Mikael87

I am building a 29" MTB with a single speed chain ring on the front and fat slick tyres for my daily commute.

Unfortunately my chain keeps comming off when going over a bump or kerb and when pedaling...
I removed the front shifter and 2 smaller chain rings and think this could be the reason it keeps coming off. I understand every occasional tooth helps guide the chain when shifting and this could be the reason for it coming off. My questions are;
Will I need to change the front chain ring, and possibly crankset and chain to a different type?
Will the different chain also effect the rear cluster use?

blakcloud

Try a new chainring, with a wide narrow tooth pattern. Wolf Components is one company that specializes in this type of chainring. I would change the chain at the same time. All this could be done for about for about 70 pounds.

Cheaper way, put the front derailleur back on, and use it as a chain guide.

Another alternative but as expensive as the solution number 1 is a Paul chain keeper.

You don't need to change the crank at all.

Chains and cogs wear together and sometimes when you change one the other doesn't like the change. So depending on how worn these parts are will determine if they need to replaced. So try the chain and chainring first and then if needed replace the cogset.

JonathanGennick 

It sounds like you may have left on the ramped and pinned ring from your three-ring set. That'll never work, because those rings are designed specifically to allow the chain to come off. You need at least a single-speed-specific ring. The wide-narrow rings like the one blakcloud suggested are even better.

You might or might not need a chain guide. I like the MRP 1x models myself. I have on bike for which just a single-speed-specific ring has been enough, and I've another bike that's required a chain guide. You just have to try and see.

CliffordK

Perhaps bashguards could help.

https://www.bbgbashguard.com/

HillRider

The other change often made for 1X systems is a "clutch-type" rear derailleur which holds the rd's cage more firmly in place so the chain doesn't go slack over bumps.