Hitting the Rev Limiter?

[Canyon Runner]

Hi all!

So I was talking to a fellow BMW rider (who has been doing it a lot longer that I have) and he recommended that at least once a week (or so) that I take the bike up into the rev limiter (on a smooth controlled acceleration, like at an on ramp or something) and hold it there for a second or two before dropping it back down into a world of greater comfort. His explanation is much like I used to hear when my car had 8 cylinders... that it would help to "work the carbon through".

Any sage advice/ opinions on this? Does it hurt the bike to hit the rev limiter (I assume that is actually why it is there), and alternately, will a good, clean, hard ride do the same thing without feeling like I am purposefully pushing the bike into the warning track just for the sake of it?

Cheers!!

[towerworker]

I'm not nearly as learned as many around here and have only about 5 years of experience with the BMW but I have heard pretty much the very same thing around here for years. The boxer engine is very hard to hurt. Alot of lugging (low rpm/high throttle setting) will eventually earn you some carbon build-up in the combustion chamber. Some guys swear that running a few ounces of sea-foam or marvel mystery oil in the gas tank every few thousand miles or so will help that too. I don't know. Hit the rev limiter a little -- sure can't hurt. Just don't do in such a way as to earn the attention of the fellas with the radar!

Wayne

[Paul Mihalka]

I wouldn't regularly hit the rev. limiter. Not because it causes damage, it just does not feel good. Occasionally running the bike up to high rpm at full throttle, over 6000, to 7000, is good. It has the same good effect as running against the limiter without the strange rough running feeling.

[Buckster]

I do it often but stay just below redline.

[boxermania]

Any thing in defect or in excess is bad. All the posts so far reflect their experiences and agree in principle.

1) It is easy to lug a big displacement torquey engine, at the expense of carbon build up.
2) These engines are strong and if maintained correctly almost bullet proof.
3) Because of the Nikasil cylinder coating (excellent wear characteristics) it is necesary to cycle the engine temperature to assist the break in process.

All of the above can be served well by sensible excursions into the "happy zone" of the tach. Sea Foam and MMO have been known to mitigate carbon formation......many years ago we used to spray water into the carburator as the steam formation in the combustion chamber pretty much "shocked" the bad, bad carbon loose and out of the engine......those were the good all days.

[pop2tu]

I've seen small block chevy's run like a new engine after some water down the carb. Be careful I've also seen Hydrostatic Lockup, Water dosen't compress very well.

[CycleRob]

The rev limiter is there to make sure the engine doesn't exceed 7,800 rpm under power. If you have the stock exhaust system, you should shift gears at 7,000 rpm for maximum acceleration because of the rapid power drop-off.

My understanding is that the Motronic stores:
--the number of times the rev limiter is activated.
--the number of total minutes activated.
It is stored in permanent flash memory that stays there, even without the battery. The dealer reads it thru the diagnostic plug on the airbox lid. It gives them warranty denial rights if/when you have an "engine problem".


.

[Ves]

I would think, to do a decent job of "cleaning out the carbon" you would need to operate at sustained, relatively high, engine loads/speeds for longer than it takes to shoot up past redline a few times. And whether you're just below redline or hitting the limiter is not going to make that much difference. You have to get the engine hot and breathing at a high level for extended periods of time.

[Beemeridian]

33

[boxermania]

Beemeridian,

The venturi at the bottom of the TB's would be a good place to inject water mist, Sea Foam, etc. Some experimentation will have to take place to size the oriffice as one wouldn't want to slug the engine with liquid.

If I remember correctly an oriffice around .040" comes to mind on a 60 lbs supply pressure, but I would have to research further.

These applications also provide excellent results on boosted engines, as it cools down the charge, reduces pinging and allows additional boost/HP levels. I have enclosed a couple of the many links available for review

http://www.coolingmist.com/

http://www.alcohol-injection.com/

Enjoy......

[Hendrikus]

Canyon runner,

Better suggestion if you want a fast bike: with a realy cold engine, start it, rev it up to 7800 rpm and hold it there for at least 45 minutes then stop the engine for cool down, the next trip will go like a hurricane.

