Crank knife edging......

[PAnut240]

Ok, well as some as you know I am finally in the process of rebuilding my SR. Now I am going no-holds-bar on this and everyone keeps telling me to get my Crank Knife Edged. I'm already geting it ballence, I've had that done before but I have no Idea what knife edging does or what they do. If someone can give me some insite I would appreciate it. This may have been asked before but I don't have time to search for it. Thanks and happy driving.
Jim

[240racer]

all it means is that they turn more material off the crank. The chops end up really sharp like a knife. It's a rotational weight reduction thing and it does make a difference. It's not quite as much weight as a flywheel, but it does make a difference.

[rubbersidedown]

its also believed that by knife edging it, it will decrease resistance when the crank moves through the oil.

[zspturbo]

imagine a fat guy swimming. thats what you stock crank is like. now imagine a skinny guy swimming. alot less drag and resistance, right? thats a knife edged crank. the leading edge is sharpened like a knife, so it slices through the oil much better. its really effective on high revving engines.

[PAnut240]

ok thanks guys. That helps me out alot. Guess I'll have to dish out another cuple hundred bucks.lol Later
Jim

[fogleroller]

Did you ever get your crank knife edged? Where and how much was it?

thanks (i know this is an old post, but it has the info i need)

[WilloW]

Did you ever get your crank knife edged? Where and how much was it?

thanks (i know this is an old post, but it has the info i need)

Any good machine shop could do it, last time I checked around my area it was around $100-200.

[Ghettokracker71]

100-200? are you sure thats right ? Sounds kinda cheap...really

[fogleroller]

Wow, so you say it's more than that? Is it really worth it? What about just balancing alone? $100-200?

[Ghettokracker71]

I don't know but it sounds cheap,$100-200...just doesn't sound right to me...but hey,if it is than I'm definitely getting my crank knife-edged soon ! What benefit would it be to get the crank balanced though ? I know that if you take off your stock dampner for aftermarket pulleys it supposedly will eat your crank b/c no balance,....After its balanced...does that not matter ?

I want to have the most efficient componets I can have...so I am definitely planning on running knife-edged,but I don't know what balanced does....I know that the 4G63E Mitsu boys are really big into knife edging...

[LanceS13]

The original idea of knife-edging back in the 70's was to reduce crankcase "windage" by sharpening the leading edge of the counterweights. Aside from the fact that you're lightening the rotating assembly, I think it's doubtful that it provides any benefit. It's pretty common knowledge that the most aerodynamic shape has a blunt leading edge and tapers to a sharp tail...not the exact opposite. Sharpening the trailing edge may actually affect windage...otherwise, it's just weight reduction. But remember, those are counterweights...if you lighten those, you must lighten the rods/pistons.
The more important thing to do is balance the assembly. If it turns out you're counterweights are heavy, it might be a good opportunity to knife-edge. Just make sure it's all balanced when done...a very small amount of metal can have an equivalent weight of several hundred pounds when being subjected to the accelerative forces found inside an engine. Making sure everything is balanced decreases bearing loads and just makes things run smoother and with more reliability.

[fogleroller]

wow, that is some good info!!! i'll stick to just balancing the crank

[WilloW]

100-200? are you sure thats right ? Sounds kinda cheap...really


This was for a honda motor a while back, I found out that it wasn't neccessary anyway so I never went through with it.

[DamnedButDetermined]

The original idea of knife-edging back in the 70's was to reduce crankcase "windage" by sharpening the leading edge of the counterweights. Aside from the fact that you're lightening the rotating assembly, I think it's doubtful that it provides any benefit. It's pretty common knowledge that the most aerodynamic shape has a blunt leading edge and tapers to a sharp tail...not the exact opposite. Sharpening the trailing edge may actually affect windage...otherwise, it's just weight reduction. But remember, those are counterweights...if you lighten those, you must lighten the rods/pistons.
The more important thing to do is balance the assembly. If it turns out you're counterweights are heavy, it might be a good opportunity to knife-edge. Just make sure it's all balanced when done...a very small amount of metal can have an equivalent weight of several hundred pounds when being subjected to the accelerative forces found inside an engine. Making sure everything is balanced decreases bearing loads and just makes things run smoother and with more reliability.


You are correct about sharpening the trailing edge but as it is now the leading edge of the counterweights are a flast surface. Not aerodynamic at all. Any kind of sharpening or rounding of the leading adge will produce desirable results. You are also correct about balancing the the entire assembly. If you are going this far into an engine rebuilt chances are you are getting aftermarket pistons/rods anyways so they will be light, therefore allowing the reduced weight of the counterweights.