if you are determined to find this, the oil pressure test port on the 112 is under the filter cap in the filter housing. hook a mechanical guage to it and watch it when starting while duplicating the knock. if the knock disapears when oil pressure reaches 20 psi or so, there you go, simple pressure build and nothing can be done for it. if you read the cleaance specs on the new v-6 and 8 they are kinda loose out of the box and it is no suprise that they clank a bit on start.

i've heard this noise in just about every 112 i ever worked on including the silicone infested monster that got a crate motor at 30k. the crate motor clanked a bit too. depending on the programming of ME for air injection delay, you might not hear it over the air pump. this is why some aren't heard and others are in my opinion.

if you listen closely to most modern engine designs, they make noise. thinwall casting, lightweight cranks, low rotating mass, self adjusting ign timing and fuel trims are mostly the culprits. if you look at the 112 block design, its shaped quite nicely for harmonic resonance. you also can send off a oil sample and a old filter for particulate analysis to see if the block or bearing are "shedding"



Joe

__________________
Project Smoker, '87 603 powered wagon
Hauler, 96 CTD can you say torque?
Toy 73 Cougar xr7 convertible
Acme Automotive Inc.
Raleigh NC
919-881-0364

Joe,

Thank you for the reply and for reading my post carefully. I have printed out your suggestion and will take it up with my dealer. I'm sure they will humor me and do the test. So far it's just been "we didn't hear anything." Better than "They all do that" I suppose.

Roger E.

Just wondering if Roger E. ever resolved his "piston slap" sound. My 02 C320 exhibits the same behavior, however, it only does it when warm. Cold startups are quiet. If you look at what a piston slap is, this doesn't quite add up. Usually the piston will "slap" when the "skirt" of the piston is at its smallest diameter in relation to the cylinder dia. On cars with iron blocks, this usually meant slap occurred on cold start. With aluminum cylinders, this supposition may go out the window. I have another WAG (Wild Ass Guess). Could it have to do with a timing advance by the computer at startup where when the engine is cold, and there is extra fuel it's OK, and when the engine is hot you are hearing more of a "knock" or detonation? Just a guess, and it doesn't jive with the folks whose engine does it hot or cold...

Thanks,
Brian

I've given up on this. I extended the factory warranty to 100K last year so the thing can blow to pieces for all I care. It's still making the knock X4 on most starts, hot or cold.

This is definitely not piston slap nor lifters so lets close that one. It's oil pressure related as I have said before and it's only on startup, never after. Of course, if the V6's chain tensioner is hydraulic, this might be it.

But, I had the opportunity to run the car flat out at it's governed top speed for a few miles last summer and it survived so it may make this noise forever.

Other than that (and the Easy Entry feature which is never going to work reliably) it's running and looking good. However, I must say that after driving a friend's 2003 E500, the old C320 seems pretty crude.

Gawd, wotta car!

Roger Ellingson/Seattle

Well, I'm going to have the dealer listen to it and log it so at least there is a record of it. I'm sure they will tell me there is nothing wrong though... I have come to NOT have much faith in dealers over the years. I'm not saying they are all bad - just the ones I've had the misfortune to deal with. That's why my hands are always bleeding and knuckles are raw :-)

I've kinda concluded that the easy entry feature works, but it's not perfect. Seats and mirrors come to the correct position about 50% of the time, however, they are rarely off by much.

Brian