Expert: John C. Bridgers Sr. - 7/5/2007

Question
QUESTION: I have a 2003 Cub Cadet with the 18.5 ELS500 single cylinder OHV engine. It has 166hrs on the motor/mower. Engine#310777 030SE1 031023ZE.
It developed a knock that would come and go. Today I was trying to see if something external was loose while running and it backfired and died. It will not start now and backfires out of the exhaust and carb, motor spins faster than it did before.
Ideas will be very helpful!
Thanks, Dennis

ANSWER: Hello Dennis:

Remove the Valve Cover and Check the Valve Clearance. The OEM Suggests .004in on Both the Intake and Exhaust. I Use .004in for the Intake and .009in for the Exhaust. Make Sure the Valve Keepers are Still Locked to the Valve Stem. If the Valves Look Good and Seem to be Operating Properly, then Remove the Flywheel and Check the Flywheel Key for Damage (Sheared Most Likely). The Knock May have Been the Fkywheel Loose or the Connecting May have Broken. What is the Cylinder Compression? Also, the Internal Counter Balance Weight May have Loosened and is Causing the Problem. You can View a Breakdown/IPL of this Engine at this Site Addy, http://www.smallenginepartswarehouse.com/parts.asp and Select the Shop Online Parts Look Up. Then Select the Model Tab. Then Select the OEM and Enter the Model Numbers. Then Double Click on the Model in the Results Area. Now you can Select the Section of the Engine you Wish to View. Hope this Helps. I am Here if You Require More Assistance. Let me Know What Happens, Please. Thanks.

Good Luck

Respectfully

John

PS: I am Allowed to Answer 10 Questions a Day. If you See I am Maxxed Out, then Try Submitting you Question at or Just After 9pm EST (US). My New Day Starts then. Thanks.

Respectfully

John

---------- FOLLOW-UP ----------

QUESTION: John,
Thanks. I did the valve clearance, found the intake to be around .015 and exhaust the same. I reset them to your recomendations and still had the knock.
I then checked the flywheel key and it was fine.
I then pulled the head and found the piston and head were beat up by metal. It was worse in the spark plug area. There were also (I call them) drops of melted aluminum atop the head and piston. The rod was also tight with no wear.
My question is, what would cause this to happen? spark plug to hot?

Reguards,
Dennis

Answer
Hell Again Dennis:

The Metal that Beat the Head and Piston Had to Come from Somewhere. Usually the Screws in the Throttle Control Valve come Out and Cause this Kind of Damage to the Piston and Head or a Compression Ring Breaks and the Piece of Ring Enters the Cylinder and Does the Damage. Locate Where the Metal came From. Is the Melted Aluminum Setting on Top of the Piston or is it a Sunken Place in the Piston that Looks Like the Piston Top was Melting? If the Piston Top Looks Melted, then the Plug is Way to Hot. Or you are Using too Much Octane Booster (Usually a Racing Engine Problem). If the Aluminum can be Chipped Off and the Piston Looks Good, then Most Likely the Aluminum is from the Metal that Did the Piston and Head Damage. Hope this Helps. I am Here if You Require More Assistance. Let me Know What Happens, Please. Thanks.

Good Luck

Respectfully

John