i dont know about the diameter of 50t sprocket, but this much is certain-you'll snap a regular bike chain when using it for the motor drive. let's say for the sake of argument it doesn't snap when you torque it and send shrapnel into the back of your leg, the width of a bike chain will fit a drive sprocket, but so narrowly that you'll probably stress out the motor . motor drive chains are the size they are for reasons.
If you can find a chain that fits, it will work fine without a problem. Engine alignment and sprocket fit is critical with narrower chains and you have greater risk of chain slipping off the rear sprocket if any of the mountain bolts/assembly loosen up with vibration-as a result of increased sprocket runout.
Your best bet is to go to www.thatsdax.com and buy this product: Precision 081 Drive Chain. Better than 415
chain. Much lighter and more precise and
harder steel. Fits up to 3mm width counter
shaft sprocket. 60 link, 150cm/59 inch length.
Includes Master link and keeper. Only
$14.99 includes shipping Lower 48 states
It is what you are looking for and has worked fine on my daily rider. You'll need to knock the chrome off of the sprocket tines to get it to fit properly without jumping or binding.
Don't see how width of a chain affects stressed on a motor. Chain tension can adversely affect drive bearings but that is another issue.
I am running a heavy duty bmx chain (KMC Z510H BMX CHAIN - 6.95 ea from www.bikenashbar.com)
I needed it for clearance with my 3" back tire, I had to change engine sprocket from dax to the one from livefast to allow smaller chain.
this chain is for stunt riding bmx'ers made for high torque, perfect for me... hasn't givin any probs yet
ps I needed 2 chains for the deviate, it's a pretty long bike 8) 8)
I've tried the .081 chain and broke it several times. The standard 415 chain works much better for me. IMO the best option is a name brand 415 or 420 chain. I've been riding for over a year with one and have had no problems at all.
the width problems for me occured because the chain felt really tight on the sprocket teeth, and even when chain was looser, under acceleration the bike felt like it wanted to go sideways. i must've had a really small chain.
You can buy a QUALITY 415 chain from D.I.D. for around 15 dollars....super tough. If a 420 will fit, go for it. D.I.D. has those too. I got a 120 link with master (428) from D.I.D. for 15 dollars. It was for a Honda, but still if one will fit, use it.
Any motorcycle shop will have them or can order one.