Keeping the RPMs Up K75

Something I just read in another thread here got me going on this.
A gentleman mentioned that the K75 wants to be run in a range of between 4500 to 7000 RPMs.

OK so I've always known it's not good to lug a motor- ANY motor. My habit is to always keep ALL my bikes running at 3000 RPMs or higher- rarely do I run 'em any lower than that. I have a variety of motorcycles that are all either BMWs, or older Brits. Does each motor have its specific needs or requirements in this regard or am I OK at just ball-parking it at 3K minimum RPMs for all my bikes?

Just curious here, is all.

Yeah, with the K75 you get the most power/fun above 4500 rpm or so. But mine is perfectly happy short shifting when puttering around town. It's a very flexible engine, much more so than the R bikes I've had.

bmwrider88 said:

OK so I've always known it's not good to lug a motor- ANY motor.
Just curious here, is all.

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Yep, that's a good way to burn up the windings!!

Ken

Just like your K-bike, your airheads will appreciate being run north of 4.5K. And depending upon how much demand you put on your motor (accelerating hard?), 3K could be considered lugging.

The other day I rounded a slow right hand corner in third gear, for some reason glanced at the tach - 2000 rpm - and slowly accelerated away with no "un-happy" symptoms from the engine.

Unless for some reason I really want to move I generally upshift around 4K RPM. As said, these are very forgiving engines. If you need to make a quick pass, a lower gear and higher RPM's may shorten your passing distance a little, but there is no "afterburner" effect on either K75 or K100 engines that I have experienced at any RPM.

Surprised that more people don't recommend K75's or even K00's for adult beginners. Low price, that forgiving engine, low maintenance and good handling (not to mention the low seat option) should work for the newcomers as well as they do for those of us who never got past our first BMW love.

BMW rider 88 (real name? We're friendly here!)

Please read: http://forums.bmwmoa.org/showthread.php?t=46057 - I've added that info to the thread title. While keeping the RPMs up is generally an OK thing, on some engines (like older twins) continual high RPM use can start to use up an engine (I know people are going to scream about that statement.. but..)

Anyway - it's a good thing if you put year/model of the bike in your thread title. I've added the model. Please do so yourself in future thread titles for threads you start in the tech sections. Makes it easier for us old pharts to spot threads of interest.

Thanks for your cooperation,

deilenberger said:

Anyway - it's a good thing if you put year/model of the bike in your thread title. I've added the model. Please do so yourself in future thread titles for threads you start in the tech sections. Makes it easier for us old pharts to spot threads of interest.

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The OP is not only about the K75. I think it would be better to take K75 out of the title.

I'm the guy the OP is talking about. Nikasil is an extremely durable cylinder coating. It reduces friction 30% over steel or iron bores, reducing ring wear and ring groove wear in the pistons, extending engine life greatly. But, one thing Nikasil will not tolerate is detonation. Even a little detonation can pit the Nikasil at the top of the bore, and this can cause premature cylinder failure and loss of power. A major cause of pitting in Nikasil in US engines is riders lugging them. For some reason, there is a class of both rider and driver in the US who use a gas engine the way you used an old low compression, long stroke, flathead six in an old 1950'sDodge. My dad used to drive this way, get the car rolling in first gear, skip second entirely, slam the thing into third and lug the crap out of the poor thing. Lazy driver! Modern high rpm engines can't take that sort of use. Detonation from low rpm lugging is death to Nikasil, even if the engine doesn't protest the abuse.
Similary, very high rpm running can lead to high rpm detonation if the ingition is not adjusted correctly. BMW uses pretty aggressive advance curves and a little too much advance, more than 2% on a K bike engine, risks destructive detonation at high rpm. The K-1200 iteration of the Flying Brick can experience this even with a perfectly running bike. Credit the long stroke and high power BMW is dragging from that old engine. It is running very hot and detonation is always a threat.
So, for greatest longevity, keep the engine spinning happily in the middle of the power band, 4500-7000. No risk of detonation at either end, and you are putting the lowest loads on the rings, pistons, bearings and cam chain/tensioner. This is where the loads on the engine are lightest and the engine will last the longest as a result.

Btw, many years ago Reg Pridmore taught this to me with my first BMW. After servicing it he asked me what RPM's I am using and I told him I keep it around 4000 or so. He could tell just from servicing my then new bike I wasn't revving it enough! He told me to keep the engine above 5 grand, and this was an '83 R-100RS. Many years later my friend who used to work for BMW in Munich confirmed the same, as I explained above.

Lee said:

The OP is not only about the K75. I think it would be better to take K75 out of the title.

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Sorry - that's not happening. The topic started with a specific question on the K75 engine.

42906 said:

I'm the guy the OP is talking about. Nikasil is an extremely durable cylinder coating.

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Agreed.. VERY VERY durable.

