i got a 07 2.7 dodger charger and the timming chain came off and i am replacing the with the water pump. do i need to change the head gasket to or no

Depends on mileage and if any damage was done to the valves when chain came off. If it was my car, I would rebuild the heads as well

it got 155 miles

Yes, do the heads now otherwise you'll end up doing this all over again very soon

the car crank but wont stay on.i don't no wats wrong with it. do you thing the chain came off

No, if the chain came off, it would't run at all. Check for check engine codes.

Does car run and won't stay on or it won't run at all?

you will hear the noise that it want to crank but it wont say on. I don't no what is wrong with it. I need help

If it doesn't run and you suspect its the chain, do a compression test

it is not running. I just need it to crank.is like you will hear the crank it want to start but it will not stay on

Ok, yeah that sounds like timing issue and it can be caused by a bad timing chain. Do a compression test to verify

how do you do compression

You go to your local auto parts store and buy or rent a compression tool. Remove spark plugs and thread compression tool in the spark plug hole, 1 at a time, crank engine for 5 seconds and see what pressure reads on each cylinder