It happens to all of us. We find that thrown away engine and are curious as to whether the insides of it are any good and decide to disassemble it.
When I was in high school I was disassembling my engines all the time mainly because I liked to. But quite honestly an engine does not need to be disassembled, unless there is a serious condition with it. The serious condition may warrant that the engine is no good anyway and will require serious or costly machining operations. Specifically for example, the engine may need to be honed out so that a larger piston can be used. The trouble with small engines is that they’re not designed to be bored out. Additionally a boring operation typically costs in the hundreds of dollars.
What warrants disassembling the engine?
An engine should be disassembled for the following reasons:
– If the engine has been frozen up because it was sitting too long or had seized
– If a loud knocking noise is observed when the engine operates
– Excessive scoring and piston wear in the cylinder bore
– Engine burn excessive oil.
– If high-performance components are going to be used such as a high performance connecting round, new piston, and camshaft.
Let’s briefly talk about the items just listed.
Engine Has Seized Up
First of all if an engine has seized up or has been frozen is because it sat too long, typically the damage that will occur inside the engine is that the connecting rod may have become bonded to the crankshaft.
Additionally, if the engine has been frozen what that means is that the rings on their piston have become rusted and partially bonded to the cylinder wall. It is a very dangerous thing to try running the engine after it has been frozen solid because the rust will cause score marks in the cylinder walls and score marks will hold oil when the engine is running. The score marks because they’re holding oil will burn the oil and cause excessive amounts of oil to channel up through the score mark. The score mark effectively becomes a ditch that the oil can travel through.
Deep score marks of over .010 inches in depth can cause excessive amounts of oil blow by. This will be evidenced by the positive ventilation crankcase valve belching large amounts of smoke out of it. Additionally the engine will run out of oil very quickly. Another symptom is that the spark plug will become fowled very quickly. Depending on what kind of oil you are using it may film up on your spark plug causing the spark plug to foul out.
The only remedy to try to save the engine is to bore out the cylinder walls so that the score marks are eradicated.
Sometimes what can occur when the engine runs out of oil is at the connecting rod can become melted and then bond to the journal on the crankshaft. This is a less serious condition than the scored bore. Usually, however, you won’t get that lucky; the bore usually becomes scored prior to the connecting rod giving way.
As a side note: typically Briggs & Stratton engines are aluminum bores. You’ll find that the engine will start to burn oil after about 50 hours of operation. This particular engine needs careful attention to the oil levels and to the intake filters. The major reason why an engine becomes scored is because it has ingested dust and the dust actually becomes burned. The dust then turns into rock hard grains that get trapped between the piston wall and the bore. They as a result grind up and down in the cylinder wall causing score marks.
The best kind of engine to get is an I/C engine which has a cast-iron bore or liner. Typically Tecumseh comes standard with an iron liner.
Loud Knocking Noise Inside The Engine
In order for engine damage to occur the engine must have been run out of oil at one time or another. When this occurs the connecting rod, as stated before in the previous section, becomes overheated. What occurs is that the oil film between the connecting rod and the crankshaft has dissipated. In plain English: there is no oil between the two parts. As a result you have an aluminum rod running on a steel crankshaft journal. The two components will become melted together in short order.
Sometimes what occurs however is that the connecting rod will have some oil but not enough. So the connecting round will become partially melted but not melted to the crank journal. You will likely get an excessive gap built up between the connecting rod and the crank pin. This will be heard as a loud knocking noise. An engine that makes a noise likely needs repair immediately. Again if the engine was ever run out of oil at one time there may be some serious damage already done to it.
Note: I am not an advocate of throwing out motors just because they burn oil. If they burn oil sometimes it can be tolerated for a time. It depends on how much oil is burned when the engine runs. A careful monitoring of the oil level needs to be maintained whenever using an engine that burns oil. I’ve been using a product in my go kart that has helped greatly with the oil consumption and wear problems. It’s called Ever Oil. And what it does is it has an oil stabilizer that has a superior lubrication property to it that keeps the engine temperatures down while also keeping the oil from getting burned up.
What will occur is that the engine will not burn the oil because the oil has a higher flashpoint than normal oils. This will actually act to increase the engine’s performance because the oil will tend to collect in the cylinder head causing the engine to seal better despite the fact that it has score marks in the cylinder walls.
The spark plug needs to be monitored every once in a while and cleaned off, however the burning oil issue isn’t not as much of a problem as it used to be. So what I’m saying is that it is not necessary to have an engine that is operating at optimal conditions to be used on your go kart. This can be a great drawback if you put a restriction upon yourself that the engine must be in perfect condition to be on your go kart. One of the criteria for building a go kart for practically nothing is that you found an engine that nobody wants. And typically an engine that nobody wants is one that might be old and tired.
If you haven’t noticed the main reason why an engine gets damaged is because it runs out of oil or overheats. There are couple reasons why an engine will overheat and they are:
-The engine has been run too fast and too lean for an excessive amount of time.
-The engine ran out of oil
-The engine could not get cooled down because the cooling fins were blocked or no air was going over the cooling fins because the fan was broken.
As you can see there are three main reasons why the engine overheats and it is because there is either no oil, the engine’s been running too lean or the engine could not cool down. The main cause for engine overheating however is not typically carburetor adjustment but usually 85% of time because the engine is running out of oil.
High Performance Parts Internal
The final reason as reported before for disassembling an engine was to basically replace it with high-performance parts internally. Typically the high performance parts are low budget items such as high lift cam shafts, low inertia high strength con rods and polished crankshafts as well as high performance pistons, rings, valves and valve springs.
All these high performance items seek to push to envelope of what the engine can actually put out normally. Most use exotic fuels such as alcohol or nitro fuels. The resultant horsepowers range (for a 5 hp brigg for example) from 6 to 20 hp depending on the upgrades. No normal 5 hp Briggs can safely put out much more than 5.5 hp before problems (the problems spoken of above) start to arise.
Next time we will talk about how to disassemble and engine and the step required…