Knife Edge Crank? Your thoughts?

[infamos]

What is your take on a knife edge crank?

 

I read mostly negative posts on the internet about the knife edge crank and that it doesn't free up of enough HP to compromise your crank. I also read an interesting post made from a SEMA attendee that if you go this route, you have to change the bearings annually.

 

Here is the quote:

I went to SEMA show and talked directly with eagle about the knife edge crank,

they said they were a great crank but, the motor should be torn down

every season to replace the bearings because since they take so much

off the crank it is impossible to balance it as well as a stock crank.

 

I may be rebuilding a motor and wanted to know if a knife edge crank was a good idea.

[Technology]

I'd do it if you plan on racing a lot with the car. And I mean road racing, then you'd employ a lot of other oil control and racing parts. I'd also only do it if you are going to go insane with the engine, like 9:1 pistons and aftermarket connecting rods, different transmission, etc.

[Lance_S]

Seems like going dry sump would be a much better option, way more power gain and much less work.

[The Rabbit1]

knife edge takes so much weight off the crank you'd never get it to balance with steel rods, you'd have to go hyper-u or aluminum or such to lose weight on everything. Are you trying to spin like 9k rpm or something?

[infamos]

knife edge takes so much weight off the crank you'd never get it to balance with steel rods, you'd have to go hyper-u or aluminum or such to lose weight on everything. Are you trying to spin like 9k rpm or something?

No. Just seeing if this is worth it. I see it as an option for certain rebuilds. The more painless the better.

[infamos]

Seems like going dry sump would be a much better option, way more power gain and much less work.

I will have to look into this.

[Chad]

the crank doesn't balance the rods, the rods balance themselves. 1 & 4 balance 2 & 3. the crank weights balance the rod journals. By removing a lot of mass from the weights without removing weight from the rod journal ends, you are upsetting the balance of the crank down it's axis. It will still be weighted equal overall, but will want to twist the crannk out of shape, 1 & 4 will still balance 2 & 3, but there will be a tug-of-war between them. The crank will want to take an excentric orbit down the line of the crankshaft at each main opposite of the rod journal, which is hard on bearings. Puts alot of stress on the crank since the crank too has uneven forces on it.

 

Its fine for a motor that has a quality forged crank (like ours are) and is race driven where this can be spotted and addressed durign annual tear downs, but not well suited for a daily driver, or even most weekend racers. It's also directly related to how often you rev it out, the imbalance is minimal at cruise RPM's, but the distortion forces greatly increase as you increase RPM's.

 

It's a good mod when you are doing "everything", but not a good mod if you are just lookign for a decent performance rebuild, better things to spent that $$ on.

[infamos]

Good information.

The intention for this build is to have speed when I need it. I'll be doing street driving, having fun at the track every now and then, but not a serious racer. Who knows, I may enjoy racing so much it may turn out to be a regular thing.

[mstieg]

I looked into this before, found similar feedback and am going with a better cam/rocker setup instead. Both are much further down the mod list of bang for buck.

 

Chad, please PM me back.

[Tim_C.]

Knife edging isn't that big of a difference as far as the extreme things that damage bearings. Those things come into play more so when the weights are completely removed. Knife edging removes considerable weight, but not enough to cause the severe things like excessive crank wobble, etc.. It does help to improve drag from hitting the oil, which can be helped with a windage tray and or a crank scraper set-up too.

It always helps to do a little lightening, and even better if you knife shape the weights while you are there. Not cutting the weights to remove a lot of weight, but just a little grinding to smooth them out and remove any sharp corners. You at least want to bull-nose it if you are going to do anything like that. Of course while you are there, it is essential to remove the flashing from the weights which strengthens the crank to remove spots where they typically crack under excessive load. That should be done to any performance engine build, but few people on here seem to even know about it.

 

There was a long time member on here years ago who said he wouldn't build a StarQuest engine without knife-edging the crank. He drove his daily according to his posts. It was TurboTSI. He lived in Miami FL.

I know a roundy racer who used to cut the weights completely off on his Toyota 22R race engine. Same basic design but non-turbo. He says the crank wobble on one with stock weights is a lot of wobble. He was also a machinist who balances them too. He says it is very surprising how much up and down flex happens in even the stock crank. He would take second place on purpose at the races just so no one could claim his engine due to the labor he had in removing the weights, not really the actual cost of parts. Winning never paid enough to rebuild the same, so he would sand bag the last few laps. He was the guy who machined my engines until he got a cush job that pays more machining rock drills of all things.

