Small Engines (Lawn Mowers, etc.): wheel horse mower, best case scenario, compression stroke
Question-------------------------
Followup To
Question -
i have a 1991 wheel horse 312-8 with a 12hp kolher engine. it was running fine and then the engine slowed then stopped. i pulled sparkplug it was dry. i had tried to choke but didnt start. also there is compresion coming from sparkplug hole but when i replace it i don't have compresion from exchaust pipe
Answer -
when you pull the starter cord while the plug is in does it pull very easy like there is no compression in the cylinder? Or pull off the filter, is the compression coming out of the carb instead? elec. start,spins easy, no compresion from carb except from small tube going in to breather. i must have dropped an exchaust valve. how do i get to it? do i need to remove head?
Answer Air from the breather tube is normal at this point. The next step is to remove the head and inspect the cylinder and valves. Best case scenario is that the intake valve got stuck open due to varnish/gum build up.
Remove the head. The intake valve is usually the bigger of the two. Spin the engine to see if it is opening and closing propperly. If the valves are moving freely then its time to check the valve seats. Bring the piston to top dead center where both valves are closed on the compression stroke. Continue to turn the engine in the same direction as it runs until the piston starts to sink about an eighth of an inch. At this point there is no presure on the valve stems inside the engine and the valves should be fully seated into the block. Press your thumb against the valve head and try to turn it. If it spins then the valve is not sealing propperly. Check both the intake and exhuast valve like this. Next step is to inspect the cylinder wall. turn the engine until the piston is fully sunk into the block. Rub your finger inside the cylinder to get some oil on it. then rub your fingers together does the oil feel gritty. dry out the oil from the cylinder wall and off your finger and feel the inside of the cylinder. It should be smoothe. If you feel some scratches then see if you can catch a fingernail in them. If you can catch a finger nail in a scratch then the cylinder may be the cause, but your explanation of the problem dosent make me think this is the case. let me know what you find.
And to answer your question how to get to the valves there is a valve spring cover plate behind the exhaust pipe. to service the valves you will need a valve spring compressor. to fix the valve seats or replace the valve(s) you will also need a lapping tool some grinding paste, a feeler gauge with .005 to .015 measurements and possibly a bench grinder
