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.
My lawnmower is a Briggs &Stratton 300 series with a 4.5 . I recently have been having trouble with it. The primer seems to have no pressure and when I check the filter its soaked with gas? What do I do?
Sounds like to me bad fuel,carburetor could be dirty where the air is suppose to go to the primer,sparkplug could be bad, and/or rust on the flywheel from my knowledge.
<p>I agree http://lawn-mower-reviews.com/</p>
<p>I agree http://lawn-mower-reviews.com/</p>
<p>Whatever you do, don't buy any mower made by MTD. As for the battery operated rechargeable mowers? What an absolute joke . . . sure love the environment as you are forced to buy new batteries every year (do you have a clue as to the environmental impact of making these batteries . . . your better of burning diesel and it will also cost far less). We've all got a pile of &quot;expired&quot; rechargeable power tool batteries in our basements . . . This is like the old razor industry or printer industry rule . . . buy our junk<a href="http://lawntoolsguide.com/" rel="nofollow"> for cheap</a> and we'll make a killing on selling you short-lived razors, ink cartridges and power tool/mower batteries.</p>
<p>Sure my MTD plastic carb warped. But I just put foam seal around it to seal where it mounts the tank. Cost me one PENNY. I even have a spots of rusty gas tank. So in 9 years I still haven't had ONE up/down rev'ing motor problem so common with these cheap carbs. No problems. No more carb kits because it's a carb warp gap problem and not a dirt problem. Just keep a carb kit handy if the spray foam seal doesn't solve your diaphragm pump issue that causes the up/down engine rev'ing. The MTD 3.75HP? mower is 15 or more years old now and works just like new with 15 year old original diaphragm gaskets. It's a seal problem not a dirt problem 99% of time.</p>
thank you, thank you, thank you. you helped me fix my lawn mower.
<p>OK its not a lawn mower but its fuction is similar. honda gx160 driving a waterpump has a fixed jet carb. origina carb missing so i bought a jap cone. the problem is it starts/runs fine on choke but if i take choke off even sightly it dies out! took carb apart to look for problem everything seems fine. i happen to come across a youtube vid by a kid who had similar motor and carb and he had the SAME PROBLEM!? i also was able to get full throttle to work by manipulating choke. so it seems to be completely missing low/midrange. i drained float bowl and it had plenty of gas in it.</p>
Can anyone help me with what they use to seal between the air box and carb intake on a honda gxv120 engine. Seems they used a black gasket sealant would this be right? Tia
<p>Keep in mind some of these small Honda engines,Carburetors,Like the GCV 160 If leaking out of the air filter box.. alot of times for me with experience of many years working on these ends up being NOT the needle valve itself but up inside where the rubber tip meets the aluminum body of the carburetor, If it has some age on it or been outside moisture causes corrosion and although you may try a new needle valve which they are sometimes up to 10.00 to purchase its 80% likely the upper seal, aluminum port hole.and you will need to replace the whole carburetor,I have a trick that sometimes works to keep from having to buy a new carb, Which involves copper piece of wire not to stiff also not to weak on a slow speed dremel tool ..At your own risk to try but I look with a jewelers loop and bright light to see this corrosion before I even attempt, I also use this loop to look at the rubber tip for rot or a deep ring on the rubber tip.So just some info while I have a moment to help anyone out thats having this problem..Now on a Briggs &amp; Stratton carb..5 to 6 H.P. These are different..You can just buy a kit that has the rubber seat up inside of its body which also comes with the needle valve.Item # 398188. If you have any questions Send me an E-mail and will try and help further.</p><p>Mr.B</p><p>Thanks!..............www.bsmmrepair.com</p>
<p>It`s nice to know that one can find a site that won`t make one jump through loops and bounds to get information only to find out that you have to pay for the information. Most of all, information that is jumbled. This is the most presented information that is simple and direct to the point. Thanks.</p>
<p>Thank you for tutorial which is very helpful to me as I am a woman. I wonder if I could ask you a question. I have a Honda GCV160e lawnmower engine. I put new oil checking that it was up to the top of the gauge at the start of the season and checked the air filter and spark plug. It started and I was very pleased. I noticed however that it was using an awful lot of petrol. I then noticed that fuel was coming through the air filter and exhaust. The carb was cleaned thoroughly last year by a professional so I was surprised that it could be a stuck float in the carb. I took the carb off and reseated the float and put it back on. I now find that I cannot deploy the cord. I have had the cord mounting off and it works fine when not engaged on the engine. The break works as I have deployed the dead man's handle and the lever goes backwards and forwards. I have taken the spark plug out to see if I can move the blade but I cannot. Can you please help as I am a widow and my husband would have probably known what to do. I didn't hit anything prior to me noticing the petrol coming through the filter. I made sure to tilt the machine the correct way as this was instilled into me by my husband when I cleaned the underside. Any help would be appreciated. Thank you.</p>
