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Converting A B To A D

Published: 9th Nov 2012 - 0 Comments - Be the first, contribute now!

Converting A B To A D
Converting A B To A D Engine out but you can leave the gearbox in situ.
Converting A B To A D Beauty of using the B-Series diesel (main pic) are the great similarities between the two although the heater valve needs locating. (
Converting A B To A D There’s a fair bit of fabricating needed but it’s all doable at home, such as mounting the fuel filter
Converting A B To A D
Converting A B To A D Engine in place, note mechanical fuel pump fitted.
Converting A B To A D The fuel side of things needs reworking with better pipework and a return tank installed.
Converting A B To A D Choke is replaced for a push button switch for the glow plug heating and starter - use ‘live 15’ for this.
Converting A B To A D While you’re about it, fit a new clutch; we really should have overhauled the engine!
Converting A B To A D Job done – looks professional and think of the mpg!
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lengths would you go to in these hard times to keep your classic on the road – like converting to diesel power? theodore j. gill

We may have gone DERV crazy but people have been extracting the petrol engines from cars, throwing them away and shoe-horning in diesel engines since the 1930s. The main reason has been one of economy natu- rally, as there’s more energy in diesel fuel than in petrol, and a compression-ignition engine is more thermally efficient so it extracts more useful work from that fuel than a spark-ignition engine can with petrol, making it cheaper to run.

Other benefits include increased torque, improved longevity, the ability to run on vegetable oils (cheap fuel!), often greater reliability, and generally better build-quality.
Of course, there are some drawbacks, too: the engines produce less power for their size, are noisy, don’t rev as high, heavier, which is likely to affect the heaviness of the steering, and don’t forget that diesel emissions have recently been classed as carcinogenic.

That’s a fair list, but if you’re a diesel fan and love the sound, smell and characteristics of a diesel-engined vehicle, then it’s all worth converting your thirsty petrol-powered classic!

The easiest diesel conversion to undertake is one that uses an oil burner that already exists in a manufacturer’s model range, as car makers usually like to keep things simple by sharing as many components as possible. For this reason, an MGB diesel makes considerable sense as British Leyland produced a B-Series diesel version which was fitted in large numbers to the Sherpa/ Freight Rover vans as well as A60s and Marinas.

Also the engine shares loads of components with the petrol engine – most of the internals are the same and racing MGBs use the diesel’s shell bearings as they’re heavier duty so that’s some- thing to boast about. Oil pumps, water pumps, and lots of other bits are identical, hence it makes a sensible choice for the MGB.

However, despite the original popularity of these engines in car and marine use, they are getting rare but they do turn up on eBay and other on-line auction, selling, and marine sites from time to time so keep your eyes peeled.

When carrying out a conversion, always carry out the work to the highest standard, trying to think how the manufacturer would make brackets, route pipes, and join wires, for instance. After all, your work will ultimately be scrutinised by an engineer for insurance purposes so make sure he or she praises you for your handiwork!


Converting my MGB was fairly straightforward and within the realms of most DIYers but choose your engine first. The B-Series came in a variety of sizes from 1.5-litre to the same 1.8 block found on the B. Found in Sherpa vans and some marine uses, all are becoming harder to track down. Once out and sitting next to the diesel engine, you can see the similarities between the two units. Buy a full engine gasket set with crankshaft oil seal and swap over the back-plate, flywheel and clutch assembly. It’s a good idea to renew the clutch plate, spigot bush and gearbox input-shaft oil seal while your about it. The engine mounting brackets can be swapped, and again, think about renewing the rubber mountings if they are tired.

You can see that the basic conversion bits are easily changed with about an hour’s work, without major expense, either. The biggest problem with the conversion is the starter motor, however, as the meatier diesel one fouls the MG’s offside chassis rail. An elegant solution is to buy a high- torque, gear-reduction starter motor that is readily available from MG parts suppliers like Moss.

