Small Engines (Lawn Mowers, etc.): timeing on2 cyl b&s 20 hp, hp model, valve clearance

Question
QUESTION: I have a 20 hp model 461707 type 0145  that iam having a problem getting in time i set the marks on the cam and the crankshaft to line up after i got it back together it will not run i have 75 lbs compreshion  on both cyls good spark and fuel but i do get a back fire thru carb at times what have i done wrong?

ANSWER: Hello Merril:

Did you have the Pistons Out of the Cylinders? Ignore the Backfire for Now if You Are Sure you Matched the Timing Marks. Were the Valves Reseated? Was the Valve Clearance Checked? What was the Reason the Oil Pan was Removed and the Engine Re-Timed, Please? Thanks.

Respectfully

John

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

QUESTION: one piston removed to replace broken rod, pan was removed to repair a crack due to former owner trying to asemble with hammer. valves not reseated they looked fine only rod broken.what position should the pistons be in could i have somethig 180 out?this is l head motor canyou ajust valves?

Answer
Hello Again Merrill:

Anytime a Piston is Removed from a Cylinder (Weither or Not the Rings are Replaced) the Cylinder Should be Deglazed. When the Piston is Removed the Rings Become Unseated from the Cylinder. You May have Gotten Lucky in this Aspect Due to the Fact you have 75psi Compression. Try this: Remove the Spark Plugs and Pour a Small Amount of Engine Oil (2oz)Into the Cylinder and Try to Start the Engine. The Oil Added to the Cylinder Direct will Cause Smoke, but it Helps Increase the Compression and Will Assist the Engine to Start if the Problem is the Rings. If the Engine Starts, Allow it to Run for a Minimum of 5 Minutes or Longer if you can. The Longer it Runs the Easier it will Start Next Time. As I have Said, If you Matched the Timing Marks, the Timing Should Not be the Cause of the Problem. The Valves are Gapped by Checking the Valve Clearance and then Removing the Valve and Carefully Grinding the Valve Stem until the Proper Clearance is Obtained. Then Replace the Valve Spring and Keepers. Remember to Set the Cylinder that you are Checking the Valve Clearance on to TDC when Checking the Clearance. Did you Check the Flywheel Key for Damage? Was the Flywheel Removed from the Engine or was Just the Oil Pan and Heads Removed. If the Flywheel Key Was Not Replaced, then Check it First. Usually when a Connecting Rod Breaks, the Flywheel Key is Damaged. A Damaged Flywheel Key will Cause the Plugs to Fire Out of Time with the Pistons Location in the Cylinder During Compression Stroke. The Cam and Crankshaft Marks Time the Piston and Valves. The Flywheel Key Times the Plug Firing. Hope this Helps. I am Here if You Require More Assistance. Let me Know What Happens, Please. Thanks.

Good Luck

Respectfully

John