What would cause an oil pump to melt?

[Adamam]

I thought I'd finished fixing up my new/old Dolmar 100, but it wasn't pumping oil, so I took off the clutch/sprocket to look at the plastic oil pump, and it is completely fubar.

 

What would have caused this to happen?

 

I think there's a shim/washer missing from between the sprocket and the metal pump cover (the sheet of metal between the sprocket and the main chainsaw casing), but would the lack of a single shim cause that amount of heat? It's not a proper bearing or anything, just a metal shim.

 

I have a nasty feeling that the previous owner used motor oil instead of chain oil (it stinks) but I don't see how that would cause the melting. Anyway it looks like it melted from external heat...

 

Edited April 14, 2012 by Adamam

[David Goss]

Can't see a difference in oil being to blame. Must be something else like maybe dolmar!

[pleasant]

If you re-read your original post, I think you will see you have actually answered it yourself.