Caliper piston seal

I've finally been able to remove the inner brake caliper piston from my 1974 Roadster. I'm pretty sure the inner piston hasn't been touched since it was installed in the factory. After trying nearly everything suggested on this site, which was tremendously helpful, I had to drill a hole in the bottom of the piston (the piston was a write-off in any event), heat the caliper body, drop ice cubes in the piston cup and then use a screw extractor in the drilled hole to get the piston to move. After applying considerable torque and colourful language, success. Once the piston finally broke free, it came out fairly easily. The caliper body cleaned up nicely. My question relates to the caliper piston seals. One of the old seals has a slight bevel on its edge. The other seal doesn't. I didn't notice when removing them which seal was the inner and which was the outer nor which way the bevel faced. Does the bevelled seal go in the outer bore or in the inner bore, and does the wider part of the seal face inwards towards the disc or outwards, away from the disc towards the back of the piston? Or does it even matter which way the seal goes?

I don't think there are bevels on new replacement seals. It could be your old one was just worn and set to look like it was an intended bevel.

Here's a good how to article on the Norton caliper rebuild:

https://www.motorcycleclassics.com/...ir/rebuild-norton-commando-disc-brake-caliper

WEM said:

One of the old seals has a slight bevel on its edge. The other seal doesn't. I didn't notice when removing them which seal was the inner and which was the outer nor which way the bevel faced. Does the bevelled seal go in the outer bore or in the inner bore, and does the wider part of the seal face inwards towards the disc or outwards, away from the disc towards the back of the piston?

Click to expand...

Assuming you are not actually intending to reuse the old seals? You should find new seals are 'square' section.

The grooves, however, are not square which is why the seals wear unevenly.

Thanks for the info. New seal kit is on order. Just out of curiosity, if the seals are square edged, why are the grooves not also square? Is there some engineering rationale?

It's to pull the piston back into the caliper after pressure is released and so give clearance for the pads to the disc. If the pistons did not pull back the pads would continue to touch the disc and heat would build up.