The trick is to compress the seal but not so much that is splits.
I've never heard of a new rubber gasket splitting due to being compressed. Have you witnessed that?
I would have thought that heat and age are the main factors causing a rubber gasket such as this one to split ....
Considering the heat the gasket is subjected to (110 degrees C has been mentioned), rapid decay is to be expected, if a low grade material is used.
O-rings are made of soft rubber and need to be compressed about 30% to form a seal. The present oil pump rubber gasket is made of harder rubber, and I'd expect a compression of about 15% to form a seal. If 7-8% is the final prescribed compression, that's a rather low value. Unless there are sharp edges causing marks, a compression of up to 15% should not cause lasting deformations on a new gasket IMO - provided the rubber quality has been carefully chosen.
Quote:
Compression set testing measures the ability of rubber to return to its original thickness after prolonged compressive stresses at a given temperature and deflection. As a rubber material is compressed over time, it loses its ability to return to its original thickness. This loss of resiliency (memory) may reduce the capability of an elastomeric gasket, seal or cushioning pad to perform over a long period of time. The resulting permanent set that a gasket may take over time may cause a leak. ... Compression set results for a material are expressed as a percentage. The
lower the percentage, the better the material resists permanent deformation under a given deflection and temperature range. Compression set results can be confusing in that they are calculated different ways under different methods of testing.
(Ref. Stockwell Elastomers)
Preferred gasket materials for this application are HNBR and Viton. Both are oil resistant. The former endures service temperatures up to 150 deg. C, while the latter may endure temperatures well above 200 'C.
- Knut