Flathead Crank Knife Edging....pro's & con's

I have a new scat crankshaft for a flathead motor I'm slowly working on and I was thinking of having the crank knife edged, has anybody done this here, I also would need a highly reccomended crank shop that would do this since I don't want a fly by night machine that are guessing at how flatheads work. Does this take away any torque characteristics? appreciate any info.

 

Go to advanced search...put in AV8 (not sure of exact form for his name?) and crankshaft---he has done and photographed some.
My flying guess: This would have zero negative effects, assuming proper balance, minor loss of rotating weight probably good, if you need more for a heavy car puttit in the flywheel...
I'd also guess benefits to be miniscule on street engine probably running below 5,000, but certainly cool and likely worth something, effects could be added to with scrper and screen like on a certain Mosel T in NJ...

Lookeditup: Put "av8" as poster, then search crankshaft. He does good sculpture!

 

The pros and cons depend on the intended application and the thickness of your wallet.

 

Save your money. The jury's still out on whether or not there is enough of a benefit to warrant the work. The idea is that the counterweights will slice through the oil, but if you think about it, it makes more sense to shape the counterweights aerodynamically. Meaning a blunt edge with a trailing teardrop. That would be expensive, and I'm not sure the benifits are there. Especially on a street motor. Another thing that can be done is to shave the counterweights down, but then you get into ultralight pistons and rods to keep the balance. The benifit is that the motor will rev quicker, but once again its mucho money. Long story short, put the bucks elsewhere. And enjoy the car

 

Some points to consider ...

Is this going to be for VERY high performance? e.g. Drag racing, Bonneville
After "knife edging" the crank; are you prepared to invest in a possibly expensive re balance of all bottom end parts.

Knife edging and weight reduction go hand in hand - removal of material to create the knife edges on the counter weights WILL reduce crank overall weight.

Extreme weight removal on a flathead crank reduces low end tourqe, even though it does allow for faster "wind up"; but the reduced weight then means a faster "wind down" - loss of inertia - which in anything, other than a "hi-perf" engine can be counter productive.

 

On a street engine there is little or no benefit.
On a race engine there is a measurable increase in hp in the mid to upper rpm range.
A SCAT crank will be much easier to balance if you take as much weight off the throw sides as possible. As they come,
they will require as much as 800 grams of heavy metal to balance...It is possible to lighten the throw sides and knife edge one so it will balance with no heavy metal. When you have about 12 lb. of shavings on the floor, you will be close.

 

"weight removal on a flathead crank reduces low end tourqe"

How is that possible?

 

In my never to be humble opinion........it would be like putting an Indy car spoiler on a UPS truck. In some situation........it might help.

 

Some background on the project at hand.....it's going in a fenderless 32 sedan with a 1964 toploader adapted to a torquetube and quickchange, the block is already ported, it will have 1.6 intake, turned down guides, ross pistons, crower rods, aftermarket main caps and a potvin eliminator grind for the cam, I just thought since I have gone this far with the motor already maybe doing the couple things left it may or may not help, it's a carbuerated motor as well, I was concerned with the weight loss as to the weight of the car and I'm not sure if I'm going to do a aluminum flywheel or a lightened steel one. it's use will be lots of street driving with the monthly visit to the local drags. Thanks for the reply's.

 

less rotating mass equals quicker winding-up of the rotating assembly. an objects momentum is a result of velocity and mass

 

There was one flathead at Bonneville that went somewhere in the 243 range, the owner claimed it had a stock Mercury crank. It did have two 2.3 turbochargers.

 

Not needed on a flathead. A streetable one will never turn the RPM where it starts to show benefits.

 

I dont understand this 'no need' thats bullshit, coz if that is true, then there is no need for dual carbs or an overbore greater than the next clean up size. Theres no need to finned heads or adjustable lifters etc.

I see it more as coming down to how far you personally want to go, every little bit helps and how much do you want to spend?

like with any motor there comes a time where the $$$ only give you a small hp increase, but for some, thats what they like to chase.

I am probably more stupid than the next. I didnt have a 4" crank to do it to, so I used my standard crank. Why? if the truth be known I was curious and thought, what the hell, its my time. would I do it again, dont honestly know, it cost me 1k US to have it ballanced and metal added, I took about 12-14 lbs off. took along time to polish it, but I was happy to have a go.

I guess I just wanted to see what all the 'myth' was about, only one way to find out - elbows deep with the angle grinder.

cant really say on the performance yet, as due to the machine shop feeling that a line bore can be egg shaped the motor not going. first problem was whether the crank was stuffed, luckily it wasnt, but I was really thinking long and hard on if it was stuffed would I do all that work again? luckily I didnt have to answer that one...

 

While I take everybodys thoughts in my heart really does lay with Flatoz, I may have to wheel and deal some parts and work some ot but I always feel and believe that flatheads are one of the best things since sliced bread, I don't care about putting an overhead in for less then half the money it's a mind set I have had since a little kid, even being older I talk to Flatdog a lot down at his shop and do you think his motors would be where they are today if he said it's not worth it.......I'll have to admit my motor has a few Flatdog tricks in it but my goal is to run the 4x2 setup without the blower and make the Mother fly, thanks again for all the input, I still don't have a shop to do the crank work but after reading Kevin's original post I think I will give it a whirl after I teach myself a bit more about it and where to be so I don't mess it up when it comes time to balance it.

 

Look around in search...somewhere on here are pictures and procedures of av8's crank massage work.