If you want to Fxxx up your engine go for the rev limiter, only idiots will go there, me twice a year.

if you want a carbonfree engine don't ride like a turtule, minimize short runs, run it through all gears and revs and enjoy it.

me as a daily commuter, start my baby and ride away immedately, thru town to have it warmed up between 1000 and 2500 rpm, after five minutes to 4500 rpm and after 15 minutes all the range
and have a 45 minute to a one and a half hour drive. my spark plugs are cleaner then my teeth

use your commen sense, germans are great technicians, don't have you fooled by bartalk.

many regards, and a lot off fun, Hendrikus

[Canyon Runner]

I thought about as much, guys!

Thanks for all the input. I hadn't started the practice yet (just heard about it), and will just continue on with my practice of trying to keep out of the low RPM range whenever possible, and fairly regularly run mine up into the 6000+ range without getting too nervous.

Not a directive I have a problem being compliant with.

Cheers!

-Kyle

[Beemeridian]

33

[Samiam]

Paul Glaves was involved in a rather lengthy discussion on MOA concerning this very topic a few months ago. His position was that low revs cause buildup. My problem with this is that neither he nor any others ever defined what "low RPMs" are, what an ideal RPM range is, nor what would cause the buildup in the first place. And, why would a momentary hit on the rev limiter be such a magical cure-all?

Either you have combustion in a cylinder or you don't and I've never seen definitive proof that combustion is more complete at 6,000 revs than it is at 2,500. Engines are tested by the EPA, CARB, et.al, at various rev bands and I've never read about an engine failing because it produced too many hydrocarbons (sources of buildup) at, say 1,500 RPM. With fuel injection, computerized engine management and the like, I tend to question the premise of the RPM=buildup hypothesis. If low revs are the culprit, why do not big, loafing engines (like Buicks) have constant carbon problems?

I don't deny that some engines do tend to build up deposits but I would like to see experimental data showing the causes. Back in the early '60s when I had an MG TD, it and most other British sportscars had to be "de-coked" every 5,000 or so miles. Cylinder head design, SU carbs and oil consumption was the cause of this. But I question if a modern design has the same propensity. But, I could be wrong....

[boxermania]

Samiam.....thanks you, as you brought tears to my eyes.....as a young man going to college my source of income was repairing foreign cars....which was nad is my love.....and did extensive work for an elite groupof MG owners, NA's TD's, TF's, MGA's MGB'S....

The key word here is oil consumption, or better yet the amount of oil in a given time that gets passed the oil control rings. Those ear;y MG's and most of the British cars had to be "decarbonised" due to the above and the very loose tolerances of the time.

Move forward to today.......in our bikes, quite old air cooled design with some new technology, like Nykasil coating on the cylinder walls, an extremely hard wearing surface.

Now, visualize this scenario......engines have to undergo a break in period, where the rotating parts "hone", polish or seat themselves to the other parts they rub against. Lets focus on the oil control ring; during the break in period the rings, not yet seated will allow additional oil to get past the rings, which will burn with the A/F in the combustion chamber. Eventually this oil will coat/cake the surface of the piston and the valves. Needles o say the process is exarcerbated since the owner, mindfull of the break in period will keep the engine witin low and moderate rpm's. In our bikes this process delays the break in period and therefore more oil is burned and the carbon deposits increase.

So in our bikes we have to accomplish two tasks, 1) Break in the engine and 2) Minimize, or better yet minimize the carbon deposits (since eventually there will be carbon deposits)

The bets way to break in an engine and has been like day one is to subject it to frequent load changes, what that means is to accelerate briskly to a high rpm and then allow the engine to return to the previuos rpm.and doing this on repeated occasions. That is not to accelerate from 2500 rpm to 3500 rpm, but to accelerate from 2500 rpm to 6000 rpm and not necesarily gtaking the engine to the rev limiter.

One will understand that above if done in sixth gear will require a long road and will probably get ticketed for excessive speed, so the thing to do is drop to 2nd or 3rd gear and do it in a less traffiqued road. Note that accelerating briskly in the lower gears will get the tach to move quite fast and sometimes difficult to catch, before it hits the limiter. Last but not least the limiter is there to protect the engine and it's setting is significantly lower that the rpm required to cause damage to the engine, so hitting the rev limiter causes problem, IMO.

