Use a high-zinc content oil like 20W-50 Valvoline VR-1 (by far, the best) or Mobile 1 Racing oil.
In 1994 the industry removed zinc from motor oils because it had a negative effect on catalytic converters. While this benefited newer engines, it dealt a death blow to older engines with flat tappet camshafts and, as a result, worn out camshafts became the norm. The lubricating properties of zinc and phosphorous are essential for maintaining the longevity of older internal combustion engines.
Zinc can damage catalytic converters. For that reason, the EPA has mandated that zinc levels be reduced in today's oils. Most, if not all, modern automotive and truck engines are using overhead camshafts or roller lifters. These motors don't require a lot of zinc because the loads on the cams and lifters aren't as great as those in flat lifter motors
Avoid the problem by choosing the right oil-- that has a zinc content of at least .11%. If you're running zero zinc content oil in an old engine
Bottom Line:
It the vehicle doesn’t have a catalytic converter, use a high zinc-content motor oil.
2014 engine oil zinc content chart sorted by viscosity, zinc content, brand name
