Found bolt in 4.3 bilge. Please help identify

[ShoalSurvivor]

Hey all,
I’ve got a 2000 Mercruiser repower engine with alpha one gen II drive.

i recently pulled engine, changed oil seals, and remounted drive.
She’s running better than ever!

however, today I found this bolt in the starboard aft area of the bilge. and i cannot figure out where it belongs. I thought it was the rear coupling cover but cannot see any missing.
any hints?

thanks!

 

[Fun Times]

How far did the engine accessories come down?

While it looks familiar, it’s not coming to mind right away…
In general looking around this bolt sort of resembles item number five to start of with,

https://www.marineengine.com/parts/mercruiser-sterndrive-parts/43l-gen-2-bbl-gm-262-v6-1998/0l010044-thru-0m614999/wiring-harness-and-electrical-components

https://www.ebay.com/sch/i.html?_nkw=10-98261&_trksid=m5467.l1311&_odkw=10-98261

 

[nola mike]

There are about 50 of those bolts on the 4.3. I'd guess flywheel cover, but also accessory mounts, grounds, harnesses, etc. Not critical whatever it is.

 

[Scott Danforth]

What size is the bolt? M6? M8, M10? How long ( under the threads) 15mm? 20mm?

That will help point you in a direction.

Other than that, as posted above, it's one of 50 or so metric fasteners from the motor.

 

[alldodge]

I'm thinking flywheel to crankshaft

 

[Scott Danforth]

Flywheel to crank is a 12.9 flanged bolt. My guess since it's a 9.8, it's most likely an accessory, or if it's an M6 it's an inspection cover bolt

 

[Bt Doctur]

thougt that too but those are a fine thread.

 

[alldodge]

Flywheel to crank is a 12.9 flanged bolt. My guess since it's a 9.8, it's most likely an accessory, or if it's an M6 it's an inspection cover bolt

We don't know the serial number so I used the first year of 4.3 and came up with part number 8M0214958
https://www.marineengine.com/newparts/part_details.php?pnum=MER10-8M0214958

 

[ShoalSurvivor]

How far did the engine accessories come down?

it was fully undressed while engine was pulled.

 

[ShoalSurvivor]

Flywheel to crank is a 12.9 flanged bolt. My guess since it's a 9.8, it's most likely an accessory, or if it's an M6 it's an inspection cover bolt

Additional clue… there is fresh black paint on part of head of the bolt.

after i reinstalled the engine and drive, I decided to wire brush and repaint the surfaces i could reach (yeah, would have done it while out, but i ran out of time using my buddies shop to work on motor). i fully painted all brackets and mounting bolts on a bench. The flywheel cover was already installed and in boat. I taped, tarped and sprayed eveything I could reach on block, top (Carb, dist, thermostat, top of flywheel cover areas), front (pump, alternator, pullys area) and sides (exhaust manifolds, spark plug holes, just above oil pan).
the partial paint seems likely to be on the rear, where I couldn’t reach, but bolt installed.

i was thinking flywheel cover, but could not reach under the PS cooler and hoses to see/feel. i will re-aim search today and try again.

thanks for info and suggestions

 

[Bondo]

Additional clue… there is fresh black paint on part of head of the bolt.

after i reinstalled the engine and drive, I decided to wire brush and repaint the surfaces i could reach (yeah, would have done it while out, but i ran out of time using my buddies shop to work on motor). i fully painted all brackets and mounting bolts on a bench. The flywheel cover was already installed and in boat. I taped, tarped and sprayed eveything I could reach on block, top (Carb, dist, thermostat, top of flywheel cover areas), front (pump, alternator, pullys area) and sides (exhaust manifolds, spark plug holes, just above oil pan).
the partial paint seems likely to be on the rear, where I couldn’t reach, but bolt installed.

i was thinking flywheel cover, but could not reach under the PS cooler and hoses to see/feel. i will re-aim search today and try again.

thanks for info and suggestions

Ayuh,..... A better clue, would be something of a known size, to estimate the size of the bolt

 

[Scott Danforth]

We don't know the serial number so I used the first year of 4.3 and came up ....

