Cranks
- Thread starter Fingers
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Measured deflection is about the same as the computer model's prediction.
I need to make a jig to hold the crank to I can squeeze on it like a piston and rod would.
I need to make a jig to hold the crank to I can squeeze on it like a piston and rod would.
I can send some old rods over if you want them to make the jig.
Could you line bore 2 old block saddles and put them together to hold it at the main journals?
Could you line bore 2 old block saddles and put them together to hold it at the main journals?
I have lots of old rods, thanks.
I need to work out how to keep the crank from turning while I squeeze it.
Tied up with piston production right now.
I need to work out how to keep the crank from turning while I squeeze it.
Tied up with piston production right now.
I'm assuming you are trying to lock it down at the output to simulate the same load across the crank as it does inside the motor?
Eventually, yes. Right now I am doing measurements piece by piece a throw at a time so I tell when additional loads are introduced.
My lbz crank that I just got pulled out of my motor is busted completely in half at the 4th journal back what do you think was the course of that? I know that this discussion was talking about the 1st journal not being so great I just found it to be very odd to be broke at the 4th journal
Looks like you had to sit through 5 days of failure analysis class too? Hope your instructor was more interesting than mine.
A crankshaft is not purely a shaft. You can't directly apply twisting or bending forces on them from the rod journals, or even the flywheel or pulley. It's a vector.
It both bends and twists at the same time.
Put a _|-|_ shaped bar in a vice. First hold just one end in the vice and see how hard it is to bend. Then put both ends in the vice and bend the journal. Way different. Equal load on both sides is hard to defeat. But with only one side stopping you, it's simple.
In any case, when you have something that breaks at a known location, the ghetto fix is not to analyze why it breaks there, but to figure out how to beef up the fracture area.
Not an easy fix.
But figuring out how to balance the loading on both ends will make it harder to break.
Not an easy fix.
But figuring out how to balance the loading on both ends will make it harder to break.
Any way to increase the radius of the mains? Isn't that what they do in high compression gas motors? Taking some material away actually helps it's longevity my relieving a stress point. Such was the thought with "delipping" pistons.
Could be way out in left field on that one...just thinking out loud. If it can be done, I'm assuming a new bearing would need to be manufactured as well....?
Could be way out in left field on that one...just thinking out loud. If it can be done, I'm assuming a new bearing would need to be manufactured as well....?
There is some merit to relieving the area near the rod journals. Changes the bending from a point (stress riser) to a larger area. Kinda the fishing rod mentality.
The problem, as is the case with most any crank, is that the transition from the rod journal to the throw is a focal point for the loads on the crank.
What causes fatigue like that back in the 4th journal? The outer parts of the break are polished looking almost
IIRC, somebody checked core hardness vs surface hardness on the busted cranks?
If so, what did the find? Could it be the core hardness is too high?
You want the surface hard enough to resist wear, but you want the core mild enough to absorb shock loads, ie - has some give to it.
This is not necessarily just a mental exercise (but close). Perhaps somebody with lots of bucks and lots of time could anneal an OEM crank, then heat treat it again, then cryo it? You'd probably have to regrind it though, and depending on how much it moves, it might be trash when you're done.
If so, what did the find? Could it be the core hardness is too high?
You want the surface hard enough to resist wear, but you want the core mild enough to absorb shock loads, ie - has some give to it.
This is not necessarily just a mental exercise (but close). Perhaps somebody with lots of bucks and lots of time could anneal an OEM crank, then heat treat it again, then cryo it? You'd probably have to regrind it though, and depending on how much it moves, it might be trash when you're done.
I have had it a couple times now... It interest me so it hasn't been to bad yet.
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