Forum for discussion of the MG factory 6 cylinder, the MGC.
After watching one of my favorite shows, Wheeler Dealers, they were forced again (on a Truimph Spitfire this time) to send the head out for repair following low compression from unleaded fuel damage. My question is, what does everyone do to avoid this damage? Do you add a lead additive? When I had my B years ago I was told that if I use the highest octane (93), I did not have to use a lead additive. Whats that urban legend?
My approach is to wait for the damage and repair it. Valve seat cavitation is not common with BMC cars. In the day, UK cars were exported everywhere to use whatever octane level was available in the area. Thus the clever Lucas designed dizzy with the advance/retard wheel adjustment. I personally use real TEL as the so called additives only highten octane and do not offer the real benefit of lead as a lubricant in the upper valve train.
On the other hand, if you are building an engine, there is no question to the benefit of upgrades from steel to stelite exhaust valves and from cast iron to "bronze" guides....that is a no brainer. Hardened seats seem to be popular but imho, not really needed in many cases. US engine iron is far more sacrificial than UK engine iron...thus US cars take chrome moly rings UK cars are best fitted with cast iron in certain positions eg. wiper rings.
I use Castrol additive, with 95 octane fuel. Have done for the last 10 years, since leaded fuel disappeared. No problems so far.
If and when ( if ever in my custodianship) I need to take the head off, I would definitely convert valves to use unleaded fuel.
Meantime, my theory is.. if it ain't broke, don't fix it.
The octane benefit is questionable imho. The lead is what served to cushion the heated valve face and head and lubed the valve stem in the guide. Xylene, toulene, benzine will all up your octane...only lead will actually serve to protect the upper valve train.
Richard
It is different things in different places. The UK still recognize corn as a food and corn squeezings as whiskey. Not so in the US. Our watered down octane is about 85 and all my cars work well with that save one. Again,over here, tetra ethyl lead is almost nearly impossible to find and the additives would have to clearly state that it was present. Almost all of our "lead substitutes are the 'enes I mentioned and only boost octane...that is more to my point...lead has always been a benefit in USA petrol which we call gas short for gasoline. More lead was called high test or Ethyl for short. It is suggested but I do not know that lead is still used in the UK and I know it is in China, maybe available in Germany and I am not sure but suspect in Av Gas just about everywhere. Without tetra ethyl lead, the OEM build exhaust valves, seats and guides stand a chance of issues down the road...more so the guides and valves and possibly in time the seats.
As said before, from around the time that the plastic bumpers came in, US market MGBs were fitted with hardened valve seats (the cast iron was treated somehow) and chrome (?) exhaust valves. This at least was the party line from BL. I very much doubt that the c engine was so lucky.
As for lead substitute - hporray for the UK because at least our lead substituutes have been proven in independent research to actually do the job. Potassium was one of the best, I think. My car has been run using substitutes since about 1993 and has been fine.
The head redo isn't that costly, all of mine have been redone. [url=http://www.freesmileys.org/smileys.php]
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250,000 miles using the cheapest gasoline I could buy and also the cheapest oil I could find and no additives. Still runs good. This MGC is my "old fishin car" so not treated with kid gloves. End of my story.
Ron
The tetraethyl-lead actually did increase the octane rating of the fuel, because of the tetraethyl part. Four parts of ethyl in one molecule with a lead.
The lead was then burned away and coated the valve seat (and anything else in the way) and cushioned the valve as it closed. Also helped to transfer heat out of the valve to the head and the cooling system to prevent burned valves and seats.
Incompatible with catalitic converters as the lead coated the converter matrix and stopped the converting, so lead essentially outlawed in the States.
As far as the rubber bumper cars having hard seats, no, I don't think so. A friend of mine bought a '74 1/2 GT in Iowa and while trying to drive it home to Oregon lost compression on all but one cylinder. Valve resession from lack of lead in the fuels. This was in the late 1990's with an original car, so not from the latest fuels.
C Ya,
Mark
IIRC, the UK uses a different Octane rating, so comparing the numbers directly is misleading.
I say drive it on unleaded until you have valve seat recession, then remove the head and install hardened seats and valves. Why would you do it before you have the problem, unless you already have the head off?
Robert: AvGas is 100LL for "Low Lead", so yes, it still has lead in it. This is why you do not want to run it in a car with a catalyst.
Tom
Tom,
My favorite girls do not have silicone and none of my cars are catalytic.
Any yes, Mark, I know octane is measured differently by different governments. If you are old enough to recall, as soon as the EPA banned TEL, they quickly shuffled the formulas for Octane so "We the people" would be kept in the dark about real, former measures of octane by real former reliable and independent manufacturers. Its about as much sense as the Government sanctioned EPA MPG guides the Auto Industry posts on their offerings.
As with many things government sanctioned, its a dog and pony show having nothing to do with reality. I just tried to get a tanker load of Toulene and discovered, the seller has to document any sales as the Fed fears loosing ROAD FUEL TAXES....what a load of Iowa natural fertilizerX(. Road tax on a private race course...8-)
And the regulations changed on dispensing Avgas as well. You used to be able to pump it directly into your car, but not anymore. If you own a plane you can pump into your plane and then taxi back to your hanger and drain it off into your car, but not any other way.
One of the "cardlock" fueling stations around here has 100 octane that you can pump yourself if you can access it (corporate members, state, county, city governments), but it is about 30 miles from me and curiously right near the oval dirt track!
The tax thing is also a problem. Lots of the diesel pickups are burning the "red" fuel even though they never work on a farm. Then there's the ones that smell like a chicken shack when they go by. They still haven't figured out how they are going to get the electric cars to pay for road use either.
Yes, the octane number system is different here now. Can't remember exactly how it changed, but it is more optomistic than it used to be. Too bad.
C Ya,
Mark
gentlemen please the burning of valve seats is not uncommon why i used to replace valves and seats in mgb and mgcs in the late 70s and 80s on b and c . i am certain that the engine shop by law has to fit unleaded if possible .and my uncle dennis who worked at the great toulmin motors in the 50s used to remove cylinder heads every other day for valve seat decokes on mgs .ps uncle dennis still works on mgs . so whe had valve recession then ,the best way to stop burning is leave it in the garage .history has taught us nothing !! have a good weekend