This post documents replacing the alternator belt on my 2001 BMW R1150GS. Newer R1150GS’s use a slightly different belt and pulley, but the replacement procedure is similar. The major difference is the tensioning of the ELAST belt requires a different tool and procedure.
The tools I used:
![2001 BMW R1150GS Alternator Belt Replacement](https://lh3.googleusercontent.com/blogger_img_proxy/AEn0k_vCFQfU2KOzZo9OWrNBeUzA5qtKpoU1v0N-VOILglydJOALVVGRqDWD7OYS7CaHgmhcBWX-mK09dLYCQpeGvbpsgdO8aPwNvg8YWLmcqMekWeyXrW3vXFJbZbU=s0-d)
1993 through 2003 50A alternators:
Poly V: 4PK611, BMW part 12 31 1 341 779
Newer bikes:
ELAST: 4PK592, '04-on Oilheads and most Hexheads,
BMW part 12 31 7 681 841
ELAST: 4PK582, R12RT/Adv, BMW part 12 31 7 690 57
Stock BMW Belt for my bike:
![2001 BMW R1150GS Alternator Belt Replacement](https://lh3.googleusercontent.com/blogger_img_proxy/AEn0k_tJQ3vqNn8vtVnC474v9-eclG79jNYhqD3AVWJKlXxkDXmDcJBb9v2ykx19-vRwYff1xofJyrdzvkATIIIr7lFXIZKbMBenk8RR4T4NF8SBmCGJGjP5-zYovQ=s0-d)
1) There are four nuts holding the alternator cover on. Remove them with the 4mm allen key socket.
![2001 BMW R1150GS Alternator Belt Replacement](https://lh3.googleusercontent.com/blogger_img_proxy/AEn0k_v-KLLSou4UhJSNYaCJVOjutRLnTq3sp0-2f_W_cLFs1biVQmf_sUyV_Ed4VLE-hfklf12Ru9AQGMUP74XxNAlUmP04ixB7A1ZIu_A8WA82hEzJVfoR8twNMuA=s0-d)
![2001 BMW R1150GS Alternator Belt Replacement](https://lh3.googleusercontent.com/blogger_img_proxy/AEn0k_s-HaQN5RYuICVqnG4r30A3fkGASGvMgvO8oMqJjrZm5eh-dDu6nvPBSvYlQb_X2z86kmkiYhBDLtyUmjIjp_i8XGyoSpexjnipi3b7Jw2zczShiRLTBmWugQ=s0-d)
2) The cover should pull out slightly and then down.
![2001 BMW R1150GS Alternator Belt Replacement](https://lh3.googleusercontent.com/blogger_img_proxy/AEn0k_sXQ-YhNyQLm9G8pDXxqJ9BbMPuieEgKEdTLiYMXajCqYjSl-KYs6vKXgRkMxtw0gN-If_CL7rLM2brakvBneTp1XqgJsmWZSmlcq25m-XLQzB29y_7QESMkPw=s0-d)
Alternator belt exposed:
![2001 BMW R1150GS Alternator Belt Replacement](https://lh3.googleusercontent.com/blogger_img_proxy/AEn0k_tgtPMFcTOsruPLm3Jm5Twbp_1Kj9GgxdxVVAeNLoJmlefJoCMvz19m-J4tDHasqLr_xxzhRBKDIp6RraKN9Ay00gQY0NvmfBQEXXo116XaBF-RkGqjkA3ryh8=s0-d)
3) Using the 13mm wrench, loosen the three bolts holding the alternator.
![2001 BMW R1150GS Alternator Belt Replacement](https://lh3.googleusercontent.com/blogger_img_proxy/AEn0k_s4i5qUYVrduOXPoFGwOkc3MQMVmohuh7rEqzzwZE5N2I6-6558R2T-4V0_3c7DFFj1sspS1x347a-4wQpjeIXaOGn-r7p29ptwrV_5l7BpdEOzqvrYwqimOQY=s0-d)
![2001 BMW R1150GS Alternator Belt Replacement](https://lh3.googleusercontent.com/blogger_img_proxy/AEn0k_usC-gBVNqJpPXwpUt7zJ8JYE36EEgMWnDuUv8EHnQFHm_TC388ZcwNu8dXplLFN5WASHZagJHwz1n2vJg85naBDbWUo8qwgQ17QSGt0sDPTvddbTdr2xLBrvo=s0-d)
![2001 BMW R1150GS Alternator Belt Replacement](https://lh3.googleusercontent.com/blogger_img_proxy/AEn0k_s4R_MG49KhkPzM-rpSLeD9uX4SOCTq7E9PnjeZDRTCy6qCtq6HAj6Tog67I1ShhOogNy9EkPCr0xEdVMEWqWd1aQ-ER28JPJatPNFa9epVss_YFl51lo1G4xc=s0-d)
4) Pull the alternator down to put more slack on the belt if it didn’t slide down itself.
