Type Bolt For Engine Mount

cyauch

Petty Officer 3rd Class
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Jul 10, 2020
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Figur ed since i had to pull the engine for leaking transom seal, i'd go ahead and clean up the motor mounts. They wouldn't budge with the engine in the boat so i remove the two lag bolts to the hull. Not a drop of rust or corrosion on those. they looked brand new!

The single bolt to the engine bracket, however, is destroyed...both sides. #3 in the pic is what i'm talking about, and want to replace. In fact, I'm probably gonna go ahead and just replace the nuts and washers too. #5 looks in good shape and the engine was super smooth prior to removal

So...i've read a number of thoughts, reviews, etc from all walks of 'marine' sites. Problem is, after two posts they all dive into a SS vs mild steel vs bronze vs you suc vs no you suc in-fighting. I get shear, dead load, etc. etc. characteristics but to be honest, I'm thinking a SS bolt and nuts should suffice right? I mean, i get the moisture blah blah, but the reality is they won't be submerged.

The existing ones i soaked for almost two weeks with PB and other chemical baths. Tried LOTS of heat. in the end, both top nuts (called locking nuts right?) rounded out so i had to cut the bolt
 

muc

"Retired" Association of Marine Technicians...
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what you working on?
 

cyauch

Petty Officer 3rd Class
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Jul 10, 2020
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My bad. VP 5.0 GXi-E also forgot to attach the VP diagram. I have the high-mount type. not the flush. Thanks
 

Attachments

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dypcdiver

Lieutenant Junior Grade
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Nov 1, 2005
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1,016
I can't see any reason why you cannot use a stainless bolt of similar size. It is not as if it is used to ground the engine or that it is highly stressed.
 

stang32

Chief Petty Officer
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Jul 16, 2004
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513
i would just use a grade 8 bolt and hardware, coat it well with anti corrosion chemicals once installed.
 

cyauch

Petty Officer 3rd Class
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Jul 10, 2020
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Thanks! I was thinking a grade ;8 fine thread bolt as well along with nuts. I was gonna re-used the existing washers since they still have the poly paint on them and are in good shape. the mounts themselves are in good shape was well.
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
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The block threads are 3/8-16. Use grade 8, then paint
 

cyauch

Petty Officer 3rd Class
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Jul 10, 2020
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91
Thanks Scott! The bracket and 3 bolts on the block are in good shape. In fact, the entire engine looks surprisingly clean with no loss of the original red paint.

#3 in my attachment above and its associated top nut are the bad actors. the top nut (locking i think its called?) is corroded so bad they both rounded off. And the threads of #3 that stick above it are an amusement park of rust.
 

muc

"Retired" Association of Marine Technicians...
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If you want Volvo parts, here are the updated numbers.
23345013Hexagon Screw $7.12p
60113763Hexagon Nut $3.37p
 

cyauch

Petty Officer 3rd Class
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Jul 10, 2020
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As always, thanks Muc! Power finally restored and yard debris cleaned up so finally getting back to this.

Stupid grease tube caused me an issue but i'm posting that in a new thread,,,
 

muc

"Retired" Association of Marine Technicians...
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The reason I recommend the Volvo fasteners.
MerCruiser uses a locking tab to keep these nuts from loosening, Volvo doesn't.
I find a lot of MerCruisers loose when that locking tab wasn't bent over.
I find very few Volvos loose.
It might be possible that Volvo uses a different thread profile that helps keep them from loosening?
 

cyauch

Petty Officer 3rd Class
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Jul 10, 2020
Messages
91
Thanks Muc. Motor and OD back on the boat. factory bolts worked great. At least a little piece of mind.
 
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