bolt that holds camshaft sprocket broke?

My first guess would be that it was over tightened at some point in the past, either by someone trying to turn it the wrong way during maintenance or tightening it after maintenance. Then again, the bolt could have been defective in some way as well, or replaced with a lesser quality bolt at some point in the past. How old is the vehicle and do you know the maintenance history on it?

Well to give a short history version... The truck is a 96 tacoma with the 3.4 v6. About 8 months ago my brother (the owner) started having overheating issues. The problem was fixed to some extent with the replacement of the radiator but if I remember correctly the truck would still over heat under certain conditions. A few months later the timing belt snapped and this is where I got involved. We got the timing belt kit, (belt, seals, tensioner, water pump, etc) and manage to get that installed. Note that we did not pull the camshaft sprockets since we could see no leaking and thus no need to replace those seals. And now 4 months later he notices the truck is running rough and then finally something breaks. I haven't actually seen the truck since this happened but he seems to think that either the camshaft end broke off or the bolt that holds the sprocket on broke...in other words the sprocket is not attached to the cam shaft. If he is reading this post he might be able to shed more light on the problem. What I'm wondering in the back of my head is if the original over heating caused some internal engine part warpage that in turn is causing some binding somewhere which caused the original belt to break and now the camshaft. What do ya'll think?

TIA

I think you need to find out exactly what caused it to stop running rather than guessing. What makes you think a camshaft sprocket bolt broke ??

He said that the sprocket fell off the end of the cam shaft.

He also said that he and his brother replaced the timing belt without removing the cam sprocket. Me thinks the sprocket might have been loose when they put the new belt on without looking at the sprocket.

It wasn't clear from the original post that he had determined what the problem was yet.

From OP: I haven't actually seen the truck since this happened but he seems to think that either the camshaft end broke off or the bolt that holds the sprocket on broke...in other words the sprocket is not attached to the cam shaft.