Starter motor issues.... Mercruiser 3.0l

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Jonny20212021

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Hi!
Ok, so coming back after winter I started the boat and she fired up no problem, then wouldn't start, I kept trying and believe I burnt the starter motor out. The original issue I believe is down to the spark plugs.
Anyway, purchased a NEW replacement starter motor and it cranks very slow not enough to fire up (or at least test to see if my original diagnosis of spark plugs was right) it cranks as if it can't be bothered or something is holding it back.
I've done the following...
Cleaned all points.
Tried a brand new battery (from a 4*4) the existing one showed as weak under load test.
Voltage drop test good
Resistance test good
Jumped the starter with jump leads
Made its own dedicated earth with a jumper cable
12.6v to the starter
Taken the aux belt off disconnecting the power steering and alternator.

Taken the sparks out, can easily spin by hand but still getting the same result when testing the starter.
Is there anything else that I may of missed before I try sending the starter back.
One thing to note is the starter was smoking when I first installed it. Then smoked again tonight when I connected 2x batteries in parallel

It was turning over fine on the old starter motor (untill I burnt it out)

This is the starter motor I purchased New Marine Starter Motor for 4 Cylinder 2.5, 3.0L with 12 3/4" Flywheel
For a 1996 Mercruiser 3.0l serial number F794151 they look exactly the same and says it matches so hopefully I've brought the right one.

ANY help or suggestions are greatly recieved
Thank you!
 
I have a high-torque geared starter on my car. Was the previous one you had a geared starter? They do turn over more slowly. The theory is they don't steal all the juice from the ignition.
 
Caraway said:
I have a high-torque geared starter on my car. Was the previous one you had a geared starter? They do turn over more slowly. The theory is they don't steal all the juice from the ignition.
Click to expand...
I'm not sure to be honest, all I know is the two look exactly the same from the outside. This will turn over slowly may one or two revolutions then start clicking like the battery is dead, although still reads about 12.3v
 
Sounds like a bad starter, if it was a recon unit I would seriously question it as often many reconditioned units are done to a price and not to a quality, basically a race to the bottom for sales figures and profits.
 
I'm going to throw one out there as a punt. I had a merc 3.0GL that had a slow starting motor and one day it just jammed solid. The bolts on them are liable to bend and shear as mine had and foul the ring gear if the guru's on i-boat are to be believed. What I am driving at is check the starter gear is mating correctly with the ring gear. If bolts can shear there must be some sort of lateral pressure that may be trying to twist it off and causing binding.
 
BruceK said:
I'm going to throw one out there as a punt. I had a merc 3.0GL that had a slow starting motor and one day it just jammed solid. The bolts on them are liable to bend and shear as mine had and foul the ring gear if the guru's on i-boat are to be believed. What I am driving at is check the starter gear is mating correctly with the ring gear. If bolts can shear there must be some sort of lateral pressure that may be trying to twist it off and causing binding.
Click to expand...

Certainly possible Bruce, seen it on industrial engines many times and sometimes cheaper replacement starters with aluminium flanges can also distort while under load and cause the same issues.
 
I had the same engine and had the original starter rebuilt locally. Think it cost me 60 quid although that was about 10 years ago. Ran fine for another 2 years until I sold the boat.

D
 
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