FSAEracer03

www.mcmaster.com Gotta love it

It's too bad they don't give the shear strength... because that's really what we need here.

adrial

Kevin,

If you download Unbrako's engineering guide it gives max load in single shear for various bolt diameters...
Approximetely divide by 10 to see how much load it can take and last forever.

I've heard of 300ksi steel...so its very well possible that those GKN bolts are stronger than anything we will buy. Especially if the threaded/non-threaded breakoff area is in a good spot on the GKN's... It's worth comparing em though.

FSAEracer03

Hey bud,

Thanks, I'll have to check that out. McMaster Carr and other fastener suppliers don't usually give that. That'll help me out in the future if I order from them.

-Kevin-

rage2

Launching hard (for me) means at a stop, rev to 5000 or so rpm and just drop the clutch for a hard launch. Once I get going, power shift (wide open throttle, clutch-shift-clutch real quick) into second gear. I never do this, that's what breaks 1st and 2nd gear.

What broke the bolts for me was just driving hard. Meaning I get off the line nicely, shift into 2nd, then floor it for that acceleration rush . Over time, the bolts get weak and just shear.

AlexE

So if I hear you correctly...........what you are saying is that I should wait until the end of the summer (ample time for the new bolts to weaken) before having a run against you on HWY2.

Zero10

^^^
Haha, that's fighting dirty, sounds like an Edmontonian :P

IceShark

You know Danno N. had some comments on the CV bolts that made sense. When you back them out you get all sorts of crud in the receiving thread. As well as dragging grease when you put the new bolts back in.

I used q-tips dipped in acetone to clean out the holes, cleaned off the plate faces and then blue loctite. Haven't backed out yet. I like this idea better than a saftey wire approach. If the saftey wire ever comes into play you have already lost the battle. The real force transmission is through the friction between the plate faces, not shear force on the bolts. The bolts back out a bit and you are a dead duck.

Ben Z.

I think that's correct. So the shear strength of the bolts shouldn't be an issue. You could get stronger bolts then torque them a little more?

FSAEracer03

That's completely false. Yes, the power transmission (torque transmission, really) is generally going to be through the plate faces. The bolts tensile strength is what holds the plate faces together, but when the bolts fail it is certainly a factor of shear strength, not tensile. They fail when the plates slip, and when that happens, they fail under single shear.

The problem can't merely be solved by torquing them down more, as the bolt strength doesn't match the strength of the threads, and more importantly, the strength of the bolt head.

IceShark

Oh boy Kevin, that is a boneheaded response. The point was the friction of the plates was what was important so you need those bolts to stay tight and not back out. How to do that? Make sure the threads are clean and loctite them. And clean the plate faces off. A saftey wire ain't going to help much as the bolts will back off enough that the plates are not torqued together tight enough by that time.

Using a higher strength bolt and torquing higher, well you are right that may not work as the threads are in the base metal. But that wasn't the original point really.

adrial

If I'm remembering my materials class correctly, isn't the shear strength determined by the tensile strength? Because even in pure shear, you can break it down to the principal stresses which are compressive/tensile.

If you take a piece of chalk and twist it until it fails, the break will be at ~45 degrees IIRC...twisting is pure shear. 45 degrees is the principal angle for pure shear.

Correct me if I'm wrong...

NZ951

inactiveuser92616

I am in a few of these classes right now, and IIRC (not gonna break out the book right now) the 45* break line is for brittle fracture only.

iloveporsches

Lots of future Mech. E's here!

If the bolts are shearing off, isn't the system already failing anyways? Under normal conditions, shouldn't most/ all of the force be transmitted through the plates, and not in shear through the bolts? So you get a stronger bolt, it survives a little longer until it backs out enough to create enough shear to snap. Back to square 1.

Unless I'm wrong, and even under "normal" conditions (ie properly torqued down and tight), a 400whp car will still transmit enough force to shear the bolts.

Re-animator

You can always spot weld the plates together.