You’re knee-deep mowing the lawn when suddenly you see smoke around you, and it’s not coming from the neighbor’s barbeque.
As you look down, you see your lawnmower is smoking like a locomotive. Immediately, you realize there’s something wrong with the engine. The grass will have to wait because you must figure out the problem and decide what is the better option, a small engine replacement or repair.
How to Troubleshoot Small Gas Engines
First, try to identify the problem. After some small gas engine troubleshooting, you'll have a better idea if a repair is possible or if you should replace the engine.
If your troubleshooting steps are inconclusive, the problem could lie deeper. A combustion engine relies on four main components: air, fuel, compression, and lubrication.
Engine problems will typically fall under one of those four categories. Since they all work together, issues with any one of them can spread across the entire machine.
For example, sand that passes through the air filter and enters the air intake stream into the carburetor causing internal wear and tear. It continues to travel to the intake valve and seat before entering the cylinder and damaging the piston rings.
Eventually, it reaches the oil and begins to form sludge. During this time, more dirt has entered the engine and compounded the damage. Pretty soon, the engine starts to smoke.
Some causes of major engine problems include:
Ingestion of an abrasive material through the air intake or oil fill
Insufficient lubrication typically caused by old oil, a lack of oil, or dirt buildup
Overheating caused by clogged cooling fins, insufficient lubrication, etc.
Overspeeding due to a failing governor system
Breakage of engine parts caused by excessive vibration
Of course, that’s not an exhaustive list of engine failures. Everyone’s specific case will be different, and if you don’t feel comfortable diagnosing the problem yourself, take it to a small engine repair shop.
If the equipment the engine powers is old, it may make sense just to buy a new lawn mower, log splitter, or whatever machine is in question rather than spend money diagnosing and fixing its engine.
If it’s a newer piece of equipment, it could be worth repairing or replacing the engine, depending on the diagnosis.
Small Gas Engine Repair Options
Once you or your local shop makes a diagnosis, determine whether a repair would be more trouble than it's worth.
First, identify your current engine’s serial and model numbers and find out if you can get parts for it. If not, fixing it may be a waste of your time, and it is time to replace.
If parts are available and the problem is a broken recoil starter or clogged carburetor, it’s simple enough for someone who is mechanically inclined to make the repairs. However, if the problem is nearer the engine block, like a broken connecting rod or damaged piston ring, it will require a complete disassembly and most likely isn't repairable.
This is because the deeper a problem has penetrated the engine, the more likely it is to have ignited a chain reaction of damage. For example, insufficient lubrication will cause grinding between the piston rings and cylinder wall, as well as overheating and blown gaskets.
Even if you do feel like attempting a repair, consider the time involved both with diagnosing the problem and making the repair. If a professional is doing it during peak season, you might be on a waiting list for weeks.
In these instances, it likely makes more sense to replace the engine unless you are 100% certain you have identified all the problems, repair them correctly and time is not an issue.
Consider the Engine Warranty
The complexity and cost of repair is not the only thing to consider when deciding whether to replace an engine. Naturally, there is no warranty on repairs when making them yourself, so if anything malfunctions again, that’s more money out the door.
On the other hand, a new engine will come with a 2-3-year warranty and is the best solution from an investment standpoint. Not only is a warranty an added value because it places more pressure to get a repair job done right the first time, but it also gives you peace of mind. When in doubt, replace.
The Bottom Line
A general rule when deciding when to replace a small gas engine is as follows:
Calculate the cost of the necessary repair parts
Double that number to estimate labor costs
Add the part and labor costs together
If the combined costs of parts and labor approach or exceed the value of a new engine, consider replacing the engine and getting the warranty.
Repairing equipment yourself will save money and makes sense only if the problem is simple and doesn't involve opening up the entire engine. I remember trying to make a fuel line replacement on a chainsaw, thinking it would be a simple task.
After purchasing the parts, I quickly learned otherwise once I opened it and saw the extent of the damage. It just wasn't worth it. I realized I should quit while I'm ahead.
The more complicated the problem, the higher the chance a professional will be needed, and the more issues may be uncovered. Also, if you do attempt to repair or rebuild an engine yourself, there is no warranty if something goes wrong.
Replacing the engine or the entire piece of equipment is always the safest option. The engine is the heart of the machine, and there is no room for error or uncertainty.