Truck Repair: oil leak

Question
I have a 1984 ntc 240 855 series engine with excess oil leaking from the tacometer drive housing and excessive black smoking any ideas

Answer
Not familiar with those engines but if its similar to the n-14 it has a weep hole in the cover and if that cover gets cracked the oil leaks out that weep hole. What i've done with that is clean it up real good and silicone the hole shut. As for the black smoke sounds like you've possibly have a injector overfueling.