I found out why my 63 170 is backfiring only out of cylinder 3. I was not sticky valve or bad spring. No. The No. 3 exhaust push rod is not lifting. The rod is not bend. Is there a way to fix lifter w/o taking engine apart? This just starting happening after I did the valves about a month ago.

Are you sure the pushrod is in the lifter? It's pretty easy to miss one.

That said the only reason the lifter isn't raising is a flat camshaft lobe and that will require a cam replacement.

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If the 170 is with original style head the lifter can be picked up with magnetic tool. After lifter removal it is possible to take a look to cam which sounds like it is damaged.

"Theoretically" it is possible to replace a the cam without pulling out the engine. In practise no.

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1966 Dart. 170 cu.in. 200 rwhp.

Well, oof. Too bad I was wrong about a sluggish valve; that repair would involve less heavy lifting.

If the engine has enough miles on it to have wiped an entire lob off the camshaft, then there is surely going to be significant wear pretty much throughout the engine. Putting in one or two new parts here and there is not likely to give a lasting satisfactory result.

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