Tips on How to Repair a Four Stroke Lawn Mower

By Philip Yiga | November 17, 2016

If you have gas-powered lawn-mower, then you should know that it operates using an engine and this implies that sometimes it will experience mechanical issues that are hard to repair. In fact, if your lawn-mower is equipped with a 4-stroke engine then this article will provide you with some of the procedures that you may can follow in order to repair that engine in case it gets any problems. However, you should know that this article is only providing you with basic knowledge on how an internal-combustion engine works and the parts it features. On the other hand, if your lawn-mower features a 2-stroke engine then the procedures in this article will not apply in its repairing process because 2-stroke and 4-stroke lawn-mowers totally feature different engine-systems. Lastly, if you fail to repair your 4-stroke engine, then consider taking it to an experienced mechanic and if your lawn-mower is still under the warranty-period then just take it for a free repair and never attempt to open its engine because the warranty will become void.

Steps To Follow When Repairing A 4-Stroke Engine:

1. Switch of the lawn-mower: before you begin working on your lawn-mower, you need to switch it off and even remove the spark-plug lead so that the machine does not accidentally turn-on during repair. In fact, if a lawn-mower turns-on when under repair then it may accidentally injure your fingers and arms which are working on it. So, try as much as you can to switch it off and keep the lead far away from the spark-plug as safety-measure.

 

2. Check some essential components of the engine first: you will need to first check the simple but essential components of the engine. In fact, this will involve checking the plug, oil and air-filter so that you can get to know if the problem is with engine or with these components. In fact, these are simple repairs that will not require you to open the engine and this is why you need to check them first before tampering with the engine.

 

3. Check the compression-system: this involves pulling the starter-cord while the plug is in the engine but with the lead disconnected and safety kill-switch bar pushed-down. So, if feel any quick and tight resistance after while pulling the starter-cord then compression system is ok but if you happen to feel no-resistance or even hear an asthmatic-sounding/puff-noise then the compression system has a problem and needs repair.

 

4. Troubleshoot a bad compression-system: bad-compression is usually caused by a bent/broken valve or blown head-gasket. So, you will first have to remove the 8 large-bolts at the front of the engine and anything else in the way and after remove the head. Afterwards, check the head-gasket for nay missing parts and if there is any then get a replacement from a nearby engine-spare shop/store. On the other hand, you may have to use steel-wool to remove any stuck debris on the gasket and then assemble it. However, if the gasket has no problem, then try inspecting the valves and make sure that none of them is bent or not fully closing. In fact, if the valve is bent then you will have to straighten it using a slotted screwdriver and if it’s not closing properly then you need to replace it with a new valve.

 

5. Check for any bent crankshaft: you also have to check for a bent crankshaft by gently tipping the lawn-mower with the exhaust-pipe up but gas will actually drip-out and this can’t be avoided. However, make sure that the plug lead is out and then turn the cutting-blade slowly. If you happen to notice that the bolt in the center is shimmy from side-to-side then consider discarding the lawn-mower because it has a bent crankshaft and it can’t perform correctly. But it the blade and bolt are well-centered then proceed to the next step.

 

6. Check for spark: incase compression wasn’t the problem then consider checking for spark by simply removing the plug from the engine-head or replace the lead but you can also consider grounding the tip of the plug against the block in order to revive it. Afterwards, you have to pull the mower-starter with the safety kill-switch down and if you see a small spark jump the gap at the end of the plug then continue to the next step.

 

7. Check the carburetor: if you noticed a spark from the plug before, then consider checking the carburetor by removing the air-cleaner and its components after check for any dirt or carbon-deposits inside the carburetor. Additionally, you may even remove the carburetor from the fuel-tank and then inspect the 2-screens for any blockage and you can even inspect the rubber-diaphragm or paper-gasket for any holes and after do replacements if necessary.

 

8. Inspect the throttle: you may also have to inspect the mower’s throttle with the air-cleaner off and then move the throttle-knob to check if can fully open and shut. So, if the throttle doesn’t function properly then consider cleaning it out and if it persists then replace the carburetor.

 

9. Inspect the manifold: you will have to check the intake-manifold for any holes by wiggling it. In case it wiggles then consider tightening the 2-bolts on the left end but if the manifold has holes or melting then replace it.

 

10. Inspect the flywheel key: you may also need to check the flywheel-key which is a small, removable notch within the flywheel and if its shattered or cracked then set the engine to TDC where both valves will be open and after align the flywheel magnets using a magneto and then replace the flywheel-key.

 

11. Recheck the engine and then assemble it: check for one last time for any problems or mistakes and then re-assemble your lawn-mower’s engine. Power it on to see if work properly and it doesn’t then it may be having a severe problem which implies that you may just have to buy a new lawn-mower.