Why not run low RPM's

[mcollect]

I was having this discussion with some riding buddies and they don't believe that running low RPM' on the R1150R will hurt it. Am I correct, that it will do damage; if so how? I think the right RPM is 3500 and up.

[Godfather]

Running a high performance machine (any brand) at low rpm's will cause carbon build up in the heads which in turn will have negative effects on performance as well as fouling spark plugs. BMW's are engineered to run continuously at their maximum torque range. You can run your oil head boxer twin at 5,000 rpm's all day long without concern. On the other hand lugging, the engine at low rpm is not the best thing you can do for your machine. Just my 2 cent$.

[chrisZ]

As the previous poster said, lugging is not good for various reasons. As for keeping the revs high, it might not hurt the engine, but does hurt the fuel economy and is quite noisy. Keeping the engine outside of lugging RPM and below5K seems to be a good range for me. This typically is between 3500 and 5000 RPM and 4K is a good 'target' for me to maintain fuel economy and reasonable performance.

[PGlaves]

Shock loads on the connecting rod big end bearings and wrist pin bearings are higher at lugging RPM. Because it is over engineered in many respects the engine won't come apart immediately, but the increased wear will take its toll eventually.

When you can feel and hear the engine complaining you need more RPMs.

My uncle had an old John Deere tractor. After starting it with a turn by-hand of the external flywheel you could almost count the power strokes - chuff - chuff - chuff. But today's BMW motorcycles are not old tractors.

[Spidereyes]

My R1150R Maintenance Instruction manual indicates under "engine flexibility" that the machine will go from 37mph to 87mph in 6th gear in 10.16 seconds. This must be very close to a full throttle exercise.

Now, going down to 37mph in top gear is dropping the revs way down into what must be lugging territory, yet there it is right from the horse's mouth. When I first got my Roadster, I read the manuals through before I ever even rode the bike home (German heritage; couldn't help it). I have found no reference to lugging nor any caution regarding minimum speeds in gears.

All this is to say that I don't completely buy the hypothesis that low engine speeds cause excessive wear, carbon buildup, bearing damage or the like. Obviously, one does not run at such low revs as to cause juddering, pinging or jerking from the powerplant but anything less than that should be OK unless the manufacturer states otherwise.

With regard to the John Deere vs "high performance engine" argument, I submit that piston rings, bearings and other wearing parts are very nearly comparable. It is the cam timing, valve overlap and mass that separates the engines and their RPM speeds.

I would like to hear from those who hold otherwise and I would like to know the logical or engineering reasons why they hold those opinions.

[AZ-J]

Is this discussion "limited to" running flat on a straight road?

Curves, aka "twisties" are another reason that require higher RPMs: more "straightening up" effect for the next curve.

[screwtop]

I've always been advised by my independant mechanic to run my GS at between 4.5 and 5 grand. I don't shift into "E" until I'm doing at least 80 indicated. Even at that speed, it seems like my 02 is lugging, and unless I'm comfortable with the stretch of road (and of course, the local LEO habits) I stay out of 6th.

[Spidereyes]

Screwtop, the Roadster has 66 lb/ft of torque beginning at 3,000 rpm and continuing through 6,500 rpm; this is the oft cited "sweet spot" in which the motorcycle feels powerful and lively. Below 3,000 rpm, torque and horse power are down resulting in less lively but useable performance.

The lower engine speeds we are discussing do apply to straight and level roads, Tweety1. Curves, dips, wind and hills will all change the power requirements.

This is a very interesting discussion and I'm glad it has come up (again).

There has been some mention of "high performance" engines. The Roadster produces 75.22 hp/litre. The NB Miata (second generation) I drive produces 77.78 hp/litre which is a fairly comparable state of tune. Mazda engineers made a big deal that dropping to 20mph in fifth gear, or 1,000rpm and accelerating to top speed, on level ground, was not only possible but safe for the engine as an indication of its flexibility.

Mazda drivers don't do this because we generally have to wring the little guy's neck just to keep up with bread trucks and UPS vans. Roadster drivers rarely drop below 3,000rpm just because 5,000 revs feels so much better. But the point is that the Roadster has a very flexible powerplant.

