From the by Graham Montgomerie
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The last bastion of the naturally aspirated engine fell with Gardner's announcement of the turbocharged 6LXCT. What were the reasons behind the change?
AUTOMOTIVE world has
in agreement for some over the merits of turboging, but several manufac-s have been later on the e to apply the technique others.
is only very recently that flier-Benz and IVECO, for nple, made turbocharging a D-spread in their respective les.
he last defender of the "rally aspirated engine has n Gardner but, as everyone r knows, the Lancashire comy has announced a turborged version of its 6LXC en
designated 6LXCT.
o find out the development :ory of this latest power unit -n Gardner, I have been :ing to company technical actor Paul Gardner, who also )Iained some of the history ding up to the Hawker Siddetakeover.
/hen Hugh Gardner resigned m the company in 1975, the irket was falling away as infla n started to bite. It was felt at time that a change of idership and some fresh blood im outside were necessary d to this end Clayton Flint (the nior partner of a Manchester m of solicitors) came in as airman.
As Paul Gardner recalled: "We id an exciting and tempestuJS time at our board discuspris around a big round table." During this period, RollsDyce approached Gardner with view to a merger or takeover id the discussions went on for ffrie time. But at the end of the ly it was felt that the respective -oducts did not complement le another.
So the whole deal fizzled out. But, as Paul recalled, about 12 onths later Rolls-Royce bought large block of Gardner shares "nbeknown to us and this led other people getting inrested".
There were in fact about six her organisations involved (inuding the National Enterprise Dard for a possible link-up with
Leyland), but by far the most satisfactory one from Gardner's point of view was Hawker Siddeley.
It should not be forgotten of course that Hawker Siddeley already had an extensive involvement in the diesel engine business with Petter, Lister and Mirrlees and into this line-up the Gardner range slotted in quite nicely after the takeover in 1977 which secured the financial future for the Patricroft company.
As far as the engineering side was (and is) concerned, Gardner was left to its own devices and this included the development work for the 6LXCT which had been formulated as an idea in 1975 under Clayton Flint.
"There is no way we could have had a turbocharger with Hugh," said Paul Gardner.
Whatever the original company hard line had been, though, there was no doubt that more horsepower was needed from the six-cylinder engine and forced induction was the only way to go.
There is more to developing a turbocharged engine, however, than just bolting a Holset or a Garrett on to the manifolds and so a lot of work went into the engine at the drawing-board stage.
As Paul put it: "It was not just an exercise to see what we could get out of the engine. We wanted a reliable and durable unit that we could put into production."
• The Gardner design team highlighted what were considered to be potentially weak areas of the engine if turbocharging was used. This led to increased oil and water pump capacity and also to a change in policy over the design of the pistons.
One limiting factor was pinpointed as top ring groove wear which could reach unacceptable levels with turbocharging using the standard Gardner piston.
Groove wear is proportional to both load and temperature, and it was conceivable that if a high inlet depression built up — through a clogged air filter, for example — then the combustion temperature would increase.
Up to the production of the 6LXCT, Gardner had always produced its Own pistons though the liners and rings were bought out from Wellworthy. For the turbo, however, Wellworthy supplied the pistons complete with Alfin insert in the top ring groove.
It took the two companies about 18 months' work to finalise on the right package including pin offset, ring pack and piston shape. In fact the first engines were run with pistons which were considered unsatisfactory on a number of counts — like oil control and bore polishing — but Gardner wanted to get running experience of the other new components.
Paul is happy with the cooperation received from Wellworthy. "The resultant piston is a joint effort, They are piston experts — we are experts on what our engines like."
The final ring pack has a castiron top ring, chrome-faced on the periphery and barrel-lapped while the second ring has a similar material specification but is taper-faced.
The oil control ring is of the slotted scraper type (not conformable) with a very low wall pressure.
This low pressure scraper ring has intrigued other engine designers for many years, but as Paul Gardner explained: "It's not just the scraper. The second ring also plays a large part in achieving the oil control targets."
The combustion bowl shape is identical to that of the naturally aspirated piston and not surprisingly so is the compression ratio of 14.2 to 1.
