The sound is probably louder toward the front of the engine because the 240 and 300 engine's #1 piston to cylinder wall clearance is greater than the other cylinders (.0011-.0019 in. for #1 and .0007-.0015 in for the other cylinders). Add in the noise from the timing chain and components connected to the chain and you should hear more sound toward the front. The turbo 300D's engine, however, does not have the difference in piston to cylinder wall clearance as the 240 and 300D non-turbo.

A worn piston like patterson had would not make as much noise when the engine is at operating temp. versus cold because the aluminum piston expands more than the steel cylinder liner does taking up some of the excess clearance and when running the noise would be greater when a load is put on the engine versus coasting when little load is put on the piston from combustion.

Patterson's problem shows what I found out a long time ago - you can do all the diagnosing you want, but in most cases the only way to know what the problem really is is to do a TDI (tear down and inspection). Just like what medical doctors often do - ever hear of the medical procedure called exploratory surgery to find the problem? For example, my old engine had low compression in three cylinders because of a blown head gasket, the other two cylinders had 325 compression (#1) and #2 had 410 compression. After a TDI , I found that #2 had no cross hatch left on the cylinder wall and the cylinder wall was as smooth as glass, but had excess piston to cylinder wall clearance despite 410 psi compression.

If you search the old posts you will find some by Wm. Lewallen who repaired M-B diesels for over 20 years as a professional. He makes reference to repairing just the problem if everything else was OK - in other words, if one cylinder was bad he would fix that cylinder and go (like a new piston and/or a new liner bored to correct clearance, etc.). My own vast experience is similar, fix what's broke and leave what's not broke alone.

Good Luck!
Tom

__________________
America: Land of the Free!

1977 300D: 300,000+ miles

American Honda: Factory Trained Technician & Honor Grad.
Formerly:
Shop Foreman;
Technical Advisor to Am. Honda;
Supervisor of Maintenance largest tree care co. in US for offices in Tex.