Yup

that all makes sense

B

It's called wear.

Cam lobes, followers and rocker arms wear, causing slack. When you're considering a few thou to go out of tolerance, a little wear can be significant.

If the oil you are using does not have enough zinc (ZDDP) cam lobes and solid lifters wear faster.

On the flip side, valves and valve seats wear. The springs continue to pull them up tight, resulting in loss of gap.

If you are using unleaded fuel without the "lead" additive, and your engine has not have hardened valve seats installed, the seats gradually erode and you get what's called 'valve recession'.

In any case. valve clearances periodically need to be readjusted. Modern cars have things like overhead cams and hydraulic lifters that have fewer surfaces to wear and automatically correct for the changes.

hello everyone

could someone explain why valve clearances go out of adjustment

i have a 1963 mini 850 restored but unmodified, set valve clearances when restored, done 16000 miles since then.   left car in garage for a few years then started driving again a few weeks ago and noticed a tapping sound.  went to check under the rocker cover and discovered that some valves had almost no clearance while others had a bigger clearance than standard.   what i cant understand is why something that is hard metal on metal that is tightly bolted down can "wear" to this extent that an adjustment is required. 

can anyone enlighten me

thanks

barry

new zealand