Merc 5.7 Keeps Shearing starter bolts

Status
Not open for further replies.
G

Georgearia

Cadet
Joined
May 5, 2020
Messages
28
5.7 Merc Sterndrive. 2nd starter installed in less than 2 years where outside bolt sheared off. Most recent installed a New Sierra starter with their supplied bolts. Torqued per specs. Started boat maybe 3 times. Fired right up. The other day...wouldn't start...tried a few brief times. Wouldn't fire up. Tried starting next day....the out bolt sheared off once again.

Thanks in advance for your comments
 
Fun Times

Fun Times

Moderator
Staff member
Joined
May 16, 2009
Messages
9,047
Might need a support bracket at the other end.

What is the engine serial number and year?

Look real close to make sure the engine block isn’t cracked at the starter bolt holes.

Also the bolts type design and/or length might be off causing issue
 
R

ROY WILLIAMS

Chief Petty Officer
Joined
Aug 8, 2022
Messages
400
the bolts are a correct length and the shoulder bolt was solid along the starter motor case . did those bolts are a high torque ,,,
look up the head bolt spec ?
 
Scott Danforth

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
49,546
Direct drive starters have a support bracket
 
S

Searay205

Chief Petty Officer
Joined
May 27, 2018
Messages
468
I have a 5.0 mpi. It had an aftermarket starter but I removed. When I did I found the Mercruiser bolts knurled shoulder had been grinned away. The POS aftermarket start also had the mounting holes 1/16" closer than Mercruiser. Went back with mercruiser/quicksilver and new bolts. hundreds of starts later and still works perfect.
 
G

Georgearia

Cadet
Joined
May 5, 2020
Messages
28
Fun Times said:
Might need a support bracket at the other end.

What is the engine serial number and year?

Look real close to make sure the engine block isn’t cracked at the starter bolt holes.

Also the bolts type design and/or length might be off causing issue
Click to expand...
Engine is a 99, Serial OL336107. I had changed the starter 6 years ago, ther was no additional bracket or brace.... is there an aftermarket one available?

Also,, does the bell housing support the starter nose cone,,does it fit in tight? I need to take a look.... I recall the plastic shield being loose and being able to see flywheel pretty easily....
 
Scott06

Scott06

Admiral
Joined
Apr 20, 2014
Messages
6,431
Would suspect your bolts are loosening up or not correct, maybe you have a hydro lock going on? Would use a mirror to see if threads are busted, try loctiting them in. My friends boat had a loose starter couple years back, dealer had replaced starter under warranty just after he bought it. Bolts got bent slightly so he would have broken one if it kept going. Put them back in with loctite and thats been three years

no the flywheel cover doesn't support the starter
 
P

pachanga58

Cadet
Joined
Sep 19, 2021
Messages
18
Just a wild off the wall comment - but how fresh is the battery? Depending on the compression ratio, a high compression motor, if it cranking slow because of a low voltage, there could be a large amount of torque being applied to the starter and thus the mounts as the starter is trying to power through trying to spin the motor over.
 
Scott Danforth

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
49,546
pachanga58 said:
Just a wild off the wall comment - but how fresh is the battery? Depending on the compression ratio, a high compression motor, if it cranking slow because of a low voltage, there could be a large amount of torque being applied to the starter and thus the mounts as the starter is trying to power through trying to spin the motor over.
Click to expand...
huh?

if you have a dead battery, you have less juice to make torque

state of battery has nothing to do with breaking starter bolts
 
Fun Times

Fun Times

Moderator
Staff member
Joined
May 16, 2009
Messages
9,047
Georgearia said:
Engine is a 99, Serial OL336107. I had changed the starter 6 years ago, ther was no additional bracket or brace.... is there an aftermarket one available?

Also,, does the bell housing support the starter nose cone,,does it fit in tight? I need to take a look.... I recall the plastic shield being loose and being able to see flywheel pretty easily....
Click to expand...
What brand model starter have you bought/installed?

Here would be your OEM starter…

Starter Motor

Starter Motor
www.mercruiserparts.com www.mercruiserparts.com

if there was any changes of types/designs/aftermarket then it “may” require a different bolt type too… In the above link click on the notes icon for reference points.

The newer types don’t use a support bracket as it’s a smaller motor but some of the older engines (1995 and under) with a bit bigger starter motor used a bracket that fits a 12 inch motor design as mentioned here within these notes under item numbers 3 and 1 taking note that this isn’t your actual part’s catalog just more of a reference point in case you may have a different design/aftermarket starter and the OEM numbers have superseded… https://www.mercruiserparts.com/bam/subassembly/31888/1014/10

Just something extra to be aware of.
 
G

Georgearia

Cadet
Joined
May 5, 2020
Messages
28
pachanga58 said:
Just a wild off the wall comment - but how fresh is the battery? Depending on the compression ratio, a high compression motor, if it cranking slow because of a low voltage, there could be a large amount of torque being applied to the starter and thus the mounts as the starter is trying to power through trying to spin the motor over.
Click to expand...
Batteries are up to charge. Starter doesn't labor at all. It cranks very quickly....
 
T

tank1949

Lieutenant Commander
Joined
Apr 4, 2013
Messages
1,892
Georgearia said:
5.7 Merc Sterndrive. 2nd starter installed in less than 2 years where outside bolt sheared off. Most recent installed a New Sierra starter with their supplied bolts. Torqued per specs. Started boat maybe 3 times. Fired right up. The other day...wouldn't start...tried a few brief times. Wouldn't fire up. Tried starting next day....the out bolt sheared off once again.

Thanks in advance for your comments
Click to expand...
The bolts should be knurled and tapered for Chevy SB V8s. Has someone ever swapped flywheel?
 
Lou C

Lou C

Supreme Mariner
Joined
Nov 10, 2002
Messages
12,654
Yep that has to be dealt with fast. If you don't have much time just remove the plugs, spin it over, and drain both the manifolds and engine, then oil up the cyls to prevent rust. Check for water in the oil as well, not just on the dipstick but also under the valve covers where it tends to show up first.
I had water in 2 cyls (not enough to hydro lock) due to blown HGs and that's what I did till I could take it apart. The engine sat from late November 2017 till February 2017 when we got a run of warm weather and I took the heads off and there wasn't any rust at all in the cyls or anywhere for that matter.

Those smaller PMGR starters do not use the front mount, that was only on the old style larger Delco direct drive starters. It is VERY important to use the correct length bolts for the starter you use and they should have a knurled surface on them. 30 ft lbs if you can fit a torque wrench in there lol. I just get em "goot n tight"....
see the bolts in this pic....starter brand is ARCO
 

Attachments

  • PMGR vs DD small.jpg
    PMGR vs DD small.jpg
    187.3 KB · Views: 7
D

dubs283

Vice Admiral
Joined
Jul 27, 2005
Messages
5,322
Unless the engine got water in it on your last outing, i.e. the failure was noted not long ago, the engine is junk

Two years of hydrolock/water intrusion says the exhaust manifolds, risers, gaskets or all are failing. Water in the combustion chamber kills engines. Moat likely even with correcting the water issue you're looking at long block replacement
 
Status
Not open for further replies.
Top