chasman414

Has anyone ever knife edged a 455 crank ? what are the advantages and disadvantages?

jensenracing77

I am not a performance guy and know little past stock builds but i have never understood the reasoning for it. i always thought it sounded silly. maybe someone can educate me on this.

Oldsmaniac

I could see an advantage if the crank touched the oil in the oil pan, otherwise i do not know a reason. Maybe it allows oil to be thrown off the crank better....

VORTECPRO

Less windage, if you can do it and still have it still balance up, by all means do it, it cant hurt.

oddball

^ +1
Reduces windage. Fairly common for max effort engines, can get a few HP out of it. Probably more useful for engines that wind over 7000 rpm.
Not something to do at home.

MDchanic

Yep - Aerodynamics.

If you figure that the outer end of the crank weight is about 5½" from the crank's axis (4¼" stroke, + half of 2½" bearing diameter), then the far edge of the weight travels through a circle of about 34½".
At 5,000 RPM (not even going to 6 or 7 thousand), that edge going 5,000 times 34½" every minute, and so is travelling through the air at 164 mph.

You can see some real benefits from making that blunt edge more aerodynamic when you're talking about speeds like that.

- Eric

chasman414

Thanks guys, I'm not a serious racer but the subject came up yesterday and I was curious. Sounds like there could be advantages but probably not cost effective enough for my budget!!!!

jensenracing77

i guess my ATV experience is very differant than a V8. I have built ATV engines that will spin 12,000 RPM and there isn't anyone in the ATV world doing anything like that to there cranks. i guess our strokes are not often over 2.75 inches. seams to me like the volume of air moved about from the pistons would be way more than the crank

MDchanic

Well, I'm no engineer, but that suckah's moving through the air at 214mph .

- Eric

jensenracing77

the flywheel is faster than that on the outside diameter. i can't remember for sure but i think it is 6 inches in diameter. We even cut 17 ounces of weight off of them. you wouldn't believe how many time i thought about the flywheel coming apart and taking off my leg.

don't get me wrong, this is not the normal engine build. My personal race engine could get to between 10,500 to 11,200 on a 2.75 stroke but rarely got that high. only time it got that high was in a panic rev or to make the guy in front of me think i was going to run him over. now and then because it took to long to shift to the next gear before the next turn.

SBORule

From what I have seen, the only benefit would be a lighter crank.

Think about this for a second, those counter weights should be treated as wings if less windage is the goal. A sharp triangle on the leading edge beat a big fat flat surface but a rounded leading edge would be better.

Do you ever see anyone knife edge the trailing edge of the counter weight ?

I don't, they leave a big ole flat edge on the trailing edge of the counter weight and try to convince you that you are reducing windage by knife edging the leading edge, try that on a wing and see how well that plane flys.

A nice rounded leading edge and a sharp knife edge on the trailing edge would be the way to reduce windage.

MDchanic

You have an excellent point there.

- Eric

442rocketdave

I have done many over the last 40 years of racing and I make a template out of fiberboard for the leading edge and the trailing edge. I use a grinder and I tape the journals up with duck tape I get it close with the grinder and then use a die grinder and then a dremel. The leading edge I dont go crazy with not to much off just 2 inches back then the trailing edge round it like an airplane wing I then polish the whole crankshaft and smooth it out. You have to re-balance.

442rocketdave

The crankshaft is traveling thru a mist of oil especially on hard acceleration and on one motor I did it ran so good it sounded like a small block and revved so quick, but I also had ultra light pistons and polished and lightened rods, Mondello windage tray and all kinds of good stuff, it was a 70 and ran 10.92 best at 133mph Monster top end I just couldnt hook up back then in the mid 70s. Its time consuming but I love to work on my motors and any advantage back then I would take to win. It used to be hard to make hp in the old days nothing for Oldsmobile at least we have some heads and some great suspension products now.

chasman414

So you sound as though you feel all that work (or money) could be worth the investment?

Run to Rund

Before going to the trouble of knife edging the counterweights, just add a commercially available crank scraper to the oil pan rail.

442rocketdave

I will post some pics of the crankshaft I just finished for my 69, when it gets back from the machine shop they are balancing the assembly and I have about 40 hrs into the Crankshaft and 90 dollars for turning it and it had absolute zero run out so I hope we can get the balancing without to much cost right now were at 225.00 for internal and external balancing. They are doing both but they are supposed to call me if the cost goes up. Also I spent about 20 dollars on sand paper, dremel parts and polish.

380 Racer

Here is the Bryant crank in my SB:


blockcrank002.jpg

Octania

wow
that makes my 403's 330 forged crank look like a bitch

[there's a story behind that line]

So, you cut the flywheel mounting flange away bewtween the bolts?
Interesting...

64Rocket

Rocketdave, explain how you internal and external balance to the same crank ?

Gene

380 Racer

I was kinda wondering that too.

442rocketdave

64Rocket, I always just balanced the assembly internally, but the last time had my engine balanced they told me I needed to bring the flywheel balancer and they checked the whole assembly once they had the internal balance finished and checked to see if the flywheel which was a billet if it was way out. I know you only have one or the other and they told me you should always check the total assembly? The engine ran so smooth I couldnt believe it! Before it had a vibration and it was not in the drive shaft or transmission. So It had to have been in the flywheel. must have been way out.

64Rocket

RocketDave did they charge you extra to do the internal and the external balance ?

