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The Leyland 500 Series Fixed Head Diesel.


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Hi all, this was mentioned a while back. A fascinating Power Unit well ahead of it's time in terms of Power Output and Size, and ultimately let down by a last minute decision to change the Cubic Capacity. 

It was an 8.2 L 6 Cylinder Overhead Cam Fixed Head Engine with Timing Gear at the Flywheel end, presumably to de-stress the Crankshaft. Combustion was aided by a Turbocharger and Crossflow layout. 

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41 minutes ago, Monitor Gold Ten said:

Hi all, this was mentioned a while back. A fascinating Power Unit well ahead of it's time in terms of Power Output and Size, and ultimately let down by a last minute decision to change the Cubic Capacity. 

It was an 8.2 L 6 Cylinder Overhead Cam Fixed Head Engine with Timing Gear at the Flywheel end, presumably to de-stress the Crankshaft. Combustion was aided by a Turbocharger and Crossflow layout. 

Not in same league but I had a Austin montego estate diesel..bomb proof and what a good engine..

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The 500 was indeed a revolutionary engine but it was not without faults in fact its main strength ( the fixed head ) was also its main weakness .

I was an apprentice when this engine first appeared and worked with the engineers when they were received  back under warranty with cracks across the valve seats and the fixed top of the block .

New valves and specially hardened valve seats could be fitted but it was a major job that involved lifting the engine block away from the crankcase , Pistons , and con rods using an overhead crane and working on the valves up inside the bores  .

After a period doing these repairs it was decided to not bother anymore and just replace with a whole new block with valves from the Leyland factory .

I once witnesses one of these engines self destruct after a rebuild we think that the oil scraper rings must have been damaged when feeding the block back onto the Pistons or the turbo seals were faulty or both but after starting and running fairly normally it slowly started revving higher and higher on its own even after it was turned off.

The revs kept rising and it just would not stop , the fitter panicked and smashed the injector pipes away from the injectors with a hammer but it still kept going running on the engine oil , it filled the whole workshop (which was huge ) with thick smoke , it was revving so high it sounded like an aircraft, it went bang and ripped it to pieces! 

One revolutionary side development of this engine was a new two part gasket compound that when mixed together hardened into a rubberised gasket , it was specially developed for this engine .

This was long before silicon gasket compounds were invented .

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Wow! That's the best write up yet! Very detailed and informative. This Power Unit has always fascinated me. 

It was used in the Mk1 Leyland National, itself a technical marvel of it's time. Styled by Giovanni Michelotti, it was an Integral bus with no separate Chassis and Body, it introduced a number of new features back in 1972: 

An ergonomically designed Driver's cab with Colour Coded Warning Lamps, thanks to the 'Human Factors Engineering Team' 

Reliable Air Suspension with 'Anti Dive' geometry on the Front Axle. 

Modular Ringframe structure based on riveted steel pressings designed to protect occupants in a crash- could support it's weight on it's roof too. (Lots of contemporary vehicles still used Hardwood framing) 

Low Profile Tyres- so as to lower the Step height. 

A smaller and lighter Diesel Engine- Most contemporary buses had 10 litres and above. 

I haven't yet driven one. By all accounts, they are lively and very solid machines. Lots of them saw three decades of service. I travelled on an ex London Transport LN in Birmingham years ago. It was 28 years old and still had it's original 500 Series Engine! 

There are a number of Rail Vehicles based on this unique Body Structure still in service. The infamous Pacer and the Class 153 to name just a couple. 

These vehicles were assembled in a purpose built factory in Lillyhall, Workington. When it opened, a visitor from Mercedes-Benz gave the Plant Director a Meschersmitt Flight Manual. 

He said that the Leyland National was "Designed like an Aircraft and built like a Car" 

The factory did set new standards as it was an Assembly Operation. All the "Dirty" operations like Casting, etc took place in Farrington near Leyland. 

😎

Edited by Monitor Gold Ten
No excuses for missing out the Driver's cab layout...
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Thanks ! 

The 500 was years ahead of it's time and paved the way for the modern HSD that is fitted to millions of cars and commercial vehicles now.

When you compare it to the Leyland 680 and AEC 760 that were the engines it had to compete with there was no contest the 500 had much more usable power and was far more economical on fuel .

