See bottom for useful part numbers.

The specter of 'unleaded fuel only' - instigated in UK on January 1st 1999 and seemingly from decades ago across the rest of the world - seems to be forcing more and more folk into frightened, panic orientated action. And Mini owners are featuring heavily in this.

The situation not at all being helped by all sorts of conflicting information from 'leaned' sources, such as lead levels in humans has declined greatly since 1935 - despite the rapidly expanding ownership of petrol-burning vehicles. And benzene and toluene used in unleaded fuels are cancerous.

Still, the powers that be are relentlessly forcing through the 'no heavy metals in fuel' bills, not being at all put off by such trivia. Not surprising bearing in mind the complete debacle on the catalytic converter front - the type decided on for world wide and universal use was developed and tested in California! As a consequence, further testing in colder climates (i.e. Europe) has found emissions produced by Cat equipped cars to be more harmful than burning leaded fuel simply because the Cat's aren't working at the right temperature. Makes you wonder, eh?
For many years now, a growing number of companies have been unscrupulously scare-mongering amongst owners of leaded fuel burning vehicles in a bid to sell their own particular solution to the problem - additive manufacturers, head specialists, and more recently commercial fuel manufacturers alike. These range from additives introduced to the fuel by either solutions/pellets in the tank, in-line fuel filters/capsules, full-unleaded cylinder head conversions, and additive enhanced fuel straight from the pump - all flaunted as the 'ultimate salvation'. Insufficient (read - 'non-existent') independent 'recognised' testing and a certain amount of 'political skullduggery' offered the bewildered owners no decent and meaningful guidelines. Only gross and confusing (conflicting) mis-information. Consequently a number of these companies have become very much richer selling products that were by and large dubious at best and some that simply do absolutely nothing at all.
Then there are all the opinions on what you can get away with. But that's just the point 'get away with' isn't a guaranteed solution. Neither is 'I've done 20,000 miles on unleaded fuel in my car that hasn't been converted for unleaded fuel, and without any additives either'. Just because it's worked for some, it has probably not worked for equally as many. Again, what you folk need to be confident in resolving the problems is something that is guaranteed to work.

I've covered the specifics about why lead's needed in fuel for certain vehicles, how it works, and alternatives in another article in Calver's Corner - 'Fuel - Leaded, unleaded and options'. Rather than repeat it all here, suffice to say that lead's needed as a lubricant between the valve and cylinder head seats to prevent the valve disappearing into the head, or burning away to nothing. Both disastrous for performance!

In an effort to curb the mounting onslaught of queries and panic developing on this subject, and pre-empt the final availability of leaded fuel, I'm going to tell you what needs to be done, who needs to do it, and to which Minis it needs to be done. Hard facts, tested in the field over many years, no salesman b*llsh*t, no commercial interest, no 'back-handers' involved. Just your interest at heart.
Those of you possessing Minis manufactured after 1990, and/or CAT equipped cars don't have a problem here. For the record, 998cc engined variants prior to this with engine numbers beginning 99HG30,31,32 or 33, 99H/F15 or 16, 99H/E20,21 or 22, 99H/D81 or latterly LBB10089 or LBB10175 are also safe. Anything else will have to be checked by removing the cylinder head - Rover never adhering precisely to mundane numbering!
Lead Memory
Although this term's a bit misleading, it's a reasonable description, and possible good news for thousands of you.
As leaded fuel's burnt, it leaves a deposit on the combustion chamber areas, most notably the valve seats on both valves and heads, and valve stems. This deposit builds up over increasing mileage to a point where after some ten's of thousands of miles a decent layer has formed - hence the term 'lead memory'. This makes it perfectly feasible to run on unleaded fuel only without any problems for many miles before the severely abrasive nature of unleaded fuel totally removes it - as can be attested by many American/Canadian Mini owners who lost leaded fuel many years ago! It also gave rise to the suggestion/ recommendation that leaded fuel cars could be run on unleaded fuel as long as every fourth tank full used was leaded - an effort to extend the 'lead memory'. And it worked whilst you could still guarantee getting proper leaded fuel. Since its general demise (although still available in the UK from a few sources) it's really time to take steps to ensure reliable, trouble free motoring.
How long the lead memory lasts is dependent on mileage and use. A vehicle that's done over 40,000 miles on leaded fuel will probably do 10,000 miles on unleaded before problems occur. Those vehicles used conservatively on mainly light throttle openings (pootling around town, demonic economists, or speed-abhorrent types) will certainly achieve this. Extended periods under maximum load (the progressive, lead-booted, fast and furious driver, driving in motorsport, 'mountainous' regions or long periods at high speed on motorways) will shorten this by about half to two-thirds. Purely because of the exhaust temperatures achieved and throughput of extremely abrasive unleaded fuel.

