RPM vs Longevity

[JerryG]

Life expectancy of our tractor engines comes up here pretty often. I would like to say that the life of any engine is decreased as the rpm is increased. I am not saying that you are to run 1800 rpm on a engine designed to run 3600 rpm. What I am saying is that, if the rpm is increase to reach a higher hp, then the engine will not last as long. Example: TC 29 vs TC 33, same engine but rpm increased to raise hp. All manufactures have examples. The more the rpm is increased, the shorter the life expectancy. Given two tractors that are identical except for the rpm limit, the tractor with the lower rpm will last longer.

 

[Henro]

<font color="blue"> Given two tractors that are identical except for the rpm limit, the tractor with the lower rpm will last longer. </font>

And if they have tach-driven hour meters, the hour meter readings of the two will reflect this... /forums/images/graemlins/smile.gif ...Well at least the lower rpm tractor will show less hours.

Still, I wonder if it is true. Perhaps there is a maximum-life-point/rpm that is somewhere in between idle and maximum rated speed.

Complicated subject! How about same speed on two identical tractors but different engine loading... /forums/images/graemlins/confused.gif

So many questions...so little time... /forums/images/graemlins/grin.gif

 

[JerryG]

This is an over simplification, but a piston moving at 3600 strokes a minute is putting on 50% more wear per minute than a piston moving only 2400 strokes a minute.

 

[slowrev]

Yes this has been discussed several times before. IMHO it has to decrease the engine life.

 

[nomad]

Yes, you are correct.
The more RPM; the more wear, the more heat, the more dynamic & thermal cycles which will cause the fatique in materials to happen, etc.

 

[Egon]

I'd think there would be more to it than just RPM. Most likely keeping the rpm in the proper torque band will result in the best life span as this should be the rpm range the motor is designed for.

There may also be vibrational harmonics which change with the rpm making a certain rpm band more desirable than others.

And many more factors such as bore/stroke/compression/ flywheel weight and ?????? to take into consideration.

Egon

 

[JerryG]

Egon,
I know that if given a choice, I would always take a long stroke, low rpm engine.

 

[Bob_S]

What about carbon deposits I keep hearing about when running at lower RPMs? Is this a different concern? Just trying to lean more about somethin I know little about /forums/images/graemlins/crazy.gif

 

[JerryG]

Carbon deposits are formed when an engine is in what I call the lugging range. I was only referring to the practice of manufactures raising the rpm to increase hp so that they can add another model to their line up.

 

[RoyJackson]

"What about carbon deposits I keep hearing about when running at lower RPMs"

This results from excessive idling at lower RPM. Carboning the heads results from unburned fuel. Dirty fuel cause it too...I just had my Explorer's heads decarbonized. In a gasoline engine, heavily carbonized engines can actually increase the compression ratio, resulting in pre-detonation (pinging) which is not good for the pistons.
Sometimes you'll see a diesel generator or other usage where the idle suddenly increases for a minute, then returns to low RPM.

Another thing to be concerned about with low RPM's from idling for longer periods of time is pounding the main bearings. Instead of a nice even rotation of the crank shaft, very low RPM's can result in excessive wear on the bearings. Cranks have counterweights for a reason...to maintain the momentum of the rotation.

Diesels have thicker bearings (at least, what I've seen) then gasoline engines, so "pounding" the bearings in a diesel isn't as harmful.

At a maximum RPM of 3000 or so, I just cannot see worrying too much about high RPM's.

Anyway, who of us sets their hand throttle to higher RPM's unless we need PTO speed?