I'd say that 99.9% of the time, it takes a catastrophic event, absolute neglect or a purposeful malicious act to cause most OPE engines of any reasonable quality to fail. Even modest care with mediocre lubricants is sufficient to keep the great preponderance of OPE engines running longer than the machines they're mounted on.
The worst engine I've worked on was a B&S L-head on a Toro lawnmower. It was running on two or three oz. of black grease. It smoked something awful but ran nonetheless. I put fresh oil in it and it didn't make any difference. Still ran and still smoked. It was slightly mechanically quieter but that was due to oil taking up space in the otherwise almost empty crank case.
The worst engine I've worked on was a B&S L-head on a Toro lawnmower. It was running on two or three oz. of black grease. It smoked something awful but ran nonetheless. I put fresh oil in it and it didn't make any difference. Still ran and still smoked. It was slightly mechanically quieter but that was due to oil taking up space in the otherwise almost empty crank case.
