Hello, This is my first Instructable so please cut me some slack ;)
This is how I repaired the knobs on my GE cook-top but seems that other brands have the same design. My first response to a broken part was to just replace the knob since they sell them on Amazon for $20.
Ouch $10-$20 for the same thing? The problem is that there is a design flaw so this will likely happen again. When you remove the knobs for cleaning if you don't have them lined up perfectly on the D shaped valve stem you can easily spit the plastic when you (or your wife) push it on. When the tube cracks it opens up as you turn the knob to open or close the valve so the burner will not work.
To fix this I wanted to install a tube around the stem of the knob. This will reinforce the plastic preventing it from opening up the crack and keep it from happening again on other knobs. A quick measurement showed that I needed a 10mm or .40 thin walled tube for this repair.
Here is an easy way to fix it and even has the added benefit of having a slightly tapered tube to push closed the split plastic.
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Step 1: Remove Knob From GE Cook Top Range
Remove the knob - and get yourself a spent or new empty brass .40 cal or 10mm cartridge. I would imagine you could get a few at a shooting range or gun shop for $1.00 or free. I WOULD NOT RECOMMEND you buy and disable live rounds.
I used a plumbing pipe cutter to cut the cartridge. You are going to want to measure the stem on your knobs or eye it. I found that .60 long sleeve worked the best because it leaves some of the taper in the back of the cartridge. 1/2 also worked well and gave me a little extra room for glue.
I found that inserting a drill bit allowed me spin the cartridge in the pipe cutter a little easier.
Next I de-burred the cut end.
Test fit it on the stem of the knob. If the fit is good add some instant adhesive or epoxy and slide it home. Wipe off excess glue and let it dry. I had to press fit mine on but I wouldn't force all the way down. When you are test fitting you will see that even if it isn't flush they still work perfectly.
Install the knob. I did all 5 knobs just so they don't break in the future.