I still maintain that carbon build up is more a function of oil consumption and faulty fuel delivery and less one of low engine speeds. In fact, one could make the argument that using higher than necessary octane fuel, with its retarded burning charistics, is possibly the reason for carbon build up.

[PGlaves]

After you have 300,000 miles on the engine, tear it down and tell me what you find. Then I'll argue the point. Until then - it's your bike. Ride it as you wish.

[PETDOC]

Curious as to what constitutes lugging. I normally run my 1150 GS between 4-5000 rpms; however, when I'm in 6th gear on a flat road constrained by a speed limit I will cruise at 3,000 rpms. The engine does not feel like it is lugging as a twist of the grip is associated with a rapid acceleration. If I see a steep incline approaching I will either accelerate to get rpms up or downshift.

[Spidereyes]

300,000 miles? I'm not sure I'll hit that mark any time soon. A police force machine might though if it wasn't recycled first. I'm just guessing, but I'd assume that a cop-cycle would spend long periods of low speed work interspersed with spurts of high speed. Do they show extreme carbonizing or bearing wear? What points of engine wear tend to show up most frequently in BMW (or other motorcycle) police fleets?

And regarding carbon build up, exactly what about 2,500 rpm would promote more build up than, say, 5,000 rpm in the same (healthy) engine? With the same load, temperature and relative fuel flow, why would the higher revs be more conductive to clean combustion?

I'm not going to argue with you about bearing wear but can you cite some studies comparing con rod/crankshaft bearing loads at various RPM and loads? I've been Googling for a couple of hours and can't find any studies or monographs on this subject which is actually kind of curious. I did find a paper mentioning shock loads on bearings during preignition but we're excluding preignition from this discussion.

I've never seen or heard of a a wrist pin failure in 40+ years of fooling with sports cars and motorcycles. I know they can fail; I've just never heard of one.

[PGlaves]

Actually the 300,000 miles was not a police bike - it was both my K75 which was running happy at 370K when run over by a mini-van and Voni's R1100RS which is still running fine at 330K, although it is getting near to needing rings for the first time. The bottom end looked and measured just fine at 295K. Plastigauge is your friend. Most police departments get rid of their bikes in the 60K range.

The key to engine damage is higher combustion chamber temps, some pinging whether audible or not, and carbon buildup related to the higher temperatures. Bearing loading is also related to the rotary motion of the crankshaft related to the speed of the flame front during combustion, and the crankshaft position which is supposed to be just after TDC when peak combustion pressure occurs. It depends on the design of the engine and its state of tune.

By definition lugging is operating an engine under too great a load at too low an RPM given the design of the engine. On some bikes that might be 2,000 RPM and others it may be 4,000 rpm. Listen to the engine and let it talk to you.

[osbornk]

When I started driving in the early 60s, I was driving standard transmission cars of the 50s. My father, uncles and older cousins kept jumping on me for lugging the engine. They claimed that lugging would "beat the bearings" out of the engine and mainly main bearings. They said they had had the problem because of that. Since they were the "experts", I followed what they said and didn't take any chances. 40+ years later, it still sticks in my mind and I still follow their advice.

[rinty]

I'm not afraid, when I'm touring, to run my 1150 RS through towns at between 2 and 3000 rpm in the lower gears (1st to 3rd). This almost eliminates the surging, and the engine seems happy. The too tall sixth gear on the 1150's is a problem, and I like at least 4,000 rpm, but it seems to run fine down to 3,600 or so.

Rinty

[Spidereyes]

The key to engine damage is higher combustion chamber temps, some pinging whether audible or not, and carbon buildup related to the higher temperatures.

By definition lugging is operating an engine under too great a load at too low an RPM given the design of the engine. On some bikes that might be 2,000 RPM and others it may be 4,000 rpm. Listen to the engine and let it talk to you.

I still haven't found definitive information on varying bearing loads at varying engine RPM and I've Googled for about four hours altogether.

What about the carbon build up question? Do you have an answer as to why low RPM might cause coking? Again, why would 2,000 revs foster more build up than 5,000? If RPM were the culprit, wouldn't huge American sedans loafing along the freeway at 2,000 revs be in the shop all the time for decarbonization? With modern fuel injection, computerized ignition and all the other technology, why should RPM be the guiding force behind the carbonizing rather than oil consumption and unbalanced throttle bodies?

