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what grade should engine support bolts be ?

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Old 03-09-2007, 12:48 AM
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Default what grade should engine support bolts be ?

have to replace many of mine, 454-420 engines. What grade bolts should I use? I went to a marina today, they did not have any and told me to get some at places like home depot !!! Went there, no stainless bolts first, and second, what they had was all grade 5. How many kind of natch on bolt head should I see according to the right bolt grade?

Thanks!
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Old 03-09-2007, 04:29 AM
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This is where I get mine but usually purchase by the box.


http://www.dlilly.com/
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Old 03-09-2007, 05:54 AM
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Bolt grade identification http://shopswarf.orcon.net.nz/boltid.htm
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Old 03-09-2007, 06:19 AM
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I would go with stainless, make sure you put anti-sieze on the threads, or they may become self-locking bolts!!! If you couldn't get stainless, grade 8 would be the other choice. Grade 5 is a waste of time for motor mounts.
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Old 03-09-2007, 06:21 AM
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Lowes in my area of Houston have Stainless Grade 8 bolts..
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Old 03-09-2007, 09:58 AM
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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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Old 03-09-2007, 10:07 AM
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Quote:
Originally Posted by boatman22 View Post
Lowes in my area of Houston have Stainless Grade 8 bolts..
As far as know, stainless does not come in grade 5 or 8.

I know whatever you put in there has a tendency to rust but stainless is weak, I wouldn't trust stainless lag bolts to hold my motor mounts.
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Old 03-09-2007, 10:24 AM
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Quote:
Originally Posted by RonS View Post
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.
Same here... I always use steel with nylock nuts and washers on both sides. I've seen people use stainless cause it looks cool but stainless is soft compared to steel.
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Old 03-09-2007, 10:30 AM
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NO STAINLESS.....I learned the hard way. Sheered them right off and motor was lying in bildge! Grade 8.....
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Old 03-09-2007, 11:35 AM
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Do not use stainless for engine mount bolts! The sheer strenght of stainless in fairly low, the will fail. Use Grade 8 carbon alloy steel, look for 6 hash marks at the points of the hex bold head.
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