ASK THE EXPERT
Our tech expert Keith Calver answers all your Mini technical queries.
“If there is no dedicated earth strap providing an easy route to earth, the engine will use something else... ”
CAMBER ADJUSTMENT Is it possible to modify the rear camber on a Mini without buying expensive new adjustable brackets? I’ve got too much positive camber on the offside, which I’m led to believe is common on Minis. I just want to level it up to zero degrees. Rick Simple one this – you just remove the brackets and file the hole that the radius arm pin comes through upwards. I would suggest scoring some guidelines into the plate faces by using a ruler or engineer’s square. You need to only move the hole upwards. Angling it fore or aft would alter the tracking at the same time – although that’s not a disaster in itself as long as it is forwards. That increases toe-in and can be adjusted out by placing shim steel between the bracket and subframe. If rearwards, that increases toe-out and is very difficult to resolve. The easiest way is to file the hole in the outer bracket to move the pin end forwards, then weld a large washer to the bracket to hold the pin end in the forward position. As for how far upwards the hole needs filing, that will depend on how much you want to change the rear camber angle by. Typically one degree of camber change at the bracket is around 0.170-inch/4.3mm. So if your Mini has one degree positive camber and you want to make it one degree negative camber you will need to file the pin hole up by around 0.340-inch/8.6mm. NO EARTH I’ve discovered that I’ve been running without an earth strap from the body to the engine for at least the last two years. Now that I’ve fitted one, the starter motor spins much faster and the car is easier to start. Other than the sluggish starting, what other effects on running will there be from not having the engine earthed? Edd The engine needs to earth to operate. The electrics associated with the starting and running of the engine, such as the ignition system and starter motor, would not work otherwise. If there is no dedicated earth strap providing an easy route to earth, the engine will use something else. Typically these end up being the control cables – throttle cable, choke cable and/or heater tap cable. The issue there is it generally doesn’t take too long RED GREASE I’m fitting new wheel bearings to my Mini, and at £50 each for the genuine ones I want them to last. I’ve seen that lots of Mini racers recommend using a red grease for the bearings as opposed to the normal LM grease. Where can I get red grease from, and is it worth using it for a road car driven in all weathers? Toby Top quality grease is always worth the investment considering the hostile environment the wheel bearings have to cope with. The only red coloured grease I am familiar with is Red Line Synthetic Oils CV2 grease. I have used this for decades on all highly stressed bearings – wheel bearings, CV joints, inboard CV (Pot) joints and so on. It is less viscous (thinner) than tradition wheel bearing (‘LM’) greases so causes less drag, and has a much higher sheer strength. All in all, it’s an excellent grease.
UPRATING BRAKES I’ve bought a 1992 Mini Cooper, which I’m delighted with. However, I’d like to improve the brakes, while keeping the standard callipers, as I have bought new AP ones. What would you recommend to upgrade the 8.4-inch brake set-up for fast road use? I’d like to fit some Mintex 1144 pads but I’m told they say ‘not for road use’ on the box. So what’s a good alternative? And should I go for grooved discs? Bartosz Grooved discs help in two ways. When the discs and pads are in their cool phase, they wipe the pad surface clean, removing before these overheat from the current they are having to deal with, acting a bit like a giant fuse. The result being smoking cables, very stiff operation (typically on the throttle cable, having it stick with the carb butterfly open), and in some cases a premature vehicle barbecue. Consequently, to have gotten away with seemingly no main earth strap, something else of a major size must have been taking the current, which leads me to suspect there may well be an earth cable somewhere hidden from view. You don’t say the year of your Mini, but older Minis had an earth strap from the clutch cover down below the starter motor bendix cover to the inner wing or front panel. This is easily missed as it was very hard to see – as many an enthusiast of such
“Having it stick with the throttle open will be a real attention-getter, especially on a motorway!”
hardened deposits on the pad face caused by high temperatures. And at these higher temperatures, they also break down the gaseous layer that forms between the hot pad and disc surfaces. Both improve braking performance, so are definitely worth it. But don’t go for discs with loads of grooves. AP Racing did a huge test on this some while back now, and found that in the majority of cases, four grooves were enough – typically arranged straight across the disc surfaces, but at 90 degrees to each other on the reverse side. This is to maintain disc strength by preventing cracking/ breakage from fatigue cracks developing between the slots.
