UNIMOG Colorado
Rocky Mountain Moggers

Unimog Valve adjustment procedure

Some notes on adjusting valves on the M180 engine in the 404S.

Ron Miller

(Ft. Collins with inputs from Seattle and elsewhere)


Background: Mechanical valve lifters require a certain amount of clearance to be set between the cam when the valve is closed and the rocker or follower. This clearance is to assure that the valve can fully seat in the closed position under all temperature conditions of operation.

Vehicles with hydraulic valve lifters use a closed volume of oil to take up the space. This is nice and quiet and adjustment isn't as critical. In this engine, excess opening will create noise while too little clearance could lead to valve burning.

An exhaust valve that cannot close completely will burn fairly quickly. Therefore it is slightly preferable to have a little too much clearance rather than too little. But too much clearance can hammer the valve seat rather badly, especially at high RPM so getting the right clearance is desirable.

The clearance needs to be checked in the same way every time. Conditions best utilized are:

1. Engine cold. Not recently run. (Clearances change with temperature as you'll see in your manual for HOT/COLD figures.)

2. Good, nominal feeler guages - not bent or nicked on the edges nor rusty.

3. Proper feel for the amount of drag the feeler guage shows. "light" drag is appropriate. Heavy drag implies that the clearance is less than the guage and should be opened.

4. Parts being checked for clearance aren't excessively worn. In the case of the M180 engine, a worn rocker might have a groove deep enough that the guage metal can span the groove and give the wrong indication of clearance.

5. Some engines are adjusted while running. This is not the case with M180. If you try it, you'll be wearing a LOT of oil.

Tools: 14 mm crow's foot wrench with extensions and simple handle. This is for moving the adjusters. (Ratchet handle would be a nuisance)

13 mm socket or wrench to remove the valve cover bolts.

appropriate spark plug socket to remove spark plugs (13/16" deepwell socket for military plugs)

.1mm and .2mm feeler guage (COLD ENGINE CLEARANCE)

paper and pencil to record which valves have been done

Whatever tools required to remove distributor cap (mine is unshielded so I just need a screwdriver to pop the retaining clips off)

Whatever tools to disconnect the coil from the distributor (primary wire)

Whatever tools to disconnect the crankcase vent hose. (probably screwdriver for the clamps)

Process: Park and block the vehicle in neutral.

If there is slope, park facing DOWNHILL. This lets oil on the cylinder head drain back to the crankcase thru the timing chain opening which is at the front. There is no drain at the back so facing uphill would release trapped oil all over everywhere when you lift the cover. We leave the gasket in place on the head to provide a little dam effect to the residual oil.

Remove engine covers from cab.

Remove the valve cover clearance plate from the bottom edge of the dashboard, below the coolant tank. This makes more room to remove the valve cover.

Remove spark plug wires and distributor cap. (do as whole assembly be sure to mark which wire goes to which plug)

Remove distributor rotor (the plastic thing under the cap, to protect it from damage from the valve cover)

Note- some people might remove the upper half of the distributor assuming that it only fits on the shaft one way. That could be true. I didn't do it that way. Since you'll be turning the engine over, if the assumption is wrong, you might have difficulty getting the distributor oriented correctly at reinstallation.

Disconnect the primary wire from the coil to the distributor. (this removes power from the points so you neither fry the points nor generate high voltage at the coil. You can then leave the ignition on as needed. It is possible that an Army mog with separate ignition switch from starter wouldn't need this step.)

Remove spark plugs.

Remove valve cover hold down bolts.

Disconnect and set aside breather pipe.

Clean the valve cover gasket and cover sides very well. This dirt could get into the valve train if not removed before opening the engine.

Disconnect the electrical system ground with the battery key. (keeps you from touching live terminals with the cover during wrestling match)

Lift the valve cover from the gasket starting in the cab. Get the cover to the position of resting on the gasket.

