There are two sets of spark plugs for each piston, there are dual magnetos that create spark for each set of plugs this is a redundant system to increase safety. If one of the magneto is not working properly when you do your mag check the plane is not considered safe to fly, performance will be decreased and the redundancy of the system is gone.
You have to disassemble the entire engine, remove the piston and check the rubber ring around that piston.
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by compression test
The only way to "check" a piston would be to remove it and visually inspect for damage and wear.Make certain that the piston is not cracked or otherwise damaged.check the ring grooves. Use a piston ring and a set of feeler gauges to determine the amount of wear. Excessive ring groove wear can result in piston failure and if the piston shatters, it can cause the engine to fail completely.Next, use a micrometer to determine the difference in the diameter of the piston between the top and bottom. The piston will wear and if the difference between the top and bottom is too great, the engine will exhibit "piston slap".Check the fit of the wrist pin, it should be tight.HOWEVERYou can run a compression test and get a good idea whether the piston is functioning somewhat correctly.
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Bad spark plug?Bad plug wire?Bad valve?*Bad piston?* Do a compression check to check engine internal condition
i adjusted tappet on cat engines by turning the engine first piston no.1 in TDC and check all (intake/exhaust) valves in close position,or follow maintenance guide book ,then check again when piston no.1 on exhaust stroke the same procedure be taken. or do it by turning the engine till the individual piston on TDC as perengine firing order and adjust both valves
make sure everything works as it should. ignition timing correct. pressure test engine to check for worn rings / piston barrel. for two strokes, check crank seals for leakage.
A 305 chevy engine has a bore diameter of 3.736". Check the diameter of your L2256 piston to see if it is that size.
Sounds like you may have a serious internal engine problem i.e. bad valve or blown piston. Do a compression check to try to determine which cylinder(s) are involved and whether problem is with a valve, piston, or head gasket.
Remove from engine and use an ohm meter on the ends
You'll need a special fixture and a press. Check with a local engine builder to see if they will do it for you.