Cleaning the Engine and 2-stroke Crankcase Dirt with Oil and Grease By Kerosene

There are riders who like to polish their motorcycles and are good at it, but they polish the exterior but never touch the inner of the cowl or cover. On the other hand, there are riders who are not so good on the outside, but are incredibly meticulous about polishing the engine and suspension. Of all the dirt on the engine, the chain lube buildup around the drive sprocket is the most stubborn and troublesome, but if you have a small displacement engine, you can take it off the frame and wash it entirely.

Spraying chain lube over and over without cleaning leads to dirt build-up

Considering that the motorcycle is half a century old, the condition of the right side of the engine is commensurate with its age, but when the sprocket cover on the left side was removed, it was covered with oil and dirt as shown in the title image. It is not uncommon to see the drive sprocket area dirty on a trail model motorcycle that has been used for forest road touring without cleaning the drive chain and only lubricating it.

The sprocket area as well as the inside of the crankcase will be cleaned, so the cylinders and pistons will be removed first before unloading the engine. This motorcycle is a two-cylinder 90cc engine, but a Honda Super Cub or Monkey single-cylinder engine is even lighter, so loading and unloading is easy, even with the cylinder head attached.

Dirt builds up in places you can't see, whether you're cleaning your house or washing your motorcycle. It is not unusual for the inside of the cowl to be covered in gravel, and the cylinder head under the gas tank and around the carburetor to be full of dirt, just as it is full of dust under a sofa that is rarely moved even if the floor is cleaned every day.

One of the most common areas of hidden dirt on motorcycles is the oil stains around the drive sprocket. While it's important to perform minor maintenance on the drive chain, it's ironic that such a motorcycle tends to end up with a sloppy, slimy finish on the inside of the sprocket cover.

Most of the dirt around the sprockets is caused by dust and mud sticking to the sprockets and becoming viscous as a result of the flying chain lube. If you clean the chain with chain cleaner every time you do chain maintenance and then apply a new chain lube, the area around the sprockets should not be too dirty.

However, if you skip this step and only spray the chain lube, the chain itself will first become overly greasy, which will then splatter on the sprockets and stick to the surrounding area. In the case of motorcycles with non-sealed chains from the 1960s, the role of the chain lube is much more important than that of the sealed chain, so dirt around the sprockets tends to be more noticeable.

Just as it is recommended to clean your house twice a year instead of once a year, it is recommended to remove the drive sprocket cover and clean the inside of the drive chain once every three times to prevent dirt buildup. However, if the desire to go out for a ride overrides maintenance, it is understandable that you would want to apply more chain lube.

Even so, the dirt will not disappear on its own if you keep pretending not to see it, and it is necessary to observe the inside of the sprocket cover once in a while to avoid losing motivation at the sight of it when you remove the cover to change the chain or sprocket.

Washing in kerosene because wasting parts cleaner is a waste of money

Although some of the oil was scraped off with a scraper, it is easier, in the end, to clean off the oil stains that stick to the engine like viscosity. The backside of the crankcase is hidden inside the press frame, so it can hardly be cleaned if it is still mounted on the frame. There is an idea that it is OK to leave dirty if it is not visible, but it is unpleasant to scrub with a brush through the gap between the frame and the engine because the juice of the dirt keeps dripping. If you use the engine alone, you can clean it without compromise.

Just by cleaning the dirt around the sprockets, the overall impression of the engine will change drastically. Once the sprocket cover is on, it will not be visible, but once it is cleaned up, maintenance will be easy. The outside of the engine is rusty, but the inside of the boxy press frame has been cleaned with kerosene so there is no smell of oxidized grease or oil.

There is no doubt that scattered chain rubs accumulate and accelerate the dirt, and if you clean it frequently, you won't have to deal with clay-like hardened dirt. Even if you try to clean it with a parts cleaner, it is difficult to penetrate the battery-piled dirt and you will consume the cleaner in vain.

Using kerosene has long been considered the best way to effectively remove oil stains. Before the 1970's, when canned spray-on parts cleaners didn't exist, people used to spray oil or kerosene with air from a compressor for cleaning. Some motorcycle shops have parts washing stations where kerosene or cleaning oil is circulated to clean parts.

It is indeed uncomfortable to spray kerosene, but it is possible to clean off oil stains by rubbing with a nylon brush while pouring it over the dirty part. However, if you don't want to spray kerosene, you can remove the engine from the frame, put it in a large metal bat or plastic container, and scrub it with a brush while pouring kerosene on it, so that you can clean every corner of the engine better than when it is on the frame.

If you remove the sprocket cover, you will find the drive shaft, change shaft, and in some models, the clutch push rod, each of which has an oil seal. It is not a good idea to soak the rubber oil seal in kerosene or gasoline, but for a short time it is first okay. If the oil starts leaking within a short time of pouring kerosene on the engine, scrubbing it with a brush and washing it off with parts cleaner, it is highly likely that sooner or later you will develop a seal failure.

