Thread: Great Article On Crankshafts

Crankshaft Tech - Popular Hot Rodding Magazine

They have great articles on just about everything. And for some reason people (even very smart, highly regarded people in our crowd) dismiss old school knowledge on that site as wrong or misguided.
Talk about the other way around...

While we are on the subject of cranks, maybe it's just me but I believe these are knife-edged cranks:







This is called a knife-edged crank, but is not.


It is still a nice thing to do and benefits are there, it's just not knife-edged. It's got to have a different name. Knife-edging is done on a lathe to the side and bottom of the counterweight and maintains the radial balance of the crank and is the preferred way to lighten a crankshaft when installing lighter pistons/rods. Sharpening the leading and trailing edge of the counterweight can't be done on a lathe and could easily throw off the radial balance of the counterweight if done incorrectly and can't remove nearly enough material to be used as a lightening technique.

Two different shaping techniques with two different application methods with two different main goals. Call them the same thing?

A true knife edged crank should have a leading edge that is knife edged. This leading edge keeps the crank aerodynamic - fluid dynamic


The 3 pictures of the cranks above are knife edged also but this process is more for removing weight while keeping the crank properly balanced

My crank has a combo of both... lol.
I guess like Andreas says, the Leading edge is the part which needs to be most Aero/fluid dynamic and is probably most important, but the whole edge of the counterweight being sharpened would also aid the counterweight's overall aero/fluid dynamic-ness IMO.



I bet that crank is ACE weight-wise, you're right.
But..
I can picture the very flat and blunt leading edge of those CW's causing drag in the air, and imagine them when they hit the oil!

SLAP!

Joe

Knife edged cranks

This process below is called knife edging but is not. This is the way you lighten a crank on a lathe this procees leaves a sharp edge where the name knife edging is missused.

From the article linked above:



Not worded very well, but the obvious is being said. If the leading edge looks like this you're in trouble:


It should look like this:


And Miko by the description above they say "knife-edging was developed more for ease of balancing" which contradicts what you've explained above. It's pretty obvious that the term isn't as well defined as I'd like and people use it interchangeably to describe both shaping techniques. Which is super annoying.

They can be distinguished by stating what edge you're wanting to knife-edge:

Leading Edge of CW.
Outer Edge of CW.

Joe

That's great, except that's not how people advertise them. They just say it's knife-edged without letting you know which edge.
I guess if they provide a picture with their advertisement it clears up any confusion.