Commence wrestling the cover out of the engine compartment by lifting the rear, shoving it forward so the rear bottom edge of the cover rests on the rear camshaft bearing housing. From outside front wrestle the cover further out.

I found that to clear the cam bearing towers the cover wants to be oriented normally up and down but to clear the brackets for the cover hold down bolts it works better to tip it toward the driver's side.

Be VERY CAREFUL with the cover in the vicinity of the distributor rotor and the timing chain plastic guide which is just forward of the distributor. This guide will wipe dirt off the cover and into the crankcase. Excess pressure could also break this plastic guide with pieces going into the crankcase and forcing replacement of the guide itself.

It may be that you'll have to loosen the coolant tank hold down bolts in order to let the coolant tank be moved upward for clearance. I did it without this step.)

If you ever get the cover out, the rest of the procedure is:

Close the battery ground switch to enable power for the starter.

Use the starter to roll the engine over so that a pair of cam lobes are pointing vertically with the heel of the cam presented to its rocker. The lobes will come up in pairs of one intake and one exhaust valve (different cylinder) at a time ready to check/set.

NOTE- You could also use a large wrench to roll the engine over by turning the camshaft sprocket bolt.

Intake valves are on the manifold side of the head. Exhaust valves are on the opposite side (spark plug) of the head. If you get confused, look at where the manifold runners connect.

Use your fingers to press down hard on one of the rockers to be checked. This is to squeeze the oil out from under the valve end and the adjuster end. (Otherwise the rocker wants to float on the trapped oil film and makes repeatability difficult.)

Select the feeler guage for the type of valve we're checking (.1mm for intake, .2mm for exhaust) BE SURE TO GET THE RIGHT ONE EACH AND EVERY TIME!


Using your fingers of one hand, manipulate the rocker carefully while inserting the feeler guage between rocker and cam heel with the other hand. Carefully move the rocker so that you feel the position of maximum clearance as the guage is pulled thru. What we're trying to do here is to find the position where the clearance should be measured. Since the rockers are somewhat free to tilt a bit, just sliding the guage thru won't tell the story. You must hold the rocker and insert the guage then fiddle with the rocker to see what the max clearance is.

Proper clearance is "light drag" as the feeler slides thru. We're looking for light metal-to-metal contact but not difficulty in pulling the guage thru. Note that motor oil will have a drag of its own that is NOT the right clearance. This "feel" is very important.

To increase the clearance, use the crow's foot wrench to turn the ball adjuster clockwise just a bit. CCW to decrease. I find that just cracking it loose a bit is enough. Turning the adjuster 1 flat is a big adjustment.

Check and adjust and re-check until you get it exactly right. Then check it again.

Record that you adjusted it on a piece of paper. (For example: #3x, #2I etc)

Do the other cam lobe.

Use the starter to roll the engine to position another pair of cam lobes. You don't need to do much more than bump it since the engine rolls freely with the plugs removed.

Repeat until they are all done.

Roll the engine over freely with the starter for a few turns. Admire the oil distribution spray bar's work. Note how the rearmost cam lobes don't get much oil at cranking speed while the forward lobes are well covered. (this should explain why too low an idle speed or too high an oil viscosity is a bad thing)

Check the adjustments again. All the way thru.

Once you think you have it, put it all back together.

Run the engine for proof and hope no extremely loudly ticking valves sound off. Otherwise you get to do it again.

Bear in mind that some valve noise is normal. That's the sound of mechanical clearance.

Thanks to Ron Miller for putting this together!

Added notes from Mark A. Hartwell

To digress a bit, I would offer a two things for your fine valve adjusting article:

1) Removing the valve cover is much easier if you initially leave the rubber gasket behind; it adds that little amount of clearance where it is quit easy to remove the cover.

2) Rather than cranking the engine by using the starter, it is much easier to jack up the rear axle and rotate the tire (transmission is in 6th gear, emergency brake off, tires on the ground blocked).

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