The Mini FAQ is a list of frequently asked questions (plus answers) about maintenance and mechanical work on Minis and Mini Coopers. The answers are mostly derived from the archives of the Mini-List mailing list and are the work of contributors to the list, edited for presentation in the FAQ.

See Mini FAQ Part 1


A-series vs. A-plus engines

The A-plus engine is the result of development efforts carried out on the A-series engine in the late 1970s/early 1980s for the Metro. The A-plus engine was available in 998cc and 1275cc forms, and very briefly in 1098cc form. The blocks and gearboxes were introduced to the Mini range at different times starting in the early 1980's. Key features are:

  • Increased block strengthening plus thicker gearbox mounting flange.
  • Gearbox and drop gears redesigned for lower noise and increased strength.
  • Dipstick is incompatible between A-series and A-plus.
  • Alternator brack altered.
  • Distributor clamp altered.
  • Verto clutch (reduced pedal effort).

A-series and A-plus engines are interchangeable, though gearboxes are only interchangeable if an adapter drop gear is used.

Adjustable oil pressure release valve construction/installation

(This article is originally by Marcel Chichak)

The problem with the design of the pressure relief valve is that the valve plunger is a cylinder which is tightly confined along its length. One small shaving is all that's needed to cause it to jam open or closed.

All that's really required is enough of a valve to seal against the seat. A ball bearing can replace the plunger and get around all the problems.

Here's how it's done:

  1. Remove the oil pressure relief valve dome nut (1" wrench).
  2. Remove the pressure spring.
  3. Insert a finger into the hole and extract the plunger.
  4. Drill and tap a 5/16" UNF thread in the centre of the dome nut, thread a nut onto a 2" bolt and screw it into the dome nut.
  5. Cut 3 coils off the pressure spring and roll the last coil over to make a nice square bearing area. To be able to use the bolt as an adjuster, you'll need to ensure the spring bears upon it properly. This can be accomplished by either rooting around until you find an appropriate washer, or make up a thin steel disk which just fits inside the diameter of the dome nut.
  6. Obtain a 1/2" diameter ball bearing. CV joints are a good source for these, or go to a bearing supply shop who will likely just give you one since it's not worth their while to write it up.
  7. Insert the ball bearing, then the spring and capture it all with the dome nut.
  8. Screw the adjuster all the way out and start the engine. Watch the pressure gauge closely: if it reads: >60 PSI, shut the engine down and take another coil off the spring; ~55 PSI, close enough, you've earned your brew;20 psi, go to the engine and screw in the bolt until the gauge reads 50 PSI;
  9. Once you've set the pressure you want, I recommend 50 PSI, set the lock nut.

An interesting thing about this setup is that the oil pressure stays at 50 PSI. Cold starts with thick oil: 50 PSI. Hot starts with thin oil: 50 PSI. Highway running at 90 MPH: 50 PSI. Hot idling: 50 PSI.

If the oil pressure flutters or varies widely, shorten the spring and pack the space between the spring and dome nut with washers to reduce the operating range of the release valve.

Automatic to Manual conversion

The easiest method of converting from automatic to manual transmission is to fit the engine and front subframe from a manual car.

The automatic engine can be fitted to a manual gearbox, but about the only compatible components are the block and head. The block needs the following modifications: a spacer for the pump recess, two holes drilled at the oil filter mounting boss, a drilling to the pump through the pressure relief valve passage, replacing of the relief valve seat for a undrilled one (factory mod). You also still need a manual gearbox, clutch, driveshafts and front subframe.

Other parts needed: gear shift, clutch master cylinder, and pedalbox from a manual car.

Block oil/water connections - threads

The oil pipe connection out of the block and the temperature sender are both tapped for 5/8 BSP fittings.

Donor cars with compatible A-series engines

The following cars have engines that are bolt-in compatible with the Mini. The only major differences are likely to be the driveshaft coupling type and gear change; the gearbox/differential may be changed to suit the car, or the car's driveshafts may be swapped for compatible ones, and a hole for the new gearshift made in the floor.

