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R1150RT alternator belt tensioning method


K11RS

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I replaced a fraying alternator belt on my '02 R1150RT and am now trying to tension the new belt.

Knucklehead question of the day: What is a good way to set the belt tension?

 

The Haynes manual says to "tighten the adjusting bolt using a torque wrench to preload the belt..." Two problems here: 1) tightening the preload adjuster bolt only locks it up; CCW on the bolt seems to tension the belt, and 2) I can't get any travel from a torque wrench on the bolt as shown in the Haynes manual; theres no room to turn the torque wrench.

 

The BMW service book says to "tighten and hold the BMW tensioning nut (PN 123551) with a torque wrench..."

Do I need to buy this adjuster nut?

 

I searched the forum, but was unable to find any history on this topic.

Any input is appreciated.

Thanks

Jeff

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Ive done about 6 of them,I just use a pry bar and tightn nuts,,It dose not take a lot of presure to tighten the belt,Never had 1 come back yet!!

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Sounds like it's not too sensitive an adjustment: 1/4" play or 90 deg. twist at belt center will set the tension. I guess the service manuals are making it more complicated than needed.?

Thanks for the input.

Jeff

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I guess the service manuals are making it more complicated than needed.?

 

Jeff

 

Yep,they sure are. Put a big screwdriver or a prybar under the alternator and lift it. Tighten one of the nuts. The belt should be able to twist about 90 degrees. If it looks good, tihgten the other two nuts and call it a day. FYI, these things fail occasionally. You may want to buy another one and throw it in the side case as a spare.

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be careful when using anything for leverage under the alternator. The wire from the ignition sender runs in the same place. Don't damage it.

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ShovelStrokeEd

Don't forget to re-tension the belt after replacement. 600 miles is the approved interval but 1000 won't hurt nor would 200 be too short.

 

Seems the belt will stretch just a bit and then just takes a "set" and is good for the remainder of its life.

 

Since I always pull the alternator cover to access the crank bolt for turning the engine while doing a valve adjustment, it is a simple matter to check belt tension/condition every 6 weeks or so.

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Sounds like it's not too sensitive an adjustment: 1/4" play or 90 deg. twist at belt center will set the tension. I guess the service manuals are making it more complicated than needed.?

Thanks for the input.

Jeff

 

I learned the 90-degree trick from Glen McIntosh. Tension the belt so that forcing a 90-degree twist at its midpoint hurts your fingers like hell. I mean REALLY hurts. It should be just about right.

 

Glen showed me how at the 24K change. The original belt was shot. I did the 48K and 72K changes. The belt was used, but still in good shape each time.

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Thanks for the ideas.

I wasn't that comfortable with the crowbar under the alternator tensioning technique, so I ended up using the 6mm hex preload bolt. Turning it CCW (as opposed to what Haynes says) walks the alternator up, and preloads the belt. Torque wrench doesn't fit in there (unless maybe the tank is removed), so the belt tension is adjusted by the 90deg mid belt twist as recommended.

Thanks for the inputs.

Jeff

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