Product review (5 stars): Used sleeve bearings on knobs for extra strength (use vasoline to lube), but push down before you turn them !
Reviewed all the current review before buying, I am a retired engineer and like to over analyze (lol)....  Appeared that knobs were an issue so I implemented Craig A. solution (1/13/2016) with the Sleeve Bearings....applied vasoline by using a q-tip to all surfaces and was able to twist on the bearings with a pair of pliers (take it slow)... the lubricant really helps !  I think that people are breaking these knobs, by not PUSHING DOWN the knobs before turning (a design for this cooktop)....this push down, before you turn is new to most cooktop owners, but once you get onboard, it is kind of nice kid-proof feature !  Cooked a few items and boiled water but didn't notice any issues with timing, as was reported, a little hard to center the pan over the heat source because of the curved nature of the grates...but just a matter of taking your time placing the pan.  All the burners fired up and work as advertised (so far)...  Once small issue for me while installing....  Replaced a 20 year GE gas cooktop, the cutout worked perfectly, but they had switched the gas inlet from the left side on my old one to the right side on the new CGP640SETSS.  The drawer immediately under the cooktop had been modified to have the gas on the left side, so I had to spend some time making changes to the drawer so the gas & regulator could be on the right and have the drawer still work (2 hrs work).  This stove-top is absolutely STUNNING....and right price @ $900 !  Hope that helps, use the bearings on the knobs, and push down before you turn, else you will for sure either bust the knobs or ruin the guts of the gas valve !