Gardner referred to theirs as ‘sprayers’) was another change on the 6LXDT. Gardner was trying to keep up with operator demand for more powerful engines (especially in the heavy goods vehicle sector), and it was said that the CAV pump and injectors could operate at higher injection pressures and at a faster injection rate than Gardner’s system could manage at higher bhp ratings. The ‘LW20’ (20bhp per cylinder) range was discontinued in 1974 Roger, and all LWs had the usual ‘Gardner bottoms with CAV tops’ injection pumps mated to Gardner ‘sprayers’.
Referring to Alan’s speculation about a Daimler V8 Diesel engine in the ‘Roadliner’, what a wonderful sound that might have made, if the 2.5 litre Daimler V8 petrol engines were anything to go by. Such ‘lazy-sounding’ low-revving V8s sounded wonderful as they burbled past, but whether the Daimler V8 Diesel was an opportunity missed or a lucky escape, we’ll never know. However, one opportunity elsewhere fortunately WAS missed, as in 1967 Bristol was looking at the feasibility of fitting a Cummins V6 engine into the RE (whaaaat!). Duncan Roberts’ excellent book ‘Bristol RE – 40 years of service’ even has two photographs of the attempt. The chassis was a standard Series 2 RESL6G due for delivery to Crosville (ERG3: OFM 3E), and the photos show the V6 supported on wooden blocks at the height and position envisaged for fitting. A Gardner oil bath air filter housing can clearly be seen, as can the ‘JAGUAR – CUMMINS’ lettering on one of the engine rocker covers, which is intriguing. The unit was very compact, but also quite tall and would have protruded well above the chassis toprail. The RE chassis was already quite high at this point, and fitting the V6 would have required the floorline to be even higher and the project was dropped (sigh of relief all round). The RESL went on to enter Crosville service as nature intended fitted with a Gardner 6HLW engine. (There wouldn’t have been a welcome in the hillside with that V6 fitted that’s for sure). In the book, Duncan Roberts states "The time and money spent on this exercise suggests that there was an influential customer in the wings, but no clue has been found to his identity. The RE was therefore spared the odium that would have flowed from the unreliability for which this engine (the V6) became known".

Brendan Smith

09/02/15 – 07:10

The Cummins plant at Darlington certainly carried out warranty work on the V6 whether or not they were actually built there. Because of the V6 problems, PMT were issued with three float V6 engines to enable units (usually by that time failed ones) to be returned to Darlington for rebuilding/upgrading. I drove the PMT Thames box van up there on one occasion to exchange three defective engines for three rebuilt ones. It would have been impractical to have returned them to the States for attention.

Ian Wild

03/12/15 – 10:56

As the author of the Wikipedia article on the Roadliner I can tell the poster who asked that it was a South African customer who ordered and later cancelled the 12m Roadliners. It may have been Pretoria, who also ended up with the last ones bodied (AEC AV810 powered) but I’ll have to dig out my copy of Buses Extra 39 first.

Stephen Allcroft

30/12/15 – 06:24

It was Johannesburg who ordered the 12m versions, before cancellation the designation was altered from SRC6-40 to SRA8-40. Chassis numbers are given in Tony’s article.

Sephen Allcroft

20/01/16 – 05:46

I think Ian’s recollections about returning the V6 Vim engines to the Darlington Plant are now a little hazy with time. Cummins Darlington plant built the smaller V6/V8 Val/Vale engine families, for Ford and Dodge. We did have a local Distributor, C D S & S, who would have rebuilt the engines on an exchange basis, on our behalf. Both Cummins plants in Darlington were for new manufacture only. All the engines supplied to Guy and Daimler were manufactured in Germany by Krupp. As an aside someone earlier suggested that the V6’s, as supplied to Guy/Daimler, were originally designed for Marine use, not so, the automotive sector was always the driving force behind new engine designs (volume), other applications came later.

