R1150RT alternator belt.

[kruuuzn]

I’m changing out my alternator belt with a new Contitech from beemer boneyard.

I thought I had the wrong belt at first because it looked smaller and doesn’t even begin to go on the pulleys but I’ve confirmed it’s the 841 like the original belt.

What’s the trick to getting this belt on the pulleys without damaging it? It’s too bad the alternator doesn’t have more travel to make this a simple job but NOOOOOO. It looks like the engineers wanted to make this a challenge.

 

[Craig G.]

It's a stretch belt.  Warming the belt with a heat gun and using this tool :

 

https://www.oreillyauto.com/detail/b/evertough-4771/belts-hoses-16454/belts-25068/belt-installation-tool-15836/f3f5501c989d/rental-tools-evertough-belt-tool-kit/67089/4700285

 

worked for me nicely just few weeks ago.  Proper adjustment required... do a search, the info is out there.  Details were covered in this forum several posts ago...

[dirtrider]

9 hours ago, kruuuzn said:

I’m changing out my alternator belt with a new Contitech from beemer boneyard.

I thought I had the wrong belt at first because it looked smaller and doesn’t even begin to go on the pulleys but I’ve confirmed it’s the 841 like the original belt.

What’s the trick to getting this belt on the pulleys without damaging it? It’s too bad the alternator doesn’t have more travel to make this a simple job but NOOOOOO. It looks like the engineers wanted to make this a challenge.

 

 

 

Morning  Kruuuzn

 

The below is a partial copy (with some additional added) of a post that I made for similar query a few weeks ago.

 

Using belt  installing tools like Craig posted above can help in getting the belt on but I can usually get the stretchy belts on without problems without the tools  but it isn't an easy task & can easily pinch a finger. You can run a piece of heavy duty string through the belt to help pull/hold/guide/lead the sun-heated belt onto the lower pulley as you turn the pulley nut with a wrench (that can prevent pinched fingers)

 

________________________________

 

 

 

The 2004 1150RT came with a free-wheeling alternator pulley & the elastomer belt  P/N 12 31 7 681 841 BMW 11.28 7681841

 

The elastomer belt  P/N 12 31 7 681 841 BMW 11.28 7681841 is too short to (easily) fit your bike even with the alternator all the way down.  It's that elastomer part that needs to stretch (significantly) to get that belt to go on.

 

I usually put the belt in the sun (on black asphalt if possible) to heat it up so it stretches easier.

 

Then it probably still won't fit so you will have to roll it on by turning the crankshaft & forcing  the belt to roll on over the pulley's.

 

The problem is in the adjustment as those elastomer belts are not adjusted the usual way-- as using the stud with double nut, or using the adjustment stud with  special BMW adjuster nut, WILL STRIP & RUIN THE BUILT IN ALTERNATOR ADJUSTER.  (that toothed alternator adjuster is NOT to be used in tensioning/adjusting the elastomer belt)

 

The 2004 1150RT with the elastomer belt is adjusted using a special BMW supplied pulley spreader/spacer fitted between the upper & lower pulley's. (tool forces the pulley's apart & holds them there while tightening the alternator attachments)

 

The home work around is to VERY CAREFULLY pry  the alternator up being VERY CAREFUL to not damage the HES wiring under the alternator & even more careful to not break the soft alternator case (easy to break the alternator with wrong prying tool or wrong tool placement)-- If you can get another person to help you that makes the job easier as they can assist you in prying the alternator up by adding some additional force using the alternator stud adjuster (caution: you still need to add a lot of prying force), can help with the pulley spacing measurements as you hold the alternator up with a pry bar, then can tighten the alternator attachments as you hold the alternator up with a pry bar.  

 

If doing the job by yourself then making a SOLID smooth somewhat narrow spacer that is 118.5mm to fit between the upper & lower pulley can make the job go much easier as you can pry the alternator up, then insert the spacer between the pulley's to hold alternator in place, then tighten the alternator attachments (problem is in getting the spacer out after tightening the alternator). 

 

The correct adjustment for the elastomer belt is--  118.5mm between the two pulleys (measured at the pulley ribs). Or 116mm between the pulley's  outer flange to outer flange, which is easier to get a scale or caliper on.

 

An alternative is to just get the belt on, then use the alternator adjuster to get the belt somewhat tight, then ride to your local dealer & have them do the final belt tensioning using their special high dollar pulley spreader adjuster tool.