In all cases, these donor engines use driveshaft joints and gearshifts compatible with the Mini equivalents; Mini gear shifters of the appropriate type should be used.

Compatible donor vehicles:

  • Austin Allegro 1100/1300
  • Austin/MG Metro
  • Austin/Morris/MG/Wolseley/Van den Plas 1100, 1300, 1300GT

Other cars that used A-series engines such as the Sprite/Midget and Morris Marina and are not compatible because the engines are in-line, not transverse. However, the cylinder heads are compatible, and the blocks may be adapted for transverse use by modifying the oil pickup and centre main bearing cap. Non-Mini twin-SU manifolds may cause the twin carburettors to foul the bulkhead.

Engine Mounts - aligning and bolting up

One of the most-hated Mini jobs is to line up the engine mounts with the mounting holes in the front subframe and installing the bolts when installing the engine in the car. Some tips:

  • Find someone with small hands to help you.
  • To align the mounting holes, keep some upwards pressure on the engine via the hoist/winch you are using to drop the engine in. Rock the engine from side to side to get the holes nearly lined up. When they are close, use a plastic-insulated screwdriver through the part of the mounting hole that is visible, to move the mount around until it lines up. Alternatively, lift the engine up about 2cm off the subframe and use an old plastic-insulated screwdriver or similar to line up the mounts via the subframe holes before lowering the engine completely.
  • If you can get one bolt installed (but not tightened up), lining up the remaining three holes is much easier. Each time you get one hole to line up, install a bolt in it (do not tighten up).
  • To get the bolts through the mounts, wrap thin wire (e.g. welding rod) around the thread of the bolt and manoeuver the bolt into place by remote control using the wire. As soon as the bolt goes through the hole, put a nut on it and pull on the wire - it should unwrap leaving the bolt in place.
  • Engine mounts with captive nuts are available that do not require the bolts to be installed from the subframe sides, making the whole task slightly easier.

Fitted new extractors/intake/stage 1 kit, engine now runs rough

If the engine runs roughly or idles at a very high speed after installing a new intake manifold or exhaust extractors, an air leak is the likely cause. This is often caused by the flanges on the new exhaust manifold being of different thickness to the intake manifold or vice versa. Since they share mounting studs, one of the manifolds will no longer be sufficiently tightened up to the head. This is often the case with "budget" type manifolds.

Fuel Injection conversion

Fuel injection systems consist of a number of sensors and actuators, plus a computer to control them. The retrofitting of a custom-made system to a non-injection engine is a complex task. Instead, it is recommended to source a 1.3TBi (single point) or 1.3MPi (multi point) Mini engine and ancillaries, and modify or replace the ECU (engine control unit) if desired.For a detailed introduction to fuel injection systems consult the Haynes automotive electrical manual, or similar books (available at the local library).

The following article (slightly edited) describes a fuel injection conversion using standard Mini components.

Date: Wed, 15 Oct 1997 02:03:24 +0100
From: (Arnoud Bordewijk)
Subject: long and kinda tech: The full Parklane Tbi story

As promised here's the recipe to create an electronic injectionized mini: You require:

  • 1 unsuspecting carby mini
  • 1 preferable complete but totalled Tbi mini
  • 1 spare MG-Metro (or other) cam.
  • Lots of patience some tech. knowledge (like: to fasten; turn clockwise;-)
  • (I think an ordinary (unleaded) 1275 engine will do fine as well)

I started by taking the Tbi apart (I bought it as a (totally bent) runner). I'd done some research, and found out the only difference in engine between standard Tbi and Cooper Tbi was a higher CR on the Cooper (probably by means of shorter block and different pistons (less deep dish), because the heads are the same), and a different computer.