Peter Hobson

21/01/16 – 06:34

Peter – PMT categorically did return V6 VIM engines to the Cummins plant at Darlington – I drove the PMT Ford lorry up there one Friday with three defective engines, returning with three rebuilt ones. This was a regular job for the lorry driver at that time. This was a campaign change instigated by either Daimler or Cummins, our contact at Cummins was Doug Strachan. Unfortunately the campaign changed engines were little better than the originals. What a surprise to see your name on the site – hope you are keeping well.

Ian Wild

21/01/16 – 15:28

Whatever the truth about the original purpose – marine or automotive – of the Cummins V6/V8 ranges, I consider the Cummins PT injection system to have been totally unsuitable for automotive applications. The response to accelerator movement was exceedingly coarse, giving the effect of the engine being either "on" or "off". I mercifully never drove a Roadliner, but I had plenty of experience with the L10 in Olympians, and it was a horrible engine for smooth progress in a bus. Some manufacturers, notably Dennis, tried out the bigger M11 for bus work, and abandoned the idea. The Dennis R series coach didn’t do very well either.

Roger Cox

21/01/16 – 17:12

Ian- I have a look on this site ever now and again just to see who’s posting. The odd name from the past that comes up rattles my box, like Peter Wyke-Smith, which reminds me of the time we jointly got Leyland over a barrel to fit the HLXB/HLXCY into the National.
On the subject of the Cummins V6 Vim engines, I have to defer to your laser like recollection (Note the tone of the grovelling!) Doug Strachan ran the Pilot Centre at Darlington, fitting various Cummins engines into new applications. George Ochs who was responsible for all Customer Service throughout the UK was also responsible for orchestrating any company campaigns, usually through the distributor network, ( via Cummins Diesel Sales and Service a subsidiary of Blackwood Hodge in Northampton). I assume that George took a cheaper/faster option, to keep costs down, by having Doug’s people cover the refurbishment ‘in house’. At the time we were in the middle of the V6/V8 Val/Vale problems with Dodge and Ford which kept everyone in our department out of mischief I can tell you. Talking of Doug Srachan, I went for an interview with him for the job of Pilot Centre Technician, at the back end of 1966. Halfway through our conversation, mainly relating to my time with Gardner, he said I might be interested in a different job. I then jumped ship and joined service department with a higher salary, company car and exes, working under George Ochs. I never did buy Doug that pint I owed him for his selfless attitude!

Peter Hobson

22/01/16 – 06:09

Peter – that’s very interesting. I’m glad my memory hadn’t failed me over the reworks at Darlington – I didn’t know the reason why until you filled in the background to Doug Strachan. Also interesting to note that Dodge and Ford had problems with the VAL/VALE engines. Were the problems similar to the VIM/VIME in bus application? What was the difference between the two groups of engines? You couldn’t forget PH Wyke-Smith!!! I can imagine he told Leyland EXACTLY what he thought about Leyland Nationals, 680/L11 engines and Leyland themselves!!

Ian Wild

24/01/16 – 07:09

The VAL/VALE were a similar design with a lower displacement, ISTR the VALE at about 7.6 litres. RPM was even higher and only one was fitted to a PSV: https://www.flickr.com/photos/1  —  https://www.flickr.com/photos/2

Stephen Allcroft

Monday 25th

Ian – The problems with the early Val/Vales in the Dodges were mainly down to excessive black smoke. We had an ‘injector train’ campaign due to excessive wear on the mating surfaces of the tappet, push rods and rocker levers. The ensuing wear severely reduced the pre load torque applied to the injector, allowing excess fuel to be injected. If I remember correctly the ball end surface finishes had to be improved on all the mating items, from the camshaft to the injector. The Ford engines were a later spec and I think they all had the later mods included from day one. The V6’s ran at 3300rpm the V8’s at 3000rpm. Getting drivers to use the full engine rev range was quite a problem and I think both OEM’s fitted rev counters marked with a green band to encourage them to make full use of the available power. Drivers using the " give it 3000 revs and drop the clutch" style of driving tended to generate less engine problems than those with a lighter touch. The V6 Vim engines in the Guy’s were a lot less hassle than the Daimlers.
My personal opinion being that the engine cycling requirement for the PSV spec, i.e. lots of idling, were not helpful given the type of fuel system employed at the time. (Keeping on top of the injector preload setting, on a regular basis, was required too frequently for most customers, to keep a clean exhaust.)
As John Ashmore mentioned in a prior forum, some of the engines suffered from dropped valves, due to crossheads ‘floating’ and pushing valve spring collars down thus releasing the valve collets. These failures indicated an overspeed condition and/or excessive valve clearances.

