What causes engine buzz sound?

March 8, 2010

I was curious what causes the engine buzz on my RT. I hadn't really noticed it at first but do now.

Thanks,

Ken

March 8, 2010

It makes that noise when the worry about excessive oil use ceases. Don't worry, it will stop when the next "obsessive" concern flares up.

Just kidding...?

March 8, 2010

How many miles do you have, ?,My 07RT smoothed out at about 20K

March 8, 2010

I was curious what causes the engine buzz on my RT. I hadn't really noticed it at first but do now.

Thanks,

Ken

Well, with the big bore twin like the RT (assume R1200RT), that's sort of the standard indicator that it's time for a tune-up of sorts, mainly sync'ing the throttle bodies, but also doing the valves, checking spark plugs, oil, tranny oil, and other "due diligence" maintenance procedures.

A good illustration of the situation is the problem that we heard about on the oil head forums (less so the hex-heads -not sure why), where the cable sleeve get's "hooked" up over the adjusting shoe, rather than fitting down in the shoe, the first time the owner has the plastics off and starts fiddling with the tuning. On the next start, the engine runs, but runs like a truck at low speeds and like a bush whacker at high speeds - really, really rough at low RPM's and "buzzy" at high RPM's. The difference between that cable seating and not, maybe a half-inch or less of tension, is just enough to make the average "noobie" owner certain that he just destroyed his once-fine-running BMW motor. Then he's twice as embarrassed when 15 guys point out the rookie mistake he just made. (Don't ask me how I know about all this ... :grin: ).

Anyhow, I don't know the mileage or how long ago your bike was tuned, but that's the likely issue - TB sync. I've had other reasons for a "buzzy" bike, like losing a screw or two on my fairings because I was too conservative on torquing, causing the lose plastics to buzz.

And then, I see you have a couple of 4 cyl engine bikes on your profile - a big bore twin will "thump" and "buzz" more than a water cooled 4 cyl engine.

Maybe you can find another RT owner in your area to pair up with, and check it out. Or just go pay for an hour of labor to have your BMW dealer's service expert diagnosis the issue (assuming you do your own maintenance separately; otherwise just bring it up at service time). Riding an identical bike can tell you loads about yours.

Regards,

Scott

March 8, 2010

I think I have to agree with Motodan here. It may well be the next ordinary step of paranoia.

Of course, just because you are paranoid, does not mean there is nothing wrong with your bike.

If I ever listened to any of my bikes, I would go crazy. I constantly hear noises when I ride, scraping brakes, loose belts squeaking and squealing, grinding, etc., and then realize it is a vehicle near me, not mine.

dc

March 8, 2010

Ken, the twin cylinder BMW boxers do have an inherent buzz (balance) problem especially at mid RPM ranges.. It was there in the smaller displacement 1100 engines & as the engine pistons got large the buzzing got stronger..

Most riders don’t notice it at first as it isn’t that distinct & new riders to the BMW boxer are usually more sedate on the throttle & keep the RPM’s changing so don’t ride in the buzz band for long periods.. Also,, in colder weather riders usually wear heavier gloves & thicker boots..

The modern BMW 2 cylinder boxer as well as most other 2 cylinder boxers are an inherently primary balanced engine with both pistons coming to TDC & BDC at the very same time so they COMPLETELY stop & start together twice on each stroke.. Here lies the problem..

Seeing as the pistons are large & also need to be on independent crankshaft throws they are not directly across form each other so as the mass of the pistons & part of the connecting rods start & stop that induces what is called a rocking couple.. The moving mass wants to keep moving so drives the crankshaft in a rocking motion.. Now seeing as the engine is solid mounted to the chassis this rocking motion ends up as a primary shake or buzz at higher RPM’s.. The 1200 engine is also a high compression engine so the firing pulses are fairly sharp..

On the older BMW boxers the balance problem was just left alone as the moving mass was smaller so the buzz was not excessive.. On the 1200 engine BMW decided to add a SINGLE balance shaft to try & offset some of the engine balance issues.. Problem is: adding a rotating balance shaft with offset weights to an engine that is inherently balanced brings on other order vibration (off order buzz & off order disturbances).. Apparently BMW engineering decided that smaller disturbances over a wider range was better than a big disturbance in a narrow range..

