STINSON 108 LOST POWER DURING CLIMBOUT AND RETURNED FOR EMER LNDG.

Narrative

I DEPARTED RWY 23 IN MY STINSON 108-2 WITH 1 PAX. MY DEST WAS APPROX 15 MI NE; SO I TURNED L XWIND AND THEN L DOWNWIND ON RWY 23 TO DEPART TO THE NE. I WAS JUST CLRING THE PATTERN AND AT ABOUT 1500 FT AGL WHEN I NOTICED A BLUR CROSS FROM L TO R - LIKELY A SMALL BIRD. IT APPEARED TO FLY RIGHT INTO THE PROP ARC AND I IMMEDIATELY FELT A THUMP IN THE AIRFRAME. THERE WAS NO EVIDENCE OF THE IMPACT IMMEDIATELY; BUT ONLY SECONDS LATER THERE WAS A SEVERE SHUDDER FROM THE ENG AND THERE WAS A SIGNIFICANT LOSS OF PWR. I IMMEDIATELY COMMENCED A L TURN TO POINT BACK TOWARD THE RWY AND LOWERED THE NOSE TO CAPTURE BEST GLIDE. I THEN ANNOUNCED MY SITUATION AND INTENTIONS ON THE CTAF. ONCE I DETERMINED THAT I HAD SUFFICIENT ALT TO MAKE THE RWY I BRIEFLY TROUBLESHOT - MOVING THE THROTTLE BROUGHT ALMOST NO RESPONSE FROM THE ENG; IT CONTINUED TO SHAKE NOTICEABLY SO I LEFT IT AT IDLE. ROLLING OUT ON FINAL I SELECTED THE FIRST NOTCH OF FLAPS AND MAINTAINED MY GLIDE SPD. I MADE SMALL S-TURNS APCHING THE THRESHOLD OF THE RWY TO WORK OFF A SMALL MARGIN OF EXCESS ALT AND THEN SELECTED FULL FLAPS OVER THE NUMBERS. AS I TOUCHED DOWN THE PROP STOPPED TURNING ENTIRELY AND I SAFELY AND UNEVENTFULLY ROLLED OUT TO THE END OF THE RWY. POSTFLT TEARDOWN OF THE ENG REVEALED A FAILED VALVE IN ONE CYLINDER THAT CAUSED THE SUBSEQUENT FAILURE OF THE PISTON IN THAT CYLINDER.