[PETDOC]

The too tall sixth gear on the 1150's is a problem, and I like at least 4,000 rpm, but it seems to run fine down to 3,600 or so. Rinty

You are correct the 1150 GS has a tall 6th, but I find it runs great at 3,000rpms (60 mph). When it was new I had a problem with hot weather pinging with hard acceleration in 5th and 6th gear. After I upgraded my left side cam chain tensioner I, despite trying, can't make it ping. Dropped it to 2,000 rpms in 6th at 98 degrees ambiant temperature and after riding all day, and then cracked open the throttle--no pinging!

[rinty]

Petdoc:

My understanding is that there are two different sixth gear clusters: a low and a high. I have been told by an owner that you could pick the one you wanted on the R 1150 R order sheet. My understanding is that the tall sixth gear is standard on the RS and RT; I am not sure what the GS's come with; they could have the lower one. At 4,000 my bike is doing 81 mph, so it's basically an interstate gear. I haven't checked it at 60 mph. Maybe some other GS owners can chime in here. And the GS Adventure gearing is different from the standard, GS, I understand.

I've gotten to the point where I can live with this transmission, but it's really an autobahn unit.

Rinty

[screwtop]

Petdoc:

My understanding is that there are two different sixth gear clusters: a low and a high. I have been told by an owner that you could pick the one you wanted on the R 1150 R order sheet. My understanding is that the tall sixth gear is standard on the RS and RT; I am not sure what the GS's come with; they could have the lower one. At 4,000 my bike is doing 81 mph, so it's basically an interstate gear. I haven't checked it at 60 mph. Maybe some other GS owners can chime in here. And the GS Adventure gearing is different from the standard, GS, I understand.

I've gotten to the point where I can live with this transmission, but it's really an autobahn unit.

Rinty

I can chime in. At 80 mph indicated my 1150 GS is spinning just under 5K and drops to about 3,800 when I shift into 6th. Hope nothing's wrong with it. Seems OK.

Chris

[twins4life]

My R1150R Maintenance Instruction manual indicates under "engine flexibility" that the machine will go from 37mph to 87mph in 6th gear in 10.16 seconds. This must be very close to a full throttle exercise.

Now, going down to 37mph in top gear is dropping the revs way down into what must be lugging territory, yet there it is right from the horse's mouth. When I first got my Roadster, I read the manuals through before I ever even rode the bike home (German heritage; couldn't help it). I have found no reference to lugging nor any caution regarding minimum speeds in gears.

All this is to say that I don't completely buy the hypothesis that low engine speeds cause excessive wear, carbon buildup, bearing damage or the like. Obviously, one does not run at such low revs as to cause juddering, pinging or jerking from the powerplant but anything less than that should be OK unless the manufacturer states otherwise.

With regard to the John Deere vs "high performance engine" argument, I submit that piston rings, bearings and other wearing parts are very nearly comparable. It is the cam timing, valve overlap and mass that separates the engines and their RPM speeds.

I would like to hear from those who hold otherwise and I would like to know the logical or engineering reasons why they hold those opinions.

I'm with you, nicely said as were Pglaves' comments.

[PGlaves]

I still haven't found definitive information on varying bearing loads at varying engine RPM and I've Googled for about four hours altogether.

What about the carbon build up question? Do you have an answer as to why low RPM might cause coking? Again, why would 2,000 revs foster more build up than 5,000? If RPM were the culprit, wouldn't huge American sedans loafing along the freeway at 2,000 revs be in the shop all the time for decarbonization? With modern fuel injection, computerized ignition and all the other technology, why should RPM be the guiding force behind the carbonizing rather than oil consumption and unbalanced throttle bodies?

Interesting comments at:

http://www.msgroup.org/Contrary/NEG037.html

It's just a website - but the second set of comments make sense to me. They are consistent with what old Smokey Yunnick was writing in Popular Mechanics back when I was just a gearhead kid.

[PGlaves]

Here is a good one, from a bearing manufacturer - more than most want to know about plain engine bearings. But it contains several references with illustrations of bearing damage where lugging is a stated cause. Good reading!

http://www.engineparts.com/publications/CL77-3-402.pdf

[PGlaves]

Another on lugging and bearing failure:

http://www.thirskauto.net/BearingPics.html

I've quit looking - this is definitive enough for me.

