When you say they need adjusting, so you mean a 0.20 gauge was a loose fit?

Exhaust valve clearance is 0.16 - 0.20, which means setting it to 0.20 would be within range, but obviously at the wide end, but fine. 0.21-0.22 would be a bit loose, engine maybe noisier? No damage will be done, as a little loose is better than too tight. Exhaust valves are the ones that tend to close up over time and cause trouble (stop lifting fully resulting in burnt valves).

If you've only got a 0.20 gauge then set them to that.

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