Knife edging a T2 crank?

[Aerosmith145]

Anyone done it? If so, which areas did you try out?

Any issues with this crank NOT being a fully counter-weighted crank like a Honda?

Just fishing for experience. I'd like this to be on the list in my franken-build

[Directconnection]

I have done this a couple times. I'm at work, so I cannot post pics until later tonight when I get home. But I do NOT recommend hacking down the counterweights. They are there for a reason, and not totally for balancing. A competitor shop did this to a Toyota 22RE and it cracked after a few races. I believe the counterweights help damper the harmonics....

[turbovanman²]

Subscribed.

We also don't have any type of balancer so that sure doesn't help,

[Reaper1]

I have a friend that has cut the weights down significantly. Keep in mind this is for a roundy round car that gets torn down quite often and has NO street drivability.

Personally, for a street type car, or something that is supposed to stay together for extended periods I'd just stick to the knife edging and polishing. Possibly having it coated with an oil shedding type coating.

[johnl]

The smooth running of an engine with the heavier Masi crank made me appreciate crank weight. I'd just polish and coat.

[Directconnection]

Here's the crank I did 2 years ago:

(btw: do NOT do this unless you have it re-balanced afterwards as it will be waaay off.)

I knife edged the *trailing* edges, and bullet nosed the *leading* edges. This might seem backwards, but is the way all the big name crank companies do it (and the shop owner was told by a crank company at one time)

I also cut down the counterweights as far as one can go on a lathe w/out cutting into the rod journal (I did machine into the rod journal thrust areas)

[turbovanman²]

Why weren't the parting lines removed?

Other than that, purdy,

I don't understand the reasoning for not knife edging the leading edge?

[Reaper1]

Here's the crank I did 2 years ago:

(btw: do NOT do this unless you have it re-balanced afterwards as it will be waaay off.)

I knife edged the *trailing* edges, and bullet nosed the *leading* edges. This might seem backwards, but is the way all the big name crank companies do it (and the shop owner was told by a crank company at one time)

I also cut down the counterweights as far as one can go on a lathe w/out cutting into the rod journal (I did machine into the rod journal thrust areas)

So how's it run? After the rotating assembly is rebalanced only the inherant vibrations of the engine will be felt and NO structural or harmonic integrity *should* be lost. How much material did you remove from the counter weights?

Why weren't the parting lines removed?

Other than that, purdy,

I don't understand the reasoning for not knife edging the leading edge?

I agree, I would have ground, peened, and polished where the casting lines are, but that is a LOT of work!

The reason for not knife edging the leading edge of the weight is because you are attempting to make it an airfoil. No subsonic airfoil has a pointed leading edge. So, make the leading edge a blunt nose. This helps guide the air around the part. Then, knife edge the back so that the air doesn't seperate, go turbulent or stagnant and cause other issues. The thing is you want to make sure that the shape is symmetric so as not to introduce lift (in this case thrust). I would also suggest trying to keep the angle of the knife edge no steeper than about 7*. I know this is hard to do, so most times it is going to be steeper. In those cases I think I would suggest some sort of boundary layer trip, or possibly try dimples to keep the boundary layer attached. I know this is a lot of aero for a part that really doesn't go anywhere, but it will all help. The only catch to a boundary layer trip or dimpling is that they will tend to want to collect oil.

[Directconnection]

Why weren't the parting lines removed?

Other than that, purdy,

I don't understand the reasoning for not knife edging the leading edge?

Sanding down parting lines is an old wive's tale. I get a kick when I see people polish the snot out of their rod beams and shot-peening them, too. Rods get stress risers out of the rod bolt holes in the cap and rod sides, and sometimes right around the housing bores. Rod beams break only from the result of excessive rpms (over-revving) and engine braking.

Part of my many responsibilities at work is magnafluxing rods and cranks... and I've literally done 1,000s now. When I see a rod/cap that is cracked and ready to fail... it's never in the beam. I've only seen one like that and it was a very old Carrillo H-beam. Cranks.... about 1% of the failures I also see when magging cranks (again, I've done well over 1,000) is right in the *radius* of a rod or main journal. (or starting out of an oil hole) Almost never does a crack start on the as cast or forged non-machined areas. I should take a picture of some common areas and show some tweaked hi-po parts...

Like Reaper said: think of it like an airplane's wing... which is the way I have always thought of it.

---------- Post added at 09:32 PM ---------- Previous post was at 09:26 PM ----------

So how's it run? After the rotating assembly is rebalanced only the inherant vibrations of the engine will be felt and NO structural or harmonic integrity *should* be lost. How much material did you remove from the counter weights?

