Tank you Two Tired for the high E string suggestion. This still doen't answer the question of the reprecussions of drilling the hole larger. Would it be detrimental to the performance of the baking system?
The raw physics says yes. But, I don't know how to exactly quantify it.
The hole releases pressure, air bubbles while the master piston and its rubber seal is retracted. Once the master piston moves past the relief hole it is no longer a factor. But, in that short period of travel, a larger hole will allow more fluid to escape, and allow more lever travel to achieve the same pressure as compared to a smaller hole. I can imagine the speed of the piston would have a relational effect.
Secondly, the lip of the piston seal has to traverse the hole. There is the opportunity that the edge of the hole becomes abrasive, especially since pressure in building in the system. This will tend to force bits of rubber into it as you are pushing it past the opening. A wider opening provides less support for the passing seal, allowing it to ingress the hole more than originally designed. The seal may wear faster leading to more frequent seal replacement requirements.
Third, if you have done much drilling in metal, you will learn the exit holes often have flash poking out proud of the hole. Many metal cutting tools don't cleanly remove metal, particularly twist drills. They can push and deform metal at both the entrance and exit of the hole. It is common machining practice to chamfer or de-burr both the entrance and exit points. If left behind, these jagged, sharp edges will certainly nick or slice the soft rubber forced across them.
There is fairly easy access to the reservoir side for a deburr operation. However, the piston bore end of the hole it not so easy. Instead of a chamfer bit, more likely a hone of the piston bore would be needed to ensure hanging metal chips weren't left proud at the drilled bore.
I can't think of any benefit for making the relief hole bigger.
Cheers,
