The interference on the seal will vary depending on which seal is being put in the groove. I have to assume you aren’t going to make your own seal. So, the seal you buy for a 90mm bore will have the proper interference to seal the hydraulic fluid. You will just need to select a seal that has the proper dimensions to fit your piston as well.

Thanks for asking. We recommend the groove height for a U-cup to be 10% taller than the seal. For example, a .550” groove would be for a .500” tall U-cup. Our nominal dimensions for the diameters will be the recommended metal dimensions. For example, our 25002500-500BLLS is 2.500” x 3.000” x .500” and will be for metal dimensions 2.500” x 3.000” x .550”. There will be clearance at the heel and interference at the lips. The outside diameter at the heel will measure slightly smaller than 3.000”, and the outside diameter at the lips will measure slightly larger than 3.000”. The outside diameter will measure the nominal 3.000” size about half way up, where the U-cup lips start to flare out. Hope this helps.

Allegheny York s

All surfaces should be as smooth as possible for seals to work properly. If the surfaces are rough or uneven there will be leakage and your cylinder will not work efficiently.

We do have a calculator "Piston Seal Groove Measurement" on our website. Hope this helps. www.alleghenyyork.com/wps/portal/c/Customer%20Service/online%20tools