[Indiana]

What do 4G63/64 stroker kits have to do with a G54B engine? Eagle doesn't make parts for our engine. Our crank is completely different from a 2.0 crank. Get the oil out of the way that's your issue anyway and you'd have to start a debate on crankcase pressure and that would take a month and 20 pages and most still not understand it.

[The Rabbit1]

the crank doesn't balance the rods, the rods balance themselves. 1 & 4 balance 2 & 3. the crank weights balance the rod journals. By removing a lot of mass from the weights without removing weight from the rod journal ends, you are upsetting the balance of the crank down it's axis. It will still be weighted equal overall, but will want to twist the crannk out of shape, 1 & 4 will still balance 2 & 3, but there will be a tug-of-war between them. The crank will want to take an excentric orbit down the line of the crankshaft at each main opposite of the rod journal, which is hard on bearings. Puts alot of stress on the crank since the crank too has uneven forces on it.

 

Its fine for a motor that has a quality forged crank (like ours are) and is race driven where this can be spotted and addressed durign annual tear downs, but not well suited for a daily driver, or even most weekend racers. It's also directly related to how often you rev it out, the imbalance is minimal at cruise RPM's, but the distortion forces greatly increase as you increase RPM's.

 

It's a good mod when you are doing "everything", but not a good mod if you are just lookign for a decent performance rebuild, better things to spent that $$ on.

I don't know what you meant, but each counterweight balances against the weight of each rod&piston assembly, that's how it's balanced. so if you take the weight off the crank you have to take weight off of the rods and/or pistons. That's what internal balancing means. the weight of the piston assembly coming down will hammer into the crank, upsetting the balance, the counterweight is being thrown up to the top thereby killing the inertia of the assembly coming down.

[Chad]

I don't know what you meant, but each counterweight balances against the weight of each rod&piston assembly, that's how it's balanced. so if you take the weight off the crank you have to take weight off of the rods and/or pistons. That's what internal balancing means. the weight of the piston assembly coming down will hammer into the crank, upsetting the balance, the counterweight is being thrown up to the top thereby killing the inertia of the assembly coming down.

 

I get what you are saying, but that misses most of the point here. How is a crank spin balanced? Not with rods/pitons on it. When a machinist balances your crank, he doesnt' ask how much your pistons/rods weight, cause it doesn't matter.

 

all four journals have the same weight and are exactly out of phase, so they cancel each other out. front/back cancels middle and vice/versa. The crank is spin balanced wtih no rods/pistons, and the pistons/rods are balanced without the crank.

 

You can lighten the crank without upsetting the balance of the rods/pistons, just as you can get lighter aftermarket rods/pistons and not have to reblance/lighten the crank.

[The Rabbit1]

 

I get what you are saying, but that misses most of the point here. How is a crank spin balanced? Not with rods/pitons on it. When a machinist balances your crank, he doesnt' ask how much your pistons/rods weight, cause it doesn't matter.

 

all four journals have the same weight and are exactly out of phase, so they cancel each other out. front/back cancels middle and vice/versa. The crank is spin balanced wtih no rods/pistons, and the pistons/rods are balanced without the crank.

 

You can lighten the crank without upsetting the balance of the rods/pistons, just as you can get lighter aftermarket rods/pistons and not have to reblance/lighten the crank.

you apparently have never balanced a rotating assembly..

 

you weigh the piston, pin and rod assembly in grams, then place a weight on the rod throw equal to that weight and then you spin the crank, this is how it's balanced. ideally you want each piston and rod assembly to equal the other within 5 grams.

[Technology]

Rabbit, what Chad is saying is that on our cranks, the weights of the rods/piston assemblies would effectively cancel each other out because they are 180 degrees apart. So why would you need them on the crank when balancing it?

[Tim_C.]

What do 4G63/64 stroker kits have to do with a G54B engine? Eagle doesn't make parts for our engine. Our crank is completely different from a 2.0 crank. Get the oil out of the way that's your issue anyway and you'd have to start a debate on crankcase pressure and that would take a month and 20 pages and most still not understand it.

Yes, and me included on not understanding everything about crankcase pressure. However, on my budget dream build, I did grind off the excessive block protrusions for more crankcase space. That was fun and back when I had time that I didn't know what to do with.