[wezul]

My impression has been that by keeping the revs lower I am being tender with the engine. These articles are evidence to the contrary. Sage advice, Paul, thank you once again!

[Prof. Robert]

It's just a website - but the second set of comments make sense to me. They are consistent with what old Smokey Yunnick was writing in Popular Mechanics back when I was just a gearhead kid.
__________________
Paul Glaves
"Big Bend", Texas U.S.A.

Smokey Yunnick?:gerg I haven't thought about him in years. :)

Thanks for the memories.

Robert

[PETDOC]

Petdoc:
At 4,000 my bike is doing 81 mph, so it's basically an interstate gear. I haven't checked it at 60 mph. Maybe some other GS owners can chime in here. And the GS Adventure gearing is different from the standard, GS, I understand.
I've gotten to the point where I can live with this transmission, but it's really an autobahn unit.Rinty

Rinty,
I believe we have the same 6th gear. At 3000 rpms I'm doing 60 mph (GPS measurement, OEM speedo hub is off to the upside by about 7-9%); at 4000 rpms doing 80 mph and at 5000 rpms doing 100 mph. I actually like 6th gear, it's first gear I'd love to trade for a lower ratio. Trying to go slow in gravel is nearly impossible.

[rinty]

Petdoc:

I like the overdrive gear for interstates and Canadian 110 km/hr roads, but the problem is when you're on two lane 60 mph / 100 kmh roads and have to use fifth, where there is more vibration. I would have preferred a 600 rpm split between 5th and 6th, instead of 1,000. The engine runs nicely at 4500 to 5000 rpm in top. My airhead RS had a split of only about 300 rpm between 4th and top gear, but then it's power was much less than the oiler.

But they got it right on the 1200 transmission gearing; they're nicely spaced.

You'll have to trade for an Adventure to get your low first gear!:)

Rinty

[Spidereyes]

Looking at the bearing pictures and reading the text was an eye-opener. However, I imagine the juddering and bucking of the poor engines would be considerable in order to do that kind of damage from lugging. Surely some preingition was present and the "web site" certainly put low speed (undetected) pinging in perspective.

So, what does constitute "lugging" in an R1150R? Would you consider 2,500 RPM in the upper gears (third through sixth) to be lugging? How about 2,000? Keep in mind, I am considering straight, level roads, with no wind and only moderate acceleration. For example, cruising in the countryside and not in urban traffic.

And, to revisit that poor, dead horse I've been beating, Why would low RPMs cause more carbon build up than higher RPM?

The reason I'm persisting on this is that when I first bought my Roadster, I rode it very conservativly and at fairly low RPM (2,500-4,000) and got over 55 miles per gallon. I usually average around 40-45 MPG now but if I want to go for that maximum MPG for whatever reason, my method is to short shift and keep the revs down. I believe a BMW gas mileage study back in the '80s upheld this method.

[PGlaves]

Looking at the bearing pictures and reading the text was an eye-opener. However, I imagine the juddering and bucking of the poor engines would be considerable in order to do that kind of damage from lugging. Surely some preingition was present and the "web site" certainly put low speed (undetected) pinging in perspective.

So, what does constitute "lugging" in an R1150R? Would you consider 2,500 RPM in the upper gears (third through sixth) to be lugging? How about 2,000? Keep in mind, I am considering straight, level roads, with no wind and only moderate acceleration. For example, cruising in the countryside and not in urban traffic.

And, to revisit that poor, dead horse I've been beating, Why would low RPMs cause more carbon build up than higher RPM?

The reason I'm persisting on this is that when I first bought my Roadster, I rode it very conservativly and at fairly low RPM (2,500-4,000) and got over 55 miles per gallon. I usually average around 40-45 MPG now but if I want to go for that maximum MPG for whatever reason, my method is to short shift and keep the revs down. I believe a BMW gas mileage study back in the '80s upheld this method.