Peter Hobson

26/01/16 – 06:44

I am not an engineer, but a working life of 43 years in many roles in the bus industry brought me into close contact with most facets of its operation. The engineers on the OBP forum are welcome to shoot at my following opinions on Cummins engines.
Legend has it that the PT (Pressure Time) fuel injection system was created because Cummins would not pay the royalties to Robert Bosch for the use of the traditional injection fuel pump. Cummins made much of the feature that ‘eliminated the need for high pressure fuel lines from the pump to each injector’. This was never a particular problem for other engine makers, and appears particularly eccentric nowadays in a world of high pressure common rail injection systems. The Cummins fuel system employed another camshaft at the cylinder head, this camshaft necessarily being much larger than that in the cambox of a normal fuel pump, to operate the PT injectors, these themselves being complicated units that did not give the accuracy or service life of ordinary injectors. PT was less fuel efficient than the Bosch system, required greater maintenance, and yielded very coarse engine speed responses to movements of the accelerator pedal in automotive applications. Significantly, the later B series engine (originally a Case Corporation design) which has spawned the present Cummins diesel ranges, abandoned the PT system. PT fuel injection made the highly stressed VAL/VALE/VIM/VINE V form engines more complicated than they needed to have been, and this, plus the poor throttle response endemic to the design, must have contributed to the mediocre reliability standard. Sadly, the promising Tilling Stevens TS4 diesel development programme was cancelled by Chrysler because of its joint venture with Cummins in the then new Darlington plant for the supply of V form engines. It is one of the wonders of the engineering world that the reputation of the Cummins company survived the fiasco of its dreadful V form engines. By contrast, the present day Cummins engine ranges are widely respected.

Roger Cox

FHL 826D_lr Vehicle reminder shot for this posting

27/01/16 – 16:08

I can vaguely recall, having no direct contact with Cummins engined Roadliners, that Black & White of Cheltenham re-engined some of their Roadliners with Perkins V engines. Did they fare any better?

Geoff Pullin

29/01/16 – 07:06

Geoff – PMT had two Roadliners re-engine with Perkins V8-510 units plus the final batch of 10 delivered with the Perkins engines. The Perkins unit was a much smoother running engine probably the eight cylinders helped. Time dulls the memory, I don’t think the Perkins buses lasted any longer than the Cummins ones. I do recall quite severe cylinder bore wear with the Perkins engines, maybe as much to do with the air induction system (and maintenance thereof) as shortcomings with the engine itself. There were other problems with the Roadliner, not least the metalastik toggle link suspension although Midland Red seemed to manage with it. Thanks to Peter H for the detail of VAL/VALE engine problems.

Ian Wild

29/01/16 – 07:06

Although slightly off-piste, I recall some years ago that British Rail had problems in some their Cummins- engined diesel trains and Cummins had to replace all of them at considerable cost.

Chris Hebbron

29/01/16 – 12:56

I think you are thinking of the Class 142,143 and 144 pacers that had their TL11/Hydracyclic drivelines swapped for Cummins LTA10H /Voith after severe early unreliability. Volvo as successor to Leyland Bus took the hit for the Cummins Engines and Cummins as successor to Self-Changing Gears paid for the Voith transmissions and Gemidner(sp?) final drives.
the 141s retained their TL11H and Hydracyclic driveline but only ran for 14 years in the UK although eight were exported to Iran which could be seen as a hostile act…

Stephen Allcroft

29/01/16 – 17:29

Thx, Stephen A, for filling in the detail. I wouldn’t think any of them are still running. I also recall Rootes Group selling thousands of Hillman Minxes CKD to Iran years ago – another hostile act!