 

 

What’s the trick to getting this belt on the pulleys without damaging it? It’s too bad the alternator doesn’t have more travel to make this a simple job but NOOOOOO. It looks like the engineers wanted to make this a challenge. -- At least you can move the alternator down some on the BMW 1150, on the later 1200 bikes the alternator is mounted solid so it can't move at all so the stretchy belt has to be run on the pulley's at full stretched  tension.

 

 

 

 

 

[kruuuzn]

Thanks for the help guys.

 

I thought the tension was set by using a torque wrench (running counterclockwise) on the left alternator bolt?

[dirtrider]

16 minutes ago, kruuuzn said:

Thanks for the help guys.

 

I thought the tension was set by using a torque wrench (running counterclockwise) on the left alternator bolt?

 

Morning  Kruuuzn

 

It is on the old Poly-V non elastomer belt (early BMW 1150).

 

On the later (like 2004 1150 bikes) the belt was changed to an elastomer (stretchy) belt (11.28 7681841)  & on those the belt tension is set by  pulley spacing NOT by torque.

 

Using the old Poly-V torque setting is not nearly enough belt tension on the elastomer belt.

 

Below is special high dollar BMW elastomer belt adjust tool/

 

 

 

  

[kruuuzn]

Ahhhh........that explains it.

 

So I need a special tool to properly adjust the tension on my elastomer belt? I can't imagine everybody invests in this tool.

Is there an acceptable back yard work-around?

[dirtrider]

13 minutes ago, kruuuzn said:

Ahhhh........that explains it.

 

So I need a special tool to properly adjust the tension on my elastomer belt? I can't imagine everybody invests in this tool.

Is there an acceptable back yard work-around?

 

Morning  Kruuuzn

 

Yes, read what I posted above. Basically a caliper and a prybar with a 2nd set of hands as a  big plus.

 

Lots of creative workarounds but none are smooth or easy.

 

In theory real easy-- just lower the alternator as far as possible, then roll/horse the stretchy belt onto the pulley's, then pry the alternator up until you get 118.5mm between the two pulleys (measured at the pulley ribs), or get  116mm between the pulley's  outer flange to outer flange, then tighten the alternator fasteners.

 

If you use the built in alternator adjuster & a double nut (or acorn nut) on the adjuster stud  then there is a good chance that you will strip/ruin the adjuster before getting the pulley spacing far enough apart.

 

Just don't crush the HES connector that is under the alternator, or crack the fragile alternator outer alloy case, & try not to pinch a finger rolling the belt on.  Otherwise, even a caveman can do it/

 

 

 

 

[kruuuzn]

Gotcha.

Thanks bud.

[Craig G.]

Installing this belt was my first experience with a stretch belt and I have to say I am not a fan.   My impression is that it unecessarily stresses the system with it's tension... idle dropped 100 RPM right off the bat.  Obviously it works as the original belt was fine at 50K and no sign of bearing issues.... still, I'm not a fan.  Think I'll use a poly belt on the next replacement.

[dirtrider]

18 minutes ago, Craig G. said:

Installing this belt was my first experience with a stretch belt and I have to say I am not a fan.   My impression is that it unecessarily stresses the system with it's tension... idle dropped 100 RPM right off the bat.  Obviously it works as the original belt was fine at 50K and no sign of bearing issues.... still, I'm not a fan.

 

 

Morning Craig

 

According to an old BMW service bulletin I have -- BMW implemented that elastomer belt to improve belt tensioning intervals & provide a longer belt life with an added improvement  in less engine over-run rotating mass (due to the also added over-running clutch alternator pulley) .

 

It (elastomer belt) works really nice on the 1200 engines as the alternator is fixed (non adjustable) so no belt adjustment or maintenance at all once installed. Kind of a pain to install the stretchy belt but once you do a few it is straight forward, quick, & quite easy (cut old belt off,  roll new belt on, put front cover back on/  done )

 

Or if a rider wants to save the old belt don't cut it off, just loop a heavy string around the belt, pull on the string very hard while turning lower engine pulley (if the belt is really  tight then you might also need to use a  piece of thin plastic rolled between the belt ribs & the lower pulley ribs in conjunction with the string)  

 

 

[kruuuzn]

Sorry for the brain fart on your first explanation Dirtrider. I skimmed through it but for some reason I had it in the back of my mind it didn't apply to my bike.

 

NOW I understand all that you guys are saying.

 

I'm going to machine up a piece of 1/4" x 1/2" pre-hardened steel, grind it 116mm long, install the belt, carefully pry up the alternator, insert my gage between the pulley flanges, tighten the bolts, then pull the gage out from between the pulleys. Voila'!

 

Thanks guys for all the help. I'd be lost without it.