I have an R1150R which I've put a little over 70K miles on. The motor gets unhappy when the load exceeds the available power. Since the transmission acts as a torque multiplier what RPM applies in lower gears is not the same as what applies in higher gears. So piddling along in town at 2500 RPM in 2nd or 3rd may still allow the engine to respond to light acceleration without consequence. But my R1150R is lugging at just under 3,000 RPM in 6th. That is right at 60 mph. I used to hate the transmission because in those states where the speed limit is 55 if I tried to fudge it to 60 the bike was unhappy in 6th and buzzy in 5th. A very careful valve adjustment and synchronization made 5th much better - and at that 60 mph it is turning just about 4,000 RPM in 5th. On flat level ground with no wind my R1150 runs along OK in 6th at 3,000 RPM, but barely and even little hills make it unhappy if it is down at 2800 or 2900.

A note about detonation and/or pinging or knock. You can't always hear it. Car manufactureres have been using knock sensors for several years. BMW has them on some of the newer motorcycle models. It is possible to be damaging the engine even though up in the riders seat you can't detect the pinging.

Finally, the references I've read regarding combustion chamber carbonization all basically say that the build up is caused by incomplete combustion. One of the references made a clear distinction between the fluffier carbon coming from oil in the combustion chamber and the harder carbon deposits characteristic of unburned fuel. I am not too old to remember the tendency to take out Grandma's or Grandpa's car and "blow the cobs (carbon)" out of it because he had been poking around town too long.

[Spidereyes]

Thanks, Paul. I appreciate your replies and the references as well. I plan to stay at 3,000 revs or above with my Roadster and I hope it lasts into the forseeable future. Roadsters seem not to have the dreaded rear drive problems (I think) and at 6,000 miles mine just seems to be getting smoother all the time.

You mentioned the old "blow the cobs out" remedy for grandpa's cars. Well, I go a bit farther back; I used to pull the head on my MG TD every 10,000 miles to clean the carbon out of it. And I seem to remember that the main bearings of the XPAG engine series were good for NOT more that six minutes, cumulative, at redline. It's amazing how far we've come in just fifty odd years.

Cheers!

[FredRydr]

The key to engine damage is higher combustion chamber temps, some pinging whether audible or not, and carbon buildup related to the higher temperatures.... By definition lugging is operating an engine under too great a load at too low an RPM given the design of the engine.... Listen to the engine and let it talk to you.I used my '02 R1150R to marshal bicycle races. One week in particular in Altoona, Pennsylvania, it was at the end of July, and the days were very hot. Parts of the courses were on steep hillsides, and I had to stay in first gear and feather the clutch - for a long time - to stay with the cyclists. The poor oilhead began to knock more and more, try as I might to avoid it. I blamed the fuel, but all the referees and marshals were provided the same fuel, and other oilheads were suffering but not as badly as my bike.

Since then, the Roadster always knocked in similar circumstances under load when hot. I suppose I should have opened and decarbonized the cylinders, but I took the cheap way out and used fuel additives (Sea Foam, Techron). I stopped doing the race circuit because of insurance issues, and rode the R1150R for a couple more years until I recently traded it at 66,000 miles. I don't think the motor ever burned out the carbon (if that is what it was) or otherwise recovered, because it would still knock all too easily under load, regardless of years of maintenance servicing, tuneups and premium fuel.

It might be my imagination, but I wish I hadn't lugged the engine so much that hot July week.

Fred
'07 R

[Andy VH]

I think the biggest issue against lugging the engine down under load is the oil pressure is reduced, as stated in one of the links given.

Many motorcycle engines use plain/journal style bearings for camshaft duty, some even use journal style bearings for crankshaft/main bearings. This style journal must have good oil pressure to maintain the hydrodynamic oil film to keep metal from metal. If an engine is lugged hard at low rpm, the oil pump delivery may not be sufficient to maintain that oil film and rotating parts can come into contact, especially when the physical load on the part actually can squeeze the oil out from the journal.

I saw this first hand on my 78 Honda CB750 which used plain journals for the camshafts. Those old Hondas regularly made 80 psi oil pressure to feed those journals.

In use, as engine speed and load increases, the oil pressure increases to support the load. In theory, as engine load is increased with rpm, the oil film can support higher and higher loads without metal to metal contact. This is also dependent on the right oil, clean oil, engine not running to hot, etc.

As to the comment about rings and such being equivalent between a John Deere tractor and a high performance bike engine, I don't buy it. There are similarities, but big differences in design and application especially relative to piston speeds.

