How to Repair a Lawn Mower Engine.

Step 8 Intake and Exaust valves

There are two valves in a 4 stroke engine. The intake valve which injects the air fuel mix into the combustion chamber, and the exhaust valve which lets out the carbon monoxide and what is left after the combustion. These valves are moved by a cam shaft that turns with the engine at a set time. Sometimes these valves will gather junk around the shaft, and will need to be cleaned by a commercial valve cleaner or by hand. The valve should look very nice and feel smooth in order to work. Sometimes the valves will get scratch and leak oil. This is mostly due to not changing your oil. There is nothing that I know you can do once the valves get this bad, and the only thing you can do is buy new ones. The valve heads can also get chipped and will inject fuel at the wrong time and reduce combustion. Once again if the valves get badly chipped you will have to buy a new valve. To remove the valves you will need to press down the compression springs, and remove the valve spring retainer. Now, putting the valve parts back together again can get a little tricky .You will have to first put the spring and the valve spring retainers back into the engine together. Once you have done this you will have to insert the valve back in place. To place the valve spring retainers back on the Valve you will need to press the valve spring retainers a little bit to the side so you can push the valve into the large hole of the valve spring retainer. Then you will need to press the spring and retainer down so you can lock the valve spring retainer in place. Some valves also have something call a sleeve which you will need to very delicately put on top of the valve and below the valve.

Comments

[knoxarama]

when i took the whole thing apart, i found what was powering the spark plug: the fly wheel and a coil of wire. the fly wheel has magnetic strips that mover past the coil and generates the spark for the plug. what i want to know is, because there were two wires, the ground that attached the the frame, and the one that went to the plug, what kind of voltage is produced, and is only one wire being used to create the spark. i looked at the thing you attach the plug into, and i only saw one contact. is the spark plug powered by static?

[livesteamfan]

 There are actually three connections with a standard magneto. The one is the shut off. Another is the two screws holding it on the engine, those two arms are using the block as a ground just like the spark plug is. The third is the thick  wire going to the plug, this wire generally carries between 20,000 and 40,000 volts. I do not know the amperage or the type of current it is (ac or dc). I will tell you the some magnetos put out so much that the plug wire can be about a 1/4 inch off of the plug and you can see a second spark while the engine is running. Other engines with the rubber boot over the wire will push the current through the insulation and it will travel to the plug. I found that out the hard way, it hurt.

[knoxarama]

huh. that might be the problem then, (at least until i took it completely apart and lost some pieces.) I tried running magnets past it to try to conduct a current but got nothing.

[Rahdzhillaxxx]

I remember my good 'ol step dad telling me " here hold this and see if it has spark"  I really hated that guy. 

[livesteamfan]

 But that's really the only fool-proof way of knowing. And it's better to have someone younger do it because some "older" people my not be able to take the shock. Plus, the reaction of someone else is kinda funny.