I have not used Mintex 1144s Minis will attest to. It often gets missed when engines are being removed, its presence only be realised when the engine also picks up the front of the car when being craned out!
I would advise carefully checking the control cables mentioned previously to make sure they are in perfect working order, especially the throttle cable. Having it stick with the throttle open will be a real attention-getter, especially at proper speed on a motorway! And while you’re looking it over, see if there is indeed that sneaky earth strap down under the starter motor cover. for a very long time so can not personally comment on their performance. I quit using them many years ago because when the regulations outlawed asbestos from brake pad use, the once terrific 1144s (then M171s) really suffered. I have been told they are far, far better now, but have yet to try them. I BRAKE BALANCE I’ve bought a set of Cooper S disc brakes to go on my 1991 Mini Mayfair project, and have been advised I need to switch the rear cylinders to restore brake balance? I have complete new built-up backplates with 0.75-inch bore cylinders from Mini Spares to go on, so wonder if this is necessary? have been using EBC pads for all my road Minis for quite some time. UK manufactured with excellent performance, and at a very sensible price, they have proven pretty difficult to beat. For normal road use go for the Blackstuff pads. For sportier driving, go for the Greenstuff pads. What cylinders should be fitted if mine aren’t right? Mel The original Cooper S braking system fitted with the MkI-type servo used the 0.750-inch bore rear wheel cylinders. The later S using the Mk3 type servo used 0.625-inch bore rear wheel cylinders. Both
HIGH-LIFT ROCKERS I’ve got some 1.5:1-ratio roller-tip rockers I’d like to fit to my Mini. It’s a mildly tuned 998cc motor with a 266 cam and a Stage 3 head, but I’m told not to fit these rockers and go for 1.3s instead. Everyone seems to say this, but can you explain why? Is there a way the engine could be tuned so that they work? Akos I have never seen worthwhile improvement in performance when fitting 1.5:1-ratio rockers to smallbore engines for road use using relatively mild cams, particularly when considering the cost to do so properly. I say properly because not too many small-bore cylinder heads are configured to take the extra lift given by the 1.5:1ratio rockers. That means staying away from valve spring coil-binding. On race engines used the same rear subframe mounted regulator valve, so patently there is something in the effectiveness of the servo that has an influencing factor. I do not know how the latest spec master cylinder-mounted type servos compare with the S Mk3 type, but I would hazard a guess that they are very similar. Consequently you could probably get away with using the same 0.625-inch bore rear wheel cylinders (part number GWC1129). But, the S system did have a reasonably effective rear brake regulator. The later braking systems did not use this type. Regulation was done partly by the master cylinder and partly by the PDWA valve. Originally I did not think the PDWA valve effected any regulation at all, but a short while back I was assured by a renowned brake systems specialist that they did provide it to some degree. I did not discover how this worked; he retired very soon after and disappeared abroad to enjoy himself for a few years! Having messed about with this some years ago now, I found that the 0.5625-inch bore cylinders worked well with the set-up as you are going to run it. I’d try that first, simply because you do not they give a few more BHP at the top end, but tend to lose a bit at the bottom end. That’s not an issue in an engine that spends all its time north of 4000rpm, but for road use, mild or fast, low engine speed performance is very important. But then again it also depends on what cam spec you use. Some cams are designed to work specifically with high ratio rockers. David Vizard had this very much in mind when he was developing the MD266 and MD286 cam specs. But then this was for the largebore based (1275cc plus) engines. The small-bore based (850, 998 and 1098cc) engines didn’t get much consideration.
Having said that, this is a subject I have discussed at length with a great many folk, enthusiast and experienced specialist alike. I would certainly willingly accept a single pound coin for every enthusiast that has said that need or want a heap of rear braking going on in a Mini. Locking up the rear wheels is an absolute no-no, particularly on wet roads. Having the rear end snap around sideways is not what you want to be happening. SMOKING START My 1996 Mini SPi smokes heavily on start-up, but then clears after the initial cloud and won’t smoke again for the rest of the day. It’s a low-mileage car, runs well and never uses oil. What could be causing this excessive smoke on start-up? I’m worried about the head gasket. Charlie It depends on what colour the smoke is as to where the problem might be. But even then that may not help as the fact the problem disappears completely for the rest of the day and it doesn’t use oil throws most scenarios out the window.
