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Fitting a Prima

Series I Engine Conversion

Part 1 - Engine Conversion

SI owner Quentin Abbs (right), with help from Mervyn Aldred, prove that the Prima diesel will slip into an 86-inch, using a remote oil filter kitWhere originality is not an issue, the Perkins Prima turbo diesel makes a practical power plant for a Series I, even though the conversion is actually designed for Sll and Sill. Peter Galilee explains...

Q: l have a 1955 86-inch Series I that I want to start using more frequently. It still has its original 2-litre engine and a few oil leaks, but apart from that it runs well. I have the chance to get hold of a Montego diesel engine. Could you tell me what sort of job it will be to fit this engine, if it will fit at all? If not, could you tell me what type of engine would make a good replacement? I've a well-equipped garage and I'm quite handy -.I have to be, as I own four Land Rovers! (P Grundy, Barnsley, North Yorkshire)

A: The Austin Montego turbo diesel engine you mention will fit your 86-inch. Products of the British Leyland era have suffered from a negative image but this engine, known as the Prima, is a good Perkins design. As you are proposing to take out a relatively good engine, I assume you're trying to achieve better driveability, which you'll get - a SI with a tired engine can be a liability in weekday traffic.

The Prima will also give you improved economy. An 86-inch with a really good engine may manage 22mpg on light road work, but wear in the bores and rings, and in the carburettor and distributor conspire to bring the figure down to typically 18 to 20mpg. With the Prima turbo diesel, you should improve this to the low thirties at least.

Installation in other SIs

Three different versions of Sis were built. The first 80-inch models had different engine mountings and the chassis was different at that point, so fitting a Prima would probably incur chassis modifications.

The petrol engine in the 80-inch was the same length as in the 86, but clearance between the back of a Prima and the bulkhead may not be enough in an 80. At the front, the Prima is shorter, so no problems there. However, there may be a problem with the oil filter fouling the front axle at full suspension travel - if so, a Perkins remote oil filter kit could be fitted to avoid this problem.

After you've taken it out, keep the original SI engine and transmission. Historical vehicles should hold onto their major units, as in the future, someone may want to return them to their original specification



Following the 86- and 107-inch models (86-inch featured here) were the 88- and 109-inch versions where the extra wheelbase was added between the bulkhead and the front axle. Basically, if the Prima will fit into an 86, it will fit into an 88,107 or 109.


Conversion parts

A fitting kit is made by Dudleigh Conversions and marketed by Intershape (Trading), Market Harborough, Leicestershire LE16 9UA, tel: 01858 439027. For technical queries email: info@dudleigh.com. Further details are available on website: www.dudleigh.com.

Dudleigh conversion kit components for installation of the Perkins Prima diesel engine


The Rover aluminium flywheel housing is replaced by a cast-iron housing that mates the Perkins Prima to the gearbox. You can make your own engine brackets or buy them from Dudleigh Conversions.

The conversion will need a non-standard alternator bracket and belt tension adjuster; again, home-made or bought from Dudleigh. I feel it's better to buy all the bits you can, then if something goes wrong, you'll know it's not something you made that's causing the problem!

You'll also need a new alternator belt (approximately 980mm length), Series III engine-mounting rubbers including the bolt-in wedge, flywheel (M111DF05) and starter motor (Lucas LSR678).

Use the clutch pressure plate (K586CF06) from a late Eighties 2.0 Di Sherpa van, pilot bearing (Bearing Services: KLNJ 7/8 ZZ) and rear crankshaft seal (4 1/8-inch OD, 3 1/2-inch ID).

Construct your own exhaust system using two-inch diameter parts, straight pieces, bends and clamps. Various bits are sourced from the donor Montego, including oil cooler, fuel filter, electric fan, air filter, alternator, exhaust down pipe, and various hoses and cables. It's best to buy the engine in a complete Montego - an MoT failure or with rear-end damage - then you can assess the engine and get the extra parts.

Making the conversion

Quentin Abbs of Norfolk has used a Dudleigh conversion kit to install a Prima turbo diesel engine in his Series I. The total cost was around 900 including the complete Montego car and a Series III gearbox.

Most of the extra parts such as the clutch pressure plate, starter motor, alternator, exhaust parts and temperature gauge were either bought new or were reconditioned. While Quentin completed the engine upgrade, I followed the job through to find out exactly what was involved in making the conversion.