As practically all Minis produced prior to 1990 may well have covered far more than 40,000 miles, there's some good news for many of you. Particularly those who use their pride and joy for limited mileages - i.e. show or club meeting go-ers only. If you're a-series engine's an old 'un, and now only does a few hundred miles a year, you really shouldn't have a problem. As a guide line gained from personal and collective experiences, your engine should cover around 20% of the current mileage accrued on leaded fuel when changing over to unleaded - bearing the aforementioned conditions outlined, and taking into account when the cylinder head was last reconditioned - if indeed it was.
There are always exceptions to any rule. A-series engine endowed with modified heads with valve seats cut to widths less than 0.060"/1.5mm will need careful attention - less area means more rapid erosion. More details on this later.

Those of you who cover mileages that will soon eat away the suggested 20%, engage in long journeys, do more than 5,000 miles a year, want to run a modified head with very big valves in or compete where unleaded fuel is a regulation you really need to use an additive as a minimum, unleaded conversion (covered later) - if possible with valve sizes used - the best option.

Additives
There's been a plethora of these on the market for some time now. Using an additive of some description makes sense, and could be considered 'insurance'. After all, most of them appear to present very good value for money - often being cheaper to run in conjunction with unleaded fuel than just using leaded fuel. The problem for the prospective user, as mentioned earlier, has been the lack of recognised endorsement or decent, reliable, confirmable test results - i.e. as conducted by 'MIRA' in the UK.
Many investors in the various types available up until now have found them to be 'completely reliable'. Particularly those that have been using them in recent years to protect their aged 'owned from new' examples of the marque, or frequent visitors to Europe in leaded model vehicles. Hardly surprising bearing in mind the 'lead memory' thing is it?

To illustrate a friend used a 'middle aged' Transit van as a tow vehicle for his race car. It had covered some 90-odd thousand miles without problems. Then he started competing in Europe. As they don't have leaded fuel readily available, he decided on using one of the much advertised and heralded in-line 'filter/fuel modifiers' - a supposed 'total solution to the problem'. Some 30,000 miles later (a mere 18 months), the engine was running badly. Checking the compressions showed three cylinders to have almost nil. Checking valve clearances confirmed why, there weren't any of these either. Severe valve seat recession was the cause. The 'total solution' didn't work. Few folk ever find this out, as they never cover the kind of mileage that unearths the awful truth.
To ensure protection is achieved, the additive must dissolve into the fuel and stay suspended in it to reach the combustion chamber. After all it's the deposits left and created by combustion that give the much-needed protection. Various additive manufacturers took different approaches. Those giving effective protection used chemicals such as sodium, potassium, phosphorous, and manganese. The careful tailoring of each additive determining the most efficient.

To assist prospective users, the Federal Bureau of Historic Vehicle Clubs (FBHVC) got together with MIRA in the UK to organise a suitable test. To avoid a long dissertation on the who's, what's, and where fore's, if you're contemplating using an additive (and I strongly recommend this) and are living in the UK, ask the prospective additive's manufacturer to supply the FBHVC/MIRA test result data, or look for the relevant 'approved' mark. If they can't/won't supply it, or the product isn't approval marked, don't use it. I am unable to suggest any such checking for the rest of the world, as I am unfamiliar with any such testing bodies and any research they have done. Word of mouth recommendation may be the best way - I use Redline Lead Substitute and highly recommend this product through extensive personal testing and use.
The motoring press issued reports on the test results. It was stunning to see that very few passed - although I wasn't so surprised based on my own personal testing I carried out some years ago. Only two products actually passed the test proper - Redline Lead Substitute and Superblend Zero Lead 2000. The former has been around for a very long time with a solid and proven background, the latter was brewed specially for the test.
Whilst investigating which to use and comparing price, carefully compare dosage per packet/bottle too. Half the price may mean half the mileage! Even long term they can be far more economical (not to mention more reliable) than a full head conversion. Again, I really recommend using an approved additive, it's cheap insurance.
Modified fuels
Very little information's available about what fuel manufacturers are going to about replacing leaded fuel. Initially they'll have to present something, as not all leaded fuel burning vehicle owners will have been privy to this information! Truth be known, they're already hoodwinking many of you. Some of them have been experimenting with additive enhanced fuels. I've had some interesting discussions with folk from around the world where a certain well-known fuel manufacturer has been testing such stuff. And the results aren't good - except when presented (mis-represented!) by said manufacturer.
What you need to remember is that they'll only tell you what they want you to hear, not all you need to know! The unfortunate thing is that whatever they do will probably be government approved - as if that's assurance!
Cylinder head conversions
The alternative for those who do huge mileages and/or don't want to have to bother with remembering to carry/put an additive in. Covered loads of times, yet some magazines have still got it wrong. All sorts of ill-informed statements have been made, so here's the 'gen' in brief.
Suitable exhaust seat inserts fitted into the cylinder head are a minimum. They don't fall out if properly fitted - all aluminium heads have them! Various different manufacturers produce these inserts. I generally use the genuine Rover types, as they are pretty cheap and small in outside diameter and depth whilst having a larger inside diameter. This is not always a good thing since there is effectively less surface area gripping the insert, but isn't a problem if correctly fitted. In five years of using these inserts I haven't had one failure (just you watch - I'll have a bunch of disasters now!). The other general-purpose inserts tend to have a much small internal diameter. The hassle here is that they need grinding out once the seat has been cut to avoid severe restriction of the valve throat area - so watch out for this. They are also hard on valve seat cutters, blunting them very quickly.
Cast iron guides are generally better than bronze types for road use, the latter only needed when un-treated stainless steel valves are used in very modified heads (where consistent and sustained rpm levels over 6,500rpm are to be used).

