I've used coins locked in vice grip with screwdriver jammed in gap between jaws to provide leverage..

Grinding down drag link sockets from Harbor Freight to 30mm and 50mm diameter to fit the slot is said to work well.. I don't find a listing for them though.

or there is Honda timing cap wrench 07709-0010001

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I use the socket type like in the picture above too. However I ground the ones for the Rebel to be curved like the shape of the grooves in the timing caps.

 

Are you removing them as part of valve adjustment? If yes, it isn't necessary.

 

I agree
rolling bike in gear the cam can be placed in position where valve adjustment can be made roll again to do other side..
I ground (2) 4mm notches in metal ruler to hold adjustment screw from moving while tightening lock nut w/9mm box wrench.. Sure beats using needle nose vice grips..

Or you can buy tappet valve wrench to fit the adjustment screws square head..

 

Opening the caps with a quarter and a screwdriver worked for me. Thank you! It left some scratches but its okay!

I read the other post about adjusting valves without opening the caps. I'll try that next time.