I'm at the same point you are. There is probably gas in the spark plug. That's what I'm trying to fix now, got the gas out and now it pulls but I don't think I'm getting spark. I had worked on my carb too and that's how I need up getting gas in my spark plug<br>
<p>Hi Mark, thanks for your comments. I have actually had it going again but the same thing happens I get fuel coming out of the air filter and exhaust. The float is working because I have attached a tube to the carburetor where the fuel goes and poured water into it and when you deploy the float up or down the water in the tube either goes down or stays in the float. I think my problem is associated to the linkages. I cannot when I deploy the choke see the linkage move by the carburetor. It moves further down but not by the carb, so I am thinking it might be a spring issue with me but I cannot see where the spring goes on the control lever. Basically it starts it runs for about ten minutes and then I get a load of fuel coming through the air filter. When I changed the oil last time it had a lot of petrol in it. I hope you sort your problem out but to be honest I have changed the oil in mine now three times and it is an expensive business. If you cannot pull your cord just keep pulling with spark plug out. It is called hydro something or other but will eventually get easier. I manged to get mine going by turning the blade which was locked solid to begin with but a little knock with a hammer loosened the whole movement, and when I turned the blade you could hear oil splurging out of the oil tube. Good luck! </p>
That something is hydro lock
<p>The float pivots and moves a tiny needle valve that rests in a tiny seat. Sometimes a little piece of dirt will get lodged there and keep the needle valve from seating and let the fuel continue to flow. Since you had the carb apart it is possible that it is missing or damaged. A drop to the floor can easily damage the trip of the needle valve and keep it from seating. Lawn mower carbs are fed by gravity. Since the tank is higher then the carb, if the needle valve doesn't close, it will continue to feed fuel and eventually overflow into the cylinder. Once enough gas gets into the cylinder, you are not able to pull the starter rope because of the gas in cylinder, which can not be compressed, stops the pistons travel. Also, floats are set to a very specific level, which vary by carburetor. If it is not set properly, it won't have enough pivot travel to close the needle valve. </p>
<p>Thanks for your comments. I have checked the float and the pin and it is engaging correctly. The experiment with the water down the fuel tube on carb and then moving the float up and down shows that it is working correctly. Someone had a quick look at it yesterday and they said that when the choke is engaged the control lever moves but when you move the choke back to its resting position after starting it, the control lever on the carb is only moving about 65% which may be my problem. I have been told to manually move it back into position and see if this works. It might also explain why it takes approximately ten minutes before the fuel leaks through the air filter. Thanks for your help!</p>
Check flywheel and magneto/ sparkplug wire on the inside of the mower for any rust.
If the mower is pretty old it sounds like internal engine damage from normal wear and tear of the mower. If it's a newer one that's still under warranty I would have them look at it just to be safe.
I think the instructions are helpful for both men and women (wink). However, I think that, unlike many instructions, these are written in a way that both men and woman can understand and that takes talent! I am sorry for the loss of your husband but so happy that you are figuring it out for yourself!
You could have a bent or worn crankshaft.
<p>Thanks for your comments but it had hydro locked. It is now working but I still have the same problem with fuel coming through the air filter after about ten minutes. I have been told that the choke after being engaged isn't going back to its resting position properly and to manually move it the last fifteen percent.</p>
Mine wouldn't start. I was told to smell the air filter. Smelled like gasoline. My advisor asked if it was a white filter. I said, &quot;no.&quot; He told me, &quot;It should be! Change your filter!&quot; I did, and it started right up. You can also check that, by trying to start it, with the filter out. If you take it out and it starts..it's probably a clogged air filter. Easy fix. I hope that helps.