Btw, many years ago Reg Pridmore taught this to me with my first BMW. After servicing it he asked me what RPM's I am using and I told him I keep it around 4000 or so. He could tell just from servicing my then new bike I wasn't revving it enough! He told me to keep the engine above 5 grand, and this was an '83 R-100RS. Many years later my friend who used to work for BMW in Munich confirmed the same, as I explained above.

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I suspect if you asked Reg Pridmore why he suggested that, he'd tell you he wanted you to keep the engine in the fat part of the power curve - in order to have good controllable power. He lives in California, if anyone knows him, I'd be interested in his opinion..

As far as K75's - I know of 3 now that have eaten their nikasil coating (it flakes off.) Each of them had in excess of 300,000 miles on the engine. As mentioned - it's an extremely durable coating. That's the only 3 I know of, and I've been hanging around K bikes for quite a while. We could ask Paul Glaves how he ran "Old-Smokey" which died at the hands of a car at well over 300k miles. It was still on the original engine that had never been opened up.

Paul?

deilenberger said:

Sorry - that's not happening. The topic started with a specific question on the K75 engine.

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Sorry I thought he was asking about all bikes.



OK so I've always known it's not good to lug a motor- ANY motor. My habit is to always keep ALL my bikes running at 3000 RPMs or higher- rarely do I run 'em any lower than that. I have a variety of motorcycles that are all either BMWs, or older Brits. Does each motor have its specific needs or requirements in this regard or am I OK at just ball-parking it at 3K minimum RPMs for all my bikes?

42906 said:

So, for greatest longevity, keep the engine spinning happily in the middle of the power band, 4500-7000. .

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It's been a few years since I had a K75, but this sounds about where I ran mine.

Not really the point here, but heh, I LOVE the way my K sounds at 4500 and above; it becomes my two-wheeled Porsche Carrera!

(or could be put another way; from a sewing machine to a roadburner with a twist of the wrist)

deilenberger said:

Agreed.. VERY VERY We could ask Paul Glaves how he ran "Old-Smokey" which died at the hands of a car at well over 300k miles. It was still on the original engine that had never been opened up.

Paul?

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Nikasil is durable. The engine is very flexible. The K75 makes 90% of peak torque at 2,000 RPM. I don't advocate running at that RPM though, but I would not expect pinging absent a sudden WFO whack or bad fuel. Unless I am straight and level at a low speed I always downshift at about 3,000 RPM and typically upshift somewhere around 5,000 or 5,500. I wouldn't do hard acceleration between 3,000 and about 4,000 but for just running along, in traffic for example, my K75s are perfectly happy at 3,000.

Yes, the "keep the rpms up" drivel heard quite often in BMW circles is mostly just macho posturing IMHO. There's no technical basis for it whatsoever. And it's clearly fuelish.

Sure, (and obviously) don't lug the engine and it's nice and probably safer to have your engine in the torque band ready to exit you quickly from danger, but otherwise there's little in it. And clearly some BMW engines are not particularly low rpm torque rich (and some are), which frankly is more annoying than it is some sort of opportunity to see big rpm numbers and feel "special" about that.

And yes Nikasil is cool (except when it isn't--see 1990s BMW car V8s) but its purpose is for sure not primarily to facilitate high rpm running, as other materials handle it equally well. It's there for its production advantages more than anything and is maybe kind of cool for aircooled motors heat management, too.

rpm

I got curious when I read another posting that running a F650 (I think) at under 4000 was a recipe for lower end problems. And it was suggested that 4 to 7000 was the right range. My k16 runs 2800 at 60 mph and my R100 about 3500 or so and I assume that BMW felt these were acceptable rpm levels because most jurisdictions have 60 to 70 as the posted highway speeds. Does anyone really need to run any engine at 7000 for any reason? High rpm, high heat, more wear and worse fuel economy?

FELAW said:

I got curious when I read another posting that running a F650 (I think) at under 4000 was a recipe for lower end problems. And it was suggested that 4 to 7000 was the right range. My k16 runs 2800 at 60 mph and my R100 about 3500 or so and I assume that BMW felt these were acceptable rpm levels because most jurisdictions have 60 to 70 as the posted highway speeds. Does anyone really need to run any engine at 7000 for any reason? High rpm, high heat, more wear and worse fuel economy?

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This post assumes that one must be riding in top gear which is not true at all. And bear in mund that your K1600 has more than 2.5 times the displacement of an F650 single so of course it's character is totally different. The real answer looks at the torque curve for the engine. For example, a K75 makes 90% of its peak torque at 2,000 rpm and is perfectly happy - except at very heavy throttle loads - cruising at 2,500 to 3,000 rpm. But an F650 single is a totally different animal and doesn't develop much torque at all below 3,000 rpm and will really stumble and rattle at 2,500 rpm. My new G310GS single redlines at 10,800 rpm and is perfectly happy at a sweet spot at 70 mph but it is turning 7,000 rpm. But that is less than 70% of redline and is nowhere close to stressing the engine. "Motor" is BMW's middle name for a reason.