[Spidereyes]

Interesting hypothesis. At what RPM does the boxer develop maximum oil pressure? At what RPM does the pressure level off? What is normal oil pressure is in a boxer engine? I'd love to know. I'd also love to have an oil pressure gauge on my Roadster but I haven't seen an oil pressure gauge on a motorcycle since the early '60s.

Maybe P Glaves or someone else knows something about boxer oil pressure. Does anybody?

As to the piston speed being key in carbon buildup or bearing loads, I'll hold on to my original position. P Glaves did shine some light on excessively low RPM being indicted in bearing damage and I learned something from his posting of photos. Yet, as I indicated, the evidence of such lugging, e.g., juddering, pinging, etc., should have been most evident. I can imagine a drunk logging truck operator lugging his clapped-out Mack "tow motor" in the woods at 700 RPM but not a BMW rider lugging his 1150RT up the Rockies at 1,500 revs.

My original argument was that a BMW boxer operated at 2,500 to 3,000 revs (in, say, fourth gear, on level ground, with no head wind) should not accumulate any more carbon than a similar engine operated at 4,000 revs and I still hold to that position. Given the sophisticated computer, fuel injection and timing of the Oilhead, why should it be more prone to build-up than my Miata? And, even if revs were a factor, at what RPM would the risk disappear? And why would the Owner's Manual not caution against low revs? On page 60 of my 2005 R1150R, there is a specific warning against "warming up" the engine. If low revs were a carbon build-up factor, wouldn't you expect BMW to caution, "Do not run the engine under 4,000 RPM in any gear above third gear?"

This is my first Beemer and maybe they do accumulate carbon in the heads. If that be the case, I would just like to see some objective data supporting that and the hypothesis that RPM is the main contributing factor.

[cardno7]

Is it me? Not sure I ever stay under 3000 rpms except for gear changing, maybe that is why tires are being replaced every 6000 miles.

Seriously are people running in the 2000 to 3000 range?

[osbornk]

Is it me? Not sure I ever stay under 3000 rpms except for gear changing, maybe that is why tires are being replaced every 6000 miles.

Seriously are people running in the 2000 to 3000 range?

My CLC turns about 3,000 RPMS at 70 MPH. I run in 6th gear over 60.

[PGlaves]

Interesting hypothesis. At what RPM does the boxer develop maximum oil pressure? At what RPM does the pressure level off? What is normal oil pressure is in a boxer engine? I'd love to know. I'd also love to have an oil pressure gauge on my Roadster but I haven't seen an oil pressure gauge on a motorcycle since the early '60s.

Maybe P Glaves or someone else knows something about boxer oil pressure. Does anybody?

Well, the specs are less than totally enlightening. The oil pressure light is supposed to come on between .2 and .5 bar. Thats about 3 to 7 psi. The overpressure relief valve opens at 5.5 bar which is about 80 psi.

The oil pump is a positive displacement pump. I expect to see about 60 p.s.i. in normal operation. It will be low at idle but ought to rise rapidly - normal pressure by about 2000 rpm.

True lugging has the speed of the flame front in the combustion chamber outrunning crankshaft rotation so maximum piston force occurs at or before the piston has reached top dead center. This places extraordinary demands on the connecting rod bearings. The engine complains and you can both hear and feel it. This almost defines what lugging is.

The relationship between engine speed and carbon relates to incomplete combustion and the scouring effect inside the combustion chamber related to the inflow of unburned fuel and the scavenging of the exhaust. It also relates to the surface temperatures inside the combustion chamber. I don't pretend to fully understand it. But I sure could demonstrate it as a kid by blowing the carbon out of my father's car after he had been its only driver for a month or two.

This is high school Gear Head 101 stuff. Any good book on performance tuning should cover it.

[PUDGYPAINTGUY]

Petdoc:

My understanding is that there are two different sixth gear clusters: a low and a high. I have been told by an owner that you could pick the one you wanted on the R 1150 R order sheet. My understanding is that the tall sixth gear is standard on the RS and RT; I am not sure what the GS's come with; they could have the lower one. At 4,000 my bike is doing 81 mph, so it's basically an interstate gear. I haven't checked it at 60 mph. Maybe some other GS owners can chime in here. And the GS Adventure gearing is different from the standard, GS, I understand.