The crankshaft journal bearings are unchanged, but the big ends now have a plain bottom half replacing the grooved bearing used before. The crankshaft is now fitted with a Holset viscous damper which has better characteristics than Gardner's own Lanchester-type.
Turning to the connecting rods, the small end has been made parallel and slightly narrower (90 thou in total). Gardner engines are conservatively loaded and the company wanted to keep the boss pressures down.
The increased oil requirements meant a bigger oil pump which in turn necessitated a different sump to fit it in while the 1:rankcase has modified oiling or the water and oil pump irives.
The liners are cast iron but hey are soft liners as opposed o the 6LXC which uses hard mes. In this respect the turbo ingine is more akin to a 6LXBT. The exhaust valve design has ieen changed considerably as rris was one area where Garder had started running into -ouble.
The original valve had been lade from EN52 steel ever since le introduction of the 6LXB in 966, but the odd failure due to iermal fatigue cracking was ow beginning to show up.
As the valve had worked ..rfectly well for nearly 15 iars, Gardner was initially mfused as to the reason. It was found that in the failed engines there was a hard deposit on the valve seats and this had come from the additives in the oil burning out at the hottest point.
High-specification oils have the biggest additive "package" and this was what was causing the problem as the valves could not shed heat through the deposit.
Paul Gardner does not believe that his engines need high Mil-C additive oils but, appreciating that most fleets are turning to one type of oil throughout all makes of vehicle, it was decided to change the valve specification.
It is now made in two parts with chrome-flashed EN18 stem friction welded to a 21/12 N head to get the best of both worlds.
The long-serving Gardner valve location method with its screwed end, pin and two circlips has also been changed to the more conventional collet location.
The location method was changed for two reasons. The thread, even though it was rolled, was a stress raiser and it was also more expensive to produce than a collet groove. It also provides instant identification of an engine which has had this change in spec which has also been introduced on the 6I_XC and 8LXC engines.
Another well-known feature of the Gardner engine is its leisurely water flow which is between 30 and 35gpm on the six-cylinder units, Gardner working on a 25 BThU/bhp/min basis. "The water spaces are generous so we don't need a high flow rate," said Paul.
The Gardner engine — be it sixor eight-cylinder — is famous for its light weight compared with its competitors and much of this weight saving is the result of using aluminium extensively. If not unique, the divided block and crankcase construction employed by Gardner is certainly uncommon with presentday engine manufacturers.
The Gardner engine uses an aluminium crankcase — which is cross-bolted for rigidity — in conjunction with a cast-iron cylinder head and this technique was not surprisingly carried over to the turbocharged engine.
The 6LXCT did come up against snags in the prototype stages during field trials — again hardly surprising — but there were no serious difficulties. One such problem concerned the cylinder-head gasket.
On existing engines, Gardner was using sealing rings and ferrules in conjunction with a gasket, but it was thought that the use of one gasket to seal the combustion space, oil and water passages would be an improvement.
In practice, however, the new gasket was not as effective as had been hoped. It was therefore replaced with the original gasket system which cured the problem completely.
The current Gardner family of engines has been around for a long time now and so an obvious question to ask Paul Gardner was: "Where do you go from here?"
While, understandably, he was reluctant to reveal too mi about his company's plans, reply did perhaps give a gent indication as to future des direction.
"We know how to produce fine engines and we feel tl anything the market requires the future can be met with ti configuration. Gardner is vsi aware that future markets v demand higher powers than have now."
It is very likely that turh charging will become the rL rather than the exception at F tricroft in the future. The leg' lation on noise will see to that. this respect I think the whole the automotive engine indust is in total agreement.
As an aside from the d velopment of the 6LXCT, I ask( Paul Gardner about the possib ity of his company resurrectir — if that is the right word —' five-cylinder engine for use in 16-ton chassis or in a bus.
Paul said that interest ha been "buoyant" at one stage bi because of the recession thinc had subsequently become vet quiet. Gardner would need a di mand for 300 to 400 units a yei to justify producing the design.
As Paul put it: "There are a h of common components whic can be used, but also an awfi lot that can't."
The future design policy Gardner's will obviously remai very conservative. Paul Gardni put it in a nutshell when he sal( "It is not our philosophy to t seen as pioneers. We must at E. costs retain our efficiency, eci nomy and durability."