 

Saved all of Mike's posts to a handy PDF

http://lonestar.texas.net/~mcdaniel/porting.pdf

 

modernbeat, outstanding... thanks for posting the pdf of mikes post.

people would be surpised at what some flatheads will do to their OHV's.. jimmy whites blue model A has and sounds like its got some heat, to the unsuspecting, people would think it was a suped up OHV but, there is still what i call that audible flathead gurgle/knock, albeit barely audible over the open exhaust.

i have found that it takes a lot of dedication to have a competition flathead, its deffinately not for everyone... one thing is for sure though, its a whole other sickness on top of the hot rods and parts sickness that the vast majority of us share.

 

Modernbeat - that's been saved on my computer for a while, thanks!

Now, if we could find av8's article on knife-edging & polishing the crank - I think he did one as Bruce mentioned - that would be neat to have too...

 

i have been looking for it but haven't found it yet.....man there are sure a lot of post to go through.

 

yea what he said ! that`s a keeper .

 

found it .

 

A book to acquire: Dave Vizard's book on Chevrolet crankshafts and rods.
This book contains an incredibly thorough illustrated rework of a cast Chevy 400 crank for racing, with full boogie prp of absolutely everything... $50 crank with $1,000 of pro prep in it.
The crank is knife edged, polished, cut undersize to allow deep fillets, throws hollowed, and so on...if you want to see a crank prepped to the max and how it was done, this is it!

How to Build & Modify Chevrolet Small-Block V-8 Pistons, Rods & Crankshafts David Vizard

 

There is misinformation on this thread....

knife-edging a crank WILL NOT cause you to lose torque. It will feel like you've got less torque everytime you let out the cluch or shift because your engine now has less inertia, however, you will accelerate faster, even at lower RPMs, because you have less mass you have to accelerate (actually less mass moment of inertia, since its rotating )

Basically, you're not going to be making more hp or torque (the two are inter-related by an equation, you can't gain one without gaining the other) you just need less to accelerate the crankshaft, so more will go towards accelerating your car.

 

hot rod artist; The lower picture is the Tardel & McKenzie Bonneville LSR.
Mike Bishop does the cranks - not sure if the one at the top is one of his - for this race car.

Somewhere I have pictures of TWO blocks that have BIG holes in the side that a polished / knife edged crank survived. The crank was returned to additional engines with only minor clean up.
(third time wasn't the "charm" though; the crank broke into three pieces - along with the rest of the engine going "six different ways!)

Mike has done many of the these cranks on the theory that by polishing the stress risers - forging marks - out of the crank, they WILL stand up to MUCH more abuse. Ford was never known for "cleaning up" the forgings, hence a large number of "stress risers" were left behind.
(it's hard to say that this a proven fact; but the case above would seem to bear out his theory)

The knife edging was a byproduct of lightening the crank for a "high winding" engine; - 6 thousand RPM plus - plus making it "cleaner" when splashing/passing through the oil.
(it also cuts down on the "whipping" or "foaming" of the oil)

The knife edging benefits are born out in the book Bruce mentions - How to Build & Modify Chevrolet Small-Block V-8 Pistons, Rods & Crankshafts, by David Vizard

 

I guess this is a case of two "wrongs don't make a right."

First of all; YOUR right in saying, knife-edging a crank WILL NOT cause you to lose torque.

If you had said, LIGHTENING a flathead crank WILL NOT cause you to lose torque - now this makes sense.

 

You can polish...knife edge ..... swing a black cat over your head or pray to Budda

NONE OF THAT WILL WORK AS WELL AS TEFLON COATING THE SUCKER

Make sure you got a good crank first.

Remember the only thing the guy that made it REALLY knew was he wasn't going to put it in his car!

 

Just talked to HM Elliot coatings, they teflon coat the crank, bearings and the skirt and top of the pistons, sounded pretty interesting, cost to do a crank is $175, basicall if you knife edged your crank and had it coated you would have the best of all worlds, you can take the strees marks off he crank but there is no need to polish it if you have it teflon coated. Here is a link to there web site.... http://www.hmelliott.com/teflon.html

 

I prefer to have the crank toss a bit of oil around

We don't have an oil with vapor lube action anymore so a bit of splash is ok

Your working with a flattie don't expect the small amt of oil that is on a coated crank to hurt you.

I don't bother with the the pistons that's a waste of money

As for coating the bearings..... that not only a waste of money but stupid

You want an oil wedge teflon just won't help

Now if your car has leaf springs take 'em apart and do them

Staymor in Compton did mine for years. Semi gloss black No one ever caught it..... and the springs rate remainer stable allowing for softer shocks

These are the tricks you learn when you have to go faster each race OR LOOSE!

 

I question whether it's the knifing effect through the oil that is causing the gain in efficiency or whether it's merely the lighter internals. My gut tells me it's the latter. Though the polishing and shaping of the counterweights certainly won't hurt, I think the majority of the power gained is seen through losing rotational mass. But if you have to get the assembly balanced anyway, you might as well go all out. However, on a streetable/moderate performance flathead, The cost/hp increase ratio may not be favorable.

Polishing the crank and removing casting flash to eliminate stress risers have been mentioned already. However, shotpeening has not. From what I understand, the process will literally hammer shut tiny cracks, thus increasing the strength. Can someone elaborate on this?

Also, what about having shorter, heavier counterweights on the crank? The reciprocating mass is the same, but the weight is closer to the centerline.