<p>Thanks for your comments. It has had a new air filter and it still does it. I am convinced it is not the filter or carb but something to do with the linkage no engaging fully in resting position. I will try to manually move it the last bit after starting and see if this helps, otherwise I am at a loss. Thank you&gt;</p>
Sedge great instructable just cleaned my briggs and stratton mower fuel tank and carb ..it starts fine but &quot; hunts&quot; and as soon as i try mow it cuts out . When its running there is a spring loaded valve that keeps moving which drops the revs then goes up does this a few times before cutting out....any suggestions please....Andy
Sedge great instructable just cleaned my briggs and stratton mower fuel tank and carb ..it starts fine but &quot; hunts&quot; and as soon as i try mow it cuts out . When its running there is a spring loaded valve that keeps moving which drops the revs then goes up does this a few times before cutting out....any suggestions please....Andy
The oil had water
Could someone help me plz my husband tore down our yardman lawn mowers crankcase and after it was put back together the pull cord won't work can you please tell me what we did wrong and ASAP thank you
<p>there are too many possibilities with that little information.</p><p>First, remove the spark plug and rotate the engine, does it rotate? Put a long screwdriver into the plug hole Rotate carefully making sure that the screwdriver does not get bound. As you rotate the screw driver should move up and down with the piston movement. If you can't turn the engine easily with the plug out then you have something inside that is wrong and binding the crank most likely. Time to open the pan again.</p><p>If that is all correct, then your problem might only be with the pull chord system. It is spring loaded and has pawls that move out when you pull the cord. They align into the top of the flywheel and force the flywheel to spin.</p><p>Take the pull cord assembly off the machine and look underneath...see how the pawls open and where they are designed to catch in the flywheel assembly. just examine it, You should see if there is a problem there. Assemble it correctly making sure the pawls are fully retracted at assembly. Then check it. Should be no problem then.</p>
I was mowing my lawn and hit a ant pile and my mower stalled out and wouldn't restart any suggestions on what it could be
<p>This is usually the shear pin on the flywheel has sheared and the flywheel has spun. The flywheel is part of your magneto system and the magnets on the flywheel must create the spark at around top dead center. This pin aligns the timing of the engine. They cost about $1-3 and actually they do NOT hold the flywheel on at all. The flywheel is held onto a conical shaft by the torque pressure on the shaft nut, the shear pin is used for alignment only, like a disposable tool.</p><p>Make sure NO OIL of any kind (even skin oil) is on the shaft or inside the flywheel. The sheer pin should slide in easily. Then tighten the shaft nut to around 40 ft-lbs. (most engines anyway), you must hold the blades from rotating to do this.</p><p>Good luck.</p>
<p>I did something like that, and the problem turned out to be really insidious: The engine timing was thrown off so that the spark was occurring at the wrong time in the cycle.</p>
<p>NEVER, EVER, EVER use a wire in a carburetor to clean any porting there. You can use nylon fishing line or similar products. Even copper wire can ruin the holes there, they are PRECISION machined and must not be damaged in any way.</p><p>It is best to use only spray cleaners and air unless there is some known blockage. An immersion tank with ultrasonic vibration and soapy water is the best thing to use. Then you can just rinse clean and perform a final cleaning with small amounts of carb cleaner and blow with dry compressed air.</p>
I have a poulan pro 195 trimmer and it will not spark. I have changed the ignition coil and have gapped the magnito with a busniss card. The spark plug is gapped and I even used a second new sparkplug that was also gapped to ensure that the sparkplug was not to be the problem. The spark tester will spark but only a dull yellowish spark not a blue spark. And there is no spark at the plug. This is the second ignition coil as I believed the the first one that I purchased was faulity as it did not create a spark. Could anyone help me with this problem with suggestions - thanks.
My mower runs for about 15- 20 minutes then dies any help with this.? I have cleaned the magneto and the flywheel
<p>I have no strength on my arms and can't pull the string hard enough to ignite the spark plug of my mower. Can the spark plug be replace with a battery clicker...? It looks to me that the only thing needed is a spark to start the engine running.... do such gadget exists....? Pardon my ignorance.... :)</p><p>alberto.padro.288@gmail.com</p>
<p>alberto....you need either an electric mower (where you have to negotiate mowing with a long lead) or an electric starting mower...or indeed someone else to mow for you. These arent machines to mess around with safety=wise.</p>
<p>The spark plug fires once for every 2 rotations of the crankshaft to ignite the fuel on the compression stroke of a 4 cycle engine. At 1000 rpm, the spark plug fire 8 times per second.</p>
<p>My favorite solvent for cleaning carbs is lacquer thinner. The composition of lacquer thinner is very similar to commercial carb cleaners, but is cheaper. It won't leave a residue like gasoline often does. Of course, DO NOT USE ON PLASTIC PARTS.</p>
<p>Great info here, although I have question regarding step 4. </p><p>If a crowbar is bad, what is the recommended way to hold the crank shaft in place?</p>
<p>wonderful.. I really like it...</p>
<p>Thank you for such a detailed tutorial. I appreciate the included pictures along with the explanation. Sometimes I hear the words people are saying, but I can't picture what they are talking about. Our lawn mower has been acting up lately so I'm going to run through these steps to try and get it working again.<br> &lt;a href='http://www.rpmsmallenginelansdalepa.com/' &gt;<br>http://www.rpmsmallenginelansdalepa.com/&lt;/a&gt;</p>
<p>I have no strength on my arms and can't pull the string hard enough to ignite the spark plug of my mower. Can the spark plug be replace with a battery clicker...? It looks to me that the only thing needed is a spark to start the engine running.... do such gadget exists....? Pardon my ignorance.... :)</p><p>alberto.padro.288@gmail.com</p>
<p>The choke on my Craftsman self-propelled mower gradually shuts itself off after starting, but when it does, the engine stops. If I hold the choke lever about midway and not let it shut off all the way, the mower continues to run. Any suggestions? It's 10 years old, but I haven't run it for 4 years. It worked fine then.</p>
<p>Hello Bill,</p><p>Sorry a late response..But if its been sitting that long its having a hard time drawing the fuel up from the bowl of the carburetor..I suggest taking the carb. apart soaking it in a chemical carb cleaner for a couple days..Its most likely gumed up inside there like tar it will never do right until that is done.Then blow it out with air hose and a spray cleaner you should be good to go.</p><p>www.bsmmrepair.com</p>

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