# (Jack knifed) crankshaft???



## sentragtr20 (Jun 8, 2002)

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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## Adam (Apr 30, 2002)

It's when you get some of the excess metal off the crankshaft to lighten it up.


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## sentragtr20 (Jun 8, 2002)

So it just like a lightened and balanced crankshaft??


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## Adam (Apr 30, 2002)

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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## sentragtr20 (Jun 8, 2002)

Not really


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## barnoun (May 7, 2002)

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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## James (Apr 29, 2002)

also the 'knife' edge helps the crankshaft cut through the oil with less resistance.


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## SE-R Kid (Jun 24, 2002)

> 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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## sentragtr20 (Jun 8, 2002)

I dont see the difference...


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## barnoun (May 7, 2002)

look at the edges...


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## sentragtr20 (Jun 8, 2002)

Edges of whay?? They both look the same..


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## barnoun (May 7, 2002)

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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## sentragtr20 (Jun 8, 2002)

Totally missed it. Now i see it.. Is this somthing that could be done at home??


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## landlord (Jun 11, 2002)

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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## sentragtr20 (Jun 8, 2002)

I wont even try....What is the between lightened and balanced flywheel and this?? 

Where did you get yours done??


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## SE-R Kid (Jun 24, 2002)

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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## 200'side (May 24, 2002)

But worth it right? How much does this usually run someone?


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## morepower2 (Apr 19, 2002)

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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## sentragtr20 (Jun 8, 2002)

What is the difference between this and a lightened and balanced crankshaft?? I said flywheel before ,but meant crankshaft..


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## sentragtr20 (Jun 8, 2002)

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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## morepower2 (Apr 19, 2002)

sentragtr20 said:


> *What is the difference between this and a lightened and balanced crankshaft?? I said flywheel before ,but meant crankshaft.. *


It is sort of the same thing but contrary to popular belief, you can just hack weight of the crank. The counterweights on the cran are to offset the force of the pistons and rods going up with a counter downward force. You can only lighten the crank by a percentage of the amount that you take weight off of the pistons and rods or you can have problems.

Knife edging is just trimming the CW's in a shape that cuts through the windage in the crank better.

Mike


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## morepower2 (Apr 19, 2002)

sentragtr20 said:


> *Oh yeah where can i get some titianiam gear for the tranny. Titianiam is light and strong... Could help for the tranny breakage?? *


No because Ti is a very poor gear material. It galls when run against itself, not good for gears. It is also only about as strong as mild steel.

It is 40% lighter than steel though and 10x more expensive, plus it is 5x more expensive to machine.

Mike


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## sentragtr20 (Jun 8, 2002)

Then what would be good to strenghten that second and third gear?? Besides cryogenics and shotpeening??


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## SE-R Kid (Jun 24, 2002)

Call Quaife


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## morepower2 (Apr 19, 2002)

SE-R Kid said:


> * Call Quaife  *


I did already and quaife was not interested. I am working with a company in austrailia to make a bulletproof gear set.

Mike


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## Guest (Jul 28, 2002)

damn its tru you really do learn something new every day.


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## sentragtr20 (Jun 8, 2002)

Red88: what did you learn??


Is there any stronger metals besides titianiam?? To do the gears..


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## Guest (Jul 29, 2002)

that its not as always as easy or simple as it sounds to do something.


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## morepower2 (Apr 19, 2002)

sentragtr20 said:


> *Red88: what did you learn??
> 
> 
> Is there any stronger metals besides titianiam?? To do the gears.. *


Titainium is not that strong, it is only as strong as mild steel. It is hella strong for it's weight though. The PAR gearset will be made from Hi Nickel chome-molly

Mike


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## morepower2 (Apr 19, 2002)

sentragtr20 said:


> *Then what would be good to strenghten that second and third gear?? Besides cryogenics and shotpeening?? *


The gearset I am working on will have all new gears that are wider and made of a stronger metal, an alloy steel.

It will also be constant mesh like a bike tranny so you can do clutchless shifts. Just like a touring car.

Mike


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## sentragtr20 (Jun 8, 2002)

what is that running you.. You must be in to road racing.. Wider gears are for a touring car,because it allows you to get higher speeds..Takes longer to redline..


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## morepower2 (Apr 19, 2002)

sentragtr20 said:


> *what is that running you.. You must be in to road racing.. Wider gears are for a touring car,because it allows you to get higher speeds..Takes longer to redline.. *


It will cost about 3000 US. The stock gears are so narrow its amazing that they don't break with a stock motor. I don't know what you are talking about the gear width having anything to do with getting to redline qiucker. It makes no difference within reason.

Mike


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## sentragtr20 (Jun 8, 2002)

Oh,I thought you were talking about spreading them apart.. Not accually makeing them wider... How about if I use an alloy on the second and third gears???


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## barnoun (May 7, 2002)

morepower2 said:


> *
> 
> It will cost about 3000 US. The stock gears are so narrow its amazing that they don't break with a stock motor. I don't know what you are talking about the gear width having anything to do with getting to redline qiucker. It makes no difference within reason.
> 
> Mike *


Is the gearset for the GA tranny, or the sr20?


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## morepower2 (Apr 19, 2002)

sentragtr20 said:


> *Oh,I thought you were talking about spreading them apart.. Not accually makeing them wider... How about if I use an alloy on the second and third gears??? *


Can't, they are fixed to the countershaft.


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## morepower2 (Apr 19, 2002)

barnoun said:


> *
> Is the gearset for the GA tranny, or the sr20? *


SR tranny, at the current stage of development, the GA cars don't make enough power to break their trannys.


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## sentragtr20 (Jun 8, 2002)

LOL, thats funny but true!! I am going to use a steel alloy for the gears...


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