Engine 157QMJ is one of the most common powertrains in the world of mopeds and scooters. However, the factory equipment often deprives owners of a forced starting mechanism, which creates serious difficulties if the battery is discharged or the starter is faulty. Installing a kickstarter on this motor is a doable task, but requires precision and an understanding of the internal mechanics.
The engine transformation process involves replacing a number of components, including the crankcase, flywheel and the gear system itself. An incorrect approach can lead to jamming of the motor or rapid wear of parts. In this article, we will analyze each stage of the work so that you can get your moped into working condition yourself without contacting a service center.
Compatibility assessment and selection of necessary components
Before starting work, you need to make sure that your specific engine 157QMJ has the ability to install a kickstarter. Many Chinese engines are available in two versions: with and without kick. The difference lies in the design of the crankcase and the presence of a seat for the mechanism.
If your engine already has a hole for the kickstarter shaft, but does not have the mechanism itself, the task is simplified. You only need to purchase the gear set itself and the lever. However, most often, owners are faced with the need to completely replace the crankcase with a version with a kickstarter, since the basic version simply does not have the corresponding channels.
- 🔧 Engine crankcase with a seat for the kickstarter shaft.
- ⚙️ Gear set for kickstarter drive (usually 2-3 pieces).
- 🔩 Kickstarter shaft with return spring and retaining ring.
- 🛠️ Kickstarter lever with mounting bolts and nuts.
It is important to check the compatibility of the variator pulley, since sometimes when replacing the crankcase, the mounting geometry of the front cover also changes. A mismatch in shaft diameter or keyway location may make assembly impossible.
Removing the old system and preparing the engine
Start by completely disassembling the engine. Remove the variator, clutch and crankcase covers. You need full access to the crankshaft and transmission input shaft. Clean the crankcase surface of any traces of old gasket and sealant using a scraper and solvent.
If you are replacing the entire crankcase, carefully remove the crankshaft. This is a critical point: the bearings can be tightly fixed or, conversely, have play. Use a special puller or carefully knock the shaft out through the back side using a soft pad.
⚠️ Attention: When removing the crankshaft, try not to damage the seals. If the seals are torn or show signs of wear, they must be replaced with new ones before installing a new crankcase.
Check the condition of the cylinder and piston. If the engine has been used intensively, the piston group may need to be replaced. Install the new crankshaft into the new crankcase, after lubricating the bearings with engine oil. Make sure the shaft rotates freely and is not jammed.
Installation of the kickstarter gear mechanism
This is the most critical stage. A special gear must be installed inside the crankcase, which will engage with the gear on the kickstarter shaft. The procedure for installing gears is strictly regulated by the manufacturer. An error in the sequence will result in the engine not cranking when the lever is pressed.
Install the idler gear into place, making sure that the gear retaining pin fits into the groove. Then install the kickstarter drive gear. Pay attention to the direction of the teeth: they should match the profile of the gear on the kickstarter shaft.
- 🔩 Secure the gears with retaining rings or cotter pins, if the design provides for it.
- 🛢️ Apply thick lubricant to all rubbing surfaces of the gears.
- 🔍 Check the gear play: they should not hang out, but they should not jam either.
Install the kickstarter shaft through the hole in the crankcase. A return spring must be installed on the shaft, which will return the lever to its original position after starting. The spring must be tensioned in the correct direction, otherwise the lever will bounce or not return.
⚠️ Caution: Incorrectly installing the recoil spring may result in the kickstart lever sticking out of the crankcase or not cranking the engine when pressed.
- 2 stroke
- 4-stroke 50 cc
- 4-stroke 125 cc
- 4-stroke 150 cc
Assembling the crankcase and installing covers
After all the internal mechanisms are installed, it is necessary to assemble the two halves of the crankcase. Apply a thin layer of sealant to the joining surface. Be careful not to get any sealant inside the engine, as this may clog the oil passages or filters.
Connect the crankcase halves and tighten the bolts in a specific sequence, starting from the center and moving towards the edges. This will ensure an even fit of the surfaces. Tighten with a torque wrench if you have one, or with moderate force so as not to strip the threads in the aluminum.
Install the covers on the shafts. Place the lever on the kickstarter shaft and secure it with a bolt. Make sure the lever moves freely and does not interfere with the motor housing or guards. If necessary, trim or bend the lever.
⚠️ Attention: If, when assembling the crankcase, you feel that the shafts are difficult to turn, do not tighten the bolts completely. Disassemble and check the position of gears and bearings.
