Unimog 404 Cylinder Head Identification and Notes

Getting a lot of questions in regards to the 2 types of 404 M180 Cylinder Head found on the Unimog.  Pictures say 1000 Words so here are a few that may help you.


The Cylinder head on the right is the most "common" M180 cylinder head found on the Unimog 404.

#1 - Examine the Valve Train.  The Old style has a MUCH more complex Valve Train with additional rocker arm pivot shafts.


Old Style Above

New Style Below



#2 - Old Style has a hollow cam with holes drilled for oiling.  New Style has a solid cam and a drip oiler tube running across the tops of the cam towers.  Old style cam is much more common to fail as it is hollow, where as the new style is solid.



#3 - Valve Covers - This can be used as an Indication, but is NOT the complete story.  The Old style Valve Cover will ONLY fit on an Old Style Head.  However, the New Style of Valve Cover can fit on Either the Old Style of Head, or the New Style of Head.  Bottom Line if you have an old style cover, you have an old style head.  However, the reverse is not true.  You can still have a New Style Cover, on an old style Head.


Picture above:  Valve Cover on the Left is an Old Style Valve Cover, on an Old Style Cylinder Head.  Valve Cover on the Right is a New style cover on a new style head.

Beware: Below is a New Style Cover Mounted on an Old Style head Left problems.


Devils in the Details: Below is the Old Style Valve Cover on a New Style Head......DOES NOT FIT!



#3 - Short Reach Versus Long Reach Spark Plugs.  This is VERY IMPORTANT.  You MUST use the right length spark plug for your cylinder head.  The old style cylinder head uses a "Short Reach" spark plug.  The New style head uses the much more common standard length spark plug.  These are NOT interchangeable.


Above is a standard spark plug "long reach" in a new style head.  All is good.

Below is a standard spark plug in a Old style head.  "Short Reach" head.  This is VERY BAD.  The spark plug thread will get damaged in the chamber and when removed will destroy the threads of the cylinder head.  EI's Ignition conversion kits come standard with the Long Reach plugs for the much more common standard cylinder head.  If you have the old style head contact us and we will supply the correct plug for that "Short Reach" head.



A few other notes about the cylinder heads.  Pictured below is THE most common cylinder head failure point on these cylinder heads.  This water jacket has the tendency to rot out and it is very close to the head gasket seal.  When inspecting a head carefully inspect the water hold between cylinders.  The one pictured below is in excellent condition.




Cylinder Head Damage from storage.....


Take a look at the chamber on this Unimog engine that was not run for 8 years.  The above cylinder had an exhaust valve open.

The below cylinder had both valves closed.  (Compression Stroke)  Keep in mind, both of these pictures are from the same head, only difference being whether a valve was open on not.



Was this article helpful?
1 out of 1 found this helpful
Have more questions? Submit a request


Please sign in to leave a comment.