I've gotten to the point where I can live with this transmission, but it's really an autobahn unit.

Rinty


Adventure (1150) has a lower first and sixth gear than the regular GS 1150. The new 1200 ones share the same gears.

[AntonLargiader]

FWIW, I just now pulled these bearings out of an Oilhead with known knocking issues during its 77,000 miles.
http://www.largiader.com/misc/shells.jpg

[Spidereyes]

...The oil pump is a positive displacement pump. I expect to see about 60 p.s.i. in normal operation. It will be low at idle but ought to rise rapidly - normal pressure by about 2000 rpm.

True lugging has the speed of the flame front in the combustion chamber outrunning crankshaft rotation so maximum piston force occurs at or before the piston has reached top dead center. This places extraordinary demands on the connecting rod bearings. The engine complains and you can both hear and feel it.

The relationship between engine speed and carbon relates to incomplete combustion and the scouring effect inside the combustion chamber related to the inflow of unburned fuel and the scavenging of the exhaust. It also relates to the surface temperatures inside the combustion chamber....

OK; the oil pressure most likely does not figure into the equation and I really didn't think that it would.

Your statement, "True lugging has the speed of the flame front in the combustion chamber outrunning crankshaft rotation so maximum piston force occurs at or before the piston has reached top dead center...." is a definition of pre-ignition or pinging. Furthermore, as you pointed out before, the rider may be unaware of pinging. I agree with you on these points.

However, when you say, "The relationship between engine speed and carbon relates to incomplete combustion and the scouring effect inside the combustion chamber related to the inflow of unburned fuel and the scavenging of the exhaust....," I have to pause. These engines have passed U.S. emissions tests at idle and at various throttle openings. If incomplete combustion and unburned fuel were an issue, I believe the engines would have failed these tests.

As I said before, maybe Beemers do have a problem with carbon build-up, but for the life of me, I can't believe that operation at, say, 3,000 revs in traffic, is the culprit.

AntonLargiader, was this engine perhaps mis-timed at the factory? It lasted 77,000 miles with "known knocking issues," so what was the cause? Are you suggesting that low revs was the problem?

[bransan]

Talk about beating a dead horse. I have owned several BMW cars and 3 BMW motorcycles. My 81' 320i had 408,000mi when I sold it in 2001. I never downshifted when entering towns and always accelerated from 30 to 6- in top gear. At 350,000 mi I broke a rocker arm,( cam follower). I decided to go through the engine. Plasti-gauge showed very little wear on mains and connecting journals. My 79' r65 had 103,000 mi when I decided to rering, very little carbon build-up. I usually run down to 2,000 rpm's when coming to towns,I'll shift to 5th gear and coast through town, then on the throttle and shift back to 6th at around 60mph. I currently have 30,000mi on My 04' r1150r and don't worry about running r's low. I've driven manuals My whole life and never had any issues with lugging gas motors. Diesel engines are a different story.

[twins4life]

AntonLargiader, was this engine perhaps mis-timed at the factory? It lasted 77,000 miles with "known knocking issues," so what was the cause? Are you suggesting that low revs was the problem?


Same here

[PUDGYPAINTGUY]

With the pistons, valves and cams being on fixed timing, and the fuel management being controlled by mapping and O2 sensor in the header/cat to sample the gasses, it surely cannot be that bad for the motor.

The boxer motor is hardly a state of the art complex piece of wizardry such as the like of the new K motors, the boxers are pretty basic in technology. A racey motor stressed and tweaky they are not. In a standard state of tune with factory compression it is surely doubtful the boxer suffers too bad with slow speed riding in higher gears...the torque curve just begs to played with down low.

I fear the damage that the new 20% Ethanol blends may do to air/oil cooled engines more than any slow speed riding will ever do to my bike.

[Spidereyes]

This has been great fun and very educational but the flies are getting pretty thick and it's time to bury this ol' horse.

[GregFeeler]

I fear the damage that the new 20% Ethanol blends may do to air/oil cooled engines more than any slow speed riding will ever do to my bike.

I don't believe the 20% blends are approved by the EPA yet, are they? The AMA is fighting Minnesota's (or is it Wisconsin's) application for a variance to the 10% rule which would allow them to sell 20% Ethanol instead. Anyway, that's the last I heard.

