RPM and wear

I’m just curious, does a high rpm short stroke engine wear faster, slower, or about the same as a low rpm long stroke engine?

 

My Honda civics all revved like crazy, and they all made it past 250,000km. Some engines are just built better. If it's properly engineered, it can survive the high rpms. I guess that doesn't really answer your question, but that's my experience.

 

think of the distance traveled like the brushes in an xj alternator the outside brush on the biggest diameter copper ring wears down quicker than the inside one same rpm just different travel distance.

that would apply if the components were of the same materials , so I guess this is a non answer.

so if your short stroke is 2 inches and has to run at 7500rpm vs long stroke being 3 inches and runs at 5000 rpm to reach the same speed the distance traveled would be the same.

you would have to also consider the transmission and its gearing as well .

 

Short answer, about the same.
Long answer requires knowing the application for the powerplant.
But, all other variables being accounted for, see my first sentence.
What matters most for longevity is the materials used in the engine's constuction, lubrication, and cooling (and the maintainance schedule being adhered to).
Consider the high RMP, no-stroke engines that power most modern aircraft and warships. Many miles of travel are gotten before overhaul is needed; many times (as in multiplying) more than from equivalent piston engines run under the same conditions.

 

If you take care of it, you don't have are to worry about it

 

I can see how the piston and ring wear would be about equal, but it would seem that the cam, valves, crankshaft and rod bearings would wear faster.

 

But they don't. Materials are engineered to suit the purpose. Lubrication and cooling systems are also engineered to suit the purpose.
It is advances in materials scince and enginering practices that made high RPM, short-stoke engines possible. While it is certian that a high-revving engine can be made to wear out faster than a low revving engine that producs the same horespower, that would only happen when the engine is being made to push to the ragged edge of a perfomance envelope (such as in racing), and not in a production engine (and a low revving engine can also be pushed to the ragged edge of a performance envelope, and break connecing rods, or bend valves).

 

Xj engines rev much higher than Harleys do. Do they need more maintenance or wear out faster?

 

Yes, Harleys need MUCH more maintenance, and they wear out faster

 

Yeah, that was the point...
I have always felt that engineering is the replacement for displacement. Smaller engine, more power per cc, longer lasting, better on gas, I love Japanese 4 cylinder engines!

 

A well made, and well designed, long stroke engine will last almost forever (I'm partial to Honda's clone of the HD big twin).
The same is true of all other engine types.

 

Are you referring to the 750 like in the Shadow, or the BIG ones like vtx? I have been looking at Shadow Spirit or RS lately... It's just so hard to find a new sport cruiser/standard with 4 cylinders.

 

Eliminating or at least minimizing vibration is a factor. The motor configuration plays a big part here. Harley has come a long way in this recently. The old British twins are horrible in this regard, the vibration is even more annoying than a shovelhead IMHO.
Then there is the Honda CBX as smooth as they come, however although offering a big visual impact provides a very dull riding experience, again just MHO.
One of the worst culprits is the KTM 625/640 dual sport thumpers, their cranks can come apart within 5000k the vibes are so bad.

 

I'm referring to the VT1100, which is the engine that H-D sued Honda over. It's a stouter power plant than H-D's big twin (of that time), though it does have the problem with the crank-assembly blank-off plug working out of he case (easy fix, but not a typical Honda problem).

 

Long stroke engines typically have a lower rpm limit (sometimes, a much lower limit), and thus the forces acting on the piston, piston pin, and especially, the rod bearings are lower around TDC and BDC, due simply to the lower accelerative force acting upon them due to the lower rpms. Of course, if a longer con rod (versus a greater crank throw offset) is used to achieve that long-stroke, then that additional mass in the rods increase those forces......a trade-off, "it depends" type of situation.

Of course, at any given rpm, a long-stroke engine will also have a great piston travel distance, increasing piston ring /cylinder wall wear and tear.

 

I would think it would be actually less wear because the wear is spread out over a wider surface areas due to increased distance. BUT-- it probably actually balances put to about the same amount of wear....except one is 'wear spread across a wider surface' vs the same amount of wear' concentrated into a smaller area' making it SEEM like there's more wear....

A pound of feathers in a barnyard still weighs the same as a pound of feathers in a pillow case

 

Unless it's one of those "My Pillows" as seen on TV.....since they don't use feathers.

Actually, a short stroke engine piston actually travels less, at any given rpm. Let's sat a stroke of 1/2", so each "engine revolution" is one trip up and one trip down the cylinder wall, or a total travel of 1". At 5000 rpm's, the total piston travel is 5000"

A long stroke engine.....say a stroke of 1".....also makes two trips along the cylinder wall for each engine revolution, so 2" total travel per revolution, = 10000" of travel at the same 5000 rpms.

And since it is typically the RINGS that experience the wear, rather than the cylinder walls, I would think that the total distance travelled would be the key factor.

But, I ain't no engine engineer.......

 

Hardness, coatings, clearances, Cooling, variables, ymmv.

I built a high revving long stroke scooter engine once (length of stroke was just a bit longer than the piston diameter).. Air cooled, topped out at 9500 RPM ( and was there a lot). I had the piston skirt and cylinder micro-bead blasted ( improves oil retention and lengthens service life). It never ran hot or lost power (but it did shred a few drive belts). While I sold it several years ago, the owner is still using it for his daily commute, including freeway time.

Of course if we eliminate all other variables, we still get a debate. Build two iron bore, side valve engines. One long stroke and one short stroke. The long stroke engine will fail once the materials strength is exceeded (probably at the connecting rod or flywheel, somewhere just above 4,000 RPM). The short stroke engine will fair better, but wear out faster. Now build two identical engines using more modern techniques, designs, and materials. Both will likely wear about the same (at least 200,000 miles of use, but likely over 300,000 miles, before needing to be rebuilt), but which one will wear out first? I don't think that there is enough real-world data to support a definitive conclusion, because industry has become really good at designing engines for specific purposes. In the past the same engine might be used in multiple platforms and for multiple applications; that's not quite as common anymore (i.e. when was the last time you could buy a 5 ton truck with a gasoline engine).

 

Honda is fond of doing that with their motorcycle engines. For example, their 500 parallel twin is used in the cb500r, 500f, Rebel, and an adventure bike. The V4 has been used in VFR and Magna. The 750 vtwin is used in about 4 versions of the shadow cruiser. It saves them a ton on design and manufacturing. Once you have a well sorted powerplant, and all the bugs worked out, it makes sense to use it everywhere you can as opposed to starting from scratch for new models.
Subaru does the same with their flat 4. It's used in Forrester, legacy, Impreza, brz, and the turbo comes in various stages of tune for different models. Obviously, the race prep WRX STI gets more go juice than the speedy soccer mom Forrester.
I've been typing so long I forget my point...

 

Those are all similar applications Matti. I'm referencing a time when one could find the same engine used in a tractor, a truck, a crane, and in use to drive a water pump.

 

Such as an international dt446. It can be found in tractors, over the road trucks, construction equipment, stationary equipment, so on and so forth. Agreed times have changed and you don't seem to see that anymore