Offshoreonly.com - what grade should engine support bolts be ?

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- - what grade should engine support bolts be ? (https://www.offshoreonly.com/forums/general-boating-discussion/153190-what-grade-should-engine-support-bolts.html)

Panther

03-09-2007 02:02 PM

In all my years doing this, 99% of all the motor mount bolts I've ever seen are steel. The zinc chromate plated helps with the corrosion. Also, most of the offshore mount thru bolts have always been fine thread steel, not coarse.

nocigarette

03-09-2007 03:17 PM

Fine thread, grade 8 especially for motor mounts, use the stainless for cosmetic stuff not to hold down your powerplants.........

Panic Button

03-09-2007 03:48 PM

Quote:

Originally Posted by Interceptor (Post 2052258)

Another thing everyone should be very concerned about is there are a lot of fake hardware manufacturers out there.
I'm in the military equipment business and virtually every fastener we use is grade 8. A number of years ago a lot of fake grade 8 stuff was being made in Taiwan.
ed

If I remember right it was the mid '80's... We had to change out hardware on about 50 F-15 & 16's due to that.:eek:

cuda	03-09-2007 04:03 PM

I've heard that grade 8 shears more easily than grade 5, even though it has a higher tensile strength. I don't know for sure. I do know that grade 8 doesn't rust as quickly as lower grade bolts.

rdp145

03-09-2007 04:07 PM

Isn't tensile strength and shear different? I would think the highest shear strength is what your after for Motor mounts. And I don't think that SS?

PatriYacht

03-09-2007 04:13 PM

There should be businesses that specialize in fasteners in any decent size city. Here in the Detroit area I can think of about 6 right off the top of my head. They are much cheaper than ARP. Get the grade 8 and you'll be fine.

Panther

03-09-2007 04:19 PM

Quote:

Originally Posted by rdp145 (Post 2052537)

Isn't tensile strength and shear different? I would think the highest shear strength is what your after for Motor mounts. And I don't think that SS?

Yes! If stainless was strong enough I'm sure mercury would use it for their engine couplers, fly wheels and drive shaft couplers. :drink:

Comanche3Six

03-09-2007 06:52 PM

Quote:

Originally Posted by Steve Miklos (Post 2052183)

ARP claims there stainless fastener is Grade 8 strength.

Bingo!

2112	03-09-2007 11:02 PM

Quote:

Originally Posted by THEJOKER (Post 2052094)

NO STAINLESS.....I learned the hard way. Sheered them right off and motor was lying in bildge! Grade 8.....

So, without any warning, you sheared of 6 or twelve 1/2" diameter bolts allowing you motor to drop? Damn.

Something I have noticed on aftermarket truck suspensions they use Grade 5 bolts. But they are very large diameter, 7/8ths etc.

Anarchy Powerboats

03-10-2007 02:12 AM

Quote:

Originally Posted by RonS (Post 2052050)

My under standing has always been that you do not want to use stainless for motormounts because of the fact that stainless is more brittle and has a tendency to shear off.

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