[Craig G.]

I've read that in the past but know that changes like this usually have more to do with cost reduction (no adjustment hardware, elongated bolt holes) than anything else. 

 

Tensioning requirement is definately eliminated but the replacement interval is not greately affected.... the poly belt interval is 35k and from what I can tell the the elast interval is 36k (2007 GS schedule).  Don't see how a functionally similiar belt can influence over-run... and, as stated, at least initially it seems less efficient based on the RPM drop.

 

Again, it works but I'm not a fan.

[Craig G.]

Kruz - Before you start machining take a look at the backside of the top bolt flange, if like mine you can see where the alt originally sat against that flange.  I adjusted mine to that point then verified by measurement. 

[dirtrider]

14 minutes ago, Craig G. said:

I've read that in the past but know that changes like this usually have more to do with cost reduction (no adjustment hardware, elongated bolt holes) than anything else. 

 

Tensioning requirement is definately eliminated but the replacement interval is not greately affected.... the poly belt interval is 35k and from what I can tell the the elast interval is 36k (2007 GS schedule).  Don't see how a funcionally similiar belt can influence over-run... and, as stated, at least initially it seems less effecient based on the RPM drop.

 

Again, it works but I'm not a fan.

 

Morning Craig

 

Well the elastomer belt does eliminate the required 6000 mile belt re-tension after install of the Poly-V belt so it does eliminate one  dealer service (BMW doesn't set service for do-it-yourselfers).

 

The belt itself doesn't influence alternator over-run but the elastomer belt does allow the over-running pulley use (but BMW themselves did backtrack on that somewhat as they did use the Poly-V on some early over-running clutch bikes as they ran out of elastomer belts). 

 

But was that RPM drop due to a new tight belt vs a well worn burnished in belt?   

[AndyS]

I only ever replaced that belt once and that was for a reason I can't remember and was at about 12000 miles and the bike was 2 years old. Then I checked the belt at every major service and it showed no signs of wear and tear up until I sold it at over 130000 miles and over 12 years of use.

[kruuuzn]

Good tip. Thanks Craig.

 

So I'm assuming there's enough room to get a 6" calipers in there to confirm the distance between the flanges?

[Craig G.]

Not really... calipers are a no go.  I simply cut a straw to the proper length and used it as a gauge.

[dirtrider]

3 minutes ago, AndyS said:

I only ever replaced that belt once and that was for a reason I can't remember and was at about 12000 miles and the bike was 2 years old. Then I checked the belt at every major service and it showed no signs of wear and tear up until I sold it at over 130000 miles and over 12 years of use.

 

 

Morning Andy

 

Yes, from what I have seen in the past those elastomer belts will go a long time (way over the recommended 36,000 mile interval). To me they are close to a lifetime belt after first replacement. I would worry more about  time / ozone degradation than mileage wear. I haven't ever seen an elastomer belt shred like the old Poly-V did (they might but I haven't ever seen it) 

 

I have seen the 1200 bikes go well over 100,000 miles on the first replacement belt (BMW changed the early 1200 belt length slightly due to customer squeal complaints  but didn't change the belt part number)

[Craig G.]

Why lifetime after first replacement?   Why not lifetime from the factory?

[dirtrider]

21 minutes ago, Craig G. said:

Why lifetime after first replacement?   Why not lifetime from the factory?

 

 

Morning Craig

 

On the 1150 bikes some were factory fitted with a Poly-V belt at original build instead of the elastomer, the front cover was supposedly marked to indicate that but apparently some are not correctly marked (or the front cover was replaced due to shipping  damage or other damage). It also gives the tec a chance to verify that the belt is tracking correctly & belt is properly adjusted. If an elastomer belt makes it to first change interval looking good then (personally) I wouldn't be afraid to run it out w-a-y longer on the replacement elastomer belt.   

 

On the 1200 bikes-- You don't know what belt the 1200 got at factory build, as mentioned the belt length was changed to slightly shorter at some point in the 1200 model run). Nobody seems to know when that  actually happened or  what bikes were effected. My personal 1200RT was a squealer so I presume it came with the longer belt.

 

So installing a fresh belt supposedly gets the (latest) correct belt on the bike.

[Craig G.]

Gottcha.  While researching stretch belts I've learned that they have become pretty common in the automotive world.  No doubt BMW leveraged the application from their car business.  

[dirtrider]

12 minutes ago, Craig G. said:

Gottcha.  While researching stretch belts I've learned that they have become pretty common in the automotive world.  No doubt BMW leveraged the application from their car business.  