Gene

442rocketdave

It was no extra charge back then at that shop and where my motor is now its 200 for the internal balance and 25 extra to check the flywheel. I am going to post photos of their shop and of my motor, they do international racing engines from all over the world especially marine off shore. They are good. I was a machinist for 6 years.

64Rocket

Dave I'm going to say, there is no way to balance the crank, the way you say.
You are talking two different types of balance.
Internal has weight (Mallory heavy weight)added to the counter weights, with after market flywheel and harmonic balancer that has no weight on them.
An external balance is done with a factory like balancer and flywheel, of which weight is added or removed to or from the counter weights.
You can NOT do both to the crank.
You need to get exact detail of how they are doing the balance.

Gene

Intragration

I would tend to agree with this. I'm not an aerodynamic engineer, but I did hear once that the ideal shape for the least aerodynamic drag is the shape of a raindrop, hemispherical on the front and a point at the back. This makes a lot of sense if you think about it. An airplane wing is designed to do more than just limit wind resistance, but I'm sure this plays into the design. On cranks, I've seen both the leading and trailing edges knife-edged. It seems you'd lose a lot of advantage if you left the trailing edge blunt, it's leaving a lot of turbulence in it's wake and the leading edge is running right into it. I'd guess if you did it wrong, you could probably end up worse than where you started.

380 Racer

To me SBOrule contradicted himself. Your raindrop theory is correct. Here is my crank I had made from Bryant:

blockcrank002.jpg

442rocketdave

64racer I know there is only two types of balance internal and external, they do the internal with weighing the rods pistons and add the weights to the crank and spin it and if needed add mallory or take away by drilling I have had engines balanced since 1973. Waibel competition used to do all my motors. and of course the other way is to add weights to flywheel. I am going to the machine shop today and take pictures and ask bruce to explain in detail what they do. I was as confused as you but they told me its something they do all the time? I dont think its a gimmick but I will find out the details today.

cutlassefi

Actually Gene you can have both. I think some early Fords were internal in the front half and external in the back, or vice versa.
But otherwise you are correct in the way it's done.

I'm a huge proponent for internal balancing, if it's practical and affordable.
Even though you're actually bringing an externally balanced crank "into" balance with the addition of the counterweighted flywheel and/or balancer, you're still spinning that extra weight out on the ends. That adds to flex and twist.

But rpm, internal reciprocating and rotating mass etc add to the effect of all that as well.

captjim

I agree with Gene, this makes no sense to me. My understanding is that an internally balanced engine uses a neutral flywheel and dampner while an external balance uses weighted flywheel and balancer. I have NEVER heard of adding weight to a flywheel. How would you add weight to the front??

"they do the internal with weighing the rods pistons and add the weights to the crank and spin it and if needed add mallory or take away by drilling"
They do this with both, it is part of the balancing process. All components are weighed, then bobweights are set up to replace the weight of the parts. Then, the crank is spun and either drilled or weight added. But it must be done using the dampner/balancer and flex plate/flywheel that will be used. If you used stock flywheel/balancer on an internally balanced engine, it would vibrate itself to death.

TripDeuces

He might have meant that after they internally balanced it they put the flexplate and dampner on (without the weights) and rechecked it to be sure they were in balance also. It's the only thing that makes sense.

captjim

But then you are talking neutral balance dampner and flywheel, which is not very common in the Olds world.

IMO, he is confusing two things; 1) weighing all the rods, pistons, etc and making them the same and 2) spinning it up and balancing the crank.

442rocketdave

Trip Dueces is right that is what they are doing, and I dont have a flexplate its a heavy billet flywheel for the 4spd, I was not able to get to the machine shop today but I will on Monday, They have a dyno and they are on youtube, type in HemiHaines 472 hemi dyno and that is John at the controls, if you look up their info on line its Express Engines they specialize in off shore racing and they are good! It took me 3 machine shops ripping me off before I by chance found these guys! I have seen some of the engines they have done and they are unreal! I watched them finish 6 big block pontiac motors and they ranged from 389s to 455s and they run!

442rocketdave

They found the problem the flywheel was not neutral balanced and somebody at the last machine shop several years ago balanced it externally! So it is now balanced internally and the flywheel has been neutral balanced they video taped the balancing. They also took pictures. they only had to weld in one plug to balance the crank after I had knife edged it. No extra charges! Great machine shop.

64Rocket

Dave,
Post some pic's of the damper and flywheel backside . Also a pic of the crank counter weights.

Gene
trip,
You have to have the neutral flywheel and damper to do the balance + the bob weights. I have never seen anyone do an internal then add the damper and flywheel.

442rocketdave

The last machine shop screwed everything up. they balanced my engine externally! This machine shop did an internal balance and when they checked the flywheel they found it was not neutral balanced so they fixed it and I have a new damper so now its internally balanced the way its supposed to be. They had an idea something was wrong. I will post photo's of the knife edged crank that I did and the only weight it needed was on number one throw. It came out nice. I will also post photo's of the flywheel and balancer. By the way their are a couple of motors that are dual balanced they showed me the spec factory book. Its not an Olds, its a chebby! They video taped the balancing job!

442rocketdave

Gene I will post some pics tomorrow on the albums section, I posted some of my pics of my 455 and 400 but the 400 did not show up, I am not too computer savvy so I will figure it out tomorrow and as soon as I learn how to post a thread I will on the restoration of my 69.