Before I would drill the head I would try an impact driver. Even though the head is stripped sometimes a good whack with the impact driver will dig in enough to break it loose.

If that doesn't get it then drill the head out CAREFULLY then simply back the headless shank out with vice grips.

The impact driver worked for me....and replaced with allen heads and never sieze..

 

if it isn't stripped to bad, put some valve grinding compound or similer on the bit..
or some sandpaper "droppings"
it gives some extra grip, if no joy follow everyone elses suggestions above..
next for me would be making into a straight slot

 

Rule number #1....never drain fluids til the cover is of. Rule #2...make sure your using a T-27.

 

If the threads are bad and you use a drill, the screw may just spin. You can use a cut off wheel and just kind of wash the head off. If you are careful, this works when a drill won't.

 

I would start by inserting the next 2 closest screws and torque a tad to relieve some of the cover pressure from the damaged bolt ..then take whatever course you choose to remove it ...and as stated earlier ...usually 27 get stripped because a 25 was thought to be the right size ..

 

Best answer. Quick and simple.

 

Go to the hardware store and ask them to sell you an Easy Out. You drill a small pilot hole through the head into the screw, insert the easy out, then back it out.

Here's how they work: http://www.youtube.com/watch?v=uhuwyGYd75g Take one of the good screws with you so that you get the right size.

 

Try impact wrench it worked on mine and replaced with chrome allen heads from ACE hardware.

 

totally agree. i got snagged by #1. Had the right torx though...

 

Thanks everyone for the tips & tricks. This one sure was a PITA.

I dremmeled a slot for a screwdriver but it would't budge. Even after cranking on it with channel locks on the screwdriver. I eventually stripped the slot i cut.

I went to the 1/4: wood chisel and it wound up working. I think the impact "cracked" it loose.

All in all i managed to freak out and break something out of frustration, so its a plus.

Got SS allen screws to replace them.

Thanks all!