I operate one IO-520 on a Cessna 185 and nine O-470 on Cessna 180 (4)/182 (5)s. All professionally flown for natural resource work in the upper midwest. We rarely get above two thousand feet MSL and spend a lot of time at reduced power settings (15-20 inches,2000-2200 rpm), but when we do cruise we cruise hard (24/2400) to get where we are going. The aircraft are keep in a heated hanger (46 f) and never spend the night outside, they average 600 hours a year.

We are half way thru the third overhaul of the 520 and have yet to change a cylinder between overhauls, we could be just be very lucky, but I am very particular about how it is operated. I personally fly 99% of the hours on the 520 and am religous about cooling the engine for shutdown.

When I was first checked out in the 185, my former boss told me they were famous for warping exhaust valves (then burning them) and the secret was to get them as cool as you could and then to minimize the windmilling at actual shutdown (lowest rpm possible). I actually pull on the throttle when I am closing the mixture. We set idles at 500 rpm and I usually see 450 by pulling on the vernier throttle. They warp because they draft in cold air while windmilling just those few blades at shutdown, particularlly in winter.

Our overhauls are done at Popular Grove airmotive and we have had good luck with them. We did have several of our engines with the bad batch of cylinder, including the IO- 520. I put 395 hours on those cylinder without any problems and they were warrantied (had to come off at 400hrs.)

We did have the cases cracked at the last overhaul of the 520, but at the bases of the middle cylinders. We have a rear mounted belt driven alternator on it.

The O-470s seem to crack more cylinders than have bad valves problems.

Again, we could be very lucky,

Luke