hi,

i have a 97 bayou 300 and am in the process of retiming it and wondered bout it. if it only fires(gives spark) every other time then i could be 360 degrees off. what would it sound like if i tried to start it with it off that much? exhuast valve should be open by my thoughts. well if anybody knows if a bayou's engine fires every rotation or every other please let me know, thanks once again.

john

 

I THINK it fires every revolution (once at the top of the compression stroke, and once ("wasted") at the top of the exhaust stroke.

Reasoning: To fire on alternate rotation, something must turn at the cam speed (half crank speed). The ignition pickup seems to be triggered with every rotation; thus, I conclude the ignition fires each 360 degrees.

From your post, I'm wondering if you have the cam timing right--line up the "T" mark on the alternator rotor with the index mark on the case (Top Dead Center (TDC)), then line up the LF300 mark on the camshaft sprocket with the witness mark on the cylinder head (about 11:00).

Both intake and exhaust valves will be totally closed at this point.

Install the camshaft chain tensioner and check the cam timing; pull the engine through with the starter rope--check to see that the cam sprocket mark again lines up when the crank is at TDC at the top of the compression stroke. If so, button 'er up!

Diogenes

 

Your Bayou has a four-stroke engine that fires every other time the piston reaches near top dead center (TDC). The first half (up) of the non-firing stroke is used to push exhaust gases from the combustion chamber while the second half (down) is used to bring in fuel/air mixture for the next compression/firing stroke.

Two-cycles are engines which fire upon every stroke. The fuel/air mixture must be brought into combustion chamber each time the piston passes through the inlet port on the side of the cylinder wall.

The four-stroke on the other hand makes use of the exhaust/intake stroke to bring the fuel/air mixture through an intake manifold near the top of the cyclinder head.

 

"Not exactly," springdrl!

For simplicity of construction, and secondarily for emission control, many modern four-stroke gasoline engines, with inductive spark-triggering circuitry, fire EVERY crankshaft revolution.

Specifically with the Bayou, a pickup coil senses the proximate passing of a "timing projection" on the alternator rotor; this rotor projection passes by the pickup coil EVERY crankshaft revolution; therefore, the Bayou ignition fires every crankshaft revolution (although the spark at the top of the exhaust stroke is "wasted," unless for emission control it burns whatever mixture is left over after the exhaust stroke).

Older, point-and-capacitor ignition sytems, typically fired every other crank revolution, at the top of the compression stroke. The point cam rotated at half crankshaft speed.

Diogenes

 

Yes, I remember now reading the same information in one of Greg Hall's responses to the same question. As you mentioned in your response, the idea is to reduce emissions by using a second spark during the exhaust stroke to burn any leftover fuel/air mixture. I also agree that it is easier to design a controlling mechanism that fires upon every revolution than every other one.

Thank you for the correction.