What was found
INSTALLED NEW ACORN WELDING LTD. EXHAUST STACKS AND MUFFLER ON FACTORY NEW IO-550D ENGINE. BOTH EXHAUST STACKS CRACKED WITHIN 60 HOURS; REPLACED BOTH STACKS WITH NEW ACORN STACKS; ONE OF THE NEW STACKS CRACKED (1" HOLE) WITHIN 30 HOURS. REMOVED FROM AIRCRAFT. I HAVE HEARD OF 10 OTHER INSTANCES OF ACORN EXHAUST STACKS CRACKING; ONE WITHIN 10 HOURS OF INSTALL ON A NEW ENGINE. THIS IS A POTENTIALLY VERY DANGEROUS FAILURE. A CRACKED EXHAUST CAN CAUSE CARBON MONOXIDE IN THE CABIN, OR A FIRE IN THE ENGINE COMPARTMENT. PLEASE INVESTIGATE.