Remove and Torque crank bolt, finally an easy method.

[Airborne]

The experiment you conducted is an exercise in the discipline of Dynamics not Statics. If you wanted to do a Static experiment you would need the force measuring tool pictured in 93rev2sev’s post above.

then tapered off the virtually nothing at TDC.

None the less, your experiment results do give validity to my free body diagram.

I am not surprised with your results and could give you a series of free body diagrams that would show and explain the forces you were observing during this Dynamic experiment. But this won’t work because it is impossible to explain 2 semesters of fundamental engineering courses over the internet.
Now, not only do I recommend you seek someone with intrinsic knowledge of statics to explain my free body diagram to you, have them also explain the results of your experiment to you. The same person can explain both to you, because the Statics instructor also teaches Dynamics.

 

[Airborne]

OK, OK. I will give it one more try to get you to understand. I showed this thread to a couple coworkers and they said “in his mind he did prove you wrong because he only visualizes the force you showed him in the y-axis. He doesn’t see the force in the x-axis. Draw another diagram showing the force in the x-axis too.” Here you go. See attached.

If you wanted to duplicate my free body diagram by experiment you would have to somehow produce over 1500 lbs against the piston in the x-axis. I don’t know what to do if you don’t understand now.

 

[pjtoledo]

OK, to make certain exactly what it is that we are disagreeing on.


After a few posts, you determined that applying 200 lbs ft to a crankshaft, whose rod journal was positioned at 5 degrees before top dead center, would cause the piston to apply 133 lbs of force to a stop tool.

Is that correct?


I maintain the force of the piston against the stop tool will exceed 133 lbs by a significant amount.

Is that correct? ( scratch correct, insert: is that what you disagree with)

I am not contesting other static forces, their directions or magnitudes. I know they exist and things break if structures cannot withstand them.


I have a working model with which to take measurements.
I'll stack approx 135 lbs on the deck surface, use spacers of various thickness on top of the piston to stop the crank at a few different angles before top dead center. Then note the torque needed to raise the weights off the deck.

Is that a suitable test procedure?
Will I get different results if I substitute a rigid bar in place of the weights?
(I have the sneeky suspicion that "static" may bite my **** there) I won't be able to measure the pressure between the piston/spacers and the rigid bar.

Preliminary testing last night went as such:

with a 1/8" spacer on top of the piston and aligned with the deck, which put the crank a few degrees before top dead center, and 50 lbs stacked on the deck I was able to rotate the crank from well before TDC, thru TDC (lifted the weights), to well after TDC using only my hand gripping the crank snout. No tools whatsoever.
I'll increase the weight, obtain some data points and post them up sometime soon.

At this point I'm kind glad I included those 2 lines.
Since the stop tool only works in the Y axis, I considered the X axis forces to be of no concern.
Yes I realize there are X forces, and that they will vary considerably as the angles change.


I recall during a visit to the Smithsonian a few years ago there was an exibit in the science section where a rather sturdy steel beam was placed vertically in an even sturdier press. After sufficient pressure was applied the beam had buckled to one side. To a layman it would appear the verticle beam was not completely uniform in its strength, one side compressed slightly more than the others, with the result being the force in the Y axis caused a deflection in the X axis.
Was that my first lesson in statics?

 

[Airborne]

Oh yes! Strength of Materials relies heavily on the application of static equilibrium!

 

[pjtoledo]

well, I'll try



Bah....







Can't seem to get the rest out.


this has been a great thread, never dreamed there would be that much difference between static and dynamic forces


now for the "brain teaser"

if during the Static procedure, an inept assistant would twist the stop tool, thus inducing Y axis motion and transforming the procedure from static to dynamic, What would happen.
The only aids one is allowed to utilize while discussing this are "12 oz. mental stimulators"


Perry