Haven't had either of the above happen yet. Studs can be replaced.
The tensioner:
1. Set it in place with a set screw.
2. Full size spoke guards
3. Replace with tractor supply spring tensioner
4. If you have axel, get a bearing tensioner, if bearing, make sure the bearing is in good condition and make sure the wheel cannot pivot on the bearing, you can stop the pivoting with a large washer.
5. Remove completely if you have room to adjust for chain stretch, and proper chain line.
6. Ride in fear. :/
#4 has only been a problem previously, the wheel would pivot on the bearing, but I put a large washer between nut/wheel and it stops the nut from eating at the wheel. This can also happen if the chain is too tight.
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Leaky Gas...
Make sure you get a good fuel filter and enough hose clamps to sinch down each part of line. Get some yellow plumbers tape( theres a real word for that, its petroleum resistant, white is not and can end up as gunk in the line if you don't have a good filter)
Make sure the carb inlet is tight but be careful as it can break.
Air leaks
Get yourself some orange(copper?) permatex sealant, you can do the intake and exhaust gaskets and not have to mess with the crap gaskets usually provided, namely the exhaust.
Get a chain break tool that fits #41 chain and/or get extra chain/master links.
Just picked up 10' of chain at the auto store for $17, numerous threads discuss it, even some suggesting normal bike chain is working well? Take the breaker and a master link in a tool bag. When you finally end up needing it... it's usually in a crappy place or you don't have it, miles from home etc. I had the master link pop. I broke the chain and put it back together with the breaker and haven't had a problem since, but I got new chain and plan to swap as it's been over 6 months of daily 30km plus riding.
Run a good rich mix during your break-in, it helps lubricate the whole engine.
I ran the first 500k with a regular 2 stroke oil and now on amsoil interceptor synth at 40:1 (its designed for 50:1) . Higher quality gases will not really benefit you.
Don't skimp out on your mounts. And try to use u-bolts or something around the frame instead of drilling the frame with oversized tubing, the the places to break down the better.
Watch your tires, with alot of riding they can wear, watch the walls. I've made it home (15km) on fix a flat, though not recommended, even on the can. That was friday night
Check all of your bolts often.
Don't let inexperienced friends ride your bike. Friend or bike usually gets hurt.
Be responsible, do what the regulations in your area require, unless it's looping you around in circles. Goto your local bike shop and grab the map of all the bike routes in your area.
Generally if you treat it well and don't really ride it like a dirt bike, it will last you a long time.
Have a good read through the forums and you will gain allot of knowledge and ideas for your ride.
Take care!