Push Lawn Mower Tune Up and Repair

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About: At 50, I have a vast array of experiences that cover many interests and technical domains. I started programming at 16, 1984, on an Atari 800 computer. I've been around, and actively involved, for most of th...

Intro: Push Lawn Mower Tune Up and Repair

So I pulled out my trusty 14 year old TroyBilt push lawn mower the other day, and after starting it would go about three feet and start chugging. Because of lots of recent rain, the grass was very high so my first thought was that it was out of gas. So I filled it, started, and the same thing; it would chug for a bit, go about three feet and then die again.

So I figured it was time for a tune up...

Tools list:

  1. One set of pass-through socket wrenches from Harbor FreightI can not recommend this set enough, as it contains both metric and SAE sockets, in a nice little case that keeps everything neat and together!
  2. Flathead screwdriver
  3. Phillips Head screwdriver
  4. 3-IN-ONE Penetrating oil.
  5. Blade sharpening and balancing kit

Parts list:

  1. Air filter [Briggs&Stratton or the air filter specific to your model of engine]
  2. Spark plug. You can either look in your manual, or get the model number off the side of the existing plug. There are several manufacturers but they will all list compatibility with each other's part number.
  3. SAE 30 oil [Briggs&Stratton or the oil specific to your model of engine]
  4. New mower blade, if you use a bagger, buy a non-mulching straight blade. You'll need the length of the blade specific to your model, so either measure the length of your existing blade, or it should actually be printed somewhere on the mower itself. It is not necessary to replace the blade every year, sharpening and rebalancing is.

Step 1: Tune Up, Remove the Air Filter and Spark Plug

I'm very methodical about doing a yearly tune up; that's probably why the mower has performed so well for 14 years! This is something that I recommend that you do every fall, when your main grass cutting season has ended. This is a bit early for me, as I usually do this after all the leaves have fallen, because I use my mower to vacuum up leaves (and mulch them so more fit into the leaf bags) in the fall.

Before you do anything, remove the air-filter and spark plug. This will allow you to find the exact replacement parts you'll need at your local hardware store. Most push mowers, regardless of the mower brand use a Briggs&Stratton engine, but having the parts in hand when you go to the hardware store is a huge advantage. The air filter is usually located on the side in what looks like a little black box, and the spark plug is usually in the front. To remove the spark plug first pull the rubber cap, straight off of the plug. Don't tug on the line, only the rubber cap that connects directly to the spark plug.

To remove the spark plug you can either use a spark-plug specific socket, or use the pass-through socket set I mentioned in the tools list. This will allow the spark plug to pass through the middle of the socket so that you can actually reach the hex part of the plug's base.

Step 2: Tune Up, Remove the Fluids - Gas

The second step is to remove the fluids. We'll start with the gas.

What I do is usually take a couple of 2x4 stacked two high (or a 4x4 if you've got it) and put the side of the mower with the gas cap on the boards, and then lift the other side of the motor over a funnel into a gas can.

You'll see from my pictures that I made a crucial mistake! I should have put down a plastic drop-cloth or a couple of trash can bags sprinkled with some Oil Absorber (I've found plain non-clumping cat litter is cheaper and works best). So as you can tell, from my third picture I, of course, spilled some of the gas; so I immediately covered that with cat litter, and ground it in with my foot.

Step 3: Tune Up, Remove the Fluids - Oil Via Blade Removal

While it is possible to remove the oil without removing the blade, I don't recommend it. So this step will also include the steps to remove the mower blade.

First flip the lawn more onto the side with the oil cap (the opposite direction you used to empty the gas).

Use this opportunity to clean out any stuck on grass, being careful of the blade
(or better yet, do this part AFTER you've removed the blade, DUH).

To remove the blade you're going to need to brace it. I do this with a 2x4 that I wedge under the blade. To loosen, the blade will move counter-clockwise so just remember to block the blade from moving in that direction.

Now to remove the blade you must remove the bolt in the center of the blade. You're also going to need some Penetrating Oil; that can be purchased at any hardware store. Cover the bolt head liberally with the Penetrating Oil, and then find the socket that matches the bolt head, and [Righty Tighty, Lefty Loosey] pull upward with your wrench, making sure that your blade is wedged well against the 2x4. The bolt is going to be on there tight, so if you need extra leverage you can slide a pipe over the handle of the wrench which will give you extra leverage. The important part about this step is that you hold the head of the wrench against the bolt so that you don't strip it by slipping to one side or another. Once the bolt is removed, the blade should come right off.

Step 4: Tune Up, Remove the Fluids - Oil

Now that the blade is safely removed, you'll need to look for the oil drain plug. This could be a bolt, or in my case it was a bolt with a female socket. Our trusty socket wrench set comes with exactly what we need. Once the bolt is loosed with the wrench, use your hand to remove the bolt fully. After the drain bolt is removed, you're going to want to lay the mower over an oil pan.

While you have the oil plug removed, it's important that you clean the plug with a clean rag or some some paper towels. The oil plug has a magnet at the end that catches any metal shavings that occur with normal wear and tear of an engine over time. So it's important to remove all of those shaving, and clean the threads of the plug as well.

Step 5: Tune Up, Remove the Fluids - Oil - [optional Steps]

While the mower is over the oil pan, I will usually add a few ounces of fresh oil, just to help flush out more of the bad. This is usually why I buy the larger oil bottle than the smaller size.

I also use a small bit of sandpaper to clean the oil dipstick.You don't want to sand off the markers, just make it so they stand out a bit better. This is not something I do every year, or the makers WOULD be sanded off, but every couple of years, it just helps removes the oil that has bonded to the steel.

Step 6: Tune Up, Screw in the Drain Plug, and Tighten.

