QuestionQUESTION: I bought this new in Nov. 2003. About 18 months later the mower would backfire when started, shortly after it was shutoff. This only happens when the engine is hot. I have scared quite a few of my neighbors, and myself, and would like to get this corrected. I have changed the air filters recently and it is still occurring. Any ideas of what is happening and how to correct? Also, how do I adjust the drive and blade belts ?
ANSWER: Hello Cory:
1- Try Re-Setting the Valve Clearance and Check for a bent/Sticking Valve when you DO this. I Do Not Use the Setting Called for by the OEMs. I have Found that the Following Works Best. Remove the Valve Cover (on the Dead Cylinder for Twin Cylinder Engines). Set the Cylinder you are Setting the Valves on to Top Dead Center (Both Rocker Arms will have Play in them when the Engine is at TDC) When Setting the Valve Clearance. Now Loosen the Valve Adjuster Locks and Set the Intake Valve Clearance to .004in -.006in and the Exhaust to .008in - .010in. I have had Better Performance Out of the Mowers and Less Burnt Valves Using these Settings. Usually the Backfiring when Starting and Shutting Off is a Sign the Valves Require Adjusting on the OHV Engines. 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 and Type Numbers (31C707-0230). Then Double Click on the Model in the Results Area. Now you can Select the Section of the Engine you Wish to View. 2- The Drive Belt has No Adjustment. 3- The Blade Belt is Adjusted by the Front Deck Supports. Go to this Site Addy, http://www3.sears.com/ and Enter the Model Numbers in the Upper Left Search Box and Click Go. Then Visually Verify the Equipment and Click Continue. From this Page you can View Diagrams or Parts Lists for you Equipment. Select the Lift File and View the Diagram. You want to Adjust the Nuts on Diagram Part #15 to Push the Deck Back Towards the Rear of the Mower. This will Tighten the Blade Belt. Be Careful and Do Not Adjust them too Far. The Deck will Rub the Rear Tires when Lifted or the Blade Engagement Lever will Not Operate Properly if Adjusted too Far. 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 your Question at or Just After 9pm EST (US). My New Day Starts then. Thanks.
Respectfully
John
---------- FOLLOW-UP ----------
QUESTION: Thanks for your prompt and thorough responses. Regarding the backfiring....I adjusted the valves as you suggested though if they were off, it was just a little. This was done when the engine was cold. Fired up and got it warm and still get the random backfire when starting only--never on shut down. I did notice something since I had the cover off. Just before the engine backfires, the starter appears to not have enough juice to turn the motor over. It sort of bumps it--then stops. I cycle the key several times and finally it turns over and starts--but with a LOUD backfire. Any other suggestions on this topic ?
Regarding the drive belt...I did a little more checking as I was testing the valve readjustment. What I noticed is that with the clutch/brake pedal depressed, the lawn more will slowly creep while taking several feet to come to a complete stop. Just a couple of weeks ago the mower would just about stop on a dime. The drive belt appears to hold well as the tires spin when I release the clutch. I am hoping that the transmission is not shot but welcome your expert advice.
ANSWER: Hello Again Cory:
Ok the Valves are Set. That Eliminates them from the Possible Causes and Narrows it Down. For the Backfire, Remove the Flywheel and Check the Flywheel Key. Usually when the Starter is Turning the Engine as you Described, Either the Battery is Low, Battery has a Bad/Weak Cell, the Valves Require Adjusting, the Magnets on the Flywheel have Moved and Require Reattaching to the Flywheel or the Flywheel Key is Damaged. Remove the Blower Housing (metal engine cover). Remove the Flywheel Nut or Starter Cup (Depends on the Model). Now Attach a Steering Wheel Puller to the Flywheel Using the Threaded Holes in the Flywheel. Tighten the Puller. Now Hit the Puller with a Hammer. Repeat this Procedure Until the Flywheel Pops Up or can be Lifted Off the Crankshaft. On Some Models you Can Not Use a Puller and Must Use a Pry Bar and a Pipe Cap that is Slightly Larger than the Crankshaft. Place the Pipe Cap Over the Crankshaft to Protect it. Place the Pry Bar Under the Thick Section of the Flywheel and Pull Up Against the Flywheel. **BE CAREFUL DO NOT PUT A HOLE IN THE BLOCK UNDER THE FLYWHEEL** Now Hit the Pipe Cap that is on the Crankshaft (covered with the Pipe Cap). You can See a Breakdown at the Site Addy I Provided Earlier. For the Belt. You Need to Adjust the Brakes. This Adjustment is Usually on the Side of the Transaxle and Looks Like a Disc Brake Assembly. The Nut in the Center Adjusts the Brake Pads. Tighten the Nut Until the Brakes are Snug, then Reverse 1/4 Turn. Operate the Mower and Make Further Adjustments as Required to Give you the Stopping Power you Require. Hope this Helps. I am Here if You Require More Assistance. Let me Know What Happens, Please. Thanks.
Good Luck
Respectfully
John
---------- FOLLOW-UP ----------
QUESTION: OK,, round three of this saga. I removed the flywheel today to do some checking. All magnets appear to be in evenly spaced and without slipping. it was REALLY dirty so I blew it off with compressed air. So far so ,good...right? Nope, in trying to install the flywhell I sheared the OEM key but not after it ran for several minutes. So off to the auto store. They had some OEM knockoffs(a little less thick in width) and I bought 4. I tried those and all sheared. One of them lasted 10 minutes and varying throttle and when I went to start--sheared the pin. What am I doing wrong ? I have worked on older outboard motors, smaller engines, and never had this issue. Now the OEMs wern't quite the same width as mentioned above, would this make a difference? I installed the keys flush with the crank shaft and then tightened the flywheel bolt with a wrench. I don't have a torque wrench to fit that size bolt, but it took an impact wrench to remove so I assume it was on pretty snug. Now the big question, why am I shearing these keys ? Sometimes they shear as soon as the engine starts. The upsetting part is that the key never sheered until I took the flywheel off and tried to reinstall.
AnswerHi Cory:
The Flywheel Nut is Not Tight Enough. The Flywheel Key is Use to Time the Firing of the Spark Plug, Not to Hold the Flywheel. The FLywheel has to have a Minimum of 100ft lbs of Torque to Hold the Flywheel Properly. If the Flywheel os Too Loose, the Keys will Shear Each Time you Start the Engine. I have Gotten a Few of the Slightly Smaller Keys and have had No Problems Unless the Flywheel is Not Tightened Properly. Hope this Helps. I am Here if You Require More Assistance. Let me Know What Happens, Please. Thanks.
Good Luck
Respectfully
John
