On a focal plane shutter, such as the Spotmatic's, the two curtains travel at a constant speed. The "shutter speed", or exposure time, is really a function of the difference in starting times of the two curtains.
On the Spotmatic, speeds or 1/60 second or longer, the first curtain fully opens before the trailing curtain begins to close. At speeds of 1/125 and higher, the trailing curtain begins to close BEFORE the leading curtain is fully open. Just as an aside, this is why you can't use electronic flash at speeds higher than 1/60 on a Spotmatic.
The higher the speed, the less the time between the beginning of the opening of the leading curtain and the beginning of the closing of the trailing curtain. This results in a moving slit that traverses the film plane. At 1/125, this slit is almost the full frame. At 1/1000, it is 1/8 inch or less. In all cases, the speed of the curtain movement is the same.
Because of this variable-width slit, any given spot on the film is exposed for only the time specified by the nominal shutter speed. It may take 1/60 second for the shutter to complete its travel, but each point on the film received only 1/1000 second of exposure.
If you decide that this adjustment is beyond your abilities, or if you just don't want to risk screwing it up, there's a guy in Tennessee named Eric Hendrickson, who is THE goto guy for Pentax film camera repair. He is a former repair tech for Pentax who now does repairs in his home. His website is
http://www.pentaxs.com/. Everyone who has ever had him work on their cameras reports that he does quality work at a fair price.