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Thread: engine that takes leaded gas
          
   
   

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  1. #1
    36chevymaster's Avatar
    36chevymaster is offline CHR Member Visit my Photo Gallery
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    engine that takes leaded gas

     



    a friend that just bought a 68 amx. the engine in it still take leaded gas.
    what needs to be done for it to take unleaded gas.

    thanks for any and all help

  2. #2
    Itoldyouso's Avatar
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    The valve seats can be changed to more hardened ones. I just had a discussion with a machinist on having this done to a set of 66 Olds heads and he says to put the hardened seats on only the exhaust valves. His comment was that without the lead in the gas the valve pounds the seat when closing and will recess it over time.

    I was surprised to hear that only the exhaust valves need it, but maybe some of our engine builder types on here can expound on this more. Conversely, the first machinist I contacted said hardened seats are only needed if you intend on driving the car a lot, as in being a daily driver. The second machinist scoffed at that.

    Also, there are lead subsitutes you can dump in your gas to replace what is no longer there at the pump, but that would get old and expensive I would think.

    Don

  3. #3
    TooMany2count's Avatar
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    Hey Don, I have always read that the Olds and AMC mtrs has a high nickle content & don't need harden valve seats.....joe
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  4. #4
    pat mccarthy's Avatar
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    yep and seats can fall out crack and fail they can be put in were there cut to deep and weaken the head and you can cut in water with a head not made for a seat. weak valve springs beat in the ex side of the head as there more heat on the ex valve.BUT seats are cheap so cheap that i will not post what i pay for them in bulk theres good money to put in seats . if a older hard to find head i may not put seats in it has alot to do with how many miles its going to see . many heads are hard from the go if 1970 many were heat inducing the ex side of the stock head and there are very hard ..try cutting one out for a seat some time i have one other thing with seats they can hide a crack or repair thats ok if you know. that s not so good if your looking for cracks in the casting as a mag check will pass over whats hinding under a seat . the lead in fuel helped lube the Ex seats keeping the transfer of iron to valve face .most stock valves are a form of stainless steel this helps alot were the pulling of metal from the seat
    Last edited by pat mccarthy; 06-30-2011 at 10:36 PM.
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  5. #5
    Bob Parmenter's Avatar
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    Here's a cut and paste from something I posted on another board a couple days ago just cuz I don't want to type it all again;

    For some it might be useful to understand the mechanism of exhaust valve errosion infrequently experienced with unleaded fuel. Basically the valve face tries to weld to the seat face (at the microscopic level). Then the weld is torn by the valve opening. The notion of "lubrication" from the lead is somewhat of a misnomer from the normal way folks think of lubrication. Anyone who is familiar with welding knows it's difficult to weld dirty work pieces. That's pretty much what the lead did, it deposited on the exhaust valve area/components and prevented the welding by contamination. BTW, since the tetraethyl lead is in solution before combustion it does nothing for the intake valve. Using logic, the trigger for welding is heat. Vehicles that experience exhaust valve errosion usually are ones that work hard (i.e. not normal driving). Examples would be heavy duty equipment, racing applications, and so on where high heat is generated/retained. Another experience of welders is the difficulty of welding dissimilar metals, thus the stainless valve/induction hardened seat/ and so on.

    I'll second Pat's comment about the dangers of a "less experienced" shop cutting into the water jacket under the seat. I had that happen on a BBC a few years back, took a while to show up so went undetected for some time.
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  6. #6
    Matt167's Avatar
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    Check with theamcforum, but I'm fairly certin that the V8's from AMC in those years were hardened seats from the factory. Even if they arn't, the limited use of a car like that, won't really hurt anything.. I do know they are high nickle content
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  7. #7
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    I was just asking & it good to learn something new.....joe
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