Grimeca M.C. cover screw removal.

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Torontonian

Torontonian

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Grimeca M.C. cover screw (one of 2) is siezed in tight from rust. The first one of the 2 unscrewed fine but rusty. The second (Philips head scew, very small ) is buggered from my attempt , screwdriver slip damage. Need to get this one out to add brake fluid. Ideas ? If I heat this cap screw area it might melt the bellows under the cover. What size are they too as they will need replacement. So tiny.
 
First measure the diameter of the screw you managed to remove. Also determine it's thread pitch. Use a pilot drill bit with a diameter smaller than the un-threaded shank of the screw, so that you don't damage the female threads in the master cylinder body. Drill down about 75% of the length of the screw. The damaged Phillips head of the screw should act as a "center punch mark" to locate the drill bit in the center. Better to do this on a drill press, but it can be done by hand if you use due care. Next, select a drill bit the same size as the diameter of the screw, just below the head. Drill down the depth of the screw head. This should remove the head of the screw and allow removal of the cover. You can try to remove the shaft of the screw if any protrudes above the surface. However, if you fail, you might ruin your chance to repair the master cylinder. I'm assuming the master cylinder is made of aluminum. That means that the steel screw has seized via galvanic corrosion into the aluminum. If the shank won't remove easily with an Eze Out, obtain a HeliCoil repair kit for that screw size. Drill out the seized screw and install a HeliCoil thread repair insert following the directions in the kit. If you are unfamiliar with this process, watch the YouTube video linked below.

Repairing damaged threads using HeliCoil Inserts

To prevent aluminum chips from the drilling and tapping operations entering the fluid reservoir, first drain out the brake fluid. Next, fill the chamber with shaving cream. The chips will rest on top of the shaving cream. When done drilling and tapping, use your shop vacuum to suck up the shaving cream and metal. Clean up any left over shaving cream.

Almost forgot, once repaired, apply anti seize compound to the screw threads. Anti Seize should be used on most screws and bolts which thread into aluminum.
 
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Reverse drill bits ? Never heard of such thingys but I'm a willing to try , if I can find.
 
Carefully drill the center of the head of off the screw until the head separates.
A small center drill might help: they provide more rigidity.
As you drill, you may need to move your hole to center. There are techniques to do this.
Once the head of the screw is removed, the cover should come off. It should give you a small bite on the top of the screw.
Putting the master cylinder in a drill press vise will help.
Unless you are really good with a portable drill. And you are feeling lucky.
If you have no jam, use a tiny carbide burr in a dremel to remove the head of the screw.
 
any progress? have you dripped a little penetration oil around the head of the screw? do you recall if the underside of the cover is flat or does it have a ridge?, have you tried wiggling the cover and using the cover as a bit of a lever to wedge and rotate the screw . because they are so small trying to drill will be difficult...
 
Success.
Soaked (2 drops) the offending tiny screw for 2 days in 3 in One oil.
Seeing as it was a Philips head screw that was buggered , centralization for a titanium drill bit was easy. More drops of oil for each of 3 drillings straight downwards and slow drilling ( and metal bits wiping away ). Once I figured the screw head was mostly eliminated as the cover cap retention factor I noticed the cover cap was moving ever so slightly. Then prised up using finger pressure only the thin remains of the tiny screw head went flying and the cover was off. Needle nose pliers removed the protruding screw stub.
I noticed a design flaw with the rectangular little cover. On the inside where the 2 screw holes exist there have been 2 tiny slot cuts machined into it that exit to the atmosphere. This lets IN moisture or water ( which is why we had to do this operation ) instead of why it was likely designed the other way , to let OUT any moisture. The top rubber bellows had moisture drops on top of it.
And now to find 2 new Metric screws using a dab of anti-sieze to them.
 
Torontonian said:
Success.
Soaked (2 drops) the offending tiny screw for 2 days in 3 in One oil.
Seeing as it was a Philips head screw that was buggered , centralization for a titanium drill bit was easy. More drops of oil for each of 3 drillings straight downwards and slow drilling ( and metal bits wiping away ). Once I figured the screw head was mostly eliminated as the cover cap retention factor I noticed the cover cap was moving ever so slightly. Then prised up using finger pressure only the thin remains of the tiny screw head went flying and the cover was off. Needle nose pliers removed the protruding screw stub.
I noticed a design flaw with the rectangular little cover. On the inside where the 2 screw holes exist there have been 2 tiny slot cuts machined into it that exit to the atmosphere. This lets IN moisture or water ( which is why we had to do this operation ) instead of why it was likely designed the other way , to let OUT any moisture. The top rubber bellows had moisture drops on top of it.
And now to find 2 new Metric screws using a dab of anti-sieze to them.
Click to expand...
Found 2 new Phillips screws in fine thread metric in stainless. Installed with anti- sieze dabs. I'm concerned about the cut slots in the cover that allows moisture to travel inwards to both screws then enter the top of the rubber bellows seal. After doing the siezure damage to the steel on aluminum body first of course. Good to go.
 
Just read this thread, although I'm late to the party, sometimes it's possible to make a Phillips into a straight slot and thereby getting another chance at getting the screw undone with a screw driver.
 
I'm assuming that those two slots vent the top of the bellows to atmosphere.
In the event that there are no other vents don't block them up.
Doing so will impede the flow of brake fluid that compensates for pad wear.

If you can find them, then stainless Allen screws will make life easier in the future.
 
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