Mercruiser 7.4 Starter Grinding/Partial Engagement?

[CLi87]

Hi there, I'm working on a mercruiser 7.4 engine and just installed a new starter, I've never had the boat running yet and when I tried cranking it seems the motor tried to start briefly then a grinding sound. I took the starter off and marked the gear with a marker, re-installed and tried to crank it again to see the contact points, it seems the starter is only making partial contact maybe halfway on the starter gear. I did some research and read about having to shim the starter, I've never had to shim a starter on countless motors I've worked on but I guess there's always a first time for everything. Does this sound like a situation I need to shim? And I know the best way would be to measure the gap but in this case that would be impossible without removing the engine. And if I do need to shim, do I need to move the starter closer or further away from the ring gear?

 

[CLi87]

Also I have already turned the motor over by hand, turns over fine, even removed spark plugs just to make sure, the engine isn't locked.

 

[tpenfield]

The 7.4 (GM 454) starters are pretty much 'plug 'n play' so are you sure you have the correct starter and the bendix is extending all of the way?

Are you able to see the teeth on the fly wheel and are their any voids of teeth.

 

[CLi87]

The 7.4 (GM 454) starters are pretty much 'plug 'n play' so are you sure you have the correct starter and the bendix is extending all of the way?

Are you able to see the teeth on the fly wheel and are their any voids of teeth.

I tried 2 new starters that both should work for the 7.4 I believe, these are the 2 starters I bought, they look the same as the one I removed from the boat:

Amazon.com

https://www.amazon.com/gp/product/B00TPM7UTI/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

and yes I'm sure the bendix is extending all the way, I "bench tested" the starter by jumping it while it was hooked to the boat power but without it mounted.

 

[CLi87]

 

[Bondo]

I tried 2 new starters that both should work for the 7.4 I believe, these are the 2 starters I bought, they look the same as the one I removed from the boat:

Ayuh,..... Those are both pmm starters,....
Are ya usin' bolts that came with the starters, or the bolts that were in the motor,..??

These new style starters use a slightly shorter bolt, by 'bout a 1/4" or so,.....

Shimmin' a chevy starter, moves it away from the flywheel, not closer,.....

 

[CLi87]

Ayuh,..... Those are both pmm starters,....
Are ya usin' bolts that came with the starters, or the bolts that were in the motor,..??

These new style starters use a slightly shorter bolt, by 'bout a 1/4" or so,.....

Shimmin' a chevy starter, moves it away from the flywheel, not closer,.....

I think my old one was a PMM too maybe? Looks the same? I re-used the original bolts, I matched them up with the new ones but only noticed a very small difference. From the markings on the paint it looks like the bendix isn't fully engaging the ring gear but I did some measurements and with the bendix fully extended it should about match up perfectly with the ring gear teeth.

 

[Bondo]

Ayuh,...... Try it with the new, shorter bolts,......

 

[Lou C]

comparing the lengths of the bolts and the amount of threads showing it is possible that the old bolts you used were allowing the starter to shift slightly under load. The bolts must clamp the starter fully to the engine block or else there will be problems.

 

[CLi87]

I just swapped out the bolts with the new ones but unfortunately still the same problem, I hear grinding when I try to crank it.

 

[Lou C]

Can you see the teeth on the engine flywheel? How do they look?

 

[kenny nunez]

To me the surface that contacts the block on the new starter appears to set the starter lower than the old one. Maybe it is an illusion but try to measure the relationship between the starter shaft and the contact pad.

 

[CLi87]

Can you see the teeth on the engine flywheel? How do they look?

Sorry for the late reply, teeth on the flywheel look fine except some light grinding caused by the starter.

I actually ended up rebuilding the original starter but it still has the grinding problem and grinds. Anyone have any other ideas? I'm almost to the point of just pulling the motor, seems silly though just for a starter.

 

[tank1949]

I think my old one was a PMM too maybe? Looks the same? I re-used the original bolts, I matched them up with the new ones but only noticed a very small difference. From the markings on the paint it looks like the bendix isn't fully engaging the ring gear but I did some measurements and with the bendix fully extended it should about match up perfectly with the ring gear teeth.

I had a helm faulty ignition switch on a MC that didn't allow enough current for the starter/Bendix. It ended up destroying the flywheel ring gear's teeth. You may want to directly jump starter and examine the difference in performance. If it was my boat, I'd paint starter teeth again and manually jump starter. Then, I'd examine paint markings. Good luck!

 

[poconojoe]

Maybe your battery is too weak or there are connections that are corroded creating too much resistance.

 

[Lou C]

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.

 

[tank1949]

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.

I stopped counting the times I have had to clean off terminal green crap. I started spraying Fluid Film on them , which just slows it down.

 

[poconojoe]

I stopped counting the times I have had to clean off terminal green crap. I started spraying Fluid Film on them , which just slows it down.

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.

 

[tank1949]

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.

Inside battery lugs too where they make contact with battery posts???????

 

[CLi87]

I had a helm faulty ignition switch on a MC that didn't allow enough current for the starter/Bendix. It ended up destroying the flywheel ring gear's teeth. You may want to directly jump starter and examine the difference in performance. If it was my boat, I'd paint starter teeth again and manually jump starter. Then, I'd examine paint markings. Good luck!

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.