Fitting alternator belt to BMW GS1200 Motorbike

From miscellus

BMW GS 1200 Alternator belt fitting kit

So simple in the end, a broken drill bit and a piece of plastic cut from a Flash bottle
the (5mm?) drill bit prevents the belt from slipping off
Rotate clockwise as you pull the slack part of the belt towards you
Slide a plastic strip under the belt

Like you, I scoured the Internet for a DIY solution to this and the common answer seemed to be the one using an adjustable wrench. My largest adjustable is 30mm but I do have a thin 36mm bicycle spanner which fits the lower nut with a little play.

After spending a few fruitless hours and putting nicks in my nice new belt I eventually came up with a solution which took a few minutes. I refitted the damaged belt twice just to prove that it was easy to do. I fitted another new belt the next day with no problems. This is how I eventually solved this problem.

How I fitted the GS1200 Alternator belt

  • Remove side panels for slightly better access
  • Remove one spark plug from each cylinder so the engine can be turned over easily. I found the bottom plugs easier to remove as they don't need a long reach plug spanner
  • Put in neutral and remove ignition key
  • Remove alternator belt cover, [5 torx screws, 2 top, 3 bottom] - marvel at the corrosion at the bottom of the plate
    • My bottom torx screw was corroded solid and eventually snapped when I tried to hammer it round with a chisel
    • I don't think I will bother replacing it. There are drain holes at the bottom of the alternator belt cover, but they plainly don't work so I have enlarged them slightly
  • Remove crash bars. The small allen screw is seized on mine so I could not separate the bars, but I managed fine by just removing all of the crash bar bolts and holding them away from the pulley with tie-wraps

  • remove the belt by running the piece of plastic under the belt and prising the belt off, very easy
  • Find an old drill bit that fits tightly in one of the 3 holes in the bottom pulley (5mm?)
  • Snap the cutting end of the drill bit off by placing in a vice, protecting your eyes and smashing with a hammer
    • If you don't have crash bars fitted you can probably forego shortening the drill bit
  • I stretched the belt in a clamp for 5 minutes which also may have helped. Soaking in boiling water was another suggestion I've seen
  • Hook the new belt over the top pulley and check it is fully on. Slip it partially over the right side of the bottom pulley
  • Push the unbroken end of the drill bit into one of the 3 holes and loop the belt over the bit. This prevents the belt from slipping off the pulley as you rotate it
  • Use a spanner or socket to turn the bottom pulley clockwise and the belt will snap on as you turn. If you can, check the belt is not running out of the top pulley
  • Should the belt hang over the edge of the top pulley, apply pressure to the loose part of the belt and rotate the bottom pulley and the belt will seat properly. (I used a clamp similar to the picture below)
  • If the belt is on the bottom pulley but partially hangs over the edge just turn the bottom pulley and press the loose part of the belt in as you turn and it will drop into the pulley

If you have an assistant, you can probably dispense with the spanner altogether, just pop in into 6th gear and use the back wheel to turn the drive shaft. Be certain of your assistants co-ordination and mind your fingers if you chose this method!

Belt Size Differences

The belt fitted to the bike originally was a 4 PK 592 (4 internal ridges and 592 mm internal diameter). The belt supplied as a replacement by Motorworks was a 4 PK 595, 3 mm longer. I called Motorworks and they confirmed that the 595 is what is fitted as a replacement. A quick Google confirmed this. I can't imagine trying to fit the 592 without the 'official' BMW tool, which seems unobtainable even if you have the UK equivalent of $200!

A $200 hen's tooth

GS 1200 Alternator Belt Suppliers - UK

The GS1200 alternator belt, 4PK595 from Motorworks cost £17.30 incl. VAT & postage and arrived the next day.

GS1100 / GS1200 / 1200R differences

The GS1200 [2004 to 2006], maybe others has a 34mm nut on the lower pulley, the 1200R and 1100 seems to have a much smaller nut on the drive shaft so you may get away with the adjustable trick on those models. Most of the videos I've seen are for models with the a much smaller drive pulley

I also stretched the belt with a clamp for 5 minutes before fitting