Chicagoland MG Club
Unleaded Gasoline? Not a Problem!
We regularly receive questions relating to the demise of leaded gasoline and the effects of no-lead fuels on British sports car engines. Some years ago we addressed most aspects of this issue but since full solutions weren't available at that time, (but are now) it's appropriate to take a fresh look at a serious problem that affects us all.
Before we get into the problems and the possible solutions, we should take a look at "leaded" gasoline and see just what the "lead" was supposed to do. In the first place, the "lead" is actually tetraethyl lead, an organo-metallic additive that has long been used in gasoline for two main reasons. First of all, the "lead" increased the octane rating of the fuel. Secondly, the lead oxides formed during combustion helped lubricate the valves and prevented excessive valve seat wear, especially at the exhaust valve seats. Octane is something we are all familiar with; high octane is hard to ignite, readily. Higher octane fuels, therefore, will not usually "detonate" from the heat of compression before the spark plugs fire (commonly called "knocking"). The idea of valve lubrication and valve seat recession is a bit harder to visualize. It is easy enough to see that a film of lead oxides deposited on the stem will aid in lubrication, but valve seat recession seems more mysterious.
The process actually occurs when iron oxides form on the edge of the valve face. When the valve is open, these imperfect lumps become superheated, and when the valve closes, they fuse to the valve seat in the cylinder head. The valve opens again - and a small fragment of the valve seat remains fused to the valve. Repeat this over and over thousands of times a minute and you can visualize the valve slowly burrowing into the head... which is what happens! It can't go forever because, as the seat is eroded, compression is lost, the valves no longer open and close properly because of adjustment changes, and so on. Eventually, the engine will be running so poorly that even the laziest enthusiast will give in and have the head rebuilt, or replaced. And, unless something is done to change the fuel or the head, the same thing will happen all over again.
The severity of valve seat recession and the rate at which it occurs increases proportionally with engine speed and load. Since British sports cars typically run at a much higher rpm than most modern cars, they are much more likely to suffer from using unleaded gasoline. How long does it take for a valve seat to burn? Dynamometer tests of a V-6 with non-hardened seats running at full load and high rpms showed .075" (over a sixteenth of an inch!) recession in 48 hours. Around town, therefore, your engine will suffer slowly but if you go on long trips with sustained high cruising rpm, your valve seats are in jeopardy!
Doubtless, your next question will be, "But can't I just add something to my gas to replace the lead?" "What about all the 'anti-knock' products in the parts store?" Most of these octane boosters do something to reduce knocking, but most of them are alcohol-based and therefore can do nothing for the silent problem of valve stem wear and valve seat recession. Since the obvious solutions involve tearing open an engine and replacing the affected parts and having some custom machine work done as well, any product that we could offer would have to address the real problem faced by the owner of a vintage British sports car. You need an additive that would in fact replace the lead that has been legislated out of our gasoline (not without good reason, mind you). After looking at a lot of products, we settled on one offered by a company called Marine Development and Research. The additive called, appropriately enough, Relead, does exactly what it says it does: it forms a coating like the lead oxide, and this coating will keep valve recession within the same limits of our leaded fuel (1.1 grams per gallon) that was available until July 1, 1985. (Current levels are restricted to 0.1 per gallon, too low to really be an effective recession preventative.) Relead is relatively inexpensive and a little bit goes a long way - 8 ounces will treat 80 gallons of gasoline. Figure it this way: it adds about nine cents to the cost of a gallon of gas, which, considering the alternatives, is not bad at all! We highly recommend Relead as a short term solution, particularly when long sustained freeway speeds are encountered. Relead is an excellent stop gap or interim method of staving off disaster until your time or finances allow for a permanent solution.
The permanent solution is now possible on all British sports cars. This entails undertaking a valve job. The valve seats must be replaced by special chrome-nickel alloy valve seat inserts. We don't stock these but they are readily available from virtually all reputable automotive machine shops, as inserts are stocked by size not by specific application. The inserts you need for your Healey 100-4 may be the same as for a Diesel Buick! The reason we do not stock these inserts is that many cylinder heads have already been fitted with valve seat inserts (which may or may not be the chrome/nickle type) and fitting dimensions vary greatly as do a number of other factors. Valve seat inserts can fall out if not installed properly so it is best for your machinist to install his/her favorite brand of inserts for best results. A possible alternative to having valve seat inserts fitted is to have a heat-treating specialist induction-harden your original cast iron seats. This was the solution undertaken by some of the motor manufacturers, but finding a specialist to handle this type of work may be difficult, if not impossible.
The new seats will solve 50% of the problem but exhaust valves and guides should also be replaced for a 100% conversion to lead-free fuel.
We stock a full range of Stellite-faced stainless steel valves which are far more burn resistant than original equipment valves. When used in conjunction with nickel/chrome valve seats, recession is all but eliminated.
>Stellite intake valves and chrome/nickle valve seats are not required as the incoming fuel insures safe operating temperatures for these components.
The final aspect concerns both intake and exhaust valve guides. Exhaust guides in particular, originally received most of their lubrication from the tetraethyl lead. Without the lead, stock cast iron guides wear rapidly and eventually cause valve seat and face problems simply because of the excess wear in the stem area. Keep in mind that intake guides have a tendency to suck oil down the guide which sometimes results in excessive oil consumption particularly if the valve stem seals are installed incorrectly or have disintegrated. Exhaust valves, on the other hand, are never well lubricated as hot exhaust gases tend to blow up the valve stem. We stock a full range of silicon bronze guides which have better "self lubricating" properties than cast iron. Most are listed in our recent update but an expanded range is now available. Silicon guides should be run a bit on the loose side as this material has a greater expansion rate than cast iron. These guides can seize if not reamed to provide adequate clearance, particularly on the exhaust side.
Many enthusiasts have experimented with fitting Teflon "umbrella type" valve stem oil seals as a way of completely eliminating intake valve guide oil consumption. This was an effective modification when full strength leaded fuel was available. However, with the currently available fuels, only stock type valve stem seals should be fitted.
With the above 3-step conversion completed, your vintage sports car is now fully up to modern standards and can safely be run on ordinary unleaded fuel without the addition of Relead or other lead substitutes.
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