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500, 472, 425, 368 Discussion, running unleaded in a classic caddy in Cadillac Engine Technical Discussion; Originally Posted by davesdeville How do you explain the tens of millions of miles people have put on these motors ...
  1. #31
    JTraik is offline Cadillac Owners Enthusiast
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    Re: running unleaded in a classic caddy

    Quote Originally Posted by davesdeville
    How do you explain the tens of millions of miles people have put on these motors without adding lead? You paid for the valvestems and hardened seats so now you're defending your purchase.
    I'm defending my purchase and you are defending your lack of, so cut the shit.

    The valve seats get damaged with mileage no matter how perfect the machining or how high the quality. Upgraded valve seats however will greatly prolong that degradation because they are designed with todays fuel in mind. The old valve seats ARE NOT DESIGNED FOR TODAYS FUEL!!! Understand that... so in turn they are going to wear down a whole lot faster. The engine will still run with damaged and pitted valve seats (which mine were) just wont run nominally.

    And another thing, quit cherry-picking everyones posts, your input is useless and argumentative.

  2. #32
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    Re: running unleaded in a classic caddy

    When I tore down my engine i found cast iron guides and they were completly worn and the valves had so much play in them that they had been letting oil into the chamber...

    But thats because 15 or so years ago some DA did headwork and had the cast iron guides instead of bronze and they were too short, etc. Not sure about the seats though...

  3. #33
    chevelle is offline Cadillac Owners Enthusiast
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    Re: running unleaded in a classic caddy

    Quote Originally Posted by JTraik
    Thats incorrect.

    Lead is used to lubricate the valve stems. Before unleaded fuel, valve stems did not have a chrome plating on them. The lead was there to lubricate the stems to keep them from wearing down. The lead also caused the fuel to burn much cooler which worked well with un-hardened valve seats.
    Unleaded fuel came around and they had to put chrome on the valve stems to keep them from wearing down due to the lack of the lead lubricant (chrome is tough stuff!) And they now had to use hardened seats because the fuel was burning much hotter without the lead in it. And so it continues.




    Perhaps that is true but they get damaged in the process. Plain and simple you need updated valve seats for today's fuel to prevent any damage. Thats fact.


    Nonsense.

    Lead in the fuel has nothing to do with lubricating the valve stems. Lead was added to improve the octane rating of the fuel. It also has a fortuitous trait of lubricating the seating surface and minimizing valve seat recession when the engine is run under heavy load for extended periods of time. The valve guides and stems are lubricated by engine oil that seeps past the valve stem seals....certainly not by the lead in the fuel.

    Lead does not make the fuel burn cooler or affect the combustion temperatures at all. It simply helps the fuel resist spontaneous combustion thus improving the octane rating of the fuel allowing more spark advance and/or compression ration without detonation.

    Detonation is the spontaneous combustion of the end gas in the chamber as the charge burns. The end gas is heated by the burn and subjected to increasing pressure as the burn progresses and it will spontaneously combust if the octane rating is not high enough. The higher the octane rating of the fuel the more it is able to resist detonation. Lead in the fuel has nothing to do with charge temperatures or the burn rate or burn temperature.

    I stand behind what I posted previously.


    Certainly if the heads are off the engine it is desireable to replace the seats with stellite seats or have the cast iron seats induction hardened but it is totally unnecessary in most cases to do this to run unleaded fuel. If the engine is in a boat or airplane or run hard in a motor home or something that is run very hard for extended periods of time it is necessary, yes, but to simply drive a classic around on unleaded fuel it is entirely unnecessary.

    Besides, what is the worst that can happen....???... If you run the engine on unleaded fuel for 100K and the exhaust seats do erode or recess then you can take the heads off and repair at that point with stellite seats. Tearing the heads off now to do it is pointless and unnecessary.

    Valve seats will NOT harden themselves or heat treat themselves running in an engine. Nice idea. Don't happen. I agree with you there. But, the factory seats will work fine with unleaded fuel in that engine until it needs rebuilding anyway one day and do them then, not now. The unleaded fuel burns at the exact same temperature as leaded fuel so there is no difference in the temp of the valves, the seats, or anything in the combustion chamber due to the elimination of lead.