Chris Hebbron

29/01/16 – 17:30

Does anyone know what the problems were with the rubber suspension on the Roadliner, and was it one or both axles? With one exception, the toggle link suspension was only used on the rear of BMMOs. It was highly successful and on single deckers extremely simple. The exception (the S19) was in principle if not in detail, more like the Roadliner. However, the S19 is thought to have retained this arrangement for its whole working life.
Any details would be much appreciated.

Allan White

30/01/16 – 06:07

Allan – the PMT Roadliners had metalastik suspension on both axles. Problems as I remember were panhard rod bush/bracket wear/failure and failure of the metalastik bonding in the suspension units themselves. also, I’d forgotten that the 24 Marshall bodied vehicles broke their backs after about three years service. I remember one was rebuilt but at massive cost particularly labour. The Plaxton bodies being timber framed were rather more forgiving. Incidentally, Plaxton was not a mainstream bus body supplier to the BET group at that time, wonder why they got the initial Roadliner body contract?

Ian Wild

30/01/16 – 06:08

Roger – I may be able to enlighten you on some salient Cunmmins details. Clessie Cummins introduced the PT system in 1924, a major update took place in 1954 to improve fuel efficiency, due to increasing competition in the US. None of the Cummins historical info makes mention of any contact with Bosch.
The mechanical injector is actuated, by a third rocker lever, from a standard engine camshaft comprising an additional cam located between the inlet and exhaust cam lobes.
The fuel pump is a very compact unit, you can hold it in one hand. It supplies a fuel pressure up to approx. 250psi max to the injectors. Injection pressures up to 18000psi can be achieved within the nozzle part of the injector. In the 1960’s the same size pump, with different internal settings, could be use on a small Val V6 up to a 28 litre V12 – 700 HP engine. The fuel pump for Automotive use was a Max/Min governor type, an ‘all road speed’ governor, used mainly for use on Gen Sets or Loco’s was available at extra cost.
In retrospect the Val/Vale, Vim/Vine engines were of very ‘Oversquare’ design. Subsequent designs increased the stroke of the engines and were more acceptable. I hope the foregoing helps.

Peter Hobson

30/01/16 – 18:37

Thanks for that clarification, Peter. I saw a number of L10 engines being worked on, and, had I looked at them properly, I should have seen that the injector of each cylinder was operated by an extra cam lobe rather than a separate shaft. (To quote Sherlock Holmes, "You see, Watson, but you do not observe".) The trouble with the PT system was its coarse response to accelerator pressure, and I am interested to learn that an "all speed" governor was an option. This, I am sure, would have remedied that problem in automotive applications. The "on/off" characteristics of the PT system would not have been significant in haulage use – unlike passengers, sacks of spuds or whatever do not complain about rough rides – but for bus work it was terrible. The PT system seems to have been best suited to constant load applications such as rail or marine. It is noteworthy that the 14 litre Cummins engine that still powers many of the railway DMUs, and was once offered in UK lorries as an alternative to the Gardner range, did extremely well in a comparative survey of maintenance costs – a reflection of reliability – compiled by the "Transport Engineer" journal in 1979. Unsurprisingly, Gardner came top, but the Cummins 250bhp 14 litre came a close second, with the AEC 760 next. The Rolls Royce Eagle was way down the list at No.11. Coming in second from the bottom at no.15, the Leyland 510 of Leyland National notoriety cost six times as much to maintain as a 6LXB. Getting back to the V form engines, I recall that, in 1969, Cummins and General Motors became embroiled in a lawsuit in which Cummins claimed patent rights on the principle of the "oversquare" stroke to bore ratio. Quite rightly, the claim was thrown out by the Maryland court. There were many oversquare engines before Cummins.

Roger Cox

02/02/16 – 06:58

PMT service 19 (I think) ran to Sandbach with some journeys extended to Over. The destination display showed ‘Over (Square)’ – quite appropriate for the Roadliners used on this service!

Ian Wild


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