[infamos]

What do 4G63/64 stroker kits have to do with a G54B engine? Eagle doesn't make parts for our engine. Our crank is completely different from a 2.0 crank. Get the oil out of the way that's your issue anyway and you'd have to start a debate on crankcase pressure and that would take a month and 20 pages and most still not understand it.

I was doing research on knife edge cranks in general and came across this article. I was assuming this information would apply to all type of engines/cranks.

[Chad]

you apparently have never balanced a rotating assembly..

 

you weigh the piston, pin and rod assembly in grams, then place a weight on the rod throw equal to that weight and then you spin the crank, this is how it's balanced. ideally you want each piston and rod assembly to equal the other within 5 grams.

 

 

 

On V6 and V8 engines, the 60 or 90 degree angle between the cylinder banks requires the use of "bobweights" on the rod journals to simulate the reciprocating mass of the piston and rod assemblies. Inline four and six cylinder crankshafts do not require bobweights. To determine the correct weight for the bobweights, the full weight of a pair of rod bearings and the big end of the connecting rod, plus half the weight of the little end of the rod, piston, rings, wrist pin (and locks if full floating) plus a little oil are added together (100 percent of the rotating weight plus 50 percent of the reciprocating weight). The correct bobweights are then assembled and mounted on the crankshaft rod journals.

 

http://www.hensonracingengines.com/Crankshaft_Balancing.html

 

I gusss you can put bob weights on an inline motor, but it won't help anything, the balance will come out the same. If they do help, you did it wrong.

[The Rabbit1]

 

 

 

 

 

http://www.hensonrac..._Balancing.html

 

I gusss you can put bob weights on an inline motor, but it won't help anything, the balance will come out the same. If they do help, you did it wrong.

I C what ur talking about now, very good point, so then the knife edging would work in his favor as long as its balanced afterwards to ensure symmetry

[Chad]

yah, you can still get it to spin out OK, even with massive lightening. The problem iwth removing too much is the counter to each weight is off to the side, on the adjacent bore. this will tend to distort the crank between the opposign forces. They are placed there so the counters are not offset like that. the difference is very small, but spin it up to redline and it becomes a lot worse. the balance is still neutral along the whole axis of the crank, but there are distorting forces between bores. The main purpose of those weights is to counter the movement of the piaton an drod shocking the crank upon combustion. If the combustion process were not so violent, the wouldn't be needed. They act a lot like a heavy flywheel vs. a light one. Goign light allows distortions to set in, but if you are going all out on the motor, that won't cause problems since you are probably tearing the motor down preventivly anyway. Heavy cranks = smooth long lasting motors.they also ruin throttle response and eat up some HP [not a lot].

[Metric-man]

Fly wheels and crankshaft pulleys are important in balancing the rotating assembly since they are attached to either end.

 

Sometimes even weight of the rings on the pistons and weight of the oil is sometimes factored on the crank balancer in the tolerance

 

 

In my experience knife edging is frequently confused with radiused journals or when they are referred to as being cut.

 

I've heard them referred to as "knife edged journals" when they are actually radiused because of the adding and removal of material, that would explain allot about the bearings if they were not edge chamfered.

 

 

I've had experience going to SEMA shows and talking to "representatives" also and have found that at times they are just stand inns and are novice in their knowledge concerning the manufactures product,

(I find this particularly true especially of the large chested blonde ones).

[strang3majik]

Don't mean to be off topic, but does anyone even make windage trays for our engines? Seems to be that would be a very worthy mod. I know big block mopars love them.

[Indiana]

Yes, and me included on not understanding everything about crankcase pressure. However, on my budget dream build, I did grind off the excessive block protrusions for more crankcase space. That was fun and back when I had time that I didn't know what to do with.

Remember what happened when someone ground off the upper balance shaft cavity?

[The Rabbit1]

Remember what happened when someone ground off the upper balance shaft cavity?

 

pls indulge for those of us that weren't around..

[StarquestRescue]

My new motor definitely revs up quicker and makes more power than the old motor. But i replaced 7-1 pistons with 8-1 pistons, and replaced the head. Head flow was probably a wash, but the new head has fresh schneider springs where the old head had stock or tired schneider springs in it.

 

http://i237.photobucket.com/albums/ff45/StarquestRescue/2012/DSC02351.jpg

 

http://i237.photobucket.com/albums/ff45/StarquestRescue/2012/DSC02355.jpg