Are Grade 8 bolts from Ace Hardware ok to use for the two long bolts you use to attach the motor mount on the engine to the motor mount on the frame?

I ordered arp bolts but they came out to be too short by an inch or more.... I have UMI motor mounts mounted to spohns k-member (the k-member never came with mounts even though i ordered it or it said it comes with mounts... long story dont want to bring it up)

I am using the factory mounts that go on the motor from my 305 TPI.

 

Which ARP bolts did you order?

 

ARP P/N# 430-3105. I could not find bolts that were longer... actually summit doesnt even tell you the length of these.

 

According to the ARP catalog that's supposed to be the right one. The stock bolts are 7/16-16 x 4.75", P/N 15529954. How long are yours?

 

These ARP's are only 3-3/4" from one end to the mounting face of the flange on the head. Obviously too short by an inch like i had figured... Might have to call ARP tomorrow. But again, I wonder if grade 8 bolts are good enough. Dont want to mess around with this since they are the only two bolts that hold the motor in place lol

 

The grade is the tensile strength of the bolt, it doesn't mean much for the sideways loading that the motor mounts are going to put on it. I doubt the factory bolts are even grade 5.

The ARP bolts are probably for the old pre-clamshell motor mounts.

 

Ok you are right then. I wonder if there are shear strength ratings. I will check online for grade 8 bolts, im sure its out there. Hopefully some other people chime in if they have used grade 8 bolts.

 

Remember, it's going through a motor mount made of rubber enclosed in sheet metal held together with rivets. If there were any forces to worry about there, any of those things would tear apart long before that bolt ever would.

 

actually i am using solid motor mounts but I do see your point there.

 

I found the same problem with the ARP bolts. Frustrating, isn't it? Jegs couldn't find any others listed either. I'm not too worried about the rivets because the 3 (or in my case 4) clamshell to K-Member bolts hold the clamshell together anyway. does anyone happen to know the size of these? i was going to order some in stainless.
grade 8 should be fine for the pass through bolts, but i'm still looking. i'll let you know what i find.
Eric B

 

I found something online that said shear strength is roughly 60% of the tensile strength.

“As an empirical guide, shear strengths of carbon steel fasteners may be assumed to be approximately 60 percent of their specified minimum tensile strengths. For example, an SAE grade 5 hex cap screw has a specified minimum tensile strength of 120,000 psi. Therefore, for design purposes, its shear strength could be reasonably assumed to be 70,000 psi.”

It's from Portland Bolt and Manufacturing Company: http://www.portlandbolt.com/faqs/bol...considerations . I have no idea if those numbers would even help. I got bolts from my local John Deere dealership, rated at 10.9 nM. Hopefully they work.

 

It specifically says "carbon steel fasteners" so maybe it'll be different for other materials.

 

What worries me more is the fact I am using solid motor mounts. The vibrations will be far greater than using the urethane mounts... I have Grade 8 bolts in there which I think are 7/16" At the very worst, if the bolt goes, the mount is still not going to go anywhere because it would drop down about 1/2-3/4" and the clamshell will hit the solid mount and nothing will be completely gone. We'll see how she does i guess