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One and only (sr20)
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Discussion Starter #1
What exactly is a jack knifed crankshaft?? What are the benifits of it.Because I saw it done on a silvia,and civic.. I didnt know what it was so i asked...
 
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It's hard to give a good visual explaination of it. Say you have a circle, and it rolls back and forth for about half it's circumference, like it's in a half pipe thing. So it never turns all the way around, just 90* from it's original contact point when it's not moving in the middle of this imaginary half pipe. The top half of this rolling circle isn't really necessary since it never comes in contact with anything. So you can effectively turn this circle into more of a crescent shape by cutting out that extra area. Get it?
 

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Driver
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You know how crankshafts have those counter-weights on the ends, well when they're jack knifed they're left really thin, so they're still balanced, but now with less mass. So the difference is that a lot of material is removed from the weights, more than in a normally lightened and balanced crank. At least that's what I understand.
 

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also the 'knife' edge helps the crankshaft cut through the oil with less resistance.
Welllll, not exactly.

The OIL is in the oilpan, not up at the crankshaft's level, unless your talking about a 20 year old V8 engine.

"Jackknifing" or "Knife-Edging" a crank reduces the centrifugal weight of the crank, by turning the weights into knife like tapered blades of metal, instead of clunky boxes. This allows the crank to spin more freely from the lack of weight, air resistance, and windage* resistance.

The 1.5 windage trays in the SR20 stop the actual oil level from sloshing and reaching the crankshaft.

*Windage - Airborne oil slung off pistons, cylinder walls, the crank, and rods.
Non-Knife-Edged

Knife-Edged
 

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Driver
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Umm, look at the sides of the weights in the pictures. Notice how the top pic has weights with square edges and the bottom pic has weights with "sharper" edges.
 

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pay your rent!
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sentragtr20 said:
Totally missed it. Now i see it.. Is this somthing that could be done at home??

i wouldnt try it you may throw the crank balance off realy bad and the engine would shake like mad! dont take my word for it all my machining work is done at my most favorite and trusty machine shop but it seems to me this would happen.
 

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One and only (sr20)
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Discussion Starter #15
I wont even try....What is the between lightened and balanced flywheel and this??

Where did you get yours done??
 

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A lightened flywheel is just another form of drivetrain lightening...

The knife edged crank, titanium rods, lightweight pistons, aluminum/chromoly flywheel, multi-disk lightweight clutch, titanium gearset in the tranny, lightweight wheels, aluminum brakes...

That is taking it to the extreme, but that is how MOST drivetrains are made lighter for hig dollar racing teams.
 

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Icy Hot Stunta
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landlord said:



i wouldnt try it you may throw the crank balance off realy bad and the engine would shake like mad! dont take my word for it all my machining work is done at my most favorite and trusty machine shop but it seems to me this would happen.
If you do this, you gotta make sure that the crank is not underbalanced which will really create some destructive vibration.

It is best done with lightened pistons and rods and mallory metal might have to be added to the crank to keep the balance correct.

Usually you are better off just Bullnosing the crank which is a little less extreme than knife edging it. Then you usualy don't have to resort to adding expensive mallory metal to the counterweights.

Mike
 

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One and only (sr20)
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Discussion Starter #19
What is the difference between this and a lightened and balanced crankshaft?? I said flywheel before:rolleyes: ,but meant crankshaft..
 

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One and only (sr20)
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Discussion Starter #20
Oh yeah where can i get some titianiam gear for the tranny. Titianiam is light and strong... Could help for the tranny breakage??
 
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