80 series

There are no tappets as such, they have a cam running directly on a upturned bucket with a shim captured at the top for adjustment purposes.
The valve clearances get less with use and that will begin to affect the sequencing of the gas flows in and out of the engine if not as they should be. ie, less power and economy.

The adjustment is done by shim thickness and requires them to be measured and appropriate substitution and or replacing with the correct shim thickness for each valve.

Bad cases cause the valves to be held open and if it happens especially on an exhaust valve, the sonic speed of very hot gas will burn the valve faces.

Often Toyota Technician serviced vehicles may reach 200,000km and have never been checked because everyone trusts everyone before them to have done it. Naughty naughty.
Quite a few on another forum with 80 series have had it happen to them.

Best done by a reputable mechanic/ 4wd repair shops, will often do it right.Check of course.

as mentioned above modern overhead cam diesel motors do not have tappets.

All the diesel performance articles will tell you there can be bing improvements from adjusting the valve clearances.....on the other hand many modern diesel motors go their entire lives without any adjustment...and by entire life I mean 300 000 pluss.

cheers

Strictly speaking any engine that uses the particular design of in head or side valve mechanism as being discussed here does have "tappets". What the overhead camshaft style of engine has dispensed with are the pushrods and rocker arms. As there is not a hydraulic or other type of automatic valve lash or clearance adjuster the necessity to periodically manually adjust the clearance between the camshaft and the end of the valve exists.
For these particular engines I would have the clearances checked and if necessary adjusted every 100,000 k to maintain optimal performance and avoid the possibility of burnt exhaust valves. As Ross has explained the adjustment involves the selection of the appropriate thickness shims.
Not difficult to do for someone with ability to read and understand a workshop procedure.

Cheers
Pop

G'day Mal,
I think the manual recommends 60,000km.
It is easy to check the clearances of the bucket tappet using a feeler gauge.
Only 2 positions of the engine are required.
Rotate c/shaft until notch on pulley lines up with pointer on timing cover. No1 firing.
Clearances Inlet – 0.15 - 0.25mm
Exhaust - 0.35 – 0.45mm
Then check with a feeler gauge
No1 - Exh & Inlet - will both be loose
No2 Exh
No3 Inl
No4 Exh
No5 Inl
Rotate 360° and line up the notch again. - No6 firing
No6 - Exh & Inlet will both be loose, and check the other tappet of the previously checked cylinders.
If you decide to go this way, be aware there are drain holes through the head and these should be covered to avoid dropping anything through.
You will at least know which - if any needs adjustment. I have found I only needed 2 or 3 tappets removed and a very small amount surface ground.

Good Luck,

Bill