I have a 97 Tahoe that had a coolant leak. I replaced the lower manifold gasket and while doing so noticed the original cap and rotor were bad. Thinking I was only doing good I replaced them too... Here's the thing, now it will crank over all day but won't fire. I returned the dampener to TDC rented the tool from autozone to turn the oil pump thinking it was a timing issue and still won't start! Every "pro" I've talked to says "oh! It's 180 degrees off and the distributor can only sit correctly or 180 off but it will sit wherever I line the driven gears on the distributor with the teeth on the oil pump... I'm confused and really need my truck. Any help would be much appreciated.

 

Chevys have a horizontel pin in the distrbuter shaft that alighnes the gear from the distrbtor to the oil pump shaft.
Being 180 out of time is what I would guess. In a 4 stroke you will have a compression, and an exhaust stroke Sorry for the spelling

 

At this point I would say to remove no. one sparking plug.Turn engine over by hand with Your`s or someone elses finger in the spark plug hole until You feel compression building then align the mark on the balancer with theTDC timing mark then take a look and see where the rotor is pointing.
If it has been messed with enough it could be about anywheres.
Does the engine act like it wants to start,does it pop and backfire or does it just crank and crank and not do anything at all ??? It could be possible that one set or the other of the distributor wires might be unplugged or partially unplugged.
On second thought,have You had the engine started and running since replacing the manifolds ????
even an after market repair manual is a GREAT help in these circumstances.