Originally Posted by
houston
Ive seen it a hundred times over smelly , rich lsn especially , that is 99% of the time the cause of front bearings seal being compromised and letting dirt get sucked back as pressures change in the crankcase
Well it does sound plausible, I have an engine where the bearings are "past it" by some slight margin, and I noticed the entire front of the seal was all covered in a thick layer of sand, so it had been sucking dust in there.
Similarly I have a healthy engine which had a small oil drip in the front there after storage, and when I took that flywheel off it was completely clean on the seal.
So the sucking in dirt bit clearly happens.