The beam framed 650 and 668 bikes have a lightweight aluminium alloy subframe that mounts to the main frame and is located by four M8 bolts that pass through the main frame and thread into threads cut in the alloy.  The bolts are thus very much stronger than the threads in the threaded holes, making it very important that the bolts are correctly tightened.

There have been a number of reports of these bolts pulling the threads away over time, possibly caused by vibration induced fretting. Also they will fail when too much force has been applied during tightening.  When it does happen, a relatively easy repair is fortunately possible.

Strip off the seat and rear bodywork, then remove the two 10 mm bolts that locate the rear of the fuel tank to the subframe.  Remove the two exhaust cans by either removing the mounting brackets from the frame or the cans from their bracket mounts.  Remove the top two bolts from the main frame mounting points and you should then be able to gently pivot the whole rear subframe enough to gain access to the mounting holes with a helicoil thread cutting tool.  Fit a helicoil thread insert to the damaged threads.  The same process will work with the lower mounts, but do make sure you don't lose the spacers that go between the frame and the subframe.  Then replace the bolts in the new threads, replace the nuts securing the rear of the fuel tank, refit the exhaust cans and rear bodywork, and you should be back on the road!

Rear Subframe

© Steve Carr, 2001-2007

Site created February, 2000.  Last modified Friday, May 15, 2009

Return to 668 Tech start page

Last updated
30 May 2005