[Bfish]

spidereyes....just ride the hell out of it. don't treat it like a high torque v-twin. after all these posts can't figure out what your low rpm mantra is all about.

[Spidereyes]

spidereyes....just ride the hell out of it. don't treat it like a high torque v-twin. after all these posts can't figure out what your low rpm mantra is all about.

Adopting my best Dirty Harry voice: "Well to tell you the truth, I forgot myself in all this excitement."

I think my point was that low revs are not really such a dirty dog regarding carbon build-up, but it could have as easily been that coordinated turns are best made using the rudder.

[Bfish]

Adopting my best Dirty Harry voice: "Well to tell you the truth, I forgot myself in all this excitement."

I think my point was that low revs are not really such a dirty dog regarding carbon build-up, but it could have as easily been that coordinated turns are best made using the rudder.


10-4, but really just ride the crap out of it. :D

[PGlaves]

However, when you say, "The relationship between engine speed and carbon relates to incomplete combustion and the scouring effect inside the combustion chamber related to the inflow of unburned fuel and the scavenging of the exhaust....," I have to pause. These engines have passed U.S. emissions tests at idle and at various throttle openings. If incomplete combustion and unburned fuel were an issue, I believe the engines would have failed these tests.

OK - lets do real empirical testing:

Remove the spark plugs. Shine a strong flashlight into the spark plug hole. Observe that black crusty stuff on the piston crown.

That is carbon. Where did it come from?

Three things get into the combustion chamber: fuel (hydrocarbon); lubricating oil (hydrocarbon); air (mostly nitrogen - some oxygen - very little carbon)

Please don't tell the EPA, but that black crusty stuff is in their because all of the hydrocarbons in the fuel and/or oil didn't burn cleanly. Or, as I said "incomplete combustion" and "unburned fuel."

The notion that BMWs don't have unburned hydrocarbons because they pass some EPA test is just silly. All you have to do to disprove than notion is look inside a combustion chamber. You could pull the head to do this, but instead just do it the easy way - look through the spark plug hole. If its black that is unburned carbon - EPA tests notwithstanding.

And, if you ever do open an engine that has more than a few miles on it and find shiny aluminum combustion chamber surfaces then look for the source of water ingestion and or a (water cooled) coolant leak.

What we need is less theory and more hands-on taking stuff apart and putting it back together. That makes it lots easier to understand.

[OfficerImpersonator]

Shesh, Paul - what would you know about "hands-on taking stuff apart and putting it back together" Why don't you go get some experience first before you come in here all "experty" and knowledgeable-ly? :)

[SIBUD]

Adopting my best Dirty Harry voice: "Well to tell you the truth, I forgot myself in all this excitement."

I think my point was that low revs are not really such a dirty dog regarding carbon build-up, but it could have as easily been that coordinated turns are best made using the rudder.


That's what I do.

http://i55.photobucket.com/albums/g125/JB_Mitchell/Launch%2007/Stockton/BudAndNancyRelaxing16.jpg

[BubbaZanetti]

What we need is less theory and more hands-on taking stuff apart and putting it back together. That makes it lots easier to understand.

yup, my cylinders/piston crowns are pretty yucky. i'm debating "water torture" vs taking the heads off and cleaning them.


on a side note:

this whole thread has seemed very silly to me.

WHY would you want to dawdle around at 2500 RPM???? the bike feels so, um, YUCKY down in that region.............

[PGlaves]

Shesh, Paul - what would you know about "hands-on taking stuff apart and putting it back together" Why don't you go get some experience first before you come in here all "experty" and knowledgeable-ly? :)

OK, that's it. Now I'm going to have to go to Osco Drug and buy that Home Owner's Tool kit and get started taking something apart:)

Putting it back together will have to way till I get the advanced kit, with two sets of pliers in it.

[bobh41]

Oh, so the advanced kit includes a monkey wrench, yes?

[mcollect]

Moderator
Please kill this thread, I only asked to satisfy my cruiser friends firm belief that low rpm's were OK. Now we are getting into the domain of an oil thread, I definately did not want that. Thanks all for your input.

[BubbaZanetti]

i'll close the thread, but i think the info provided is useful, so it won't be deleted