![2001 BMW R1150GS Alternator Belt Replacement](https://lh3.googleusercontent.com/blogger_img_proxy/AEn0k_uqK0yC98sOVEf4jyY-BBiNCujwg8bfUwMqKty0wwOjOoyofU3QbGdVk95dtaZyNB0UOwo7jEEQ9nC-W_3nXaBL9LMolwMd7Hop7pGtpgTbS3qO40HG9wBP5Xk=s0-d)
![2001 BMW R1150GS Alternator Belt Replacement](https://lh3.googleusercontent.com/blogger_img_proxy/AEn0k_sWAqmh6HFBXrk35DOU4vgKjnV7Y6w2ORHFBFK2bSImJYoK8qE8OdvviLkXYUKYeHNs_UZlXbulpZmu0HhRYBggIZ8-GkcpZQsHNEMD7mAK7Ym4EeakQ5YgNg=s0-d)
5) Pull the belt off
![2001 BMW R1150GS Alternator Belt Replacement](https://lh3.googleusercontent.com/blogger_img_proxy/AEn0k_uvO_6LWD4TTbAcIOmAJkuLaRmfko0GeJeaZgeqIzKNFIcXF72qIAhOs6_TclEpR30HSpgiu_JB4vTv6miEXv4jKQI-IEb3D5g7NtDP4IzAjyl3IfRmOIwNP3U=s0-d)
Old vs New belt:
![2001 BMW R1150GS Alternator Belt Replacement](https://lh3.googleusercontent.com/blogger_img_proxy/AEn0k_uxC2eFbGq4mLXfWHdmLNLNrNrjW3muFuIsS2NrfLil8YM5t9ZaJfmFTPcChOQ_8nWx3uowPUJJfcOrUpZmQ8pHynTZgWT4y2cKLbn-l4aCStcaH56bWkz4stk=s0-d)
Mine was apparently past the 36,000 mile replacement. It was making a bit of a noise. Pieces of the belt had started to come off inside. Checking the belt tension is critical to belt life. Check when you change the oil.
Old belt:
![2001 BMW R1150GS Alternator Belt Replacement](https://lh3.googleusercontent.com/blogger_img_proxy/AEn0k_sP76pXtqIGXcnM6aEUmJMSFLSjNqrmJhTFiIz7ogYtXmzu8M1F4jY_hEEQk4mBP771Shp9f9Z_SfSepdWgk8HgzHUM_PegRYDwliFeFAqihJ0S0BVz_NGAVxY=s0-d)
New belt:
![2001 BMW R1150GS Alternator Belt Replacement](https://lh3.googleusercontent.com/blogger_img_proxy/AEn0k_voN3i1Wvrzv_KbiVL3V6530IN0vyQJZSM-alXD8jTqDNRITrYwzab2pTZ7dZxGNHJuExrU1soHenXLN5O9LQGwUnrcuHQVSW3D2umRL8IRSoS__teJuYgL9QM=s0-d)
Notice the four ribs on the belt. They match up with the ribs on the pulley. Make sure to line them up when reinstalling the belt.
![2001 BMW R1150GS Alternator Belt Replacement](https://lh3.googleusercontent.com/blogger_img_proxy/AEn0k_vBsTS4XgMgy-F7487BeBeFAkFzYSmUrseWR0IncKaDzyIgIVbJr_Rd8q6giqxTqx8EzG02G_5ypgMwnaX3NLETdG2G2nd-jhkxnaAn9J6QstPttS1k1nOYPQg=s0-d)
6) The new belt just barely slipped back on.
![2001 BMW R1150GS Alternator Belt Replacement](https://lh3.googleusercontent.com/blogger_img_proxy/AEn0k_sguPWlE_E7X6VyUig25UqwRbc41HO-uQN5rCmaeNBKEy8B9JIEw5floczSRbzih2w6dfRqf4LC1-ci77ZfMli-4J3jv0v2NDJUAmO1SbejrRFrLR5uvV6ENb4=s0-d)
7) BMW has very specific belt tensioning specifications. Don’t be tempted to treat this like a car belt and do it by feel.
