1963 Motor Mount Bolts - Grade 8?
Are the motor mount bolts for 1963 all suppose to be Grade 8? I am talking about: (i) the 6 bolts attaching the motor mounts to the engine block [ 3/8-16 x 7/8]; and (ii) the 2 bolts that attach the motor mounts to the frame [ 7/16-20 x 4]. I'm not sure if the bolts from my car are original and the frame bolts appear to be Grade 5 (three slash marks with "BS" initials). Thanks, Rob.
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Re: 1963 Motor Mount Bolts - Grade 8?
Grade 5 is likely proper. There would be little point to screwing hardened grade 8 bolts into the soft (relatively speaking) iron block. -
Re: 1963 Motor Mount Bolts - Grade 8?
Rob------
The GM #3774078 bolts (motor mount to block) were GM-280M material grade (SAE grade 5; 3 radial lines).
The GM #3817224 bolts (motor mount to frame bracket) were also GM-280M material grade. These bolts were 7/16-20 X 3-7/8" and were zinc plated. These bolts had a piloting, chamfered tip.
By the way, in 1974 GM did go to GM 300M grade bolts (SAE grade 8) for the motor mount to block application on Corvettes. These bolts were GM #331246.Last edited by Joe L.; June 3, 2017, 04:52 PM.In Appreciation of John HinckleyComment
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Re: 1963 Motor Mount Bolts - Grade 8?
Thank you both for the help!Comment
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Re: 1963 Motor Mount Bolts - Grade 8?
A few months ago I sold a pair of 63-65 Corvette motor mount bolts that were 7/16"-20X 3 7/8" and marked "UR" with 3 radial line segments (grade 5). I have a few photos of them if anyone is interested.
DaveComment
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Re: 1963 Motor Mount Bolts - Grade 8?
Joe,
I believe that the bolts were zinc plated. Lately I've been having trouble inserting photos to my imgur account. When my son visits us I'm sure he will figure things out.
DaveComment
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Re: 1963 Motor Mount Bolts - Grade 8?
Joe,
Here are the photos.
Dave
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Re: 1963 Motor Mount Bolts - Grade 8?
Dave------
These are exactly as I would expect them to be (although, of course, manufacturer's headmark could vary).In Appreciation of John HinckleyComment
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