Then you have the other off order disturbances like firing frequency buzz,, exhaust system off order disturbance,, accessory off order shake or buzz,, intake drone,, etc.. If one of more of those ends up on top of a primary engine disturbance then it amplifies the problem & also disturbs the rider more..

Bottom line: the BMW 2 cylinder boxer is not as smooth of an engine as a 4 cylinder boxer.. The engine is solid mounted (no rubber mounts),, the engine runs at higher RPM’s at cruising speeds.. Unless your vibration is excessive or worse than other like BMW 2 cylinder engines there isn’t much you can do about it short of adding more cylinders..

Twisty

March 8, 2010

What Twisty said. I'm on my 6th R12 {4 RTs and 2 GSs) and they all had a "vib" come on between 4,000 and 4,200 RPM. All to a different degree. One RT was very smooth above 4k, but the rest let you know there was an engine spinning between one's legs. However, only one, a GS seem to have more vibs than average.

March 8, 2010

It makes that noise when the worry about excessive oil use ceases. Don't worry, it will stop when the next "obsessive" concern flares up.

Just kidding...?

I knew this post was coming before I clicked "submit" .

March 8, 2010

Whoa... slow down guys... the O.P. never said what bike he has. He said RT, but what years?.. if he has an '05/06 it just might be the brake servo....

March 8, 2010

Thanks for all the comments. The bike really does run great. I was asking because the sound was more noticeable now and I thought I had read at some point that buzzing sounds being inherent with boxer engines.

Regardless, the bike is much quieter than all of the HD's I have owned. Now that's an engine with serious valve train noise. The only bike that I have now that makes no engine noise (that I can hear) is my Ducati Streetfighter. Of course that's only because I can't hear anything over the open clutch and exhaust.

Ken

March 8, 2010

You could put a pipe on the BMW and get the same effect...

March 8, 2010

Whoa... slow down guys... the O.P. never said what bike he has. He said RT, but what years?.. if he has an '05/06 it just might be the brake servo....

2010 RT.

Ken

March 8, 2010

You could put a pipe on the BMW and get the same effect...

But nothing sounds like a Duc.

March 8, 2010

Ken, my experience with a new boxer engine was that there was noticeable vibration at 4.5k+. After the first 6k miles this largely went away. I do not believe it was just me getting used to it as I rode two other bikes (including a 1700cc metric twin) during the break in. From 6k on the bike was much smoother and got better mileage and stopped using oil.

Drive it hard and all your problems will go away!

JT

March 8, 2010

Whoa... slow down guys... the O.P. never said what bike he has. He said RT, but what years?.. if he has an '05/06 it just might be the brake servo....

We are slow, but apparently still faster than you...his prior posts indicate one of the first 2010 models we can comment on. Appreciate Ken sharing the "newness phase" with us.

March 8, 2010

Whoa... slow down guys... the O.P. never said what bike he has. He said RT, but what years?.. if he has an '05/06 it just might be the brake servo....

We are slow, but apparently still faster than you...his prior posts indicate one of the first 2010 models we can comment on. Appreciate Ken sharing the "newness phase" with us.

What a nice way to put it...

March 9, 2010

Appreciate Ken sharing the "newness phase" with us.

You are being kind. I think it's the obsessive faze.

Ken

March 9, 2010

Try wearing really good earplugs.

I notice that all of my bikes have seemed smoother when you cannot hear every little sound

March 9, 2010

Does the 2010 model have the foam insert behind the belt cover?

I noticed a buzz (sound, not feel)when I binned mine from the R12ST, However when the new front cover was fitted to my RT and the foam not installed I must say I don't notice any sounds.

May be I noticed it on the ST as one day the foam was there and the next not.

hth

\v/

March 9, 2010

Pardon me for trying to help...

I do not feel responsible for reading and remembering every post on all the boards.

He hasn't even updated his profile, but at least he has some information there, as opposed to some others.

I also want to thank you for your feeble attempt at humor, if that is what it was.

March 9, 2010

Does the 2010 model have the foam insert behind the belt cover?

I believe BMW relieved us of the chore of removing the insert sometime before the '07 model year.. (my 10/06 production R12R doesn't have it..)

March 10, 2010

The bike seems to have more vibration now than when I first got it. Tomorrow I am going upstate NY to visit my brother.That's close to 500 mile round trip. I can make a better assessment after that.