Since my goal was a little more than the standard 54 Hp, I had the head skimmed to get the CR a lttle over the Cooper's (some 10.3 vs 10.1 (9.4 is standard Tbi). It's also possible to go to a hairier cam, since the MEMS-ECU (Modular Engine Management System Electronic Control Unit) can adapt to "new" circumstances. I opted for a MG-Metro cam; 1. because I read in Minimag that 255 deg is the fastest cam that still makes for a "civil" engine (I do a lot of village/city driving), 2. because it sat jobless on a shelf in the garage. I didn't bother with changing the followers since it was a used cam (we'll see if this was a good plan;-), and I didn't feel like separating the block and 'box.

First I removed the head and send it to the machine shop to be skimmed. Then I tilted the unit on the bellhousing (using some wooden blocks for support), and turned the cam a few times before lifting it out vertically. This made sure the followers were way up in their bores. Then I lowered the 'new' cam in the same way. It was precisely on time, but DV writes that this cam works best if timed in at 106-107 deg instead of 110, so this I did. I put the engine together and gave it a nice fresh coat of red paint.

I wanted to ditch the cat, because I didn't feel like buying a new RC40 rear section when I had a 1 year old Maniflow LCB/RC40 system already. This was one of the most complex things: the original Lambda sensor had to be retained, but in my LCB there was no hole for one to fit, on top of that for some reason the thread on the sensor is neither metric nor UNF (but Bosch' own I guess). Luckily with the Tbi came a section of manifold, from which the correct nut, was ground out and welded to my LCB.

Then: horror! When I offered up the LCB to the engine (still not in car), the lambda sensor fouled the fuel pump blanking plate:-( Had to do that all over again. It also turned out the intake manifold's water cooling pipe fouled the center branch. You have to use it because the temp. sensor is in the throttle body now. I had to heat the pipe up really well and had to bend it totally to make it clear the branch. I also applied some DV tricks to the butterfly and spindle (slimming spindle down, knife-edging butterfly and removing butterfly screws' split ends).

After all that I turned to the poor old Parklane, who was suspecting something by now, since his engine had been removed and dropped into the Mayfair to have at least one car on the road. I removed the interior (just for easy acces) including wooden dash and switchpanel (to be replaced by 5 switch type), steering column and pedalbox, heater, fuel tank, complete clutch system, wiring loom except the rear section and master brake cylinder (+ front brake pipes, which needed replacing anyway).

Then came the process of planning fuel line routes, putting in the new (2 section) loom in the engine bay (I used some of the rear section too, but that's later). I bought 6 metres of rubber fuel line and laid it out; it was only just enough, since there's a return line as well. It now goes through the 'gap' between rear seat upright and rear wing panel, then through a drilled hole in the LH companion box, along the floor, through holes in the crossmember, upward along the bulkhead and it comes through the bulkhead a bit to the right of the clutch master cyl.,from where the original pipes lead to the injector housing.

Nearly the same route is followed by the rear section of the Tbi's wiring loom, which is used only for the in-tank-fuel pump and the screen washer bottle, which now sits in the LH companion box (keeping it a bit warmer during winter, but it's really noisy!).

Finally time to fit the engine, which was not anymore difficult than usual. Fitting all the wires and hooking up all sensors took me a full day. Then came the big moment; I turned the key to II, the ECU clicked and the fuel pump span. I turned the key to III and it cranked, but that was all:-( No fuel from the injector and no spark. At first I was affraid I had made a bad connection and blown the ECU, but that didn't seem the case, because when I took the key out, it made another clicking noise (which Johnmar told me it was supposed to do). So I tore out the injector, thinking it might be blocked, but that wasn't it. In the end I phoned the dealer. He told me to check if the flywheel TDC sensor received signals. It then started to dawn on me that I could have fitted the wrong flywheel. I ran to the garage and in the corner it sat, waving it's reluctor ring at me;-). After I fitted it the next day the engine burst into life on the third stroke :-).

The car is a lot quieter now (when stereo off:-), because I also fitted the more extensive Tbi sound deadening material. I've now driven it for some 70 miles and the ECU is adjusting quite well. At first it would stall when I took my foot off the loud pedal, but it now happily idles at some 850 revs.