The engine can now be fitted, which will make the job feel as if it’s going somewhere! The oil cooler take-offs on the diesel are on both sides of the engine instead of just one side, so you’ll have to drill a hole on the nearside of the bulkhead to accommodate the hose. The exhaust mani- fold needs to be swapped over, too, relieving the flanges slightly with an angle grinder as they foul.

The diesel fuel system needs a return to the tank from the injectors’ and injection pump’s leak off. The return can be fitted by drilling a hole in the existing tank (catching the swarf) and fitting a bulkhead fitting – alternatively, earlier fuel tanks have the fuel take-off mounted on the tank, so if the later fuel gauge with integral take-off is fitted, one of these can be used as the return.
The electric pump is disconnected. It’s a good idea to renew the fuel pipes with nylon or similar, routing the feed to the mechanical lift pump. The diesel engine also requires a micronic fuel filter, so find a place on the inner wing that would accept a bracket to hold it.

Electrically, the diesel engine has no ignition system but the wire that would go to the live, ‘15, terminal’ of the coil can be used to go to the injection pump’s stop solenoid. The engine also needs heater-plugs for starting, so again, find a suitable place to mount a remote starter solenoid suitable for carrying the high current drawn by the glow plugs; taking a wire from the starter’s main feed is a good idea, for example. Because the choke is now redundant, it can be swapped for a push button switch wired into the solenoid. It will be necessary to buy a new length of vacuum pipe to reach the vacuum pump, which is not the same as heater pipe. Talking of heaters, a new rigid pipe was made from 15mm steel tube from B&Q bent with a domestic pipe- bender, connecting the bottom radiator hose with the heater unit. A bracket has to be made to mount the heater valve as there’s no take-off on the diesel’s cylinder head. As for the radiator itself, some people have got away with using the original, but keep an eye on the temperature gauge if you do. If it runs hot, an uprated radiator is the solution. And really that’s it – apart from a few gallons of DERV to get it going!


Really the conversion is a mix of surprisingly good and not so good. To start it, you need to push the glow-plug button for 30 tedious seconds before turning the key and firing up. There’s more engine noise in the cabin of course but it’s not intrusive at all and you can always add a sound insulation kit if it bothers you.

But the real bugbear has to be the compro- mised performance, even with the 1.8 unit. Power output is 50bhp at 4000rpm and the torque figure is 69lb ft at 2000rpm. But while it’s no sports car, the diesel’s torque, makes it feel surprisingly lusty – not unlike an MGB GTV8! Overdrive still works well when allied to the diesel. The top speed on my car isn’t great and don’t ask what the 0-60 time is but the car is happy enough at 60mph. I’m sure could go faster but mechanical sympathy prevents me from pushing the revs nearer to the governed speed.

But speed isn’t what it’s all about with a diesel is it? So how does about 70mpg sound? Thought that would interest you… Mind you, when adding up all the incidental bills, including the engine, the conversion came to over £300 although there’s always a market for an MGB engine.

Overall not an unsuccessful conversion and is proving reliable as well as economical in service. Things haven’t all been plain sailing, however. The B-Series diesel I bought turned out to be very tired and an overhaul is ideally needed.

On reflection, a turbocharged Perkins Prima from a Montego or later Leyland DAF 200 van would be a better option, albeit requiring more fabrication. Surprisingly, its architecture is remarkably similar – most of the holes line up in the back-plate, for instance. Again, the major problem is with the starter motor, but by sourcing a gear-reduction unit it has been done. Because of the turbo, it doesn’t even need a silencer in the exhaust. Now there’s food for thought.

Or you can go modern. Classic Cars For Sale has heard of several of today’s TDi wonders nestling under the lid of older cars, although if you are contemplating such a swap bear in mind the hassles with modern electronics, and so on.
Finally, before you dismiss the idea as bonkers, Frontline Developments, the specialists who produce the fabulous 50 grand, 160mph LE 50 MGB celebration, is seriously considering introducing a diesel alternative after a number of enquiries – so there!

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