ORIGINAL: Ram Jet
Your point is wll taken in the case of my new Enya SS.40BB 2 cycle with merely a shielded front main bearing. It's hard for me to understand why there isn't crankcase leakage. I'll know more when I diasseble it.
Bill
2 stroke Glo engines get by with only shielded front bearings because of very tight clearances between the crankshaft and the front crankcase. Some of lesser quality do leak from the front bearing area causing a constant fuel spray and idle problems due to leakage. Its more common than you might think. Gassers are larger engines and depend more on the bearing seals to prevent crankcase leakage. Many gassers do not have a tight crankshaft to crankcase fit so the only seal can come from the bearing or external seal. I have never measured it but I would guess that larger engines have greater intermal pressures making seals even more important. Other than the front seal, I really have no opinion regarding completely sealed bearings in gassers. Seems like more are being used these days though. MVVS / Evolution even has a grease zert near the front bearing on a few of their newer engines.