Mercruiser 7.4 Starter Grinding/Partial Engagement?

CLi87

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Maybe your battery is too weak or there are connections that are corroded creating too much resistance.
My battery 1 is at 12.8v and my battery 2 is at 13v, I cleaned all the cable end terminals for both positive and negative and the terminals at the power switch. I also cut open a small square in one of the wires just to see if it was corroded inside but it looked fine.
 

Bondo

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My battery 1 is at 12.8v and my battery 2 is at 13v, I cleaned all the cable end terminals for both positive and negative and the terminals at the power switch. I also cut open a small square in one of the wires just to see if it was corroded inside but it looked fine.
Ayuh,.... How 'bout on the starter's solenoid,..??

If that don't work, pull the starter, while yer down there,...... :)
 

CLi87

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And the pinion gear is not being fully extended, which could cause the grinding. Check voltage at the large terminal on the solenoid that is fed from the battery switch common, or battery if no switch. Should be at least battery voltage. Then disconnect the yellow/red wire from the solenoid, hook a voltmeter to between it and a ground and have someone turn the key to start, this will tell you if you are getting a full 12V at the solenid start terminal. If not you have to go back and clean every connection between the switch and engine harness.
Your ignition switch will have 3 terminals, one labeled B (battery voltage, red wire, has 12V anytime the battery switch is on), I for ignition (purple wire, gets 12 V when ignition switch is turned to On), and S (yellow/red wire, gets 12V when ignition switch gets turned to start). I'd pull the swtich out of the dash if your start terminal on the solenoid shows low voltage and start there. Places to check, battery terminals, battery ground points on the bell housing, connections at the starter solenoid, connections at the assist solenoid, connections on the ignition switch and the big cannon connector for the engine harness. Corrosion anywhere can cause a problem like this.
If you have wingnuts holding down your battery cable terminals on the battery get rid of them and use locking nuts, or bolt on marine quality battery clamps, Make sure the cables are not corroded and don't forget to check the grounds, its usually a stud on the bell housing behind the exhaust hoses. DC electricity must travel in a circle to do anywork lol.
Voltage at starter positive terminal is good, I'll check the voltage from the yellow/red wire but should that matter if I'm using a power probe to directly jump the starter solenoid? I have nuts on my batteries and cleaned off every connection with a dremel so they're nice and shiny. I also just ordered a power switch, I wonder if that might have internal corrosion causing a problem but I'm getting good volts to the starter.
 

CLi87

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I use a product called Kopr-Shield made by T&B (Thomas and Betts). This stuff is fantastic.
It's a conductive anti-corrosion surface compound.
I clean the connection, apply the Kopr-Shield to all the parts, connect it all up, tighten it and it never corrodes...ever.
You don't need much, just coat the surfaces lightly.
A warning though...don't get that stuff on your clothes, it won't come out.
Thanks for the tip! I'll definitely be buying some and putting it on every bolt lol, I hate dealing with corrosion problems and these older boats are just full of them.
 

CLi87

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Ayuh,.... How 'bout on the starter's solenoid,..??

If that don't work, pull the starter, while yer down there,...... :)
Yup :) cleaned off the terminals connecting to the starter relay and it's also a new starter relay and key switch is new as well, but key switch shouldn't matter because i'm using a power probe at the starter relay.

I've pulled this starter on and off at least 30 times by now -.- I've tried every which way configuration of shims with no luck so i'm leaning towards a power issue causing the starter not to extend all the way.
 

QBhoy

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An earlier post asked if you had made sure the engine can turn by hand. Thought I’d ask again. Just in case.
 

CLi87

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An earlier post asked if you had made sure the engine can turn by hand. Thought I’d ask again. Just in case.
Yes engine turns over fine by hand, I have spark plugs loosely in, no wire connected.
 

QBhoy

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Yes engine turns over fine by hand, I have spark plugs loosely in, no wire connected.
No worries. As long as you’re sure she does. Was just checking. Although even with the plugs loose…jeez, you’ll still have some compression there
 

CLi87

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No worries. As long as you’re sure she does. Was just checking. Although even with the plugs loose…jeez, you’ll still have some compression there
With the plugs completely out the engine will turn over fine, I guess the starter teeth get enough contact to turn the flywheel when there's no resistance, but once I put the plugs in it'll just start grinding when I try to turn it over.
 

tank1949

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Sorry for the late reply all, it started getting cold and I put the boat away in storage but now that it's starting to get warm again time to jump back on the problem.

