The bracket across the front of the rear subframe, and to which the seat and faux tank are attached, seems to be a weak point on the 650/668. The bracket is 2 mm thick, and suffers from fatigue over time, so that it eventually cracks, either at the point where it is welded to the frame or at the bend approximately 20 mm from the weld. It pays to check it from time to time for signs of fracture, as it often goes at one end first and this places extra stresses on the other end, eventually leading to both sides breaking. When this happens, the rear of the faux tank is no longer adequately supported, which can lead to further problems. In the case of my yellow bike I now have a small tear in the tank, adjacent to the locating tang.
When the bracket completely fails the seat pad will become noticeably loose, which can obviously lead to safety concerns, so attention to the bracket is definitely a good idea.
Matt Callaghan reports that his bracket broke at around 10,000 kms, mine broke at 18,800 kms, others have had this happen at 23,000 and 25,000 kms.
Here is Matt's description of his repair:-
"I replaced the 2mm thick bracket with 6mm plate fabrication, fully welded it to the subframe, and passivated the welds with acid paste. It's a real pain, you have to dismantle the entire rear end of the bike to remove the sub-frame, but as Siggi says it's character! Now done 25000k and no signs of a repeat performance."
It should never be welded back up while the subframe is still connected to the bike - remember that the EFI unit is mounted in the tail section and is a sensitive electronic device, the last thing you want to do is fry it using a welder!
Phil Stephens has had a bracket break too, here's his thoughts:-
"As the subframe does flex a little outwards when bolting up to front section (and the three I have do vary in hole position and width etc more than I'd expect from jig built components), when it needed welding after breakage like yours, I took it to the welder bolted into position so that the new weld would be based on the installed position width. It has not yet broken again. I suspect that the seat bridge and its welds may be under significant stress when the subframe is pulled out to the width of the front frame section."
© Steve Carr, 2001-2007
Site created February, 2000. Last modified Friday, May 15, 2009
30 May 2005