Well, it won the championship in '09 hehehe

I can't remember how much I took off.... I just kept going until I was just into the rod journal's radius. So.... maybe around 3/16 to 1/4" ?

Like I mentioned earlier, that 22RE crank BROKE shat up. I think it made the block break after just one race amongst other things.... In an inline motor, even though they are called "counterweights" they really aren't counterweighting anything. On a V-8 yes, they absolutely do, but not on an inline. Hence why I stand by my theory that they are also part of a buffering/damping effect of sorts, otherwise Chrysler never would have them in the 1st place as they don't "balance" much of anything except for the lone crank journal.

[Reaper1]

I agree that holes, sharp radii, and abrupt changes in geomestry are all causes of stress risers and those are the areas that will see the most failures. However, it is a fact that casting lines and machine lines are ALSO stress risers. Now, it just may be that in this case the stresses that are inflicted on the part put very little load on those areas. If this is the case, GREAT! I'd STILL remove them, peen them, and polish them! Why? Well, #1 ANY removal of material is contributing to a lighter part overall. This is a good thing! In the process, you are still removing a stress riser, no matter how trivial. You are also removing an area for oil to collect. By peening you are helping to reduce any other surface stress risers on the entire part. By polishing, you are making sure that oil doesn't stick so well.

The old train of though was you were simply helping the part not meet a premature failure. The BETTER train of though is outlined above.

Id also STILL look into oil shedding coatings. I don't know much about their longevity, but if it's pretty decent it might be worth it to some.

[Directconnection]

Anal retentive polishing and oil shedding coatings ain't worth it on a $500 turbo mopar. Those are Super Stock tricks to get .1432hp here, and .2984hp there... hehehe

I know it all adds up in the end, but at what cost? In a Strammer situation, it's worth it... but for a 12 second TM you're better off spending $ elsewhere (like the cylinder head)

[Reaper1]

I also look at it from a longevity standpoint as well. For me, I plan on using my car both on the street and on road courses and such where prolonged WOT and high rpm are going to prevail. I believe in that case being anal retentive about engine prep can be the difference between an engine that not just survives, but keeps going, and an engine that needs rebuilt in short order.

[shackwrrr]

My boss built a jeep 4.0 and took 2 pounds off the crank and the thing idles like its got 80 year old spark plugs in it.

[puppet]

I have done this a couple times. I'm at work, so I cannot post pics until later tonight when I get home. But I do NOT recommend hacking down the counterweights. They are there for a reason, and not totally for balancing. A competitor shop did this to a Toyota 22RE and it cracked after a few races. I believe the counterweights help damper the harmonics....

Harmonic vibration is a pretty big deal. I know of some applications that have had issues with al flywheels and resultant crank flex. Wears the snot out of bearings.

[turbovanman²]

Good explanation on the knife edging, makes sense.

Maybe removing the parting lines is a waste but WTH, I do it all engines, the blocks too. Too bad I have issues with pistons and heads, lol.

[Directconnection]

Good explanation on the knife edging, makes sense.

Maybe removing the parting lines is a waste but WTH, I do it all engines, the blocks too. Too bad I have issues with pistons and heads, lol.

It won't hurt... unless you do a horrible job....

---------- Post added at 03:16 PM ---------- Previous post was at 03:14 PM ----------

I also look at it from a longevity standpoint as well. For me, I plan on using my car both on the street and on road courses and such where prolonged WOT and high rpm are going to prevail. I believe in that case being anal retentive about engine prep can be the difference between an engine that not just survives, but keeps going, and an engine that needs rebuilt in short order.

Well, this was a circle track engine that raced every weekend w/out issue. Doesn't get any harder than that (especially if you knew the way the owner drove the car (overdrove/revved it all the time)

[contraption22]

Of the two 2.2 crankshaft failures that I know of, one of them was a local guy that knife edged his. Coincidence? Maybe.

[4 l-bodies]

Here is Pat's M. cool ultra rare 2.5 forged crank. Velasco made it. Knife edged. 6 bolt +dowel pinned. Around 36lbs, which is not much heavier than the cast version.
Todd

[turbovanman²]

That crank is pure sex,

[RoadWarrior222]

Interesting... I always thought knife edging the front was kinda daft sounding, and was gonna try bullet nosing the next crank I had out. Probably gonna aim for clean edge separation, or if that looks undoable, vortex control on the trailing edge rather than mowing it right down.

Apparently, buffing powdered teflon into a surface is as effective as any other method of applying it. I tried buffing plumbers tape into the back of the intake valves on my Escort head, seemed to work, water ran off it nice, don't know if it has held up though.