Chromed valve stems are preferable, though not essential - unleaded fuel is severely abrasive so can wear untreated valve stems very quickly. Stainless steel valves will wear more quickly than current standard material valves unless treated (Tuftrided or chromed). Tuftrided/chromed stem valves are a little more expensive but definitely worth the extra outlay. Inserting a 1275 head restricts the valve sizes usable - maximum 30mm exhaust, 36mm inlet. 37.2mm inlet is usable if standard Rover inserts are used and 29.3mm exhaust valves. Some companies are fitting much larger exhaust valves into unleaded inserts - up to 32mm - and report no problems. This makes no sense as the inserts would be ground down to little more than a thin-wall tube to allow such large valves to be effective (as opposed to ineffective through choked-down valve throat area). A recipe for disaster - the insert would definitely fall out. Using a very big insert to allow such fitment and be mechanically correctly retained would encroach on the inlet valve seat area too much - causing a whole load of different problems such as poor valve seal with the engine at running temperature.
You don't need Tuftrided or any other fancy rocker shaft. Compression ratio is influenced by cam type, carb type, and head efficiency, but suggest 10.5 to 1 maximum for the road. Modified cams will need modified distributors to suit.
Conclusion
Unless you're contemplating inter-galactic mileage, you don't need a converted head. If you're a-series engine has ingested hoops of leaded fuel over many thousand's of miles, and you only do limited casual mileages, you are likely to get away without the need of a conversion or additive. My personal recommendation and experience has proven that using an endorsed additive is the best way to go.
On race cars or where larger than sensibly usable valves can be fitted where exhaust seat inserts can be used and unleaded fuel only is usable - don't bother about inserts, just use a reputable additive.
Useful part numbers:
TAM2068 Genuine Rover small-bore head unleaded exhaust seat insert - 4 required
TAM2069 Genuine Rover large-bore head unleaded exhaust seat insert - 4 required
TAM1059 35.7mm MG Metro chrome stem inlet valve - triple collet

groove only.
TAM1061 29.3mm MG Metro chrome stem exhaust valve - triple collet
groove only.
12G1963 Valve guide, cast iron, latest bullet-nosed spec.
12G1111 Valve guide, cast iron, old style square-nosed spec.
C-AJJ4037 Manganese-bronze valve guide set.
C-AHT110 37.7mm race spec inlet valve, 12G940 casting.
C-AHT55 37.2mm nitrocarb race spec inlet valve, 12G940 casting.
C-AEG544 35.7mm nitrocarb race spec inlet valve, 12G940 casting.
AEG593 35.7mm race spec inlet valve, AEG163 casting.
C-AEG569 33.3mm race spec inlet valve, 12G940 casting.
C-AEG588 30.94mm nitrocarb race spec inlet valve, small-bore casting.
C-AHT376 35.7mm nitrocarb race spec inlet valve, ally 8-port casting.
C-AEG570 32mm race spec exhaust valve, 12G940 casting.
C-AEG107 31mm nitrocarb race spec exhaust valve, 12G940 casting.
AEG594 31mm race spec exhaust valve, AEG163 casting.
C-AEG106 29.5mm nitrocarb race spec exhaust valve, 12G940 casting.
C-AEG587 26.5mm nitrocarb race spec exhaust valve, small-bore
casting.
C-AHT377 30.9mm nitrocarb race spec exhaust valve, ally 8-port
casting.

ADU4905 Latest A+ type tensioned top hat valve stem seal.
AEG327 'S' type top hat valve stem seal.
All above valves ate to latest proven high-flow profiles. Check inventory for a limited range of Rimflo valves.
This article written by Keith Calver