Egg shaped cam lobe

[ToothbrushMan]

Have a FIAT Punto with the old Lampredi 8v OHC motor and pulled the rocker cover off to check the clearances and noticed on lobe 1 exhaust and lobe 6 inlet the lobes have worn into a sort of egg shape. The point being less of a half moon as new and more of an actual edge or poi t line. The other 6 have no signs of wear with the opening and closing ramps still being pretty much flat.
Wgats causing the unusual wear on the other 2 lobes?
Thinking as its the old shim and bucket type that the shims under those 2 libes were perhaps already work into a concave shape ?
Tried finding some suggestions on the Guy Croft site but drew a blank. The valve clearances all checked out fine.

[Tyrell Corp]

A picture tells a thousand words here, normally most of the wear on a cam is on the opening flank and acceleration ramps.


My guess is skipped services, with a couple of clearances way out for a long time, or maybe even a factory manufacturing defect that took a long time to show up

Looking at the shim sizes gives an indication of wear, if you have
two are much thinner than the others then they have the most valvetrain wear and cylinder head valve seat recession. In extreme cases the minimum thickness shim still won't allow for correct valve clearance.


If you ever get a file or grinder on a scrap cam you realise just how tough the hardened steel is-also the bucket and shims are hardened (why grinding down shims not recommended-as it goes through the case hardening) So once you have worn through the case hardening the metal underneath will wear out super fast.

Does it sound rough? maybe very slightly bent or sticky valves from a previous cambelt failure?

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Edited by Tyrell Corp on Wednesday 26th July 06:42