www.brantly.info

http://www.avweb.com/news/maint/182849-1.html

note # 7 especially the exhaust valve comments

i have been leaning engine on ground prior to lift off

fuel consumption went from 14 gal to 10 gal per hour on training flights

exhaust valves are the weakest link in this engine, can get very expensive

had conversation with lycoming, they concur.

Try this site it will tell you that this is a reocuring problem with Lycoming
http://www.prime-mover.org/Engines/Marvel/tbo3.html
Read it and weep the customer pays.