How to Fix Up an Old Lawn Mower

As the days warmed up and the grass started growing again, it wasn’t too long afterward when it was time to awaken my riding mower from its slumber. When a nice sunny day came, I went out back to the shed, hopped on the mower, and turned the key.

Nothing happened. I turned the key again, and again. It was just making a whirring sound. I couldn’t even try applying the choke because the engine was not even trying to turn over.

After trying a few more times, I was dismayed.

I knew I would have some trouble starting up the mower after the winter break, but not like this. It was clear that today was not the day for mowing. It was time to do some investigation and perform some mower maintenance.

I bought the used riding mower on Craigslist last summer. I got a great deal because it was 20 years old and was showing a lot of cosmetic wear. However, the previous owner kept up with the maintenance, and it ran pretty well for its age.

I was also not too of how to fix a riding lawn mower because I had confidence in my repair skills (having brought some old push mowers back to life at my previous home with some replacement parts).

How to Fix an Old Riding Lawn Mower

To prep for my maintenance project, I tracked down the mower manual online, located the consumer replaceable parts, and ordered them online.

Then I put together Ash’s grand maintenance plan for reviving your riding mower, as outlined below.

1. Spark plugs and battery
2. Oil filter and oil change
3. Air filter and precleaner
4. Fuel filter
5. Clean out mower deck
6. Replace mower drive belt
7. Lubricate
8. Check tire pressure

Here’s a picture of the left and right side of my mower engine, with some of the areas above outlined:

1. Spark Plugs and Battery

The first thing I did was check for activity in the spark plugs.

Using a special spark plug socket, I pulled one of them out, still connected to the battery, and turned the key. There was no spark. I tried another spark plug that I knew was working (from my push mower), and still no spark.

This led me to believe the battery was low on juice. I had a 12 volt car battery charger, so I was going to try recharging it. It made sense that the battery would be low as the mower had not been run for a few months.

Before I recharged, I wanted to rule out a bad battery (incapable of being recharged). I tested the battery with a volt meter and got 12.4 volts which was actually normal. Any lower readings (especially in the 11 volt range) would have suggested a bad battery.

So I hooked up the battery to the recharger, setting it to 10 amps with an automatic shutdown on a full charge. An hour later, the recharger said the battery was ready. I hooked it back up to the mower and tried starting the engine. Still no luck.

So Eileen picked up a new mower battery for me at Lowes (they seemed to have a better selection than Home Depot). I got a 275amp battery (suggested for mowers up to 21hp) making sure that the positive terminal was on the same side as the old battery (or else the wire hookups would not reach). Here’s a picture of the new battery installed:

Here’s a picture of the exposed spark plug (which I was able to remove using a special socket):

We did bring in my old battery to Lowes for recycling. They give you a small discount (which covered a core charge fee for a new battery purchase).

We also picked up two new spark plugs. I installed the new battery and spark plugs and tried starting the engine…

Success!

The starter motor did not hesitate at all. The flywheel immediately began spinning, trying to start the engine. It did take a few tries to get the engine running but eventually got it going. That leads me to the next maintenance steps.

2. Oil Filter & Oil Change

Now it was time to change the oil and oil filter.

I located the oil drain plug and set up a funnel and plastic container to collect the old oil. I then removed the oil dipstick from above, loosened the drain plug, and out came the oil – pouring out slowly.

When the oil stopped coming, I screwed back in the plug and went to work on the filter. I put a rag under the existing filter to catch any oil that would spill. I twisted the filter and pulled it out of the mower.

Good thing I had the rag in place because a lot of oil came out of the filter. I grabbed the new oil filter, put a little oil on the gasket, and screwed it into the mower.

Now it was time to pour in new oil. I poured nearly two quarts of 5W30 oil (picked up at the nearby gas station) down the oil dipstick hole, pausing every now and then to take a measurement with the dipstick to make sure I didn’t overfill.

Here’s a picture of the new oil filter and drain plug:

3. Air Filter And Pre-Cleaner

Next up was the air filter and pre-cleaner.

It’s important to have a steady flow of filtered air entering your engine. Disruptions to this flow can lead to a lack of power, excessive fuel consumption, or problems starting up.

You can normally clean out the old filter, but I had no idea how long the existing one was in there. Therefore, I disposed of the old one and replaced it with a new one.

Accessing the filter was easy. I just removed a wing nut and the metal housing. The air filter itself is just a cylinder with wire mesh and a paper filter.

The pre-cleaner is a piece of sponge wrapped around the filter. I unpacked the new pre-cleaner and followed the installation instructions. I moistened it with some motor oil and wrapped it around the new filter. Then, I replaced the old one on the mower engine.

Here’s a picture of the new air filter and pre-cleaner installed (without the metal housing so you can see it):

4. Fuel Filter

Now for the fuel filter. It’s recommended that you change the fuel filter on your mower once every season.

There can be lots of impurities in your gas tank (think about all the times you opened the tank lid for refueling with grass still settling from the blades), so a season of mowing can clog up your filter.

Using the mower manual, I located the filter on the engine. If you’re having trouble finding yours, just follow the fuel line from the gas tank to the engine. The fuel filter is along that line.

To remove the filter, I first clamped the fuel line in between the filter and the tank. I didn’t want fuel dumping out of the tank once I removed the filter. I also put a container beneath the filter to catch any excess gas stuck in the line and filter.