If the smoke is mostly black, that suggests over-fuelling. A weird one if it is, as the fuelling is their chosen cam spec fitted with 1.5:1-ratio rockers in their 998 gave tangibly better performance than when fitted with the standard rockers. The problem here is almost no existing back-up data to try and fathom as to why. There are so many factors that can affect the performance of any given engine spec; it could be that the rockers are making up for a deficiency in the cam spec, or the modified head spec. The overriding explanation, then, being that it is just a combination that works. Not at all scientific!
A specific explanation on why very high ratio rockers do not generally work on small bore engines would take chapters, especially as there has been little investigation into exactly why the phenomena occurs. The fact is, specialists worth their salt determined by the ECU. Even on the get-you-home safe mode it should not be over-fuelling enough to create clouds of black smoke at start up. It could be a leaky injector that is dripping fuel in to the plenum that is then ingested at start up. Once the engine is running the leak is not causing an issue as the injector is squirting fuel as demanded, who advise one way or the other will have tried various combinations and tested them thoroughly, and thus come up with their own conclusions. I am no different. In all the small-bore engines I have built over the years and have properly dyno or rolling road tested, only a few have given surprisingly better performance over what has been seen before on similar builds when a set of 1.5:1-ratio rockers have been strapped on in place of a set of good 1.3:1 or even 1.4:1-ratio rockers. And of most of those, I suspect the cylinder head performance had a significant part in that, where the head has been a particularly effective one. controlled by the ECU. I doubt it’s anything to do with the fuel pressure regulator as that would cause over-fuelling all the time.
If the smoke is mostly bluegrey, that suggests excessive oil entering the combustion chamber. As the problem only happens at start-up, the most likely cause is valve stem seals. With the engine not running, oil
“Having the rear end snap around sideways is not what you want to be happening...”
pooled around the top of the seal leaks past it, runs down the valves and drips off into the combustion chamber on to the piston crown, or collects on the back of the valve if shut, causing a burst of excess oil at start-up. The elephant in the room here is that there is no oil consumption.
If the smoke is white, that tends to be coolant. The problem here is, if there is a coolant leak in to the combustion chamber, it tends to get worse as the leak point gets larger as the engine heats up. I have not come across such a leak that goes away as the engine gets warmer. Without knowing what colour the smoke is, it is hard to know where best to start investigating the problem. AUTOMATIC ECU I’ve just picked up a Mini Sprite automatic, which I’d like to change to manual. I have the complete engine and gearbox from a Mini Sidewalk, which is also a 1995 model. What else would I need? Can I use the same ECU for the auto? And is there any other wiring I have to do? I only have the engine and gearbox unit, so I’m hoping to retain as many bits from the Sprite donor car as I can to save on costs. Malcolm This is not something I have done, or know anybody that has either. I do know that the ECUs are different for the automatic and manual applications, the main difference being that the auto ECU raises the idle speed when selecting reverse. So you can use the auto ECU for the manual application. The auto uses a kickdown system to boost acceleration when the go-pedal is buried, but as the sensor for this won’t be plugged in, it simply won’t activate anything. And as you are swapping a like-for like spec engine there shouldn’t be any other issues. These units are the 53bhp-spec engines. The Cooper spec engine uses a different camshaft and has a different ECU to go with it, giving the higher 63bhp output. WHAT COATING? I read with interest your piece on the pitfalls of power-coating in the October issue. I’ve just stripped my subframes and hubs back to bare metal and am looking for a resilient coating that wont strip off or flake. What approach would you recommend? Martyn I have been using POR-15 products as sold by Frost Auto Restorations (www.frost.co. uk). For many years I have been using their chassis black top coat supported by the relevant surface preparation products. This has given fantastic performance in all weathers and conditions, giving a hard, chip-resistant gloss finish that is easily cleaned and looks great. More recently they have introduced supposedly an even tougher chassis black. I am currently using it to re-finish all the front subframe and suspension components for my Clubby Estate. I have yet to do the top coat, but so far the initial surface prep looks very good.
“If the smoke is mostly blue-grey, that suggests excessive oil entering the combustion chamber...”
Red Line CV2 is highly recommended by Keith.
Rear camber can be altered by modifying the stock brackets.
Grooved discs and decent pads can really improve your brakes.
Several types of rear wheel cylinder are available.
An extra earth strap on a Mini is never a bad idea.
Exhaust smoke can have a plethora of causes.
1.5-ratio rockers are generally best suited to big-bore engines.
POR-15 products are ideal for coating bare subframes.
An auto ECU should work OK on a manual engine.