Mercruiser 4.3 Starter Motor Disengaging

[Birdsboat]

I have a 1991 4.3L Mercruuser which I've recently brought out of storage after 3 years. I had problems starting it and diagnosed a lazy starter. I purchased and fit a new starter but while attempting to start it then sheared off teeth from the flywheel ring gear. Engine has now been removed, a new ring gear was fitted to the flywheel and everything rebuilt. I am now attempting to bench start the engine before refitting to the boat. When turning over I've noticed the starter was moving and the starter gear disengaging from the flywheel gear. I checked and found the bolts had slightly bent maybe from when the flywheel gear teeth sheared. I replaced the bolts and refitted and have managed to start the engine a couple of times with no starter problems. However, the starter has started moving again and is occasionally disengaging from the flywheel gear again. I suspect the bolts have bent again. Does anyone have any ideas what is causing this??
I don't want to keep turning it over in case it damages the flywheel again or even worse I have seen on YouTube someone showing the block casting sheared off where the starter motor bolt thread is!!!

 

[Scott Danforth]

There should be a bracket at back of starter to block.

Make sure the motor turns over easy and it's not hydrolocked

 

[Bondo]

Ayuh,.... Welcome Aboard,..... My 1st guess is the starter bolts weren't tight,....

Have ya check for flywheel run-out,..??

Are ya usin' the proper starter bolts that matches the starter,..??
I've switched to permant magnet starters, 'n the proper bolts are ever so slightly shorter,.....
Bolted on with the old bolts it tightens up, but ain't actually tight as it should be,....

Maybe ya oughta look into buildin' a bracket/ strap to hold the front of the starter,....

 

[Birdsboat]

I have turned it over by hand a few times and apart from the resistance of compression it seems fine. I have also had it started and it run for around a minute.
There wasn't a bracket on the old starter which I took off. The starter is the staggered hole type.

 

[Birdsboat]

I have checked the flywheel and it's fine. I've checked the bolts by fitting them without the starter and measured the distance which is then less than the width of the starter housing

 

[Bondo]

I've checked the bolts by fitting them without the starter

Ayuh,.... How are the threads in the block,..??

Are the 2nd set of bolts bent,..??

Are they knurled starter bolts,..??

 

[Birdsboat]

I haven't removed the starter again yet to check to see if the bolts are bent again but I think they are because I'm getting the same outcome as when they were bent the first time
Yes they are knurled bolts
What do I need to check on the threads in the block?

 

[Bondo]

What do I need to check on the threads in the block?

Ayuh,.... Whatever it takes to See 'em,....

Run a bolt in, 'n out, by hand,.... how does it Feel,..??

 

[Birdsboat]

I have checked the bolts, and they have bent again!! I checked the threads in the block and they seem fine, I'm able to run a 3" bolt in both holes and there is no run out.
Could it just be the bolts are "cheap"?. Should I buy high tensile bolts? The worry I have is that if there is something causing it and I replace with high tensile bolts, if the bolts don't bend the block casting could shear where the outside bolt locates!!
Really struggling here!!

 

[Birdsboat]

There should be a bracket at back of starter to block.

Make sure the motor turns over easy and it's not hydrolocked

Is it possible to create a hydro lock if excessive fuel is put through the carb? I ask this because while attempting to start the engine I was supplying fuel to the carb free hand from a bottle. Reason for doing this is because I am also having issues with getting fuel from the fuel pump and was told by doing this would assist with getting the pump to work faster via the pump push rod when the engine is running.

 

[Bondo]

Ayuh,..... Lets get into the details,.....

Don't go to any other bolts, other than Chevy starter bolts,....

Is this an old style energized magnet starter, or a new style permanent magnet motor starter,..??

You'd have to be dumpin' massive amounts of gas down the carb to hydro-lock the motor,...
Does it fire off, when yer pourin' gas down the carb,..??
If not, lets figure out why,...

