Poly V-Belt (Alternator Belt) Replacement and Tensioning

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Poly V-Belt (Alternator Belt) Replacement and Tensioning

Postby DSKYZD » Thu Jun 19, 2008 8:36 am

Earlier this year I replace my belt. I had the tank off at the time (installing new omegas thanks to a broken QD) and I tried to tension the belt just by loosening the 3 nuts and prying the alternator up. It just didn't seem to slide enough. I ended up using the torque wrench method described in the service manual and apparently also described in the Haynes manual as others on this board have noted.

For those not familiar with this technique you apply AND HOLD 8Nm of torque to a bolt. Holding that torque is key because there seems to be some sort of gear mechanism that adjusts the alternator upward as you twist that bolt. If you release the torque the alternator just slides back down and your belt goes slack. That, at least, was my experience. Once the belt is under tension you must tighten one of the other nuts before you can release the torque and tighten the remaining nuts.

Well, I did this and found that I had a belt that chirped terribly upon revving the motor or pulling out. This drove me crazy and worsened I guess due to belt stretch. I submit for discussion that 8Nm is not enough force to bring the belt under proper tension.

"Proper tension" might be a point of contention as well. To me, "proper tension" is enough tension to prevent belt slippage and thus chirping noises. You may heard about the "1/4 turn" method where you try to twist the belt 90 degrees. It is said that if you can twist it past 90 degrees it isn't tight enough. I like to flick my belt and hear a "ting" in the key of C. Just kidding about the c note but it does ting now when I flick it.

Here's how the service manual says to do it:

Image

I found that I needed to take the tank off, not to get access to the adjusting screw, but to get enough clearance to work the wrench.

So how do YOU tension your belt?
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Re: Poly V-Belt (Alternator Belt) Replacement and Tensioning

Postby Boxer » Thu Jun 19, 2008 12:57 pm

When I changed out my belt...at around 40K miles, it still appeared to have many more miles of use left on it. I saved it.
The tightening technique shown in that illustration is what I used, and was able to access the 8nm bolt up in behind there with only taking off the oil cooler cover. It never squeaked or squawked at all after I torqued it to 8nm.
Its about time to do that again I suppose, but I check it every time I do a valve check, with the finger half-turn test.
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Re: Poly V-Belt (Alternator Belt) Replacement and Tensioning

Postby awagnon » Thu Jun 19, 2008 11:11 pm

Did you get the correct belt? They changed it in July, 2003, to a slightly shorter, but stretchier belt. If you have a newer bike and put an old model belt on, it would be too long, but probably would still work. The new system has a free-wheeling alternator pulley with a smooth, black front face. The old model has a big nut in the center of the alternator pulley and doesn't free wheel. The new model is not tensioned the same way as the old belt. You don't use a torque wrench, but instead a device that wedges between the pulleys and pushes them apart. Otherwise, I'm not sure why it chirps.
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Re: Poly V-Belt (Alternator Belt) Replacement and Tensioning

Postby DSKYZD » Fri Jun 20, 2008 8:06 am

Yes, thanks awagnon for reminding me about the different belts. My bike was made in June or July of 2002 (sticker is mostly gone), I was riding it in July of 03 so it definitely the old style belt. I got it from www.beemerboneyard.com. It is the Dayco Poly Cog. Size is 4PK0610 and I think the BMW one is 611. Seems like that is a size specification, 4PK is the width?? and 610/611 is the lenth in mm.

Also, after putting on a new belt (the old ones, not the new ELAST type) you are supposed to retension them after 6000 miles. I've got about 2000 miles on this one. It always chirped, but the chirping got worse. I'll just chalk it up to belt stretch.

By not using a torque wrench for the final tightening all my ranting about how much force it took tighten it goes out the window. I was using a shorter ratchet so it may seem to me like I had to use more force.

No one else seems to have the trouble I did with this (I can hear you grinning MikeCam) so it must be something I am doing.

Boxer, does your torque wrench have a narrow neck? I use the Crafstman click type torque wrenches and the telelever arm gets in the way of being able ratchet it. The stroke from where it hits the edge of the tank (I tried just removing the oil cooler cover before taking the tank off) and where it hits the telelever arm wasn't enough get the right torque applied. I kept removing the wrench and twisting the bit one ratchet click at a time trying to find enough range.

I know I always say "ride more, agonize less", and I am DEFINITELY agonizing over this one. I call these things "fiddly". Procedures that are simple but require the right touch, or a certain twist...they're fiddly. To me, tensioning this belt is "fiddly". I understand it completely, and even consider the gear driven mechanism and torque spec tensioning method kind of elegant. I like the exactness of it. It just irks me that I personally can't get this right.

The bike is quiet now. These cool (50's F) morning starts and pull outs haven't produced any more chirping. I guess I'll let this one go and wait for the bearings in my alternator to fail because my belt is now too tight :roll:

Thanks guys!

