Gas talk for ‘72 J4000

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Niko617
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Joined: Wed Oct 27, 2021 6:35 pm

Gas talk for ‘72 J4000

Post by Niko617 »

Been getting a lot of flak about the type of gas to run in my old truck project. Also head about replacing some valve seats to allow for the running of unleaded gas, over adding in a lead additive. Does anyone know how to find out if an old engine like this is capable of running on unleaded? Do I need to replace the valve seats in order to do so? And how hard would that be to convert an engine to be able to run on unleaded gas?
-Niko

rocklaurence
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Re: Gas talk for ‘72 J4000

Post by rocklaurence »

The Lead in the past added octane to the fuel and lubricated the exhaust valves. If your heads dont have the hardened exhaust seats, you will sooner-than later need to have them added [when you need a valve job due to the failed seats]. IMO, I wouldnt consider a Lead additive because its too much trouble to purchase and add to every fill-up.

will e
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Re: Gas talk for ‘72 J4000

Post by will e »

I would be a bit surprised if the heads had never been rebuilt. How many miles are on the engine?
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Herk
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Re: Gas talk for ‘72 J4000

Post by Herk »

Most American made engines had hardened valve seats starting in 71 or 72. Not 100% sure on the AMC engines. I've been running unleaded since the late 80's without a problem in a lot of older vehicles. If you ever have an issue down the road you can either have your heads rebuilt with hardened seat inserts or just rebuild later cores.
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