Lower Quality Sample (RHF4)
To the untrained eye, initial impressions are that they look ok, however looking at the parts in more detail:
- The surface is very pitted – pitting can score the thrust parts and lead to premature failure;
- Badly de-burred;
- The edges are not clean and sharp;
- Often they have an over polished surface (focus is on aesthetics, rather than function);
- No controlled scratches to create surface tension.
Melett Sample (RHF4)
- Clean, sharp edges;
- Machined surface;
- No de-burring – when manufactured correctly this process is not a requirement;
- Performance mirrors the precision of the design;
- Controlled scratches to create surface tension.
When an engine is switched off overnight, if the surface is too smooth the oil will run off. The scratches create a surface to retain the oil and prevent run off, so when starting the engine in the morning there is already some oil present to lubricate the turbo.
OEM Sample (RHF55)
- Clean, sharp edges, similar to the Melett sample;
- Controlled scratches on the surface finish to retain oil.