1985 Mercruiser 140 3.0L Problem

Robson921

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Nov 6, 2017
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I recently bought a 1985 Chris Craft Scorpion 186 project boat with 1985 Mercruiser 140. And here my problem starts. The engine turns really really slowly. I'm pretty sure the boat wasn't in the water for few years. I changed the oil checked plugs there was no water in the cylinders. When I removed the plugs it turns kinda faster but still not fast enough. So I went went ahead and tried to do the compression test with all plugs out thinking that it will be okay but still when I put tester in first cylinder it was cranking so slow and hard. So the test failed. I changed the old oil which was still clean to rotella t1 sae 30 and oil filter as well. Don't know if that's the starter or what. I used my chevy truck battery that has 350 engine. Please help me as I'm getting more confused, also the cables from positive and negative are getting so hot & starter solenoid too. I really appreciate your help guys. I didn't try to start it by key I disconnected the round connector because the cables to dash are mess. So I shorted pin 5 & 6 together then touching pin 7 to 6.šŸ˜”
 

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alldodge

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Turns over slow when plugs are in or if doing compression test. Without knowing more it sounds like the starter may need replaced, or battery cables need cleaning/replacement
 

sogood

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Yes to the above and poor or loose connections will also cause cables to get hot. Possibly pull the starter if needed and do a bench test. Eliminate one thing st a time.
 

Robson921

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Turns over slow when plugs are in or if doing compression test. Without knowing more it sounds like the starter may need replaced, or battery cables need cleaning/replacement

Yeah when plugs are in it makes that clunk clunk noise then it turns really slow. When take all plugs out it does turn faster the cables start to smoke..
 

Robson921

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Yes to the above and poor or loose connections will also cause cables to get hot. Possibly pull the starter if needed and do a bench test. Eliminate one thing st a time.


Yeah i have to do that don't know the history of that engine but I know for sure there is no water and it's not seized
 

Bondo

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, also the cables from positive and negative are getting so hot & starter solenoid too.

Ayuh,.... Have ya pulled the drive,..?? if not, do so, as it turns with the crankshaft,....

With electricity, Heat, equals resistance,....
Either yer cables, or their connections are corroded,....
 

Robson921

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Ayuh,.... Have ya pulled the drive,..?? if not, do so, as it turns with the crankshaft,....

With electricity, Heat, equals resistance,....
Either yer cables, or their connections are corroded,....


Yeah there must be some resistance somewhere don't know exactly why. You mean to take down the outdrive? Then engine should turn without problem? I was about to take it down today my problem is there is that locking nut can't take it offšŸ™ I have to leave just gimbal right?
 

Bondo

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my problem is there is that locking nut can't take it off

Ayuh,.... Beat a tight fittin' socket onto it, 'n turn it off,....

Ya might also pull the starter, 'n bench test it,....
 

porscheguy

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Jan 17, 2013
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441
Just curious, are you sure that?s a 186 scorpion and not a 168? I?m asking because I didn?t think the 186 would have used that engine. I had a 168 years ago.
 

hoowahfun

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Sep 1, 2016
Messages
186
Check all of your battery cables. I had a similar issue where mine started to smoke earlier this year on a recent boat purchase w/ a 130 HP Merc in it. I cleaned all the connections really well, but didn't check the cables themselves. Turned out I had a cable with a nick in it that was corroded and probably shorting out. Replaced the cables and the symptoms went away.
 
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