small 4cyc lawn mower engine - TDC? exhaust open?

[werwer]

A Toro with a small 4cyc suddenly will not start. It 'kicks back" when you try and start it. A friend suggested that perhaps the flywheel had sheared it's pin and the timimg is bad.

I took the cowling off and I'm not sure if it's sheared or not. I appears I'd have to hammer it off to take a closer look.

The fly wheel mounted magnet passes over the pickup twice for every one cycle. Is there something that shorts out the energy durning the non firing exhaust cycle?

Could the ignition be 180 out? On one pass, as the magnet passes over the coil, the value is wide open. On the other it is closed.

[John Lawrence]

DO NOT HAMMER the flywheel. You need a puller. Rent, borrow one or bring it to someone to remove. Most likely you hit something with the blade which can shear off the flywheel key. This is very common. It only needs to move a fraction to put the timing off.

[Oren]

TDC is not on the exhaust stroke, but the power stroke [long time?]. Stick a long pencil (any up-stroke of piston) in the plug hole (plug out - wire away), rotate the strokes by hand TDC should/will have both valves closed. Pencil pushed out. Like I say, long time.

TDC needs both valves closed to fire....

-- Oren

"Well, it doesn't happen all the time, but when it happens, it happens constantly."

[LARRY]

Hello The person who wrote about hammering the flywheel is correct,you must also never hit the top of the crankshaft where the nut is.The reason...the threads on the top will pean over and or you can break off the threads making your lawnmower into a very expesive paperweight also never use a 3 armed puller on the flywheel it will only break your flywheel. depending on the type of engine (you said toro)that is the make of lawnmower deck not the engine. you must make an effort to see and get the model number--ie;briggs&stratton

100902 or tecumseh Lev80 then with the proper text book and the proper tool you can learn how to do this simple repair. one last thing,the blade hub the part that the blade connects to has on some models a half moon key known as a woodruff key that could also bee sheared.inanycase please remove the spark plug before attempting any repair. hoping this is helpfull. larry the small engine mechanic

[lwasserm]

I won't say it's good practice, but there are plenty of small engine repair shops that remove flywheels from B&S engines without using a puller. Once you see the technique, it's easy, really... provided you have 3 hands.

[Stormin Mormon]

I got a knock off tool, which slips over the end of the shaft. And two for Tecumseh, as they have two different thread patterns on their crank shafts.

Big screw driver under the fly wheel, and give it a good whack on the top of the knock off tool. So far, works slick as can be.

-------------- Now, to the original poster. Sounds like you did hit something and sheared the flywheel key. With the old points ignition, there was no spark when the flywheel key sheared. With the new electronic ignitions, they don't care. Yes, there are two sparks. One is in the compresson stroke, near TDC. The other one is wasted, in the exhaust stroke with the exhaust valve open, and the exhaust gasses blowing out.