The plugs have a healthy color and it pulls like a train from 2000 RPM (probably due to the MG cam). At 60 Mph there still seems to be enough power left, but I'll try that once it's all a bit settled. It also apears to be economic, because in 70 miles, the fuel gauge is now just below the top mark:-) In all I think it was a succesful operation, but it requires plenty of time (I took my time: 2 months, in odd hours and a number of full days) to do properly.

How to build a quiet engine

Replace the noisy components with quieter (expensive) ones and lower the revs.

  • Belt drive cam kit.
  • Roller rockers.
  • Carbon fibre push rods.
  • Alloy rocker cover.
  • Fit the lowest-ratio diff that is suitable for your application.
  • Use an A-Plus block and gearbox.
  • Fit an electric fan, preferably with front-mounted radiator.

Oil filter replacement - cartridge type

Owners of earlier Minis, particularly vans with non-removable grilles, may find changing the cartridge type oil filter easier if the filter is removed by unbolting the filter head from the engine with the filter case still attached, then replacing the filter on the bench.

This method makes fitting the rubber o-ring seal in the filter head far easier, but requires a new oil filter head gasket at every oil filter replacement. A suitable gasket can be made from gasket paper for minimal cost.

Oil filter - cartridge to spin-on conversion

Early Minis may be converted to the later type spin-on oil filters (which are easier to change), by fitting the filter head and feed pipe from a later engine. If the car has any collectible value, retain the original parts so the car may be returned to original specification.

Oil pressure problems caused by relief valve - ball bearing mod

Many A-series engines, especially 1275cc, suffer from low or inconstent oil pressure. If this is not caused by a worn crank or bearings, it is often caused by the oil pressure relief valve. This can get jammed or partly stuck open, leading to low oil pressure readings.

A common modification is to remove the oil pressure relief valve plunger, cut a coil or two off the relief valve spring, and replace the plunger with a 9/16" ball bearing (that can be had from a bearing company or an old CV joint). To start with, cut one coil from the spring, then start the engine. Remove more coils until the oil pressure is around 60 psi (any more is wasteful, a lot more will just force oil to leak from the engine). Oil pressure should be relatively constant over the rev range with this modification.

Painting engine/exhaust

Engine lacquer and exhaust enamel can be purchased in brush or spray form from automotive accessory shops and automotive paint shops.

Exhaust paint is designed to withstand far higher temperatures than engine paint which will burn off.

When painting the engine or exhaust, the surface must be clean, free of dirt, oil, grease and rust. Clean using degreaser and a wire brush, and remove surface rust by sanding; exhausts may be media blasted. No primer coat is needed.

Mark 1 engines are painted green, but there is no paint code for this colour and it varied from batch to batch. Mini specialists can supply the correct colour paint.

Swapping engine - driveshafts do not fit into inner CV joints

The internal diameter of the inner CV joints were changed circa 1978. Therefore, the driveshaft-end of the joint from a post-'78 car will not fit in the "cups" on either side of the differential on a pre-'78 car, and vice versa.

The solution is to remove the inner CV cups from the old engine and install them on the engine that is being installed - drain the oil first.

Which cylinder is No. 1?

Cylinder no. 1 is the cylinder closest to the radiator (pre-1996 cars with side mounted radiators), or the cylinder furthest from the clutch.


Is there a list of SU carb needles/specs?

There are several hundred SU carb needles. Full details, including needle profiles, can be found in the Haynes SU Carburettor manual. Alternatively, Burlen Fuel Systems (present manufacturer of SU carburettors) can supply a list.

SU carburettor spring chart

Colour Load (oz) Length (in)
Black, green 5.25 2.5
Light blue 2.5 2.625
Red 4.5 2.635
Yellow 8 2.75
Green 12 3
Brown 14 3
White 18 3.625
Red/Yellow 24 4.812
Red/White 40.5 3.875
Red/Green 11.25 3.875
Lt. blue/Block 4.5 3.875
Lt. blue/Red 18 3.875
Red (HIF carb) 4.5 1.53
Yellow (HIF carb) 8