 

 

Morning Craig

 

Yes, a lot of vehicles do have stretchy belts now, also a lot of those same vehicles also have over-running clutch alternators. It eliminates belt re-tensioning requirements (longer service intervals are a BIG thing in the auto industry now) and/or eliminates the use of noisy vibrating spring loaded belt tensioners. The elastomer belts will definitely go a lot of miles before replacement is needed.

[kruuuzn]

15 minutes ago, dirtrider said:

The elastomer belts will definitely go a lot of miles before replacement is needed.

 

Yup, mine looked brand new when I took it off at 32,000 miles.

But I also started worrying about it's age when I got to thinking about it being FIFTEEN years old! LOL

[dirtrider]

51 minutes ago, kruuuzn said:

 

Yup, mine looked brand new when I took it off at 32,000 miles.

But I also started worrying about it's age when I got to thinking about it being FIFTEEN years old! LOL

 

 

Afternoon kruuuzn

 

That does give a rider something to think about.

 

If you have a welder & some scrap laying around you could build a homemade belt tensioning tool.

 

[kruuuzn]

Man, that would be way too easy to whip that up. It would save the need of prying on the alternator. That doesn't sound too appealing.

 

You wouldn't happen to know the diameters of the two pulleys would ya? I could probably reach in and measure them with calipers but I'm at the office.

[dirtrider]

10 minutes ago, kruuuzn said:

Man, that would be way too easy to whip that up. It would save the need of prying on the alternator. That doesn't sound too appealing.

 

You wouldn't happen to know the diameters of the two pulleys would ya? I could probably reach in and measure them with calipers but I'm at the office.

 

Afternoon kruuuzn

 

I think the upper pulley is 57mm diameter,  I'm not sure on the lower pulley but that is easy to measure (contour probably doesn't have to be exact) just close enough to keep the  ends from turning on the pulley.

 

If you are making it at work just make the contour by guess as once you have the initial arc it is pretty easy to re-from when you get home.

 

 

[Craig G.]

Kruz - Unless you enjoy fabrication (and especially if don't) this is overkill.  With a warm belt and small distance to go prying from the left side is a piece of cake.  Very little force is needed.  I work with aircraft engines and know how not to abuse hardware.  I did have the gas tank off, access may be impeded with it installed.  At minimum the storage box will need to be removed.  Try it and get a feel for it.

[kruuuzn]

I'll do that. Thanks Craig.

 

I planned on pulling the tank anyway to change the fuel filter and run some new wires.

[Craig G.]

2 hours ago, dirtrider said:

But was that RPM drop due to a new tight belt vs a well worn burnished in belt?   

 

Just saw your edit..

 

A question I pondered as well.  I'll say a new tight belt.  I'll equate a burnished belt (certainly wasn't worn by appearance) to a properly adjusted poly belt.  Ultimately we'll never know but I do trust my mechanical intuition....

 

Would love to be privy to BMW's engineering substantiation for this change.

[dirtrider]

3 hours ago, Craig G. said:

 

Just saw your edit..

 

A question I pondered as well.  I'll say a new tight belt.  I'll equate a burnished belt (certainly wasn't worn by appearance) to a properly adjusted poly belt.  Ultimately we'll never know but I do trust my mechanical intuition....

 

Would love to be privy to BMW's engineering substantiation for this change.

 

 

Afternoon Craig

 

I kind of mis-spoke when I said burnished in though a burnished-in belt should have less parasitic drag.  I probably should have used the words stretched a bit from usage.  

 

If you have ever re-installed a well run in elastomer belt they go on much easier  after being used for a long while.

 

I don't think we will ever know what goes thorough BMW engineering's minds (the belt type change might not be,  probably isn't, an engineering decision). My guess, based on similar circumstances in my automotive engineering  background, would be the change was initiated by the design team not the engineering side. The design team said lets do it  so the engineering side had to make it work in a live engine hostile environment  ( I deal with similar daily) 

 

Just an educated guess on my part  (having gone through very similar situations many times in  the past) is that the change was driven by the pre-production BMW 1200 hexhead. That bike was designed to use an elastomer belt, whether  in the original pre-design packaging requirements, or morphed into using an elastomer belt in very early engine design/testing changes. Possibly  an original design requirement  to get that generous 7+ gallon fuel tank to fit around the alternator.

