RPM vs Longevity

[RalphVa]

If you look at cars, look at typical miles possible on 4 cylinder Volvos or 4 cylinder Benzes or 4 cylinder Toyotas or Honda that run probably closer to 3,000 rpm vs. big V-8s that lumber along at around 1,500 to 2,000 rpm. Both will go 300 to 400k miles before overhaul (possibly a valve job on either). The Volvo 4s will run near 300k before they even start to use any oil.

Most wear on an engine occurs at startup, if it is maintained properly. To keep an engine running properly keep it revved up. On a tractor or other low-speed-governed engine, this means running it at maximum speed most of the time. The diff between 2,500 and 3,500 rpm is nothing.

Ralph

 

[KubotaBling]

Higher RPM does decrease life expectancy tho too low an rpm will too having too much load will decrease life expectancy also.. so if u have a high load on medium rpm could be worse than high rpm and capable of sustaining the load with less wear. This equation must be figured as also.. tho it's likely higher rpm is 95% more likely..

 

[Egon]

Ralph:

[The diff between 2,500 and 3,500 rpm is nothing.]

For my truck that little difference may mean a new engine.

But I know what you mean.

Egon

 

[BIGUN]

</font><font color="blue" class="small">( 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. )</font>

I had a twin cylinder Kohler 17 hp Ariens that I mowed two acres with for 20 years. Kohler recommended removing the heads and cleaning the carbon off of them every 100 hours which I never did. After all those years I tore down the engine after it threw a rod. The heads definitely had a lot of carbon on them and had literally beaten the top edges of the pistons down to the point that the rings were stuck in the smashed aluminum. This engine was run full throttle 90% of the time.

 

[OkeeDon]

I'm not sure of the basic premise involved. According the the NH website, the TC29D and the TC33D are both rated at 2800 RPM. Also, I'm not sure, but I believe the PTO RPM on both is the same, yet the TC33D has more PTO HP. If your premise is correct, then the 33 would have to run at a higher PTO RPM in order to achieve the higher PTO HP.

It seems to me I read somewhere else on the forum that HP on the same engine is increased by increasing fuel pressure or some such.

One way to check would be to look at the red line on both. Is the TC33D red line higher than the TC29D? I don't know the answer; perhaps owners of both could check and post the max RPMs shown on their tachs.

Now, getting down to the discussion at hand, one theory has been proposed that an engine has a shorter life span at 3600 than it does at 2400. This would depend on how you define life span. In terms of hours alone, this may be a valid theory. But, there is no reason to increase the RPMS to do the same work on both. The higher horsepower tractor has the potential to do more work than the lower HP tractor. If both are used to their maximum capability, the higher horsepower tractor will do more work in a given number of hours than a lower HP tractor. Thus, in terms of work accomplished, both will have the same life span.

To put it another way, assume the 3600 RPM tractor has a shorter life span in terms of hours, but accomplishes the same amount of work in those hours as the 2400 RPM tractor does in it's longer number of hours.

Perhaps a better way to look at it would be to compare two engines of the same HP, but achieved in a different way. Sticking with the 33 HP example, you could have a higher revving 3 cylinder engine or a lower revving 4 cylinder engine, bit rated at 33 HP. The larger, lower revving engine may have a longer life span in terms of hours and work accomplished, but at a higher cost. In other words, the only way you get the longer live span is to pay for it. The ratio of life span:dollars may actually be the same.

 

[nomad]

</font><font color="blue" class="small">( The diff between 2,500 and 3,500 rpm is nothing.)</font>

Not always so. Especially at such high speeds, you are in the vicinity of critical speeds where sudden increase in some vibrational wave amplitudes may appear and that may shock your tractor. At least, the probability of occuring such shocks is much more in the vicinity of the critical speed where overall net force balance is critical. BUT, according to the science philosophy today, you get the best efficieny/performance at the critical speed. So, it's like doubled-edged sword. You take the risk of damaging your tractor (due to the wear, heat and dynamic&thermal cycles causing fatique, etc) and you MAY get the best performance from your tractor.

Things in the technology is analogy to human life. We have a saying "hizli yasa, cesedin yakisikli olsun" that is said by young boys "living fast" to defend their lifestyles- Its literatlly translation is that "live the life fast (bars, discos, etc etc), let your dead body be handsome."

 

[JDgreen227]

"Kohler recommended removing the heads and cleaning the carbon out every 100 hours..."
That's really frequent, on my '89 JD with 18 hp Onan the manual recommends that service every 250 hours if using leaded fuel and 500 hours using unleaded fuel. I did mine at 900 hours and there wasn't a lot of carbon to remove.

Could anyone tell me why these type of engines build up carbon deposits? I have never known of an automobile engine that requires this type of service.

 

[CTyler]

</font><font color="blue" class="small">( Things in the technology is analogy to human life. We have a saying "hizli yasa, cesedin yakisikli olsun" that is said by young boys "living fast" to defend their lifestyles- Its literatlly translation is that "live the life fast (bars, discos, etc etc), let your dead body be handsome." )</font>

We used to joke about that as kids/young adults.
Live fast, die young and leave a good looking corpse.


I think the premise of the question is basicaly this.
If I can do the same job/work with less RPM will My tractor live longer?

 

[Egon]

Its not the suppossedly high teck higgly piggy gobbldey gook that cause the problems. It's usually the valves hitting the top of the pistons that make for self destruct because the valve train is not designed for that RPM in order to limit camshaft wear and reduce engine power loss.

There was a time floating points limited RPM unless modifications were made.

Don't know if they were in Real or Integer mode.
Egon

 

[BIGUN]

After posting that I was thinking it was more like 300 hours to clean the carbon off the heads. My memory ain’t what it used to be. /forums/images/graemlins/confused.gif I know the rubber valve seals on mine were hard as glass when I tore it down. The new gasket/seal kit didn’t have new exhaust valve seals. When I ask where they were, the answer is that they get so hot that they are ruined in a short time, so they just don’t bother to replace them. That doesn’t really explain the carbon buildup though since a lot of overhead valve engines have leaking valve seals and don’t require routine carbon removal.