8) I had to turn the direction adjuster on the torque wrench to “loosen” not the tighten motion to get the alternator to lift.
![2001 BMW R1150GS Alternator Belt Replacement](https://lh3.googleusercontent.com/blogger_img_proxy/AEn0k_sXiSMRSe1-BDCOeM59B_HDxumkRGR2lLOAdd4VcgaM86pjE7lqgitdtWr9s__jSz-ilWXCOnQt-5UhsId1lH3JN-40V5Mo-4IgDQiX3fDttBqwsut5GdkyVpw=s0-d)
9) Using the 6mm allen key socket, extension, and torque wrench tighten the adjusting nut to 8 N-m. This will raise the alternator and pull it against the belt.
I found I needed to lift/tilt my gas tank slightly to have room with the torque wrench. See my air filter replacement guide for tips/photos.
BMW makes an adjustment tool that goes on the front rather than the back. Much Easier! I will think about getting it for the next tightening.
Adjuster for Poly V belts: tool 12 3 551, part 83 30 0 401 69
![2001 BMW R1150GS Alternator Belt Replacement](https://lh3.googleusercontent.com/blogger_img_proxy/AEn0k_vDwykbOHwfG-41AAyg9ue0sYRQImJ3Yvat8iuHbQfVFdR1S7ogOGlXTpbSG9wt9_9mbw3jTjADU_vNfCIFeTSyxlzib-kv34yN6HUsbyo_KCsDqfM87UpPlWQ=s0-d)
10) While holding the torque wrench, use the 13mm wrench and tighten the other two nuts holding the alternator.
![2001 BMW R1150GS Alternator Belt Replacement](https://lh3.googleusercontent.com/blogger_img_proxy/AEn0k_thgdSVLR50z1pcbPz_J32eEbcE6PZHB3XLZMc-JD1Wxflvm9hpEONvFaU589KVvYy-u6mC13QpuQw26BapJ4NPWeiVRZePLNFDwKh1GhRhh8fLoK-1TvMITXE=s0-d)
11) Using the torque wrench and 13mm socket, torque all three nuts to 20 N-m.
![2001 BMW R1150GS Alternator Belt Replacement](https://lh3.googleusercontent.com/blogger_img_proxy/AEn0k_upeFLM46omm9QcZ0X39anbR1Bi2OO3S8S1MLgZHrpPsrin1_2pqr09lasvyp-UyBupVgChfeMmZagz6X6SP1op5XKnQPaIex__AqtPjrUChYpGxWl7wcOWVaY=s0-d)
12) All three tightened up. Use the starter to crank over the engine a couple times, but don’t start it. This will help seat the belt on the pulleys. Loosen the bolts and repeat steps 7-11.
![2001 BMW R1150GS Alternator Belt Replacement](https://lh3.googleusercontent.com/blogger_img_proxy/AEn0k_sguPWlE_E7X6VyUig25UqwRbc41HO-uQN5rCmaeNBKEy8B9JIEw5floczSRbzih2w6dfRqf4LC1-ci77ZfMli-4J3jv0v2NDJUAmO1SbejrRFrLR5uvV6ENb4=s0-d)
13) Replace the alternator cover and tighten the four bolts with the 4mm allen key socket. The cover is plastic, so be careful not to over tighten.
![2001 BMW R1150GS Alternator Belt Replacement](https://lh3.googleusercontent.com/blogger_img_proxy/AEn0k_uQz0q98EJrQw-lyw32TWVUKWb9wvTLE4bs1FyD6MNi8Nc68KOLi-iAR9LFJTJ9XA5pub-324SBtkvANO04F7BupnH0zYqZGOlV1FsFBXVDb-B-zA2_1IfvIVo=s0-d)
14) Cover replaced
![2001 BMW R1150GS Alternator Belt Replacement](https://lh3.googleusercontent.com/blogger_img_proxy/AEn0k_unfIuHdztTUlI3KI4b6fzLRxI_mUZtvq0-8UtXf9fC6_yG69ASfvNA892H3ZoFiS5Pim-aUpQwDZGy7YCvu5DUF-nbH1TbLp5EqMJ_aA6jZG4eEpwSeiWfxcY=s0-d)
15) Check the belt again in 6,000 or the next time you change your oil.
16) Go for a ride!
Good pictures/discussion of the Poly-V vs ELAST here.