Converting an engine running on leaded gasoline to an unleaded engine

Since July 1, 2021, the National Fuel Distribution Company NAFTAL has stopped distributing leaded gasoline, remains in its catalog unleaded gasoline, diesel and LPG / C - CNG.

Switching from leaded petrol to unleaded is not without consequences, especially for old cars. Indeed, the old engines as well as certain recent engines designed to run on leaded gasoline intended for certain markets, one imperatively needs lead to lubricate the valve seats and to increase the octane number of gasoline thanks to to its role of anti-knock which prevents the air-fuel mixture from exploding too early.

At the time, the valve seats were machined from the raw material of the cylinder head which was a so-called "cast" part, usually cast iron. However, the hardness of the castings is quite low and requires a high level of protection where the metal is beaten with force. The lead, in its oxidized form, therefore had the second task of playing the role of a damper between the valve and its seat and thus allowed to "cool" and protect the valve heads as well as their seats in the cylinder head.



Leaded gasoline (Tetraethyl) made its appearance in the 1920s and over time, engines becoming more efficient and therefore requiring more octane, so more lead additive becomes more and more harmful for the vehicle. health, lead then represents a third of the weight of particles emitted by exhaust gases. It then becomes banned in the majority of countries starting with the United States of America in 1975, European countries follow much later in the 90s, but it is the obligation of the catalytic converter that will give a large suddenly, with leaded gasoline, January 1, 1993 for gasoline engines and January 1, 1997 for diesel engines, even if the latter are not concerned with lead since diesel engines do not require it, then it is the European Directive 98/70 / CE which will sound the death knell in 1998 by banning its use. However in France as in most European countries, the definitive substitution of unleaded gasoline on leaded gasoline has been applied since January 2, 2000. This removal has reduced lead emissions into the atmosphere by 60%. since the 80s.

It was in the mid-1980s, manufacturers anticipated the discontinuation of lead in gasoline and began to design engines that could run on unleaded. The valve seats will now be hardened steel instead of cast iron, so they no longer need lead to "protect" them. At the same time, advances in refining, the addition of MTBE (Methyl Tertiary Butyl Ether) in gasoline and various techniques make it possible to increase the octane number and therefore to maintain the anti-detonating effect without having use of lead. It is then that the majority of vehicles put into service after 1987 will be equipped to run on unleaded gasoline.



In Algeria, it is only now that it is no longer distributed, but if the idea has been studied for a few years. But you should know that the rolling stock in Algeria is made up of a high percentage of old cars that run on leaded gasoline and that a large part is used by the economic sector. A way of letting the economy run low to the detriment of public health. Anyway, whether it is for vehicles which have to continue to run for economic reasons or simply for those who are passionate about old cars and who think hard, what are the solutions for them to continue driving?



We present here, 4 solutions:

- The first, which is undoubtedly the most economical, is the use of additives, or the use of fuel already with additives sold at the pump. But on condition that you make the right choice.

- The second is the modification of the cylinder head, passing by the installation of special seats (frets).

- The third is a variant of the second: the standard exchange for a so-called "unleaded" cylinder head.

- Finally the fourth solution which is radical, luxurious and which is only available for a few vehicles: the purchase of an aluminum cylinder head treated for unleaded fuel.



1 - The potassium-based additive

It is the simplest of solutions, it suffices to add a dose of this additive to each filling, but in the long run it is also the most restrictive solution, because it is always necessary to have additive with either . The lead substitute additive is potassium, which is the major component of all lead substitute additives today.

The rest of the composition are additives, which differ depending on the manufacturer:

Detergent additives to ensure the cleanliness of the valve seats and heads: essential to prevent them from overheating.

Combustion catalyst additives.

Additives to prevent fuel oxidation during prolonged immobilization.

In Algeria, these additives have been found for a few years, in particular to increase the octane rate and sell for around 1250da, a 250 ml bottle is needed to treat up to 250 liters of gasoline.

However, the use of the additive, a controversial practice, some claim to be responsible for fouling and premature wear of the engine. These are only statements and it is difficult to prove that the additive is directly responsible for these negative consequences, which can be caused by many other factors. As it is difficult to prove that the substitute has played its role of protecting the valve seats.


2 - Modification of the cylinder head

Modifying the original cylinder head requires a minimum of knowledge. The operation consists in compensating for the recession of the valve seats. This recession is intimately linked to the weight of tetrahethyl lead, and turns out to be in direct correlation with the speed of rotation of the engines and their combustion temperature.


The English have become accustomed to treating only the seats of the exhaust valves by affixing frets, or added seats (a kind of special steel rings). But not just any fret: frets for unleaded gasoline and not the old frets that were used to repair seats that were cracked or have gone beyond the repair ribs.


Replacing the 4 exhaust seats (in the case of a 4 cyl.) Is not enough, you must also change the 4 corresponding valves because the original ones are too loose.


These valves are most often made of special steel type EN21 / 4N, but it is still necessary to have access to the composition of their metal: this is rare, so, in this case, only the price remains an index of quality.


So avoid low-cost valves. All that remains is to replace all the guides to avoid any sticking or seizing phenomenon, because let's not forget that “lead-free” is not very lubricating.


In summary you need (for a 4 cyl.):

- 4 "unleaded" valves

- 8 guides "lead-free (phosphor bronze)

- 4 “lead-free” seats


Some companies already sell these elements in the form of kits, more often called "lead-free kit".



3 - Standard exchange for a so-called "unleaded" cylinder head.

The simplest and most reliable process in appearance. For this, you have to be sure that the new cylinder head which is delivered to you has 4 new valves, 4 frets and 8 lead-free guides, 4 new intake valves (normal) as well as all the springs (i.e. 16 springs). , with all the seats placed at the same height so as not to modify the combustion volumes. To this it must also be said that it is the expensive solution compared to the first two.

4 - Change its cast iron valve seats with hardened steel seats

It is the must in the matter, when nothing is too good for your car. Offer him hardened steel. So your car can run smoothly on unleaded gasoline for as long as possible. Moreover, if you are renovating your engine, take the opportunity to change or have your valve seats changed, it does not cost much when your engine is already disassembled.


Thanks to its intrinsic qualities, easy-to-machine aluminum makes it possible to obtain:

- better machining tolerances,

- improved conduits and gas chambers (facilitating flow, hence power gain),

- superior heat exchange (3 times greater than that of cast iron),

- weight gain (greatly influencing road holding, not to mention performance),

- better vintage and current specifications linked to small production runs,

- better quality control always linked to "small series".


It is a bet that some will run on gasoline without any additives and without any changes, what we can say according to the experience feedback is that the duration of their engine will depend among other things according to the compression ratio of their engine, the less it is high, the longer it will last, anyway which will say that the old engines have a limited lifespan, so no need to make unnecessary expenses, when what will adapt their engine to gasoline unleaded, will keep their cars until the end of time.



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