Awesome blog, keep up the good work.

That’s a tricky question. Like a car engine, it depends on the brand, but it especially depends on how well a particular mower engine has been maintained. If a seller can show you written records and receipts of regular maintenance as recommended by the manufacturer, and the mower has good compression (have a mower mechanic do a compression test), it should last quite awhile if you continue to take care of it.

If it has been abused, a fairly new mower won’t last. Maintenance is the most important set of facts you need when evaluating a used mower purchase. And you need them in writing with receipts to back them up. Don’t just take someone’s word for it.

Engine knock can have a lot of causes, fuel quality and moisture content to needing an engine rebuild. I recommend cleaning out your fuel tank and fuel lines and installing fuel filters. Have your carburetor serviced and make sure engine timing is within acceptable range. Clogged carburetor ports are a frequent problem. Also, change the spark plugs and wires.

If that doesn’t work, your compression is too low and you will need to rebuild the engine. Either the cylinders are out of round, the pistons aren’t sealing or you need a valve job. If this turns out to be the problem and your mower isn’t that old, you need to change the oil more frequently and make sure you are using a good quality oil made for mowers. Auto oil grades are not all suitable for use in mowers. Mowers typically (not always) take single grade oils, like SAE 30 weight. Some may require SAE 40 in very hot weather, or for heavy use. Check your owner’s manual for their recommendations.