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The dreaded 3.7

R

Rob f

New member
I was given a 1987 Wellcraft 192 Classic with the dreaded 3.7.I checked oil and coolant before I ran the engine.I ran it on muffs for about an hr before putting the boat in the water.Put it in the water and found that the direct drive alternator was no good.Converted it to an external alternator so we are good on that.I ran it a few times while diagnosing the alternator issue.Took the boat out on its maiden voyage and it ran like a top.The next day my son my wife a friend of my son and myself loaded up and shoved off.Took an hr and a half ride,I kept a close eye on the temperature and the oil pressure . We stopped at an island for about an hr.The boat fired right up and we were heading home.After 10 minutes or so we heard a rapping coming from under the hood I happened to be looking at the oil pressure when the noise started and the oil pressure never moved from where it had been(around 52-55 lbs)and the temp was around 150 degrees.Shut it down checked the oil all good,started it and the noise is steady.Ran it back to the marina at about 1/2 throttle and besides the noise it is running perfectly no change in oil pressure or temperature.2 hrs this boat ran and the noise didnt change didnt get louder and didnt get quieter.Tied it up and left,didnt want to try working on it at 7PM on a Sunday.Went down a few days later and checked the oil again,and again right at the full line.Started it up and let it warm up as Im looking around pulling the valve cover and unplugging plug wires.Didnt find any problems under the valve cover and the noise didnt get any louder when I took the valve cover off.But when I unplug #4 the noise goes away,doesnt get quieter it GOES AWAY.I drained the oil and ran it through a coffee filter and not a spec of metal and I put 5.5 qts of 10W40 in it with a new filter and the noise hasnt changed.Im an ASE auto mechanic and have heard MANY knocking rods and this doesnt sound like a rod especially since its been run for hrs and hts with this noise and the noise hasnt changed.Any ideas?
 
Broken wrist pin or cracked piston where wrist pin goes through? just a guess, sounds like time to pull engine and have a better look.
 
I actually just did that,put 20w50 and a quart of Lucas and the noise didnt change at all and not a spec in this oil either.I have one more.thing I want to try.I have heard about carbon buildup sounding like bad bearings so Im going to dribble some water in the carb.I figure what the heck,it cant hurt.It did have some older marine gas in it.The boat was.sitting since summer 2015.Thats how I got it for nothing.I work on forklifts,I was working on a marine forklift and talking to the owner about wanting a boat.He had 3 he wanted to get out 1 had a 305 but the engine and stern were underwater for awhile and the transom had some soft spots another had a 4.3 but was left uncovered and the interior was shot.This one was in great shape inside and out and was told bybthe marina owner that it ran good and was winterized by the marina.He pulled it out of.the rack and put it on a trailer he let me borrow and told me to make it go away,he handed over a signed title and said the old man who used to own it had some health issues and couldnt use it and didnt want to pay the storage fees so he signed the title but didnt put a buyers name on it.I asked if the marina owner wanted any money and he said he cant thank me enough for making it go away.
 
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