Hardness for idler shaft

[inline6]

what sort of hardness should i be targeting for an automotive idler shaft? its the idler for the timing belt. i'm interested in the hardness of the face for the oil lip seal and journal for the bearings? the material is EN26 with harness 32HRC is this ok for the seal face and for a typical journal bearing? i can get it heat treated / nitrided but maybe this is over kill?

 

[Tmoose]

The seal folks have some pretty specific recommendations regarding hardness and surface finish, and how to achieve it ( plunge grinding).

You mention journal bearing. So this "idler" is in the crankcase, oil lubricated along with crank, cam, etc?
If the idler shaft size and material is otherwise very adequate for any applied loads, I'd consider the recommendations here -

http://www.mahle-aftermarket.com/media/local-media-north-america/pdfs/eb-40-14.pdf

Journal and housing tolerances near the very end. page 177

Importance of directional polishing around page 20.

Some pictures of what can go wrong starting around page 6

 

[inline6]

yeah its in crankcase, i know about grinding direction and need for no swirl/lead and finish Ra etc. SKF say 30 HRC minimum and the material meets this only just but does this mean the life will be noticeaby reduced compared to say 50HRC? cant find any info on the bearing journal hardness

 

[CoryPad]

Bearing journals usually are around 60 HRC for surface hardness, which usually helps with durability and efficiency (linked with low surface roughness).

 

[tbuelna]

Modern elastomer radial shaft seals are quite durable. However, one way they can fail is when abrasive grit/debris becomes trapped between the elastomer seal lip and the shaft surface. The debris becomes embedded in the soft lip and causes no harm to it, but the debris also slowly abrades a groove in the shaft surface which eventually produces an oil leak.

 

[Tmoose]

I think many hydrodynamically lubricated camshaft and even crankshaft journals are way softer than HRC 60 and give 100s of kmiles of service.

Maybe designing in a SpeediSleeve for the seal would be justified.

 

[CoryPad]

Rolling element bearings have contact between two hard metals, so 60 HRC is common. Crankshaft journals ride on softer plain bearings, so they usually are lower hardness. For induction hardened crankshafts, hardness is around 55 HRC.