My last 6 O-200 have failed to reach TBO all with centre main bearing failure. They fly on average around 450 hours a year. All fitted to C150’s all with Macauley props. Basically the oil pressure drops in the cruise and when hot at idle the oil pressure is next to non existent, In one aircraft the main bearing failed failed at 1800 hours. Overhauled with new crank, new crankcase, new cam, all new cylinders. Main bearing failed again at 1200 hours. Rebuilt new crank, new crankcase, new cam, all new cylinders. The main bearing again failed again at 1200 hours and again it needed a new crank, crankcase and 4 new cylinders. Since the last rebuild it has done 200 hours and so far without incident. Another aircraft had a cheap overhaul done by its previous owner in 2001 and it went all the way to TBO. Good quality rebuild with reground crank and original crankcase. New cam and cylinders. Main bearing failed at 1400. Since replaced with a factory rebuilt engine. I brought another C150 with a factory rebuilt engine the main bearing failed on this after 1400 hours. Currently being rebuilt. Finally my other C150 is showing the same oil pressure signs and I’ll be discussing it with my maintenance provider today. Its done 700 hours on a new crank, new crankcase and new cylinders. I should add I have always used well regarded engine shops. About two years ago we changed from aeroshell mono-grade to 15-50W to see if that has made any difference. We always used a good engine shop, but we then changed to what most people would say is the best engine shop around (certainly the most expensive). We even tried the factory built route. Finally we have used a well respected local shop. But all seem to have given the same results. We started fitting them with spin on oil filters again it doesn’t appear to have made any difference. The next suggestion we are going to work on is getting all the props dynamically balanced. However I am starting to think its simply the quality of the parts that are being supplied? Does anyone else have any thoughts? I should add I’ve operated C150’s for many a year but never without the problems we are now having.