Dealing with a stuck JIS screw

[Stichill]

The brake/clutch fluid is supposed to be bled/replaced every two years. Has that cover ever been off before?

Oh yes. I have speed bleeders and do this once a year.

Went to bleed the brakes on my CBR250R and one of the cover screws wouldn't budge, even using the proper JIS screwdriver. It started to cam out and displace metal in the screw head.

I decided to get a ball-peen hammer and carefully beat the protruding metal back down into the screw head. This made the screwdriver fit very tightly and I was able to break the screw loose by momentarily turning it clockwise and then counter-/anti-clockwise.

This is the screw after I loosened it:


Looks like there's some galvanic corrosion happening between the screw and the cover, so both will be replaced with new + a small amount of anti-seize compound.

This method was less scary than a drill and a tiny back-out, and saved the master cylinder itself from being damaged.

I replaced the phillips screws on my reservoir covers with star-pattern screws I got off ebay. They work a lot better. Tighten easily and remove without stripping. If you are interested I can find the seller on ebay.

Definitely, yes that would be far superior. Thank you!

Good point Joe, and Stitchill i apply a heavy grade grease to the inside of the lids especially in the seams and screws for that reason and wipe the excess off after, there are usually some condensated droplets under the lid, it is exposed to air to allow the membrane to adjust for deminishing fluid level due to brake pad wear.
Also don't over tighten the lids, they deform and create a gap for the fluid to creep out and go to work on the metal bits,
Good work on the jis driver sir, only ones that i have is on my vessel impact driver, had it for ages and with perfect results.
never had any stuck screws in a long time, sometimes you have to " assist "the design by good maintenance, not doubting your skills but having grease in important places ( most bolts ) extends their service life, grease is cheap but messy to work with but paper towels clean fingers very well, still nicely saved screw, could have been a lot worse.
The other overlooked place is under the boot on the back of the piston, if not greased it can create a mess with escaped traces of fluid in the circlip area.

I'm a big user of anti-seize for most bolts that are prone to sticking, which are usually the larger ones that aren't removed often. It's a bit unusual for small screws like this to seize. I think it's the large surface area under the head that forms a bond which can't be overcome by the rather weak JIS crosshead. (Edit: I see that jtopiso agrees.) I saw the ball-peen method of screw rehabilitation on a gunsmithing channel. It's very common for people to use the wrong type or size of slotted screwdriver on gun screws, and end up damaging the screw slots. It would be tempting to file off the displaced metal, but the integrity of the screw is better preserved by lightly tapping the metal back into place with a polished ball-peen hammer.

A countersunk bolt has a lot friction under the head, specially if it hasn't been loosen for a while. A drop of wd-40 on the perimeter would've helped.

Good point. It was a surprise to me that this one was stuck. The other one loosened without incident.