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Mercruiser 7.4 Starter Grinding

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97CapriSS

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Hey all, I've been working on a 93 Mercruiser 7.4 and the starter is grinding when I try to turn the engine over with the spark plugs in, with the plugs out the starter won't grind. I've already replaced the main power switch, starter, starter solenoid, 2 new fully charged batteries, and I went through all the wires and anything with corrosion I cut the wire back until it was clean and put new terminals on and cleaned off all grounds on the engine block. This has got me pretty stumped, not really where to look next, any help would be greatly appreciated!
 
What about shimming the starter? Or a loose starter bolt?
I know, it sounds weird, but my buddy had the same issue. I can’t remember his engine, it’s a Mercruiser, in a 20’ Stingray, V6 I think, but I’m not sure of the displacement.
He experienced a grinding starter, & did most of what you mentioned. Then an old time mechanic told him the starter needed shimming, said it was not an uncommon thing on these essentially GM engines.
I had never heard of this, & asked my brother, who was a GM dealer mechanic for years. He said the same thing, it was not unheard of to have to shim the starter.
My buddy did that, bingo, problem fixed.
Another option, loose starter bolt. The bolts hold the starter on, & also align it.
Has the starter ever been changed?
It’s possible a bolt has come loose & got bent,there is a lot of torque there. If the bolt bot bent, even slightly, it will bind, feels like it’s bottomed, but isn’t. If you replace starter bolts, use OEM, the length is critical. Only take out one at a time. Some engines can be a real b*tch, no room to work, & unfavourable angles.
 
Last edited:
Edchris177 said:
What about shimming the starter? Or a loose starter bolt?
I know, it sounds weird, but my buddy had the same issue. I can’t remember his engine, it’s a Mercruiser, in a 20’ Stingray, V6 I think, but I’m not sure of the displacement.
He experienced a grinding starter, & did most of what you mentioned. Then an old time mechanic told him the starter needed shimming, said it was not an uncommon thing on these essentially GM engines.
I had never heard of this, & asked my brother, who was a GM dealer mechanic for years. He said the same thing, it was not unheard of to have to shim the starter.
My buddy did that, bingo, problem fixed.
Another option, loose starter bolt. The bolts hold the starter on, & also align it.
Has the starter ever been changed?
It’s possible a bolt has come loose & got bent,there is a lot of torque there. If the bolt bot bent, even slightly, it will bind, feels like it’s bottomed, but isn’t. If you replace starter bolts, use OEM, the length is critical. Only take out one at a time. Some engines can be a real b*tch, no room to work, & unfavourable angles.
Click to expand...

I've tried shimming the starter back and forth with no luck, i've put this starter in and out probably 30 times by now, and tried 3 starters total including the original and 3 different size shims. I painted the teeth on the starter bendix to check the engagement point but regardless which direction I shim it the engagement stays the same, the starter bendix makes about 2/3 contact with the flywheel. And I used the new bolts that came with the new starter and they are tight.
 
fastjeff said:
Hate to say this, but the ring gear on the flywheel may be shot and causing this problem.

Jeff
Click to expand...
Possibly but I don't think so, I can take pics and would like to see what you think though, the teeth look a bit ground down on one side to me but should still be fine, I never ran the starter for long with the grinding, the second it grinds I stopped cranking. And I did rotate the flywheel all the way around, while there's patches of teeth that were grinded a bit there are no missing teeth or big chunks missing. And how would that explain the starter bendix engagement problem, is the bendix only supposed to make contact with 2/3 of the flywheel? I just assumed it should make full contact.
 
Did you or someone take the engine out and do anything with the Flywheel? It sounds like the starter is hitting something like the cover plate.
 
Question,

Have you tried to replace the starter with a new or rebuilt one?

Starters dont last for ever and that noise could be the starter itself. Hard to tell as you do not move phone close to the starter itself.

A good quality Marine (NEW STYLE Smaller and lighter) here is a link to a replacement for your engine, It is an example only. But it shows the size. You would also need to confirm staggered or straight bolt pattern

https://www.marineengine.com/newparts/part_details.php?pnum=MER50-863007A+1

When setting starter gear to flywheel engagement it is done with a dowel pin of a certain diameter between top of tooth on starter gear and the valley of the engaged tooth on flywheel. The pin should fit and not any slop

I forget the proper diameter but I believe it is like 0.06" But I could be wrong and it is almost impossible to do on a marine engine as you cannot visibly see the teeth engagement anyways .
 
97CapriSS said:
Ok, i'll go try that tomorrow, just curious why would that make it stop grinding?
Click to expand...

If your the dist pick up is bad it will lock the engine up like the timing is at full advance.

Put all the plugs in Pull the coil wire and ground it see if it cranks freely.

I watched your video, there is definitely damage to the ring gear.....
 
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