Steel replacement flywheel housing mates the Perkins engine to the gearbox, leaving similar chassis crossmember clearance to the original Left side Dudleigh engine-mounting bracket bolts to the chassis without wedge or shims


Right side engine-mounting wedge overhangs the chassis mount. This extension tab is then welded in under the bracket to provide a bolt hole The low-mounted oil filter clears the axle casing on this 86-inch, but may foul the axle on an 80-inch. Use a remote filter kit from Perkins

Installing the engine

The Dudleigh conversion was really designed for Series II and III, with just two or three kits sold to SI owners. Some of the SI bellhousing holes don't line up with those on the Dudleigh flywheel housing, but Quentin thinks drilling and tapping the flywheel housing to suit the SI shouldn't be a problem.

However, in this case he decided to fit a Series III gearbox because a rebuilt unit was available for 75 and it's a nicer box in use - a sensible option for anyone doing the conversion.

The Series III clutch is hydraulically operated, so it's necessary to use the flexible-jointed clutch cross-shaft parts from the SI box.

The battery tray has to be moved forward 2.5-inches; but before welding, refit the radiator panel to check clearances.

The SIII engine mount, with wedge that fits at the driver's side, overhangs the SI chassis mounting position so Quentin welded a small tab in this position to secure it.The engine is a close fit against the bulkhead (a few millimetres clearance) but the bulkhead didn't need any adjustment.

A power-steering pulley at the rear of the engine can be unbolted from its driving flange and a cover fitted over the flange.

A plastic coverplate is fitted in this position on the non-turbo engines.

Making the exhaust system from pieces means that sections can be easily and cheaply replaced later. The Montego silencer will fit under the left side.

Series III gearbox provides full synchromesh, and drops neatly into place in the SI chassisSeries I's flexible-link cross shaft parts can be used to operate the SHI hydraulic clutch


The battery tray has now been repositioned 6.5cm further forward to clear the alternator, and also helps the Montego air filter to squeeze in Original Series I parts were used to provide the extra diesel fuel feed and return systems


Unique exhaust system is made in plenty of sections so pieces can be easily replaced If it's any good, the Montego silencer can be reused, and mounted underneath on the left


 The electric cooling fan from the Montego fits neatly inside the Series I radiator panel Clearance between the back of the engine and the bulkhead is tight. The diesel fuel filter needs to be mounted high up on the bulkhead


 A coolant temperature gauge (very useful) and diesel heater plug warning lamp (vital in a diesel) have been added to the dashboard

The final stages

The installation is shown here in its final stages. Quentin is not aiming to have everything neat and tidy at this point; instead, he wants to get the vehicle running so that it can be assessed.

After that, there'll be time to go back and maybe relocate a few items and tidy up the wiring and the pipework.

How much does it cost?

The adaptor plate/flywheel housing costs 299.92 including VAT and delivery. The remaining parts: engine-mounting brackets, alternator bracket and adjusting link together cost 125.45. A good running Montego with MoT can be had for a few hundred pounds or less.


Part 2 - Road Test

The Perkins Prima engine fits neatly into the Si's engine bay

Peter Galilee tests a Perkins-powered Series I, and finds an intercooled version of the same engine in a Series II

In the last issue of LRO Workshop we followed Quentin Abbs' installation of a Perkins Prima turbo diesel engine into his Series I. Quentin also fitted a Series III gearbox, which mated easily with the Dudleigh engine conversion kit that was originally designed to mate the Perkins with Sll and Sill vehicles.

Quentin's converted SI has now been on the road long enough to establish whether this conversion really is worthwhile.

Road test

this Series II has been fitted with an intercooler to boost power from its Perkins turbo engine

The Prima engine has completely changed the Land Rover's character. I've driven well set-up Sis with good engines that are surprisingly competent, but this SI is in a different league - much more powerful.

The engine revs freely as the SI whizzes along, ignoring hills that would normally have you reaching for the gear lever. It's uncanny - you wait for the point where the revs are going to drop away, and they don't. Though Quentin and I felt a five-speed gearbox or overdrive would gain even more advantage from the increased power and torque.

Living with the Prima isn't too noisy. Even without soundproofing, the diesel hum is not intrusive and we could converse at normal levels while driving, as you'd expect from a car engine.

More pulling power

the intercooler fits neatly behind front grill

Quentin tested the towing capability on a favourite long hill, pulling a large loaded trailer and getting almost to the top before having to change down to third gear. That's thanks to the Prima's extra torque which, in turn, gives more relaxed driving with less gear changes and improved fuel consumption.

Fuel consumption

Quentin reckons the engine is returning around 35mpg on short-run local driving over narrow, winding and hilly roads. He says that by fitting road tyres, an overdrive and an intercooler to gain further benefit from the turbo (see pictures of a Prima engine with intercooler fitted in a Series II, opposite), 40mpg could be possible. After all, Montego diesel cars achieved over 50mpg in government tests.

