1994 mitsubishi mighty max valve tapping noise(occationally) when warm or cold. i took the valve cover off to try to adjust the rocker arms but it is non adjustable, what could it be? Bad oil pump?

question edited for full year make model.
Question moved to the correct sub category.

Sound like the clutch is over adjusted and the the clutch isn't making contact. Or something went back wrong, or wrong part.

https://www.google.com/search?q=1994+mighty+max+4x4+clutch+adjustment

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The 24-valve overhead system is a "low-maintenance"
design. Routine adjustments are no longer
necessary, however, measurement should still take
place when trouble-shooting performance problems,
or upon completion of a repair that includes removal
and installation of the valve train components or
injectors.
(1) Disconnect battery negative cables.
(2) Remove cylinder head cover (Refer to 9 -
ENGINE/CYLINDER HEAD/CYLINDER HEAD
COVER(S) - REMOVAL).
(3) Using the crankshaft barring tool #7471-B,
rotate crankshaft to align damper TDC mark to
12:00 o'clock position.
(a) If both number one cylinder rocker levers are
loose, continue to next step.
(b) If both number one clylinder rocker levers
are not loose, rotate crankshaft 360 degrees.
(4) With the engine in this position, valve lash can
be measured at the following rocker arms: INTAKE
1-2-4 / EXHAUST 1-3-5. Measure the valve lash by
inserting a feeler gauge between the rocker arm
socket and crosshead (Fig. 32). Refer to VALVE
LASH LIMIT CHART for the correct specifications. If
the measurement falls within the limits, adjustment/
resetting is not necessary. If measurement
finds the lash outside of the limits, adjustment/resetting
is required.
VALVE LASH LIMIT CHART
0.152 mm ( 0.006 in.)
MIN.
0.381 mm (0.015 in.)
MIN.
0.381 mm (0.015 in.)
MAX.
0.762 mm (0.030 in.)
MAX.
note:
If measured valve lash falls within these
specifications, no adjustment/reset is necessary.
Engine operation within these ranges has no adverse
affect on performance, emissions, fuel economy or
level of engine noise.
(5) If adjustment/resetting is required, loosen the
lock nut on rocker arms and turn the adjusting screw
until the desired lash is obtained:
² INTAKE 0.254 mm (0.010 in.)
² EXHAUST 0.508 mm (0.020 in.) Tighten the
lock nut to 24 Nm (18 ft. lbs.) and re-check the valve
lash.
(6) Using the crankshaft barring tool, rotate the
crankshaft one revolution (360°) to align the
damper TDC mark to the 12 o'clock position.
(7) With the engine in this position, valve lash can
be measured at the remaining rocker arms: INTAKE
3-5-6 / EXHAUST 2-4-6. Use the same method as
above for determining whether adjustment is necessary,
and adjust those that are found to be outside of
the limits.
(8) Install the cylinder head cover (Refer to 9 -
ENGINE/CYLINDER HEAD/CYLINDER HEAD
COVER(S) - INSTALLATION).
(9) Connect the battery negative cables.

That is a ridiculously high price to replace lifters on a 4 or 6 cylinder engine. On the Mitsubishi 4 cylinder motor, the only thing that is needed to do is remove the valve cover and remove the rocker rod. (2 rods which hold the rocker assembly.) Next is remove the lifters from the bottoms of the rockers and pop in the new ones. Be sure to soak the new lifters in oil for 24-48hrs prior to install so they are pre-filled before install. Replace the rocker assembly and torque down to specs. replace valve cover and then start the vehicle. Check that there is no loud tapping noise and do not race the engine until the lifters have pumped up with engine oil. You should replace oil and filter for this engine work as well.

Not familiar with this specific engine, but I think you have adjustable rocker arms to adjust valve lash. May just need adjustment, but inspection will show if something is damaged.