Yes, Gen 1/2 SBCs and the 4.3 until the metric block had used the 7/16-20 flywheel bolts

The Metric block used M11x1.5 crank bolts like the Gen 3/4/5 SBC

The 9.8 metric stamp on the head points to the 4.3 90M metric block (1999 and later)

 

[ShoalSurvivor]

Ayuh,..... A better clue, would be something of a known size, to estimate the size of the bolt

I was still in bed and don't usually keep my caliper or spare bolts with me

Looks like the bolt length is 25/32"

Diameter: 11/32"

11 threads

 

[ShoalSurvivor]

In general looking around this bolt sort of resembles item number five to start of with,

I was able to verify that both wire harness bracket bolts are still secured.

 

[ShoalSurvivor]

Not critical whatever it is.

Wishful thinking! I certainly hope not.

Because of the paint - I'm pretty sure it's not the flywheel coupler (already assembled under housing when painting) and those bolts look longer in online photos.

This is one of the flywheel housing bolts, and I think they were all the same.

 

[ShoalSurvivor]

This is quite the stumper! I'm hoping someone has seen this bolt on an engine, or has an engine out of the boat.

I have reviewed every component and bracket that I removed and reinstalled - all are secure and all bolts still installed.

It had to be installed somewhere and fallen out - I'm certain that the bilge and bay were clear of any excess hardware.

the partial black painted head indicates that it was installed while spray painting and sprayed from the side or top. it was not sprayed head on.

Before painting:
I tarped off the flywheel cover (and below), oil pan, starter motor, timing chain cover & balancer).
I taped over spark plug holes, exhaust ports, valves, thermostat port, water pump ports, etc.
I sprayed from the top, sides, and front, where I had access.
Based on what was exposed and how I sprayed, my gut tells me it had to have been installed in the aft side of the engine (above or to side of flywheel cover)or near the starter or oil pressure switch, or below the exhaust manifolds. Everything fully exposed (top, front, sides above exhaust ports) was completely painted.

When painting, there were no exhaust manifolds, risers, alternator/bracket, water pump, spark plugs, hoses, power steering pump/bracket, PS cooler, steering assembly, fuel pump or bracket, carb, thermostat housing, distributor, coil, ignition or shifting/throttle assembly, wiring harness or brackets. The oil pressure switch, and starter were the only components still installed.


The black paint gives me confidence that it's not the flywheel coupler or flywheel mounting bolts - as these were all installed along with the flywheel housing cover when I painted. It's not the balancer or water pump pulley.

I could not find a matching bolt head ANYWHERE on the engine.

 

[Scott Danforth]

The bolt is an M8 x 20mm

That means it is not a crank bolt.

Could be a coupler to flywheel

May be an inspection cover bolt

May be an accessory drive bolt

May be an accessory bracket bolt

Spend $11 on a borescope for your phone and check the coupler

 

[Mc Tool]

I was still in bed and don't usually keep my caliper or spare bolts with me

Looks like the bolt length is 25/32"View attachment 417260

Diameter: 11/32"View attachment 417261

11 threads

So 5/16 x 3/4 ....do they even spec bolts as 11/32 x 25/32

Thank you Scott, M8x20 .....see its so much easier ....metric verses inch

edit: @Mc Tool stop the language

 

[ShoalSurvivor]

The bolt is an M8 x 20mm

That means it is not a crank bolt.

Could be a coupler to flywheel

May be an inspection cover bolt

May be an accessory drive bolt

May be an accessory bracket bolt

Spend $11 on a borescope for your phone and check the coupler

Thanks, Scott!
I have verified that all belt/drive accessory and brackets are ok.
I have a borescope - how do I get it inside the flywheel cover to see the coupler? If I pull the starter, I can see the flywheel teeth - do I need to snake in from there?
I'm not aware of any inspection covers on this block or on the flywheel cover.

 

[ShoalSurvivor]

So 5/16 x 3/4 ....do they even spec bolts as 11/32 x 25/32

no need to mock people, tool!