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Old Sep 25th, 2021, 21:40   #3
142 Guy
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Location: Saskatchewan, Canada
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Not exactly sure what noise you are referring to since noise is a normal part of a B20. I do on occasion hear what appears to be a knocking. That could be consistent with a broken tooth (or teeth) on the cam gear. If the hub fails completely on the cam gear that usually creates a lot of noise leading to no noise at all. The other cam related problem might be wear of the spacer on the cam gear which allows the cam gear and camshaft to move in and out creating a rhythmic tapping / knocking. Put you stethoscope right on the timing gear cover to try to determine if that is where the noise is originating from.

My only other advice would be is to set the valve lash in an attempt to reduce the normal B20 racket. This may allow you to discern the source of the particular noise you are concerned about. While you have the valve cover off setting the lash you can check the lift on each valve. Low lift on any of the valves would indicate a wear problem on the lifter / cam lobe for that valve - a problem that cams and lifters on the B20 are notorious for unless the 1974 already had the later lifter design. The noise could also be caused by excessive clearance on a particular valve.

If the engine was moving around a lot I would suggest looking at the support bracket for the exhaust system that attaches to the transmission. The bracket frequently fractures leading to a banging noise when the engine moves during acceleration / de acceleration. It typically does not generate a rhythmic tapping during idle unless the engine is rocking a lot at idle.
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