    Chrome plating of the valve stems has no correlation to lead or unleaded fuel. There are a lot of leaded fuel engines with chrome plated valve stems from the OEM and there are also unleaded fuel engines without chrome plated stems. The chrome plate has nothing to do with lead in the fuel. The need for it is determined by a variety of things including the valve guide material, the valve stem material the operating conditions of the engine, etc. Intake valve stems are typically chrome flashed if at all and exhaust valve stems are chrome plated for added scuffing, galling and wear protection but there are a lot of unleaded fuel engines that run exhuast valves with no chrome plate at all and they work fine. Interestingly, the other engines in the Cadillac family, the 4.1/4.5/4.9 and the Northstar have both been produced with and without chrome plated valve stems at different times and they were both designed for unleaded fuel.

  4. #34
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    Re: running unleaded in a classic caddy

    Quote Originally Posted by Chevelle
    The higher the octane rating of the fuel the more it is able to resist detonation. It has nothing to do with charge temperatures or the burn rate or burn temperature.
    Well, intake charge temps have a lot to do with detonation. It's more pronounces in forced induction engines but it's similar with N/A. If you were saying something else, sorry.

    Quote Originally Posted by JTraik
    And another thing, quit cherry-picking everyones posts, your input is useless and argumentative.
    Because it disagrees with your input?

  5. #35
    chevelle is offline Cadillac Owners Enthusiast
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    Re: running unleaded in a classic caddy

    Quote Originally Posted by davesdeville
    Well, intake charge temps have a lot to do with detonation. It's more pronounces in forced induction engines but it's similar with N/A.

    Yea, sorry, that was poorly worded. You are correct and I absolutely agree with you. I edited the sentence to say what I was thinking and meant, that is that "Lead in the fuel has nothing to do with the charge temp or the burn rate or the burn temperature. I was referring to "lead in the fuel" as the "it" in the sentence, not detonation but the way the sentence flowed it was completely misleading the way I had worded it. The other poster was implying that lead in the fuel changed the burn rate and/or temperature and that is what I was focusing on and trying to straighten out. duh. Sometimes I type faster than I think. LOL LOL

  6. #36
    JTraik is offline Cadillac Owners Enthusiast
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    Re: running unleaded in a classic caddy

    Quote Originally Posted by chevelle
    Nonsense.

    Lead in the fuel has nothing to do with lubricating the valve stems. Lead was added to improve the octane rating of the fuel. It also has a fortuitous trait of lubricating the seating surface and minimizing valve seat recession when the engine is run under heavy load for extended periods of time. The valve guides and stems are lubricated by engine oil that seeps past the valve stem seals....certainly not by the lead in the fuel.
    Ok... the heads were designed for leaded fuel. The guides are simply cut right into the cast iron. So now you have iron guides and steel valve stems... The only way this would last without wear is if you had the lead lubricant!!! Yes some oil does seep past the seals, but if the valve stems were designed to be lubricated off oil alone than your car would be smoking like uncle buck's!!! Engines nowadays that are designed for unleaded have this chrome plating on the stems that does not wear out as fast as bare steel does and the guides are usually made of some bronze or copper composite. Oil seepage just happens, and of course it will help, but idealy it is not needed in lubricating the stems. Also in unleaded gas there are small amounts of lubricant called TEL which also helps the valve stems but the need for valve stem lubrication is not as pressing as it used to be.


    Quote Originally Posted by chevelle
    Valve seats will NOT harden themselves or heat treat themselves running in an engine. Nice idea. Don't happen. I agree with you there. But, the factory seats will work fine with unleaded fuel in that engine until it needs rebuilding anyway one day and do them then, not now. The unleaded fuel burns at the exact same temperature as leaded fuel so there is no difference in the temp of the valves, the seats, or anything in the combustion chamber due to the elimination of lead.
    I can see where you disagree, however, i cant seem to find anything to back up either of our statements, perhaps you could provide something...

  7. #37
    chevelle is offline Cadillac Owners Enthusiast
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    Re: running unleaded in a classic caddy

    I repeat. Lead has absolutely nothing to do with lubricating valve guides. The guides are designed to operate with the oil that seeps from the seals...and the natural wear resistence of the steel of the valve stem and the cast iron guide.

    Valve stem seals are not designed to stop all the oil, the are designed to allow some oil down the guides for lubrication. It has to happen.