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Re: Poly V-Belt (Alternator Belt) Replacement and Tensioning

Postby MikeCam » Fri Jun 20, 2008 3:34 pm

Ya can't inherink a wink! An ya can't hear a grin.
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Re: Poly V-Belt (Alternator Belt) Replacement and Tensioning

Postby Beemeridian » Fri Jun 20, 2008 4:00 pm

This procedure is much easier with a cheap BMW special tool (yes, there is such a thing) # 12 3 551

Here is the service bulletin:
http://www.venturello.com/moto/Various/vbelt.pdf

This tool allows you to adjust the belt tension from the front of the motor.
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Re: Poly V-Belt (Alternator Belt) Replacement and Tensioning

Postby Boxer04 » Fri Jun 20, 2008 11:47 pm

I replaced my belt and tensioned it from the front. I could not access it well from the back as shown in the manual and I did not want to take the tank or oil coolers off.

I use a 3/4 inch long internally threaded joiner ( i.e.female) and a hex headed bolt that fits into it. Both are 8mm and can be purchases at any automative store or bolt supplier. It is a similar tool as the one described above but cost me 20c. I take the nut off the alternator bolt as described and screw on the threaded joiner until it is about 1/16 inch from the alternator mount (this is to ensure you do not push the alternator bolt out). Then I screw the hex headed bolt into the joiner until it hits the alternator bolt and nip it up (don't need much tension as it works like a lock nut). I then put my tension wrench on the hex head and turn clockwide until 8NM and tighten up the top alternator bolt.

All can be done from the front and the only thing to remove is the cover. Cheap and easy.
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Re: Poly V-Belt (Alternator Belt) Replacement and Tensioning

Postby DSKYZD » Sat Jun 21, 2008 10:46 pm

Beemeridian, Boxer04,

Thank you both very much!! Those devices should take out a lot of the "fiddliness" of that task. Awesome!
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Re: Poly V-Belt (Alternator Belt) Replacement and Tensioning

Postby awagnon » Sun Jun 22, 2008 3:16 pm

Beemeridian wrote:This procedure is much easier with a cheap BMW special tool (yes, there is such a thing) # 12 3 551

Here is the service bulletin:
http://www.venturello.com/moto/Various/vbelt.pdf

This tool allows you to adjust the belt tension from the front of the motor.


You can do the same thing with a hex acorn nut. However, using a torque wrench on an R1150R after 7/03 isn't the correct way to tension the alternator belt. It requires another tool that costs even more.
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Re: Poly V-Belt (Alternator Belt) Replacement and Tensioning

Postby Beemeridian » Sun Jun 22, 2008 4:54 pm

Thanks Al. BMW...figures!
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Re: Poly V-Belt (Alternator Belt) Replacement and Tensioning

Postby riceburner » Tue Jun 24, 2008 7:47 am

I read somewhere that the correct tension for the belt was such that it allowed approx 1/2 inch movement AND NO MORE of each side of the belt when it was pinched.

did that to mine about 6 months ago when fitting a new belt at 30K miles and it's been absolutely fine ever since. :) (I ride around 60 miles daily, minimum).

I also tensioned it by ramming a "helper" between the alternator and engine cases because using the torque wrench simply didn't maintain the right tension no matter how I tried to work it.
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Re: Poly V-Belt (Alternator Belt) Replacement and Tensioning

Postby toolinalong » Sat Jun 28, 2008 3:44 pm

Once again, nice timing you all; I was just about to do my 72K maintenance stuff and there it was, info on the Vbelt renewal.

So after reading what riceburner had to say about it, I thought, jeez, it is after all just a darn alternator belt, I bet I can do that....

Note: I already had the tank off because I was replacing my fuel filter at the same time. My bike is vintage March of 2002.

First, I figured out that if you put a ruler laying flat on the telelever arm it lines up with the center (top to bottom) of the belt. So I measured how much deflection there was and it was 1/4" (both sides).
Image

Second, I loosened everything and removed the old belt. It showed little sign of wear, no cracks or other obvious problems, but when I held it up to the new one, it seemed to be somehow "thinner".
Image

Once I had the new one in place, which was quite easy to do, I put a torx head socket on my ratchet, and pulled down (ccw) on the tensioning bolt somewhat less then 1/4 turn,
Image

and voila, the new belt felt tight. So I tightened up it's nut, then the other two bolts, and checked it's deflection.
Image

It was perfect, so I put the cover back on and tackled the fuel filter project. When all was done, I started it up and went for a 50 mile test ride. No problems.

Image
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Re: Poly V-Belt (Alternator Belt) Replacement and Tensioning

Postby prepostman1 » Fri May 24, 2013 9:05 pm

I just replaced my 2003 1150R unbroken (but 40% missing) belt with 42,700 miles on it with a Gates #K040233 $19 (14mm x622mm) at O'Reilly auto parts because it has a 3 year warranty. SF BMW's belt was $24 with a 2 yr warranty but unless you paid them $50 to install they would not warranty the BMW belt. It only takes about 1/2 hr the 1st time but you need extra hands to hold the new belt up & a thin 5"-6" pry bar under the alternator to lift it & re-tension the belt, I did not see any tension applied from re-tightening the 13mm alternator bolts, so using a 8nm toqure wrench would not have helped me, (no need to remove the gas tank as one shop said).
I did not get the alt. up as high as before. Started for visual check with cover off, looked good. Rode off into the sunset.
PS: O'Reilly auto parts search for the BMW part # turned up nothing.
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