Ok, so I noticed that my timing cover gasket was leaking pretty bad so I need to replace it. I pulled the hoses, the water pump, radiator, fan, etc no problem. Then I get to the harmonic balancer. I have all the bolts out (4 small ones and the main bolt) but can't get the thing off. I'm using the puller on it. I've put an impact on the puller, ive tried good old muscle and a breaker bar.. Nothing. I'm leaving it overnight with the puller on it with pb blaster on it. Any ideas?

Did you look to see if there is a washer in there? Your puller center bolt may be pushing on a washer instead of the crankshaft.

As far as I can tell, there isn't one there

It seems like I remember there being a half moon key on mine. It's been a few years, though, so I may be remembering incorrectly.

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2000 Ford Ranger XLT
Extended Cab
3.0 Flex
4x4
Manual Transmission
Offroad Package

Yea, check for that washer can hang it up.

If original it might have got a little extra love from the assembly guy 'pressing' it on.
Give the threaded bolt on the puller a couple of whacks then a turn then repeat. The balancer might be 'cooked on' from the leaking fluids.

Yes, there is a woodruff/half moon key on the sleeve that lines up...but you are pulling out so that should not hang you up.

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2008 FX4 Ranger. Black/ Black
Undid the full size Mod.
Kept the power rear window
https://m.youtube.com/watch?v=82y5AyI5eEY