    The operation of the valve stem inside the valve guide is (thankfully) not too stressful of a situation. The valve does not go far in terms of travel and there is minimal side loading of the valve stem in the guide. So it doesn't take much to make it live. The oil coming down from the valve stem seal is what does it. That is why it is important to have some oil coming past the seal in a properly designed seal.

    Granted the chrome plating on the stems helps with wear but the use of chrome valve stems did not start with unleaded fuel nor do all engines with unleaded fuel have chrome valve stems.

    Lead only works for lubrication at the valve seat interface. It works there due to the high temperatures and pressures of the seat. The presence of lead means nothing to the valve guides.

    The engines will run fine with unleaded fuel as long as they are operated at part throttle under normal driving. Proof...???....there are hundreds of thousands of older "leaded fuel" engines running around fine on unleaded fuel. More proof...???....look at what the OEM's did when unleaded fuel was introduced. They went to induction hardened valve seats in the cast iron heads. That is all. No changes to the valve stems or valve guides. Just the seat material or hardness was changed.

  8. #38
    lux hauler is offline Cadillac Owners Connoisseur
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    Re: running unleaded in a classic caddy

    Quote Originally Posted by Kev
    I would have to disagree on this idea. There are two basic ways to heat treat steel (there are many other more complicated methods but for this converstation let's keep it simple).

    1. Heat the metal evenly until it is cherry red and then dowse it in cold water. This causes the steel molecules to condense quickly creating a more dense and brittle structure.

    2. Heat the metal evenly until it is cherry red and then dowse is in oil (30W). This causes the molecules to condense more slowly than the first, the effect being a hardened exterior with a softer core. The metal is less brittle, more durable in the long run.


    Now, with either of these methods, if the steel is heated again it will loose it's temper, either become softer again or become fatigued and subject to damage. Here is the problem with the idea that the seats are hardened with the heat of the engine. They are heated and cooled over and over, but not enough to truly temper them, though the expansion and contraction resulting from the heating and cooling that they experience will have the effect of fatiguing them in time.
    That's what a local engine builder told me.

  9. #39
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    Re: running unleaded in a classic caddy

    Tetraethyl lead, or just "lead" was developed as a result of research done by Charles Kettering in the early 20's. He and his staff were reserching "combustion roughness" at elevated compression ratios over 4.5:1 which was about as high as was possible in those days.

    A side benefit was longer valve life due to the cushioning and lubricating effect of the lead on valve seats.

    Starting in 1971, all GM and many other manufacturers engines, incorporated harder valve seats and valves in anticipation of the new low and no lead fuels that were being mandated by the EPA, and in preparation for catalyst equipped cars. This was also the reason for the lower compression ratios.

    Now, lead is not essential for the longevity of valve seats in a moderately driven engine. It helps, but is not needed. But if the heads are off, and being gone over, then it wise to upgrade to the better seats and valves. I would not tear a healthy engine down just to perform this operation.

    Also, lead does not lubricate the valve stems. This is done with oil in very small amounts.

    Mike

  10. #40
    chevelle is offline Cadillac Owners Enthusiast
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    Re: running unleaded in a classic caddy

    Quote Originally Posted by lux hauler
    That's what a local engine builder told me.

    Not surprising, there is a LOT of misinformation out there. Wonder what else he has wrong...??? LOL LOL LOL

  11. #41
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    Re: running unleaded in a classic caddy

    Quote Originally Posted by JTraik
    Yes some oil does seep past the seals, but if the valve stems were designed to be lubricated off oil alone than your car would be smoking like uncle buck's!!!
    Nobody mentions changing the cylinders when switching from leaded to unleaded gas. Reason: Your cylinder walls are also lubricated with oil, and don't cause smoking if all is working correctly.

    The fact is, it is just a very thin layer of oil, just a film. Some of it is taken away by the air going past the valvestem, but most of it stays, and most of the valvestem stays covered by the valveguide anyways. The tiny, tiny amount of oil stripped off the valvestem IS burnt by the engine, but we are talking about such a tiny amount that you'll never see it. That's why engines have an allowable oil comsumption rating. The oil doesn't just evaporate, it IS burnt, but if you burn 1 qt over 3000mi, it's never enough to notice. Cars with a blue trail are burning more like 1qt every 300mi...

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