Valve Adjustment

Print
The 4.2L and 5.3L engines do not require a periodic valve lash adjustment.
The 4.3L engines are equipped with screw-in rocker arm studs with positive stop shoulders. Because the shoulders that allow the rocker arms to be tightened into proper position, no adjustments are necessary or possible. If a valvetrain problem is suspected, check that the rocker arm nuts are tightened to 18 ft. lbs. (24 Nm). When valve lash falls out of specification (valve tap is heard), replace the rocker arm, pushrod and hydraulic lifter on the offending cylinder.

your choke adjustment or cold start are not working to bring it to high idle cold start.
mike

Could try running additive like Wynns Engine Tune-Up to free up stuck hyd. lifter. Another old remedy is to run ATF 50/50 with 5W30 motor oil.

well the lifter is a problem, your better safe than sorry cause if you don't tear it back apart and check the lifters then all that work you did is gonna be history.and you will be doing it again, i'm sure you know this. do this before you try to solve the ticking.

SOUNDS LIKE YOU HAVE STICKY LASH ADJUSTER(LIFTER)..MANY MILES ON IT?HAVE YOU BEEN GOOD TO CHANGE OIL AND FILTER?TRY CHANGING THE OIL AND FILTER AND ADDING AN OIL SUPPLEMENT ..IF THIS DOESN'T WORK,YOU WILL HAVE TO ISOLATE WHICH BANK OF ENGINE NOISE IS COMING FROM,REMOVE VALVE COVER AND YOU CAN TO SEE WHICH ONE(S) ARE MAKING NOISE..PUSH DOWN ON EACH ROCKER ARM..A BAD ONE WILL BE SOFT..A GOOD ONE WILL BE HARD..NO LASH..TO REPLACE..YOU REMOVE ROCKER SHAFT BOLTS AND ROCKER SHAFTS..YOU CAN PURCHASE ONLY THE ONE(S) YOU NEED..BE CAREFUL WHEN YOU REMOVE ROCKER SHAFTS..THE LIFTERS CAN FALL OUT..GET A STICKY GREASE TO HOLD THEM IN ROCKER ARMS DURING REASSEMBLY..I HOPE THIS HELPS

ENGINE CLICKING NOISES
A clicking or tapping noise that gets louder when you rev the engine is probably "tappet" or upper valvetrain noise caused by one of several things: low oil pressure, excessive valve lash, or worn or damaged parts.
First, check the engine dipstick to see if the oil level is low. If low, add oil to bring it back up to the full mark. Is the engine still noisy? Check your oil pressure. A low gauge reading (or oil warning light) would indicate a serious internal engine problem that is preventing normal oil pressure from reaching the upper valvetrain components. The cause might be a worn or damaged oil pump, a clogged oil pump pickup screen or a plugged up oil filter. Using too thick a viscosity of motor oil during cold weather can also slow down the flow of oil to the upper valvetrain, causing noise and wear.
COLLAPSED LIFTER NOISE
Worn, leaky or dirty lifters can also cause valvetrain noise. If oil delivery is restricted to the lifters (plugged oil galley or low oil pressure), the lifters won't "pump up" to take up the normal slack in the valvetrain. A "collapsed" lifter will then allow excessive valve lash and noise.
VALVE LASH NOISE
If you can rule out lubrication-related problems as a cause, the next step would be to remove the valve cover(s) and check valve lash. On older import engines, mechanical lifters require periodic valve lash adjustments (typically every 30,000 miles). Too much space between the tips of the rocker arms and valve stems can make the valvetrain noisy -- and possibly cause accelerated wear of both parts.
To measure (and adjust) valve lash, you need a feeler gauge. The gauge is slid between the tip of the valve stem and rocker arm (or the cam follower or the cam itself on overhead cam engines) when the piston is at top dead center (valve fully closed). Refer to a manual for the specified lash and adjustment procedure. Also, note whether the lash spec is for a hot or cold engine (this makes a big difference!).
On engines with hydraulic lifters, oil pressure pumps up the lifters when the engine is running to maintain zero lash in the valvetrain. This results in quiet operation. So if the rocker arms are clattering, it tells you something is amiss (bad lifter or worn or damaged parts) or the rocker arms need adjusting.

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