Tappets

Depends on vehicle, my Navara is every 20,000km, should be listed in handbook servicing intervals.

I do my own, but if I had to put it in, I would be expecting it done in an hours labour with no parts except possibly a rocker cover gasket which is bout $20 tops.

Worth doing as recommended by manufacturer.

Rgds

Ron

Hi Stephen.

Tappet or more correctly valve clearances can increase and cause a slight noise.
However due to valve seat socketing and stem stretch the clearance is more likely to decrease.
This causes the valve to "ride" or stay slightly open in a severe case.
The ultimate penalty of this is a burned out valve\seat.
This usually causes a miss at idle as a first sign.
Your mechanic will willingly take your hard earned to set them for you but is money well spent.
It used to be an essential part of any major service but many vehicles now have hydraulic valve lifters\adjusters so it is gradually becoming a thing of the past.

p.s. use a good mechanic.

I hope this helps you.

Eddy