[N61WP]

I finally settled on a machine shop to do my block this week. I'm going to have them bore it and then balance the rotating assembly. I asked them about knife edging the crank while they were at it. They gave me a pice of $100-$150 to do it, which didn't seem all that bad to me.
I have always been told that knife edging made a substantial difference on small, low powered engines, but I have no first hand experience.
Any opinions,
ThanX,
James

 

[kwilford]

Knife Edging?

James,

It's probably obvious, but what exactly is "knife edging", and why do you do it?

 

[N61WP]

Keith, as you probably know by now, I'm a "Jack of all trades, but a Master of none", so I'll do my best to explain knife edging, as I understand it.

Knife edging is grinding an edge on the squared off counter weights of the crank shaft. This reduces the total weight of the crank, but more importantly, cuts down on the area of the counter weight that has to cut through the oil that's returning to the pan. The sharpened edge cuts through with less force required, so HP is saved. I've been told that this is more notable on smaller engines. That's about as good as I can do!
Bestus,
James

 

[webster]

I haven't done it but the price sounds good. Is there a set-up charge also or is it included? Is $150 for the whole crank or is it for each counterweight? Here's some info in an attached file (hope it opens)

 

[webster]

oops

 

[webster]

cant reed it. it says knife-edging reduces power loss from hitting the oil and also removes several pounds of weight from crank allowing higher RPM with reliability.the results in the higher RPM
ranges are startling!

Initial set-up charge--------$100.00
for each counterweight knife-edged---$40.00
(if you do 2 or more identical cranks then only 1 set-up charge)

 

[Travis]

Dave Jackson has a couple pics of an aftermarket CIH crank that's been knife edged on his web site.

http://www.qb65.dial.pipex.com/engine 2001.htm

-Travis

 

[wrench459 (R.I.P.)]

James,

It's probably obvious, but what exactly is "knife edging", and why do you do it?

Very old post...
First lets look at nature's fastest fish.
Most have a blunt nose with a very sleek taper to the tail.
As far as I know it's the most efficient shape.

So with a crankshaft you'll want to round the leading edge of the counter wieghts
then go crazy on the trailing and cut the beepin' crud out of it. Very time consuming!

Newer engines cranks have very narrow throws for this reason. But that's
another story.

 

[hrcollinsjr]

Very old post...

So with a crankshaft you'll want to round the leading edge of the counter weights
then go crazy on the trailing and cut the beepin' crud out of it. Very time consuming!

Old school was to 'knife edge' the leading edge of the counterweights to cut windage. As Wrench has pointed out, new thoughts are to make it more aerodynamic with a blunt or rounded leading edge and a thinner trailing edge. Think of an airplane wing BUT symmetrical, no 'lift' or in this case 'thrust' is wanted. Hope this makes some sense.

Harold

 

[opelnut10]

Knife edged crankshaft

Old school was to 'knife edge' the leading edge of the counterweights to cut windage. As Wrench has pointed out, new thoughts are to make it more aerodynamic with a blunt or rounded leading edge and a thinner trailing edge. Think of an airplane wing BUT symmetrical, no 'lift' or in this case 'thrust' is wanted. Hope this makes some sense.

Harold

Knife edging the counterweights is only part of the modification process in preping a HP crankshaft. Most every CIH crank that I ever checked was so close on the balance weight that they would not light up the numbers on the balancer (never checked a fully counterweighted crank though). My method was to bull nose the leading end then taper the counterweight back to the trailing end, THEN chuck the crank in the lathe and cut down the diameter of the counterweights until it started striking on the journal side. Once that operation is complete you take material off the taper to get the balance right. This achieves two things needed for HP engine, it revs quicker and it is not as hard on bearings because the crank is lighter.

 

[wrench459 (R.I.P.)]

Thats good to know Lloyd I've only checked a few cranks.
So far all of them has been just a few grams out of balance.