Just know that going as far as the chain is a huge job compared to just the pump. Took me a couple days.

 

It's six more bolts, and another gasket....... and there it is. Yeah, and the balancer.... I suppose that does lend a bit more interest to the job. But, I had all the tools to do it in my toolbox....... I suppose not everyone does.

 

If the chain and gears haven't been changed before, its best to do them while you're in there. The necessary tools can be rented at most parts stores these days.

 

at what mileage is the chain supposed to be replaced, as per the OE manual??

 

I don't think it is on any maintenance schedule.... I am sure there is a spec for how much slack is 'allowed' though. Generally, if the truck has over 100K miles on it, the chain is going to be pretty stretched in any event. If you are in there doing the water pump anyway, it's isn't a bad idea to go after the timing set (if they are still original), as it isn't that much further into the engine. Also, the cover over the gears is held in place, at least partially, by the water pump bolts.... So, swapping the pump has the possibility of disturbing that gasket.... You put it all back together, and end up with a leak somewhere else, and you get to do it all over again.

I changed my pump because the timing cover gasket was leaking...... While I had it off anyway, I put a new double roller timing set in as well.

 

A test for a bad timing chain would be with a timing light. If you see the timing mark bouncing all over with the light on, well then its sure pretty sure bet.