 

An elastomer belt removes a belt tension check  or possibly two, eliminates all the related parts needed for an adjustable alternator (eliminates assembly line alternator adjustment also reduces cost due to fewer parts & less assembly man hour labor), allows the solid mounted alternator to be mounted much closer to the engine as no adjustment packaging space is then needed (this is a big gain as that then allows a larger fuel tank as well as couples the alternator tighter to the engine with very solid mounting so there is less possibility of alternator off-order buzz or excitement (plus that large alternator front plate mount is not needed),  (if you have ever worked on the alternator area of the 1200 bike it is packaged very tight & tidy (you can barely plug the wiring in). 

 

BMW probably didn't want to go cold turkey  into an elastomer belt on a brand new model without some customer real world testing & real world belt performance feedback . The timing of the elastomer belt release on the 1150 bikes would time out just about right for mid term 1200 hexhead component release dates (or pre-release dates anyhow).

 

Bottom line-- my 'guess' (just a guess)  is that late 1150 elastomer belt release was to get some real world elastomer belt experience  in a real world motorcycle environment.   

 

Releasing a brand new belt style/alternator pulley design that late in an established production run sure wouldn't gain BMW any more profit, too late in the 1150 production run to get any advertising hype (they sure didn't brag about the belt change), added more parts to the already over stretched parts chain, added a lot more complexity to service as a big change like that (even the belt adjustment & tools) made dealership work more difficult. The only real gain that BMW could brag about was the elimination of the 6,000 mile belt re-tension & less rotating mass on engine over-run (find me one non-engineering type customer that even noticed that?)         

[kruuuzn]

The heat gun was the ticket. Along with a little grunting, cussing, swearing, and a couple of large crow bars.

Man, the new belt is as tight as a banjo string. That outta affect the ‘ol gas mileage! LOL

 

I gotta say though, having the tank off gives you much more room to work.

[Craig G.]

It just occured to me that my first tank after installation dropped to 39 mpg... usually in the low 40's and has always been consistent.  

 

Yup...it's a banjo string.  The tool I mentioned worked slicker than snot, especially with the limited access.  There are YouTube videos out there showing how it works.

[Rx_Mich]

Hi Dirt Rider,

                       One quick question on the measurement. 118.5mm measuring tool measures  ribs on pulley1 to ribs on pulley2 and not the lip of the pulley correct? Sorry, re-read it and answered my own question. :o)

[christianf]

I am having issues with a slipping alternator belt ( as per my mechanic, who does not have time to change it) and it looks like I am going to have to do the work myself.  This is all very intimidating but I have a good friend who offered to help. Thank you very much. 
i am doing my homework trying to figure out what is what and how to do the work. So please forgive me if I sound like a debutant, i am very skidish about doing this project and you will see it below.  
I own a 2004 r1150 rt, I am not sure if was manufactured in 2003 and if it makes a difference as far as the belt is concerned. I seem to understand that you need an elastic type belt.

YouTube video from Chris Harris at time 6:50 mentions that if the 841 measuring 592mm belt does not fit when the alternator is all the way down CH suggest to use  a 779 belt which is 611mm. I am not sure, if I should buy both belts and how to judge the best one to use if I do. Is it advisable to `use either one? It is my understanding that the 841 was the one to use but it looks like people in this bread have issue installing it because it is too tight.
This is the link to the continental belts. 
please advise,

thank you so much

 

 

[dirtrider]

Quote

 

I am having issues with a slipping alternator belt ( as per my mechanic, who does not have time to change it) and it looks like I am going to have to do the work myself.  This is all very intimidating but I have a good friend who offered to help. Thank you very much. 
i am doing my homework trying to figure out what is what and how to do the work. So please forgive me if I sound like a debutant, i am very skidish about doing this project and you will see it below.  
I own a 2004 r1150 rt, I am not sure if was manufactured in 2003 and if it makes a difference as far as the belt is concerned. I seem to understand that you need an elastic type belt.

YouTube video from Chris Harris at time 6:50 mentions that if the 841 measuring 592mm belt does not fit when the alternator is all the way down CH suggest to use  a 779 belt which is 611mm. I am not sure, if I should buy both belts and how to judge the best one to use if I do. Is it advisable to `use either one? It is my understanding that the 841 was the one to use but it looks like people in this bread have issue installing it because it is too tight.
This is the link to the continental belts. 
please advise,

thank you so much

 

Morning christianf

 

Sorry, I won't watch any Chris Harris videos so you are on your own with that part. 

 

Your 2004 1150RT uses an elastomer (stretchy) belt so the proper belt tension is set by pulley spacing, not torque, so you need the correct belt to achieve the correct tension with the proper pulley spacing. If you use a longer belt then the given pulley spacing would not work so I have no idea on how you would properly tension a longer elastomer belt.