Once the oil has drained completely, flip the mower back onto the side with the oil dipstick (making sure you replaced the dipstick if you did the optional sanding).

Now apply the cleaned plug back into the drain hole. Do this by hand first, and then using the same tool as before, tighten the screw, but don't over tighten this one. Basically my rule of thumb (literally) is to use the force that I can apply with both thumbs pushing down on the wrench.

Step 7: Tune Up, Sharpen and Balance the Blade

So part of my problem is that last year I replaced the blade, but I purchased the wrong size (22" instead of the 21"), so I basically cut off 1/2" on each end and installed it. What I didn't realize is in that process the blade was probably VERY off balance. So this time I purchased a new blade, the right size, and a sharpening/balancing kit.

The blade I chose was a universal blade, so it came with a set of additional hardware to fit different types of mowers. Fortunately for me, the blade itself fit my mower without additional parts. If it's been a few years since you've done a tune up (if ever) I recommend that you replace the blade. You should sharpen and balance the blade every year, but I find I need to replace it about every 8-10 years.

A note here: If you use a bagger, do not buy a "mulching blade" as that forces some of the grass back down into the lawn. When not using a bagger, but using the side exit instead, this kind of blade makes sense as it decreases the amount of blowout the side, but if you're using a bagger, you just want a regular straight blade.

So the first thing I did was mark the blade so that every time I put it on the balancer it would always be measured the same way. Putting the new blade on the balancer, one side was drastically heavier than the other. So I used the sharpener to sharpen the blade (following the instructions on the package), and that helped a small amount, but to get it balanced I had to use the sharpener to take off a good deal of metal from the heavy side. I did this by using the sharpener to sharpen larger areas of the heavy side. Even sharpening the back of that side of the blade, and the end of the blade as well. After lots of trial and error, I got the blade balanced.

Step 8: Tune Up, Reinstall the Blade

Reinstall the blade (bevel sharpened side toward the mower, the flat side of the blade should be facing [down] away from the mower), tightening the bolt by hand so that it's secure but not tight. Once the bolt is hand tightened, you'll going to want to use the 2x4 wedged under the blade again, remember we want to block it from rotating clockwise this time, so you'll need to wedge in a different place.

You're also going to need to use another board to wedge under the 2x4 to cover the sharpened blade edge along the bottom. THIS STEP IS CRUCIAL BECAUSE WHEN YOU TIGHTEN THE BOLT, IF YOU SLIP YOU WILL SLICE YOUR HAND BADLY!

Then using the same socket you used to remove the bolt, tighten the bolt as tight as you possibly can!

Apply a liberal dose of the Penetrating oil to the bearing where the blade stem exits the mower housing.

Step 9: Tune Up, Add New Oil, Air Filter and Spark Plug

Flip the mower back to it's normal position, and add the oil a little bit at a time, using the dipstick to test when it's filled. Since the mower has been on it's side, when you first remove the dipstick you'll want to use a clean rag or paper town to dry the dipstick first. This should allow you to get an accurate reading.

Replace the air filter, as shown.

Reinstall the new plug, but DO NOT OVER TIGHTEN. It is very easy to strip the threads on the spark plug hole and if you do, the motor is pretty much ruined. Apply the cable.

Fuel it up!

Step 10: Tune Up - Start It Up.

Don't forget to add the fuel.

This mower uses a primer bulb that's normally takes 3 pumps. Since we've emptied all the fluids, pump it 10 times, then crank it up.

It was running better, but it was still chugging and after trying to cut some high grass again it would chug and die.

So while the tune-up wasn't a waste, as the tune up need to be done anyways, it clearly wasn't the real problem.

Step 11: Fix, the Real Problem.

Modern push mowers have automatic throttle systems. Based on the resistance the blade meets, a spring increases/decreases the throttle.

I removed the cover, and found the throttling mechanism, and I noticed that the spring that worked it was quite rusted, and "sprung" (expanded over time). If I had to guess, the last blade I added was badly balanced, which caused extra strain on the spring to constantly adjust the throttle to compensate, that and just rust.

At first I tried oiling both the throttle mechanism and the spring, but neither helped. Then I noticed that the piece of metal that the spring connected to was quite bendy, I bent it forward, putting more tension on the spring.

It cranked right up, and stayed running, but it was also running at full throttle! So I decided to replace the little spring.

This spring is called a Spring Governor. You can order it on Amazon once you find the part number. This was a bit of a challenge but with some internet sleuthing I found it.

Fortunately, as mentioned, most brands of push mowers use Briggs&Stratton engines. To find the specific model number for your engine, there is a model number that is typically above the muffler. With this being a 14yr old mower, I had to wipe away several years of grime to uncover it, but once I had that model number, the Briggs&Stratton website had the parts list available, and the part number for the spring. Once I had that I was able to find it on Amazon. (by the way, Briggs&Stratton themselves wanted 3x the price that Amazon did, plus $5 shipping {shrug}).

I replaced the spring, and re-adjusted the bendy piece of metal that the spring attaches to, until I had the throttle running its normal speed.

After this, it worked like a charm, and hopefully I'll get another 10 years of use out of it!

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    4 Discussions

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    ChipsWoodShop

    5 weeks ago

    You get my vote, too! Another thing I have done when resurrecting my old mower after a long period of not running was to clean the carburator.

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    rayp1511

    2 months ago

    Good information and reminder, thanks. Nice tip on the pass through sockets too.

    2 replies
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    ZacWolfrayp1511

    Reply 2 months ago

    Thanks very much! And I rearranged the steps based on the info from your private note, thanks for that! Please pass the link along to your friends, and ask them to vote for the FixIt contest! Thanks again!

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    rayp1511ZacWolf

    Reply 2 months ago

    Your welcome, and you have my vote :)