I haven't been cranking using the key, I've been cranking using a power probe attached to the starter relay and it still grinds every time.
I fear that sometime in the past, the teeth were being gowned using corroded helm switch. Mine switch was corroded. We tested with multimeter and saw major voltage loss threw switch. Just a suggestion before you POSSIBABLY ruin a new ring gear. U may have additional problems that seem to "grow" during down times when moisture collects in boat.
 

Scott Danforth

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number one cause of starter grinding is bad electrical connections. not enough juice to throw the bendix then get the starter spinning. it starts spinning and lazily moves the bendix effectively turning the starter into a mill and taking out ring gear teath.
 

CLi87

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I fear that sometime in the past, the teeth were being gowned using corroded helm switch. Mine switch was corroded. We tested with multimeter and saw major voltage loss threw switch. Just a suggestion before you POSSIBABLY ruin a new ring gear. U may have additional problems that seem to "grow" during down times when moisture collects in boat.

By helm switch are you talking about the key switch? Several had mentioned that but I'm testing the engine using a power probe sending 12v directly to the starter relay so that should completely bypass the key switch and wiring being a potential problem I believe? And I'm trying really hard not to ruin my ring gear, it's chewed up a bit but still fine, then second I hear it grinding I stop immediately.
 

CLi87

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Have you checked for loose starter mounting bolts?
Yup, I didn't torque the bolts because space is so tight it's hard to get a solid 1/4 degree turn in but I did tighten them as hard as I possibly could with a 3/8" ratchet.
 

CLi87

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number one cause of starter grinding is bad electrical connections. not enough juice to throw the bendix then get the starter spinning. it starts spinning and lazily moves the bendix effectively turning the starter into a mill and taking out ring gear teath.
Yea that's what I was thinking too, I just can't figure out what part, I just got a new main power switch yesterday so I'll throw that in and see if that helps, the original had corroded terminals that I cleaned off but not sure what the inside looks like even though it's supposed to be sealed. It's a Perko 1-All-2 switch. I'm using a power probe at the starter relay to turn the starter so I'm not even looking at the key switch wiring. I also cleaned all the power terminals and ground points. Only thing left is the main power cables themselves, but I had cut a small square in one of the cables to look inside and didn't see any corrosion really.
 

nola mike

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Yea that's what I was thinking too, I just can't figure out what part, I just got a new main power switch yesterday so I'll throw that in and see if that helps, the original had corroded terminals that I cleaned off but not sure what the inside looks like even though it's supposed to be sealed. It's a Perko 1-All-2 switch. I'm using a power probe at the starter relay to turn the starter so I'm not even looking at the key switch wiring. I also cleaned all the power terminals and ground points. Only thing left is the main power cables themselves, but I had cut a small square in one of the cables to look inside and didn't see any corrosion really.
Have you measured starter voltage while cranking for a drop? That can let you stop chasing electrical problems before the starter...I forget whether you're jumping it at the starter solenoid or the slave?
 

CLi87

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Have you measured starter voltage while cranking for a drop? That can let you stop chasing electrical problems before the starter...I forget whether you're jumping it at the starter solenoid or the slave?
I wanted to check the voltage drop but the grinding is so bad right away that I didn't want to hold the starter down long enough to get a good reading.
 

CLi87

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So I decided to dedicate today to working on the boat. Installed the new master power switch and checked every single wire end, those that had some corrosion I cut back until it was clean wire and crimped on new terminals. Took forever but now I know I have solid connections. The starter does seem to work better and I can hear it turn the engine over on the exhaust stroke but then it'll still grind on the compression stroke. This is with all plugs in, it'll turn over easily with plugs out. So it seems the bendix is making slightly better engagement but still not seating all the way to the flywheel.

Any ideas? And would it help if I took a video to describe what I'm experiencing?
 

salvageyard saviour

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So I decided to dedicate today to working on the boat. Installed the new master power switch and checked every single wire end, those that had some corrosion I cut back until it was clean wire and crimped on new terminals. Took forever but now I know I have solid connections. The starter does seem to work better and I can hear it turn the engine over on the exhaust stroke but then it'll still grind on the compression stroke. This is with all plugs in, it'll turn over easily with plugs out. So it seems the bendix is making slightly better engagement but still not seating all the way to the flywheel.

Any ideas? And would it help if I took a video to describe what I'm experiencing?
Is it possible the ring gear has came loose from flywheel?
Since it seems to work with plugs out, but makes noise under compression.
 

CLi87

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Is it possible the ring gear has came loose from flywheel?
Since it seems to work with plugs out, but makes noise under compression.

I don't think so, but is it possible the flywheel could come loose from the motor?

I actually just took a video of the engine cranking over with plugs out, cranks fine but it does make a weird noise.


Any ideas what's causing that noise?
 
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