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I have a 1993 C1500 with 4.3L that has a motor (also a 4.3L) from another truck installed. The truck is originally a 1993, but I'm not exactly sure what year the "new" motor is - it was pulled from a truck in a junkyard. Possibly a 1992. Anyways, how can I know what to gap the plugs to?

On the web, I've seen .06, 0.45, and even .035 as recommended. AutoZone's database showed 0.35 as the recommended gap, which is what the plugs (NGK) are pre-gap'ed to.

Is there a vin number somewhere on the block that can tell me?

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Don't worry about the motor, worry about the ignition system. I take it you must be using an HEI distributor in the vehicle to warrant a .060" gap. Be aware that GM reduced this to .045" gap due to longevity issues. If it's not an HEI, I believe the .035" is correct. If you are running the same ignition you were using before the swap, gap it as you had it before.

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