Breaking starter bolts....Merc 1996 3.0 I/O

I am replacing the starter on my 96 Mercruiser 3.0 I/O Is there a steel bracket required that spans from the engine block to one of the small terminals ? My starter had previously broken two of the long bolts requiring engine removal to drill and tap the bolt hole but this time this guy installed this bracket saying it was a retrofit to fix the broken bolt problems...is this legit ?

What causes broken starter bolts ?

Re: Breaking starter bolts....Merc 3.0 I/O

yes it is legit and the only way to stop the brokin starter bolts. This guy your using is knowledgeable.

What causes it is vibration of the engine, loosens the bolt and then it snaps, nothing you can do short of the bracket to stop it i had the same problem, i replaced the original oem starter with the new type did not install the bracket cause it didn't fit cause the new starter is smaller.

4 bolts broke till i fabricated a new bracket and installed it.

Same thing happened to my friends boat same motor and others i spoke to with the 3.0 / 2.5 motor.

Happens also with larger motors also.

Re: Breaking starter bolts....Merc 3.0 I/O

Measure the new bolts!
Just got done replacing the flywheel ring gear (lot of work to get to a $20 part) because the bolts that came with an aftermarket (API) starter were about 1/8" too long. They bottomed out in the block before tightening the starter sufficiently. The bolts bent, the starter shifted, and about 20 teeth on the flywheel were sheared off.

Re: Breaking starter bolts....Merc 3.0 I/O

troym said:

Measure the new bolts!
Just got done replacing the flywheel ring gear (lot of work to get to a $20 part) because the bolts that came with an aftermarket (API) starter were about 1/8" too long. They bottomed out in the block before tightening the starter sufficiently. The bolts bent, the starter shifted, and about 20 teeth on the flywheel were sheared off.

Click to expand...

I've done a lot of research on this. You can get the same starter bolts from your local Chevy or GM dealer for $1.68ea rather than pay $14ea from Mercruiser. the GM part number is:12338064 or the Dorman bolt from most Auto parts stores: Dorman 678-107. (This is for the style of starter with the 2 long bolts of the same size)
Mercruiser started making a mounting bracket for the end of the stater to help relieve this problem. That part number is: 863212. The bolt for the bracket is a 5/16-18 x 3/4. The nut for the starter is a #10-24. I would suggest getting these in stainless steel.

To get the broken bolts out: If you have the style with the 2 long bolts one of the bolts is relatively easy since it's a through hole, you can get to the bottom of the bolt from the top of the engine. Center punch the bolt exactly in the center, start with a small drill bit to get a good center hole started so the bit doesn't wonder, then drill down about 1/4" or so with a #10 drill bit. Most likely the bolt will just come out while you're drilling into it. If not, then start a 1/4-20 tap into the hole and this should definitely turn the bolt out. Make sure you use lots of PB Blaster or something like that if your bolt is corroded.
The second bolt, the one closes to the port side is the tough one. I suggest using the piece of bolt you just took out from the other side or a new bolt and drill into the center of it, then cut it off about 1/2 long. Use this as a guide for a center punch and a drill on the blind bolt since you can really see it from the bottom. Then get a reversed 7/32" drill bit, McMaster #2876A24 and a drill extractor #57195A514 you'll most likely need a right angle drill, run the drill in reverse. Take your time and try to use a dental mirror to keep it as straight as possible.
I got lucky, since my bolts were brand new they came out very easy.

Hope this helps everyone who is having this problem.

This thread was started in April 2010.

Do NOT use OEM starter motor mounting bolts for a possible non-OEM starter motor!
This gets people into trouble!!!!

Let today's starter motor nose housing determine the correct special bolt lengths!


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RicardoMarine said:

This thread was started in April 2010.

Do NOT use OEM starter motor mounting bolts for a possible non-OEM starter motor!
This gets people into trouble!!!!

Let today's starter motor nose housing determine the correct special bolt lengths!


.

Click to expand...

Can you elaborate on this? What is a starter motor nose housing? Where do you get custom length bolts and how do you know the size?

To simplify it:
install the new starter bolts and torque to spec WITHOUT THE STARTER
measure the distance from the block face to the bolt head face.
measure the starter housing where the bolts pass thru .
distance must be more .the same or less results in loose bolts even though you tightened them

Bt Doctur said:

To simplify it:
install the new starter bolts and torque to spec WITHOUT THE STARTER
measure the distance from the block face to the bolt head face.
measure the starter housing where the bolts pass thru .
distance must be more .the same or less results in loose bolts even though you tightened them

Click to expand...

Good advice. I don't recommend torquing to spec without the starter though, I would run them in until snug as torquing them without the starter in place may damage the bolts or threads by running them in past the threads .

Regards,
gasitup

Re: Breaking starter bolts....Merc 3.0 I/O

Thanks Giosso:
Your reply was from 5 years ago, but your technique sure helped me out. I have the Mercruiser 140 (3.0L) and it has the starter with the long and short bolt which both frustratingly snapped off. They both had to be drilled from the bottom.

The inspection mirror idea helped immensely. To drill them out I could not use a right-angle drill because the chuck was too large. I ended up purchasing a DeWalt Right Angle Flex Shaft Bit Holder (https://www.dewalt.com/products/acc...rive-guides/12-right-angle-flex-shaft/dwarafs) for my cordless drill and that did the trick. One problem is I could not find reverse cut drill bits with a hex shaft. I ended up using a 5/32” hex shaft bit. I wrapped the shank with electrical tape and built it up close to the size of the bolt hole to get as close to center as possible. I drilled into each broken bolt about a half inch.

After that I used a number 3 easy out bolt extractor, however because of the clearance I could not use a tap wrench so then I simply used an adjustable wrench, turned them counterclockwise, and voila! So much quicker and cheaper than pulling the engine out. We are back on the water! Much cheaper and quicker than pulling the engine to repair it!

Thank you again,

Cholly364, you have posted to a thread that was started way back in April, 2010, and was then resurrected in 2014.

It's always best to start a new thread for your specific topic and issue.






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That bracket on the front of the starter to the block is absolutely essential to prevent the bolt breaking. Ask me how I know!

Jeff

Yes, I get that. I just wanted to pay thanks to the poster of the 2010 comment because he helped me out immensely with my particular problem.

Thanks for keeping the old posts available!