The engine used for the sample was more than 50 years old, and although there were no major functional problems with the engine, the area around the drive sprocket was covered with layers of chain rub, oil, and mud, making it look like a stratum. I scraped off the deposits with a scraper and a flathead screwdriver, and when the surface of the ground was visible to some extent, I washed it with a brush while bathing it in kerosene, and the beautiful cast surface appeared because it had been coated with oil.

Removing the engine has the advantage that the frame can also be cleaned. Many business motorcycles, especially the Super Cub, have frames made of pressed steel plates, and the engine mount area may be covered with oil and mud stains on the inside of the frame. If you spray parts cleaner inside the frame half-heartedly, the dirt inside the frame will keep flowing incessantly, and you may be horrified to find out that the frame is actually quite dirty.

Furthermore, even for the purpose of disassembling the engine, cleaning the oil stains in advance may prevent unnecessary problems. In many cases, the crankcase of a single-cylinder engine is aligned to the left and right, and although the screws that fasten the case together were removed with the intention of cleaning them after disassembly, the screws were buried in oil stains and were forgotten to be loosened. There are some examples. It is a pity that the crankcase would not have been ruined if the oil stains had been removed first, even if it was troublesome. In order not to get caught in such a trap, it is important to clean the engine before disassembly.

The inside of the 2-stroke crankcase where engine oil accumulates is also cleaned with kerosene

The inside of the crankcase of a 2-stroke engine should also be cleaned with kerosene. If there is a problem with the oil pump check valve and oil is flowing in, turn the crankcase upside down and dump the oil out before washing. The ease of mixing with gasoline depends on the engine oil, which in turn changes the amount of oil that accumulates in the crankcase.

When I put kerosene in the crankcase and turned the crankshaft by picking the connecting rod, the engine oil mixed with the kerosene quickly became dirty. If the kerosene is replaced and the washing is repeated several times, the transparency increases and the inside of the case becomes clean.

The basic premise is that engine oil is always present in the crankcase of a 4-stroke engine, but the oil in the case of a 2-stroke is supplied by the oil pump only when the engine is performing and only as needed.

In a 2-stroke engine, the mixture is sucked from the carburetor, compressed in the crankcase, and pumped into the combustion chamber. The engine oil for the 2-stroke engine is supposed to lubricate the parts inside the combustion chamber and burn in the combustion chamber to form exhaust gases. This is why 2-stroke exhaust contains white smoke from the combustion of the engine oil.

This two-strokeExcessive engine oil buildup in the crankcase will cause white smoke that will never go away. This can lead to the following symptoms. Oil accumulation in this case can be caused by a faulty check valve inside the oil pump, which allows oil to flow from the oil tank by gravity even when the engine is stopped. This is a common symptom on old and out of print oil pumps from the 1960's and 70's.

Also, a poorly adjusted oil pump can cause an oversupply of oil to build up. Engine oil is designed to mix with gasoline and burn, but if there is an oversupply there will be residue, some of which will continue to accumulate inside the muffler or remain in the crankcase.

To drain the remaining oil from inside the crankcase, you need to remove the cylinder and piston, but unlike a 4-stroke, the cylinder head of a 2-stroke is just a lid, with no valve area or cam chain, so it's easy to remove.

By removing the cylinders and pistons and reversing the top and bottom of the crankcase, the engine oil that has accumulated inside the crankcase, sometimes called the primary compression chamber, can be drained out. Since oil is more viscous than gasoline, some of it will remain inside the case, so pouring kerosene and rinsing will clean the oil more effectively.

However, if you remove oil from around the crank bearings and piston pins, lubrication immediately after starting will be compromised, so it is advisable to spray lubricant when restoring the pistons and cylinders and to start the motorcycle on a mixture of petrol initially, even if it is a separate fuel supply motorcycle.

In addition, while removing the exhaust system when you lower the engine, you can also drain the oil that has accumulated inside the exhaust system due to incomplete combustion. It is not uncommon to see oil dripping from the exhaust pipes of older motorcycles, and cleaning the oil will greatly reduce the amount of white smoke from the exhaust.

In this way, by cleaning a dirty engine by itself, you can clean not only the exterior, but also the interior if it is a 2-stroke, thus killing two birds with one stone in maintenance.

Once the crankshaft, connecting rods and pistons have been cleaned of oil, oil is applied to the assembly. If a large amount of engine oil is applied here, the cleaning process will be meaningless, so a Superzoil spray suitable for engine assembly is sprayed.

After dumping the engine oil that had accumulated inside the crankcase and muffler exhaust pipes and restarting the engine, the white smoke was clearly reduced compared to before the cleaning. Cleaning not only the outside of the engine but also the crankcase and exhaust system will make your old motorcycle perform better.