Thread: Great Article On Crankshafts

BennFenner you need to read what I said again. I hope this does not go into another I dont understand what you wrote or you are reading diffrent from how I typed it.

No, I understood what you said. But the quote I pulled from the above article just seems to contradict what you've said, that's all. I'm pretty sure that contradiction is due to there not being a standardized definition of what "knife-edging" actually is.

Unless you define it as:
"Creating a sharp edge on the crankshaft counterweight to reduce windage and/or remove weight from the counterweight either by sharpening the bottom edge, the leading/trailing edge, or a combination of the two."

You need to read what i said again. starting from post 4.

Yep, I understand what you're saying. I'm inclined to agree with you, except for one thing. This is a quote from the article linked in the first post:

"knife-edging was developed more for ease of balancing"

So you're telling me that sharpening the leading and trailing edge of the counterweight is true knife-edging. But the article says at one point that knife-edging was developed more of ease of balancing. How does creating a sharp leading and trailing edge aid in balancing?

Actually looking at the three cranks I posted all of them seem to have a pretty good point on the counterweight that should spear into the oil pretty well. It might look blunt from our angle, but imagine the counterweight rotating and plunging into the oil. It looks like they've got a pretty good point going on, especially the crank image you quoted.

I never said creating a sharp leading edge and trailing edge was an aid in balancing.

I said clearly above it is done for aerodynamics - fluid dynamics.

They said that the only way that they could balance a crank propely was in a lathe which gives a sharp outer edge, which is known as knife edging

None of these pictures above show a crank with a complete leading knife edge and knife edged outer edge.

The sharp outer edge would be centralized just like the leading edge of the crank.

Not from where I'm sitting lol... the leading edge is still Square and Blunt as fuck ....
Excuse the MS paint job lol..
(now I know there aint a massive square area.. but its still frigging square/blunt! that shit needs knife edgine on the leading edge!)

Hope this clarifies things a bit for you man...
Joe

I had enough with this take from it what you will.

If you think the crank spins - plunges into the oil then you are crazy.

You need to get an upper and lower oil pan an put 4 q of oil in there and tell me that the crank is plunging into the oil. Then consider how much oil is in the motor when it is running and then ask yourself again how the crank is plunging into the oil.

There is no more than 3 q of oil in the oil pan when the motor is running,


All the crank does is spin through air mixed with vapor.


No more please leave it alone.

Shaggy_master I see exactly what you're talking about, but if you look at that flat edge and think about how it will encounter the oil (assuming the oil is flat and level like a calm lake) you'll see that the flat edge doesn't actually hit the oil like a belly flopping diver. The point should hit the oil first and the edge will gradually enter the oil.

I'm talking about the "flat" face on the counterweights. The flat face on the rod journal side looks worse I agree. It does look like it would slap right into the oil, except that it too seems to have a pretty good shape to it upon third inspection not being as blunt as it looks.