Had an older fella come into the shop last week who after a little discussion turned out to be a mechanic who worked on B-29s.
I asked him about 29 engines being prone to fires, he said he had never seen that.
The only fire he remembers was on a 29 that was set up as a refueling plane.
From
http://www.pbs.org/wgbh/amex/flygirls/sfeature/waspsb29.html:
"The B-29 was not only much larger and heavier than any bomber the U.S. had flown before, it also hadn't gone through the years of operational testing to which Boeing had subjected its predecessor the B-17. Initially engine fires were one of the major problems. The planes' Wright engines were often called the Wrong engines. Part of the trouble could be traced to the engine cowlings that were too tight and often caused fires even before the planes had taken off. Although engine improvements were made over time, fires remained a problem throughout World War II."
And from
http://www.skytamer.com/Boeing_B-29.html:
"The most common cause of maintenance headaches and catastrophic failures was the engine. Though the Wright R-3350 would later become a trustworthy workhorse in large piston-engined aircraft, early models were beset with dangerous reliability problems, many caused by demands that the B-29 be put in operation as soon as possible. It had an impressive power-to-weight ratio, but this came at a heavy cost to durability. Worse, the cowling Boeing designed for the engine was too close (out of a desire for improved aerodynamics), and the early cowl flaps caused problematic flutter and vibration when open in most of the flight envelope. The 18 radial cylinders, compactly arranged in front and rear rows, overheated because of insufficient flow of cooling air, which in turn caused exhaust valves to unseat."
"These weaknesses combined to make an engine that would overheat regularly at combat weights, particularly during climbs after takeoff. Unseated valves released fuel-air mixtures during engine combustion that acted as a blowtorch against the valve stems. When these burned through the engines disintegrated and caught fire. A fire that was not immediately contained in the forward part of the engine by fire extinguishers became impossible to put out. An accessory housing manufactured of magnesium alloy in the back of the engine would often catch fire and produce heat so intense it burned through the firewall to the main wing spar in no more than 90 seconds, resulting in catastrophic failure of the wing."
