To the mechanical geniuses from those mechanically challenged

banjoboy

banjoboy

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Dec 16, 2010
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Port Townsend, Washington
I don't understand how our NTs or any bike can go for hours an.d hours and high rpms. Yesterday I rode 815 miles with the rpms between 5000 and 6000 rpms. It is partly a trust exercise for me from what others have said that you can run these engines all day at high revs without damage to the engine. Can anyone explain to me in non technical terms how this can possibly happen. BTW, I used zero oil on this run or any run since I had major tuneup and valve set, etc. on this 3000 mile trip. I had fear on this trip that somehow something would fail. Yet after several hours, I could simply tune in to the hum at 5500 rpm and mildly enjoy it, knowing that in the back of my mind, something would go wrong. Any thoughts.

Terry
 
I forgot to add as I was riding that at 6000 rpm, the cycle goes 100 times per second. I think this is a limitation of my brain to understand how fast this goes.

Terry
 
All I can say is that they were designed this way. The NT is a slow revver compared to a Kawa Ninja. You run those at 10,000 RPM all day without a hiccup. A friend who is an excellent wrench says "It's engineering and metallurgy" 6000 RPM is no big deal for the NT--besides, it has a rev limiter so you can't hurt it. Our motor oils have come a long way in the past 20 years so the engine will will not be lacking in lubrication.
 
Terry, somebody else can give you more technical details, but engines are designed to have accelerations and velocities that fall within the mechanical limits of the metal alloys used to build them. There are limits that they can't exceed without failure, but those limits are well on the other side of our 8500rpm red-line. Engine designers calculate the velocities in feet-per-second, figure out how many times things stop, change directions, accelerate, and stop again. They figure out how heat transfer works in the top of the piston, the cylinder head, and the exhaust valve. The exhaust valve probably gets hotter than any other part of the engine, and it cools because it's against the valve seat so it can transfer its heat to the cylinder head which is cooled by water flowing around the exhaust port. The other thing that's important is lubrication. There has to be an oil film between things like crankshafts and the main bearings in the block; crankshafts and connecting rod big-ends; piston wrist pins and connecting rod top-ends; between camshaft lobes and valve rocker arms and then between the other ends of those rockers and the top of the valve. Modern oils have amazing molecular strength that allows them to form and maintain that film.

In the "olden-days," engineers used roller bearings on the crank thinking that lowered frictional resistance. Now they know that no bearing can have as little friction as a one-or-two molecule thick oil film. Plain bearings and incredibly precise tolerances keep that film there.

Temperature control from liquid-cooling is also essential to maintaining those tolerances. It all works together to produce some amazing machines, doesn't it.

I remember thinking the same kind of thing last year when I was bombing along in northern Newfoundland (only running about 70mph there because our Canadian friends have a 100kph/62mph speed limit which they enforce fairly seriously. Ignoring the fact that I wasn't always in 5th, and pretending that my average rpm/mile was 4250 (that's the rpm at 60mph), I figured that in the 21,070 miles I rode on the Epic Ride saw the engine turn over 88,494,000 times (and have 88,494,000 explosions in the pistons. Each piston had 44,247,000 combustion events.

And the only trouble I had on the whole ride was having a low-beam headlight bulb and two brake/tail-light bulbs burn out.

[Today I've got 87,572 miles on the bike. That means the engine has turned 372,181,000 revolutions, plus whatever factor needs to be added for the extra revolutions when I was in lower gears.]

Pretty cool, huh?
 
Honda has been making high-RPM engines for many decades. One of my first bikes was a CB160. This had a 10,500 RPM redline. (It also used the engine as a frame member.)

I also go through these kinds of ruminations. Here's another one: For each mile you drive in high gear, each NT piston traverses about .35 miles. So if you've got, say 50,000 miles on your bike, each piston/ring set has traveled well over 17,000 miles within its bore. Yet they keep on ticking.
 
Rich said:
Honda has been making high-RPM engines for many decades.
Click to expand...

In 1964, the year I began riding, Honda raced a 2 cylinder, 50cc Grand Prix bike, the RC114, that developed 14 HP at 19,000 rpm with a red line at 20,500 rpm. It was capable of 23,000 for short periods. That was a half century ago!
 
Modern metallurgy, modern oils, liquid cooled relatively short stroke engine, built by Honda.

In 1968, Suzuki (RP 68) had a water-cooled, 50 cc, three cylinder 2-stroke. Produced 19 hp at around 20,000 rpm. the FIM killed it in 1969.
Transmission: 14 speeds
 
It's all in the balancing and metallurgy. What has changed in the past years is the ability to produce items with VERYclose tolerances. That makes the balancing issue much simpler than the 'old days' when everything had to be CAREFULLY hand built to get those same tolerances. That makes higher rpm motors cheaper to produce.

As has been noted, 5-6k rpm is not all that fast, even for all day running.

The basics of design mean that for higher rpm you shorten the stroke. But, there are trades. If you stay with a certain number of cylinders it means the bore gets larger, which means larger pistons. But, shorter stroke also means the con rods can be shorter and lighter. Crankshaft can be smaller dia which means less mass as well.

Then there are other issues, like valve float and methods to avoid that (like more than 2V per cylinder and using things like titanium).

Then you can get to extremes, like current F1 cars. They need to be heated up just to be able to turn the engine over (parts are set for tolerances at operating temp, not at room temp).
 
[...In the "olden-days," engineers used roller bearings on the crank thinking that lowered frictional resistance. Now they know that no bearing can have as little friction as a one-or-two molecule thick oil film. Plain bearings and incredibly precise tolerances keep that film there...Phil]

To me the use of crank & rod roller bearings was borne on the sad reality of babbit bearings of that era. They were made of poured metal that had to be hand finished so tolerances were all over the map plus the babbit material wasn't very durable. It wasn't until the dual or tri-metal insert bearing was fully developed that roller bearings were mostly discarded by engine designers.

The two keys to high RPM durability are piston speed and having good valve springs. Although our NTs will register around 4200 rpm at 60 mph, the piston isn't moving very far (up & down total distance) compared to a typical domestic car with V8 engine registering 2000 rpm at the same road speed.

Japanese makers have been designing high RPM engines for ages and about 10-years ago I was amazed to hear from a friend that Hendrick Motorsports, a dominate team in NASCAR, was buying valve springs from a spring maker in Japan. I'd thought that wire spring metallurgy had already migrated here by the mid-1990s. At the time, he was working at Hendrick as an outside contractor for their computer systems.

ps. I consider myself "mechanically challenged but well read." :)
 
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