Saying that my heart was won by the old Gardner engines,  they were a very old design but the engineering was superb , they were just run in at about 500,000 miles they were also the perfect marine diesel.

The horizontally opposed  two stroke diesel Foden engines were weird beasts that sounded amazing but they were fazed out before I had much to do with them, I would have liked to have rebuilt one before they disappeared. 

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That's a really good point. With the smaller capacity and high output, it did indeed pave the way for the modern HSD. 

The basic layout of Volvo's Current D9 engine is very similar; although it does have a Cylinder Head! 

Good point about the AEC 760 and the Leyland O.680. From what I've read and from talking to drivers, the AEC Lump was well respected and reliable. 

I've a soft spot for the Leyland O.600/680 and TL11 Lumps. I've driven two Leyland Leopard Coaches and one of them was extremely forgiving when. I buggered up a Gearchange going up a hill. 

It pulled from 15mph just above Tickover in 4th! Was highly entertaining driving them enthusiastically around Wales with that Leyland Music echoing around the narrow streets! 

I've recently driven a Leyland Titan RTW with an O.600 and I much prefer driving that to the AEC RT with its 9.6. The Leyland seems to have the edge on Torque. 

I've driven one bus with a Gardner Engine. A Leyland Olympian with the Legendary 6LXB. Wow! What a lump. Shit loads of torque from Tickover. A real pleasure to work with. 

I knew someone who had a Foden Two Stroke coach. I couldn't believe the sound. It sounded like a BMW! So smooth! He called it "The Beast" 

In spite of all this though, my favourite engine is the Leyland O.680.

I learned it was in production until the early 2000's in Poland as the Mielec SW680. I believe it got through to the Euro 3 Emissions era too. Not bad for a concept that started in the 'forties with the O.600!

Ps: DAF also developed their own version of the O.680...

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We used to have a tanker with a gardner in it

I remember starting it up on  cold winter mornings, my job as an apprentice mech was to start all the diesels up when it was cold.

What a beast, you could cover a football field in thick smoke in a couple of minutes

Got all the offices evacuated once, we had to get our fun some way:o

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1 hour ago, cwarchc said:

We used to have a tanker with a gardner in it

I remember starting it up on  cold winter mornings, my job as an apprentice mech was to start all the diesels up when it was cold.

What a beast, you could cover a football field in thick smoke in a couple of minutes

Got all the offices evacuated once, we had to get our fun some way:o

The secret is to light a small fire under the sump to warm the oil up before starting it, they fire up :) quite easily with a bit of heat assistance .

Some of the old Cummins diesels had a built in canister filled with Ether on the inlet manifold ,  you gave it 2 or 3 measured squirts before starting and it fired up with a crack and rattle and gave off a lovely smelling smoke . :cool:

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9 hours ago, Electro said:

The secret is to light a small fire under the sump to warm the oil up before starting it, they fire up :) quite easily with a bit of heat assistance .

Some of the old Cummins diesels had a built in canister filled with Ether on the inlet manifold ,  you gave it 2 or 3 measured squirts before starting and it fired up with a crack and rattle and gave off a lovely smelling smoke . :cool:

We used to have the ether canister on John Deeres although never needed in UK. They also had the option of a couple of 3kW heater elements; one in the engine and another in the rear axle / gearbox.

In Canada the instructions to combine drivers were to never stop the engine in field; if you did it would have to wait until next April to be started again. (My SiL had snow until about four weeks ago)

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I had a propane heater, it was used for melting lead (I worked for the local water authority, it was to seal pipes)
Used to light it and place it under the fuel tank, get the wax liquid. Also had a blow torch, used that on some of the fuel lines.

Health and safety, whats that?

Seem to remember that we used to add a bit pf petrol in the tank as well.

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Yes I remember those days , I've done the very same thing .

Modern diesel has an anti waxing agent to keep the diesel Liquid during the winter months so it is very unlikely to have waxy diesel now unless it is several degrees below zero degrees C for a longish period of time .

A small amount of petrol mixed with the diesel definitely helped in the old days but it is definitely not recommended for modern vehicles, in fact it could be the kiss of death ! 

Many modern diesel vehicles have automatic fuel heaters and some also have electronic coolant heaters that cut in if the temperature drops below a certain point.

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