Crankshaft Harmonics

[Lazy JW]

This is brain-bending stuff :mrgreen:

http://speedtalk.com/forum/viewtopic.ph ... 61#p222261
http://speedtalk.com/forum/viewtopic.php?t=16279

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Joe

 

['68falconohio]

Yes Sir. I've been following that first one in hopes of some good formulas being presented because my next build is going to operate in those bad areas. I think 'Panic' is the same 'panic' that's on inliners.org.

 

[StrangeRanger]

If he's the same Panic that used to hang out here, take his stuff with a grain of salt ...and don't post anything that might hurt his feelings :rolflmao:

 

[Lazy JW]

Yup. Jeff Diamond; he still is a bit sensitive and deletes stuff over at Speedtalk. He does have a lot of good info, just filter it carefully.

I do like reading most stuff from David Redzus.
Joe

 

[Thad]

Help me if I'm stupid. Thought in inline 6s and even fire 60 degree v-6s harmonics were self cancelling? :

 

[Lazy JW]

Help me if I'm stupid. Thought in inline 6s and even fire 60 degree v-6s harmonics were self cancelling? :

I believe you may be confusing firing impulses with crankshaft vibrations. It is my understanding that you are correct about firing impulses, but nothing is going to stop the vibration nodes from traveling back and forth along the crankshaft, they can vibrate just like a guitar string.

We studied this phenomenon in the saw business; when the forward traveling wave equals the backward traveling wave then we have reached what is known as the "critical speed" and the saw goes unstable (sometimes REALLY wacko!). The same thing happens in a crankshaft, and the longer the crankshaft the worse it gets. Short and stiff = good. Straight eights had a real problem

It is amazing how much effort was put into studying this during WW2.

I personally know two men who have earned their Phd's studying saw vibrations and there are no doubt more who have done so studying crankshaft/engine vibrations. Makes this poor old hillbilly's head spin around like the knob on the outhouse door, it does!
Joe

 

[JackFish]

The 200 has big supporting mains on each piston though, so wouldn't that have an impact on reducing the effect?

 

[Lazy JW]

The 200 has big supporting mains on each piston though, so wouldn't that have an impact on reducing the effect?

Yes.

 

[80broncoman]

You want to see a crank that looks scarry? Look at a pontiac 301 V8 crank.
It has 2 counter weights. one at each end.

 

[Anlushac11]

I have seen talk of some companies coming out with main stud girdles made of a specific grade of aluminum. The specific grade aluminum was supposed to be stiff enough to reinforce the bottom end but soft enough to absorb some of the vibrations to reduce harmonics.

D.S.S. makes one from 6061 T6.

I know main cap webbing helps strengthen block. I have no knowledge as to whether their main cap web actually absorbs vibrations.

Made of 3/4” Billet 6061-T6 aluminum, the D.S.S. Main Support System effectively dampens damaging harmonics, virtually eliminating main bearing walk. The Main Support Plate is fastened to the main caps using custom ARP main studs (included), effectively tying all five main caps together. By adding another main web structure you dramatically increase the block’s strength, helping both block and crankshaft life. Our Main Support System makes it possible to produce 650-plus horsepower from a production block.

http://www.dssracing.com/SearchResults.asp?Cat=6

 

[STEVEN.]

Panic also frequents the Inliners.Org 'site quite a bit as well. Personally,I've never had a problem with 'ole Panic . ~OO6.

 

[CNC-Dude]

Panic also frequents the Inliners.Org 'site quite a bit as well. Personally,I've never had a problem with 'ole Panic . ~OO6.

Panic was just recently banned from the HAMB and has been back on Inliners a lot, unfortunately. You wont ever have a problem with him as long as you dont challenge any thing he says.

Main girdles can help to dampen crank harmonics from spreading through an engine, especially if they are aluminum. Most girdles today are steel, probably for economic reasons instead of engineering reasons. And the severity of the harmonics is proportional to the stroke also. Fully counterweighted cranks are helpful in dampening them, but are still vulnerable to them.

 

[Anonymous]

You want to see a crank that looks scarry? Look at a pontiac 301 V8 crank.
It has 2 counter weights. one at each end.

Or really old Chevrolet inline sixes: spindly crank with no counterweights at all and a total of three main bearings

Thad had a thread elsewhere on Sir Harry Ricardo, who, among many other things, did some of the first development of quench-type cylinder heads during the time of that Chevy six and similarly crude machinery. Recommending specific quench/squish clearances is a frequent activity here . . . can you imagine what poor Sir Harry was up against in trying to come up with proper quench clearances for those hilarious old engines with no counterweights, no proper crank support, solid dampeners, poor balancing, "generous" manufacturing tolerances, etc.? Makes me glad I came to piston engines after they had a few more decades of development on them!