flywheel key

Joined
Dec 2, 2012
Messages
30
Location
iowa
my briggs quantum is 12 years old with a occassional miss.i was wondering about the flywheel key maybe being partially sheared.this mower has NEVER hit any kind of hard object while running.can the key deteriorate with time?is this key a normal maintenance item? if i inspect the key how would you tell if it is faulty? thanks all.
 
Joined
Jun 25, 2014
Messages
2,581
Location
IL
It is not possible to inspect the flywheel key without removing the flywheel from the crankshaft and sometimes it is very difficult to remove the flywheel. On many engines the keyways can be seen after removing the flywheel nut or bolt. To get a good indication of the condition of the flywheel key, position the piston at top dead center and note the position of the flywheel magnet in relation to the ignition module. When a key is sheared the ignition timing is usually retarded. A good key timing looks like this:
 
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Joined
Jan 22, 2011
Messages
5,826
Location
Ohio
I always keep a couple on hand. If it is totally sheared, you will be able to see it once the nut is removed. Why not just pop the flywheel loose, they often get distorted over time. You do not have to hit something for this to happen over time. I have had several partially shear and the engine had a miss.
 
Joined
Apr 5, 2015
Messages
2
Location
Ohio
You have been given good info on the key by the previous replies. If the key is compromised the problem would be constant and not an occasional miss. What is putting it back in time after it has moved out of proper timing? Most likely it is Non-Mechanical: I would look for corrosion on connections and magnet/magneto surfaces. Given the age, over a 50% chance the issue is related to a bad plug wire - insulation degrading. A cracked spark plug will give the occasional miss. Given the age it could be carbon build up creating hot spot(s) or a number of things.
 
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