Then I removed the hose clamps holding the filter in place and pulled off the fuel line. Luckily no fuel leaked out. The tank must have been nearly empty. I then attached the new filter, making sure the arrow indicated the direction of fuel pointed towards the engine.

With the fuel lines clamped back onto the filter, I removed the temporary clamp pinching the line and installation was complete.

Here’s a picture of the new fuel filter installed:

At this point, the engine was now ready for the upcoming season. I turned the ignition key and the engine fired up without hesitation.

I didn’t even have to apply the choke. Then, I let the engine idle for 10 minutes to make sure it ran okay and didn’t have any fuel or oil leaks. After, I took it for a test drive, and it drove like a champ.

5. Clean Out Mower Belt

Now onto the mower deck, which was giving me some trouble. While mowing the front lawn, I noticed a lot of squealing noises coming from the belts in the deck. Also, the collection bags were barely filling with grass. It got so bad that I actually had to disconnect the automatic bagger because the tubes were getting clogged with grass.

I switched to side discharge for the grass, which meant I spent a lot of time raking up the grass when done. Finally, a few times the engine actually died with the blades engaged.

After inspecting the mower deck, I concluded that the three problems I had stemmed from a worn mower belt and debris wedging against the belts. The debris particularly was causing a lot of friction with the belt and putting strain on the mower, causing the engine to stall out sometimes.

This also impacted the bagger because the blades could not spin at full speed and expel the grass fast enough. The belt also had clear evidence of being worn down. There were lots of cracks, and I was surprised the belt hadn’t broken already.

REMOVING AND CLEANING THE MOWER DECK

To address my mower deck issues, I first removed the deck from the mower. It was not that difficult.

Following directions in the manual, I located and removed some retainer springs holding the deck pinned into the mower chassis. Then I slid the deck out from under the mower.

Here is a picture of the deck removed from the mower.

Technically I didn’t have to remove the mower deck to replace the belt. However, the debris was really hard to reach and was easier to remove this way. I also wanted to take the opportunity to inspect the blades and underneath the deck.

Once I opened the deck, I removed all the debris with ease. There was a lot of it too, from packed dirt to wads of dried leaves. I could see why the belts were making so much noise. I’m sure it was a fire hazard too, with friction from the belts heating up the dried leaves and possibly igniting them.

Soon the deck was looking very clean. I flipped it over and inspected it underneath. It wasn’t too bad under there. I just used a flat screwdriver to scrape off some grass patches that have been building up over time.

SHARPENING THE MOWER BLADES

When I checked out the blades, they were extremely dull. The sharp part was actually round and smooth. All this time mowing the lawn, I could have just whacked the grass with a baseball bat.

So I removed the 3 blades with a socket spanner, clamped each one in place, and sharpened with my Dremel and a grinding stone bit.

After I sharpened both ends of the blade, I stuck a bolt in the blade to see if it was properly balanced. If either side of the blade dipped, it meant the blade was imbalanced and would cause a lot of vibration when spinning. Luckily, I did the job evenly when sharpening and the blades were balanced well.

Here is a picture of a blade clamped down right after I finished sharpening it (see how the sharpened part gleams):

Here I am reattaching the sharpened blades (I made sure to wear gloves so I didn’t cut myself):

Here’s a close-up of the mower deck showing some of the debris that I had to remove (it was a lot worse before):

6. Replacing The Belt

Now to address the worn-out belt. I took a picture of the belt route with my phone and then removed it. I installed the new belt matching the route from my picture.

Mower deck maintenance was now complete. I slid it back under the mower and reattached the retainer springs to secure it to the chassis. I started up the motor and engaged the blades. Nothing happened. Oh no, what happened? The blades did not spin.

I looked underneath the mower and discovered the belt had too much slack. I compared the new belt to the old one and saw that the new one was slightly bigger. Unfortunately, this model mower did not allow you to adjust the tension in the belts, so the new belt was unusable for me.

I ordered the correct part number online, but it was a third-party belt. I should have spent the extra money on a factory replacement instead. Disappointed, I put back in the old belt, so I could at least use the mower and ordered a factory belt in the meantime. I’d install it in a few days when it arrives.

Let that be a lesson, be wary of third-party replacements especially when the price looks too good to pass up.

7. Lubricant

I had almost completed my maintenance plan. Then, I applied all-purpose grease to a few key areas on the mower.

I used the mower manual to identify these areas and applied grease where needed. A few areas also required silicone lubricant, which I was lucky enough to have a spray can of (I use it to keep my foosball table rods spinning like new).

I broke in the new lubricated parts with a drive around the yard, making sure to turn the steering wheel a lot. The neighbors must have worried what state I was in zigzagging the mower across the yard!

8. Tire Pressure

The final step was to check the tire pressure. I grabbed a pressure gauge from my car’s glove compartment box and compared the mower tire pressure to recommended specs in the manual.

They were a little low, so I used a bicycle pump to bring them back up to the correct PSI. Low tire pressure will cause excess drag when driving and consume more fuel, so it’s important to keep your tires properly inflated.

Finally, the mower was in proper working condition for the new season. I documented what parts I replaced along with the date. This way I would remember for next season the parts I replaced.

Not everything in my maintenance plan needs to be done every season. I just wanted to hit all my bases this one time, since I had no way of knowing what the previous owner did.

If you are in a similar position, wondering how to fix your old riding lawn mower, then go through the above checklist. It’s been tried and proven.

Look out tall grass, I’m ready for you this season!