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"
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