Practical power

There are many Series Is like Quentin's: basically sound, but with a tired engine giving sluggish performance and high fuel bills. They are weekend workers and sunny-day fun cars where usefulness is more important than originality. In these cases, a transplant is a sensible option, especially considering a full SI engine rebuild can cost over 1000.

So it looks like this conversion is very worthwhile. But anyone thinking of fitting the Perkins Prima should first ensure that the brakes and suspension are up to the job. And don't forget to inform your insurer. In fact, it's not a bad idea to ask your insurer of the potential cost consequences of a conversion of this type before you do it -especially if you're a young driver.

The adaptor plate/flywheel housing costs 299.92. Remaining parts: engine-mounting bracket and adjusting link together cost 125.45. A Montego with MoT can cost a few hundred pounds or less.

Comment (By Teflon)

A few years back there seemed to be a bit of a 'craze' for fitting old Montego engines into Land-Rovers; debate raged on the forum's as to whether it was really a worthwhile conversion, whether it could REALLY be done for 'next to nothing', and whether any-one REALLY managed to make one go 40MPG! And, yeah, actually it WAS a pretty darn good conversion for many.... but note the past tense! Times change.

Ten years ago, Rover were still in business, making cars, and the ones that they inherited from Austin/Morris, like the Montego, had a rather alarming habit of dissolving in front of your very eyes. If thy happened to reveal a Turbo-Diesel engine when the bodywork rotted away, THAT was good news!

The Prima, in Turbo guise at least,  WAS a very good little engine, and salvaged from oxidised Austin's amazingly cheap, and some people DID manage to do Prima conversions for virtually no overall cost, and they WERE 'economical'. Hugely so by Land-Rover standards, AND they had some modicum of 'poke'. That little Turbo mill chucked out a very creditable 90bhp, as much as ANY engine Land-Rover fitted as STANDARD to a Series Land Rover.

Most powerful engine they fitted to a leaf-sprung Landie was the carburetted 3.5l V8 fitted to the Long Wheel-Base 'Stage 1'. That had 90bhp, detuned with restrictor plates in the inlet manifolding, and used the four-speed Range Rover gearbox and permanent four wheel drive, NOT the questionable series main-box and selectable transfer, though mainly because of the torque the V8 could subject the drive line to. Prima made most of its power from revs, so didn't cause that problem, and for a Diesel of it's era, the Prima was a remarkably 'revvy' little lump, and a big part of its appeal, I think, was that it responded far more like a 'normal' engine.

Any way, the Montego Motor acquired almost 'Cult' following; there were probably three of four suppliers offering adapter kits commercially, and many amateurs were 'scratch-building' their own; the web-forum's were awash with comment on them, and for a while, there was even a forum entirely devoted to Prima-Power! But that was THEN!.

If you are contemplating possible conversions, then firstly you need to consider the economics very carefully. The Prima WAS reputed to be durable enough to survive moon and back mileages with little more than routine maintenance. But they haven't made one for probably more than ten years....

Your first problem with a Prima conversion today, will be sourcing a 'good' engine. There isn't the dearth of rotten Montegos there once was, and if you do happen upon one, then be very wary of the condition. It's likely to be well worn or well neglected.

Next, those that did 'next to nothing' conversions, tended to achieve that by a lot of 'scratch build' DIY fabrication, saving the cost of a conversion kit, and by selling off unwanted parts of the donor Montego. Not much demand for Montego bits these days, so might not be AS chap to do as it once was.

300 for a conversion kit, and you are a long way into the price of a DIY rebuild, or another, more 'exiting' conversion. The article, commented that the conversion, all in, cost around 900, and compared that to a 1000 for a full and detailed engine rebuild. It's not a huge saving, and you'd probably loose more in the 'residual value' of the car for doing it!

Practically, the 'attraction' WAS in the performance and economy, with the bonus of a light service Montego engine having quite a lot of life left in it, while a conversion was easier than a rebuild.

Today, I'd be wary. With diesel now more expensive than petrol, the improved MPG isn't SUCH a bonus; and with the likelihood of finding a 'good' Montego engine diminishing, I'd say for economy, you would be as wall to spend your money on your original engine; See Eco-Drive & Fuel Frugality, you can achieve a lot without major surgery, more if you are prepared to pull the engine to bits, or convert to LPG.

However, of the 'common' Diesel conversions, the Prima Conversion IS still a good one. It is a relatively straight forward swap, that doesn't demand any MAJOR fabrication work, and the engine is well suited to the application and doesn't have too many 'knock-on' implications as far as the durability of the drive line or suitability of gear ratios.

IF you can confidently source a 'good' engine, and the other assorted parts mentioned in the article, and are comfortable with the implications of the conversion, it COULD still b a very good one to go for.


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