 

[Birdsboat]

Ok, I will order the new bolts from Mercury for the starter motor.
I'm pretty sure its the new style permanent magnet starter motor.
When I poured fuel down the carb, it did fire up a few times. I even had it running for about a minute or so, at which point I thought the fuel pump was then delivering the fuel. The idle revs were a little high so I adjusted the idle screw, it cut out but then wouldn't start again until I poured fuel down the carb again. It was after these few times of firing with pouring the fuel down the carb was when I then started having the starter disengaging and bent bolts.
Can you suggest a method of checking the fuel pump? If I can eliminate the need of pouring fuel by hand, I at least know there's not too much fuel going in which may cause the hydrolock

 

[Bondo]

Ok, I will order the new bolts from Mercury for the starter motor.
I'm pretty sure its the new style permanent magnet starter motor.

Ayuh,.... The standard Mercruiser bolts will be to long for a permanent magnet motor starter,.....

Go to the supplier of the starter, they Should know the difference,...

Can you suggest a method of checking the fuel pump?

Take the fuel line off the carb, direct it into a catchcan, 'n turn the motor over on the starter,...
There should be massive amounts of fuel pumped into the catchcan,...

 

[Birdsboat]

Ok, I have ordered a new set of bolts from the starter supplier. I have removed all the plugs and turned over again by hand to confirm there is no mechanical binding and apart from a slight increase in resistance at certain points (which I assume is the push rod operating the fuel pump) everything seems fine.
I disconnected the fuel line into the carb and turned the engine over using the starter but I had no fuel. I then removed the fuel pump top housing and removed the old type "ceramic filter" and turned over again and had large amounts of fuel into the bottle.
So, I have ordered a new fuel pump filter and new plugs.
I will now fit the new starter bolts, fuel pump filter and plugs when they are delivered and try again. I am starting to be convinced the problem has been created from me hand pouring fuel into the carb and either creating a hydrolock or the backfires when attempting to start off the starter were creating too much force back through the flywheel.
Thanks Bondo for your help, I will post an update with the outcome.

 

[NHGuy]

One thing that was mentioned stands out to me. If the starter bolts were too long the starter won't stay tight to the block. So after the bolts are back in try to wiggle the starter. I once did a later starter on an older engine and was able to get the starter good and tight by adding a couple of washers. But the shorter bolts are preferred.
The extra washers kept the bolts from bottoming but still allowed the bolts full clamping force.

 

[Birdsboat]

One thing that was mentioned stands out to me. If the starter bolts were too long the starter won't stay tight to the block. .

I've checked the bolts by fitting them without the starter and measured the distance when they are bottomed out which is then less than the width of the starter housing

 

[NHGuy]

OK so you are getting full clamping force, right? If that's correct see how the starter drive gear hits the flywheel ring gear. Just run the starter off a set of jump cables. If they don't mesh well and are crashing into each other that can cause the starter to twist. Can't leave that alone.

 

[Birdsboat]

No Title

I have fitted the new plugs, fuel is pumping to the carb, fitted new correct length bolts but I'm still having the starter motor disengaging!!
So, I have fitted the old starter powered the solenoid only so the bendix gear advances to engage and I have taken a photo of the gear mesh. I have also done the same for the new starter. See the photos below. I think there is a fair bit more gear mesh with the old starter compared with the new. This can only be if there is a different dimension from the mounting bolts centreline and the starter rotor shaft centreline. Therefore, I am now trying to rebuild the starter using the old mounting housing with all the new starter parts.

 

[Birdsboat]

Ok, I have rebuilt the starter using the old starter motor mounting housing, the new starter bendix gear and engagement mechanism, new starter solenoid, new starter sun and planetary gears, old starter rotor and rotor housing with new starter brush plate and brushes.

I fitted it and it was turning over great the engine fired and had it running for a minute or so, it cut out.........when I attempted to start it again the starter was disengaging AGAIN!!!! It looks like the bolts have bent once AGAIN!!!

I really need help with this.... I have checked absolutely everything and have now run out of ideas!!! It seems to bend the bolts at the point of the engine firing??

 

[Birdsboat]

Just an update to close this thread.....I have found the buying a cheap starter motor off ebay. The bolts were of a poor quality causing them to bend but the main problem was, when the starter was mounted, the centreline distance between the starter shaft and the crank was bigger which was giving less gear mesh between the bendix gear on the starter and the ring gear on the flywheel. I purchased another starter from a marine supplier and have had no disengagement issues since fitting it.

I do now have new problems which I will start in a new thread