Knowledge does not equal understanding, yet again

[B00mb00m]

I get it, but the only time we actually have a shear plane is when the connection fails. I'd prefer to keep the connection viable by maintaining the bolt tension. The constant hammering of the bolt to the insides of the mounting holes would destroy the mount in a few miles.

Sounds like its one of those things that just works in practice.

To put some numbers behind this, if we're using a 1/2-20 bolt, grade 8, torqued up to 90 ft-lbs (plated), makes a clamp load of 18,000 lbs. Mu of roughly .15 for a plated steel (source) gives the ability to react roughly 2700 lbs at each friction surface, which is more than 1/4 of our vehicle weight but not by a huge margin when you include dynamic factors. It makes me think you probably do see some movement from the bolt in the clevis under big loads since we don't really prep those surfaces to keep lubricant or paint out and at some points and under deflections the bolt carries the shear load as well.

If the bolt were designed to carry the shear load entirely the clevis to bolt fit would be designed to be as close to 0 backlash as possible and you would probably see bushings used.

 

[toximus]

I have another one. How can 3 little 3/8"ish bolts be all that connects 500hp from an engine to the transmission? It blows my mind.

 

[mrblaine]

I have another one. How can 3 little 3/8"ish bolts be all that connects 500hp from an engine to the transmission? It blows my mind.

Simple leverage. Look at the TJ 4 liter crank. Small bolt circle at the end of the crank uses 6 1/2" bolts to do the same job that the 4 smaller ones do bolting the converter to the flex plate because they are on a much larger bolt circle. That and the flex plate has to be less than 1/8" thick steel.

 

[toximus]

Simple leverage. Look at the TJ 4 liter crank. Small bolt circle at the end of the crank uses 6 1/2" bolts to do the same job that the 4 smaller ones do bolting the converter to the flex plate because they are on a much larger bolt circle. That and the flex plate has to be less than 1/8" thick steel.

I love it when a solution is accomplished with total understanding of the forces involved. Sure enough, 6 bolts flex plate to the crank, 3 flex plate to the converter (on my LS3).

 

[mrblaine]

I love it when a solution is accomplished with total understanding of the forces involved. Sure enough, 6 bolts flex plate to the crank, 3 flex plate to the converter (on my LS3).

Typically, the bolts that hold the flex plate to the crank are place bolts. They have a specific design to the head that allows it to flex and when it flattens under torque, the friction is more uniform at the faying surface since it has a spring action and that prevents them from working loose under cyclical loads far better than a typical hex head cap screw.

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