☑️ Check before final assembly
Setting up and checking the operation of the mechanism
Before installing the engine back on the frame, you must check the operation of the kickstarter. Remove the spark plug to make it easier to turn the cylinder. Press the kickstarter lever several times. You should feel a distinct resistance as the gears engage and the lever returns to its original position.
If the lever falls without resistance, it means the gears are not engaged or the mechanism is worn out. If the lever does not return, check the spring tension or the presence of foreign objects in the mechanism. Also check whether the lever does not touch other parts of the moped when moving at full speed.
- 🔊 Listen to the sounds of the mechanism: there should be no metallic grinding or knocking.
- 📐 Measure the stroke of the lever: it should be sufficient to fully rotate the crankshaft.
- 🔋 Check the gap between the gears: it should be minimal, but without friction.
If everything works properly, you can install the engine on the moped. Connect the wiring, install the carburetor and exhaust system. Don't forget to check the engine oil level, as oil may have leaked when replacing the crankcase.
What to do if the kickstarter is jammed?
If the mechanism is jammed, do not use brute force. Disassemble the crankcase and check to see if the gear is broken or the alignment marks are out of alignment. Often the problem is solved by cleaning the metal shavings and replacing the lubricant.
Technical specifications and compatibility table
For the correct operation of the mechanism, it is important to comply with the technical parameters. Below is a table with the main characteristics that must be taken into account when selecting spare parts for the engine 157QMJ.
| Parameter | Meaning | Note |
|---|---|---|
| Kickstarter shaft diameter | 10 mm | Standard size for most models |
| Number of gears | 3 pcs. | Leading, intermediate, driven |
| Gear material | Steel 45 | Increased durability against wear |
| Return spring type | Spiral | Provides quick lever return |
| Crankcase bolt tightening torque | 8-10 Nm | Avoid overtightening the aluminum housing |
Using low-quality soft metal gears can cause them to wear out quickly. After several hundred starts, the teeth may become flattened and the mechanism will stop working. Therefore, choose spare parts from trusted manufacturers.
Common mistakes when installing yourself
Many moped owners make mistakes that lead to repeated disassembly of the engine. One of the most common problems is incorrect spring installation. If the spring is not tensioned in the right direction, the kickstarter lever will bounce back with great force, which can cause hand injury.
Another mistake is ignoring lubrication. The kickstarter mechanism operates under conditions of high loads and the absence of a constant oil bath. Applying thick lubricant to the gears and shaft is mandatory. Neglecting this rule will lead to rapid wear of the teeth and jamming.
It is also worth paying attention to the tightening of the lever mounting bolts. If the bolt is not tightened enough, the lever may fly off during operation. If it is tightened too much, it will not rotate or will strip the threads in the crankcase.
Before final tightening of all crankcase bolts, rotate the crankshaft by hand several times. If the rotation is smooth and without jamming, you can assemble the engine completely.
Don't forget to check the condition of the crankshaft seals. When replacing the crankcase, old oil seals may lose their shape and begin to leak oil. Replace them with new ones, using a mandrel or an object of suitable diameter for careful pressing.
⚠️ Warning: Never attempt to kickstart the engine if the mechanism is not yet fully assembled or if you are not sure that the gears are installed correctly. This can lead to broken teeth and costly repairs.
High-quality assembly of a kickstarter requires not only the presence of all parts, but also strict adherence to the installation sequence and the use of the correct lubricant.
FAQ: Answers to frequently asked questions
Is it possible to install a kickstarter on an engine without a proper crankcase?
No, that's impossible. Engine crankcase 157QMJ Without a kickstarter, it has no internal channels or seats for gears. You'll need to replace the crankcase with a kickstarter version or look for special adapters, which are often unreliable.
How long does it take to set up a kickstarter?
If you have all the necessary parts and tools, the process takes from 3 to 5 hours. If you have to completely disassemble and replace the crankcase, the time may increase to 6-8 hours, especially if this is your first time.
Do I need to change the oil after installing the kickstarter?
Yes, definitely. During disassembly of the crankcase, some of the oil may leak out, and contaminants may get inside. Replace the oil with fresh oil to ensure normal operation of all engine components.
What should I do if the kickstarter lever does not return?
Check the return spring tension. It may be loose or installed incorrectly. Also check to see if the lever is touching the motor housing or other parts. Sometimes the problem is solved by lubricating the kickstarter shaft.
Can a kickstarter be used on a cold engine?
Yes, the kickstarter is designed specifically to start a cold engine. However, at very low temperatures, try not to press sharply or forcefully to avoid damaging the gears. First, warm up the engine slightly by cranking it without starting it.