IO 520 BB

The crankcases are designated Phase I, II, and III. The early cases were the more prone to problems. The Phase III are the 7th-stud variety, and also include other features, such as heavier bosses at the backbone. An IO-520-B Phase III is a good case, same as an IO-550-B has.

Cylinders has a lot to do with the care employed during fit and assembly of the valves, as well as pilot technique including proper TO fuel flow.

Buying an used airplane (engine) can come with secrets; although an unexpected engine change is one of the more expensive ones.

A Bonanza that is equal in every respect will be slightly more expensive if it has an IO-550, simply due to the cost of the engine being slightly more.

To my understanding, the largest differences between the B, BA and BB has to do with main bearing size. The 550's share the same size as a 520-BB.

Mike
ABS Tech Advisor

I had an IO520BA that I flew until it had 2200 hours.
My current engine has 1200 hours and has no valve problems.
The key to the valve problems is to keep the cylinder head temperatures at 380 or less. This is easily accomplished with an EGT device and / or the willingness to operate lean of peak fuel flow during cruise and enough fuel during take off and climb.

I would note that I usually installed used engines in my Bonanza. Should this be what you are contemplating, I would recommend that before you install the engine, you have the oil pan removed and the sludge cleaned out. I would also suggest that if the engine you have purchased was not properly preserved for storage, that you have the cylinders removed and IRAN'd.

Tom

Thank you both for the info. and quick response.

Bill G.