Scion xD Head Gasket replacement?
 

Is it possible to replace the head gasket without pulling the engine ?

Can I pull the engine without a lift?.

Can I replace the timing chain without pulling the engine?

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I'd bet that it's 200% easier with the engine out. You should also check the timing chain while it's out, and check the idler pulleys as well. Since you're gonna have to pull the chain...

I replaced the water pump without pulling the motor, so i suspect you can do the timing chain too. May have to unbolt top engine mount on passenger side and jack the engine up some, which is what the water pump required. it's not fun, but def do-able.