As the engine reaches the higher rpms the the fater combustion and the resultant peak cylinder pressures "shock" the carbon deposits and these in turn come loose and exit the engine via the exhaust port........in old, not cat engines they went out the tailpipe, in the engines today they stop and get trapped in the cat......oops, I've opened Pandora's box.......

[Samiam]

Boxermania, sports car repair, and a Biology assistantship, is exactly how I made it through undergrad school. Following a stint in the Army, the same thing got me through grad school. Interestingly, the sports cars I worked on in the early 60s were much different from those in the late 60s and early 70s. "T" series MGs and TR-3s were replaced by MG-Bs and TR-6s. The British had lots better engine designs in later years and I don't remember decoking any "Bs," TR-6s, big Healys or Jags. My most common internal engine job became valve jobs on Spridgets and Spitfires.

I agree with you on engine breakin and also on the premise that high-RPM combustion cycles and manifold pressure may act to erode away carbon build up but I'm still not convinced that Oilheads are any more prone to this condition than other engines. With our electronic management and fuel injection, I'd be surprised if carbonization was anything more than an isolated and rare condition on a properly broken-in engine.

I'm no expert on motorcycle engines but I just don't hear about carbon build-up being a problem with modern motorcycle engines. Heck, back in the 70s and 80s, I commuted daily on a Sportster in city traffic and rarely got up to 65 MPH. After 18,000 miles I had a professional bore scope done to check for carbonizing and found no remarkable build-up. And this was in a '74 AMF Sportster, supposedly the lowest point in Harley quality.

I read lots of anecdotal tales about low RPMs causing build-up and the need to blow the carbon out but I have seen no SAE studies to support the RPM hypothesis. Again, if low revs were a problem, we would have Harleys, Victorys, Buicks and Cessnas in the shop for decarbonizing on a regular basis.

[boxermania]

Samiam......we had parallel paths while growing up.....my favorites were the Healey's 3000. Owned four, the first one was a 61 with aluminum body....should have never sold that car, a 3000 MK II, with the 3 SU's, a 3000 MKIII and back to a 62 with a 351Cleveland and a C4. A hell of a car, but had loose and broiken spokes and had to tighten the spinners every time I gassed up......

I know that you are not convinced yet regrding the oilheads. Let me just say two things, Aircooled and horizontal cylinders.......with a hard coating on the cylinders. I'm sure you can see through the fog.....

[Samiam]

Samiam......we had parallel paths while growing up.....my favorites were the Healey's 3000. Owned four, the first one was a 61 with aluminum body....should have never sold that car, a 3000 MK II, with the 3 SU's, a 3000 MKIII and back to a 62 with a 351Cleveland and a C4. A hell of a car, but had loose and broiken spokes and had to tighten the spinners every time I gassed up......

I know that you are not convinced yet regrding the oilheads. Let me just say two things, Aircooled and horizontal cylinders.......with a hard coating on the cylinders. I'm sure you can see through the fog.....

Aircooled, nickasil, horizontal....Yep, that's a formula for some blowby and potential buildup, alright. And, cynic that I am, I still hit the limiter every so often in second and third just to blow the "soot" out. But I still don't worry about putzing around town at 2,500. Actually, I worry more about the final drive and I realize that for my 2005 Roadster with low miles that's a pretty irrational worry.

Man, you had an aluminum Healey? I never graduated beyond the MG-B and TR-3b. Healeys had the best sound this side of a Ferrari. As much as I love older sports cars, I sometimes daydream about what it would be like to take my Miata back to 1967 in a time machine.

[jb44]

Samiam
Aircooled, nickasil, horizontal....Yep, that's a formula for some blowby and potential buildup, alright. And, cynic that I am, I still hit the limiter every so often in second and third just to blow the "soot" out....

I think threre is a bit more than soot building up. Cyclerob previously posted pics of his pistons when he disassembled his engine.

And here's a more recent pic of a bike that has 40,000 miles on it:






jb

[Beemeridian]

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