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06-04-2007, 14:01
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1977 Ford F-100 6.2L Diesel Conversion

By Rod Gudgion, Member #514

This article first appeared online here in TDP in 1998

The answer to the obvious question (why?) is hidden in my make-up I suppose. I served a five year apprenticeship as a machine tool fitter and up until my retirement spent most of my working life inside, on top or underneath machines of all shapes and sizes.

I have always maintained my own vehicles and made various modifications mainly as a challenge, but also to have a vehicle I am comfortable and familiar with. One such vehicle being a 1966 Ford Falcon which I ran for 22 years during which time it had four different engines, various gearboxes and two paint jobs, the most radical modification being the installation of a Jaguar 3.8 engine with a Toyota 5 speed gearbox and a Mark 10 Jaguar independent rear axle.

Having retired earlier than anticipated I set about our planned tour of the Australian continent. However, I soon found that my 1977 Ford F100 was not well set up for the job of towing a 1700 lb trailer. The 351 Cleveland was running on an LPG (Liquid Petroleum Gas) which is the ideal fuel for in and around the major cities, but is not always available in the more remote parts. The four speed F100 gearbox was also unsuitable for towing when in a hilly or mountainous terrain because first gear is too low for normal driving and the gap between third and fourth gears being to large.

I decided to install a five speed gearbox and also investigate the options of a diesel engine (not forgetting the limited funds at my disposal), the most popular seemed to be the Isuzu. I hadn't any experience with diesel engines, but I knew I would need at least a 6 liter engine. Most truck wrecking yards could only talk in horsepower, however I eventually became familiar with the various engines, horsepower and torque ratings. I was primarily looking at Perkins, Hinno, Nissan and Isuzu. I was not aware that GM or Ford made a light V8 diesel (being rare in Australia) until one day I was in a local engine rebuild shop and was shown a 6.2 diesel and straightaway I could see the benefits of the compactness and lower mass of the V8 over the in-line sixes I had been looking at. The 6.2 is just under 41 kilos heavier than the 5.9 Cleveland.

After locating a 6.2 (previously the power unit of a US Army Hummer) the next move was to get some information on the 6.2, a phone call to the local Detroit Allison dealer was no help at all, I asked if spare parts were available for a GM 6.2 and was promptly told the 6.2 was obsolete, end of conversation. This matched the reply from Isuzu when I asked how heavy a particular engine was. They replied that they didn't know.

Undaunted, I logged onto the internet, typed the word diesel in the appropriate box of Alta-vista and "bingo", I got Marks 4 Wheel Drive and The Diesel Page. The former gave some performance details of a range of engines which enabled me to get a comparison between the 6.2 and a 350 Chev or a 302 Ford. The Diesel Page of course was like Aladdin

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06-04-2007, 14:02
I am using the original mechanical lift pump, but have fitted an electrical fuel pump to the chassis rail close to the mechanical pump. This assisted in the initial priming and will be left in position as a backup or for any future need to prime the system.

The Ford throttle cable was unsuitable for modification so I reverted to my usual choice of cable for this type of situation. I used a good quality bicycle rear brake cable. These are a tenth of the cost of automotive cables and the good quality ones are Teflon lined.

A second battery was installed next, then a Pontiac starter motor in good condition was obtained, but the aluminum nose casting had to be changed (they are fitted to the opposite side of the engine). The fuel system was easily purged of air after loosening the injector fuel lines and leaving the glow plugs out so the engine could spin easily. Once fuel was evident at the injectors I replaced the glow plugs, tightened the injector lines and the engine fired up almost immediately. A quick trip around the block saw plenty of blue smoke as the excess oil and fuel (the result of the oil I had squirted into each cylinder when I first turned the engine over after its lengthy state of immobility and the fuel from the air purging process). A quick look around confirmed there were no fuel, oil or water leaks.

The second trip was not without problems, as I climbed a fairly steep gradient the engine developed a terrible knock which subsided once I eased off the throttle. I had covered about ten miles when this happened and was about six miles from home. Whilst not really knowing what the knocking was (and although being inexperienced with diesel engines), I was confident it was not the bottom-end of the engine. The knocking seemed to me like a valve or push rod, so I got the rest of the way home on a light throttle. Once home I checked my Haynes engine manual. Under Knock it lists injectors as probable and one or two other causes as possible. A diesel injection service specialist located the faulty injector and now I have a smooth running 6.2L diesel.

I recently made a 300 mile round trip which included about 60 miles of stop and go driving in the city with the remainder mainly in fifth gear. I was impressed by a 20 miles per gallon (Imperial gallons) fuel consumption.
The gearbox currently being used is from a Toyota 2.8 liter turbo diesel van, this was chosen for convenience as suitable bell housing and clutch were readily available from a local Hot Rod shop, but a heavier box will need to be fitted for serious towing. The overdrive fifth gear through a 3.70 differential produces a speed of 60 mph at 1500 rpm.

This conversion project has turned out quite well and I am pleased with the flexibility of the 6.2L diesel engine.

Rod Gudgion, Member #514
Victoria, Australia

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