Sooner or later every moped driver with a 2-stroke engine is faced with this task: the cylinder has to come down. There may be various reasons:
- either you got hit and ended up stranded on the side of the road with a piston seizure ;
- your cylinder has suffered external damage;
- you want to upgrade to a tuning cylinder;
- or the race management has issued you a defect certificate.
No matter why you are facing this challenge, we are here to help you. For a newbie, replacing cylinders can be challenging. Let me tell you: no master has yet fallen from heaven. Be sure to bring patience and time before you get started.
First of all: Replacing cylinders differs from model to model. But basically they are always the same activities. Once you understand this, it will also work with other models. We have put together general instructions for you here. You can also use this as a checklist.
Thorough cleaning of the engine
Before you start working, you should clean your engine or, better yet, your entire moped thoroughly. Focus particularly on the area around the cylinder. This will prevent dirt from getting into the crankcase after you have dismantled the cylinder.
Fix the moped and remove the cylinder head
Next, make sure your moped is secure. It's best to use a repair stand so that your moped stands upright. Depending on accessibility, you may need to remove the side panels.
For water-cooled engines, you now drain the coolant. As a rule, you will find a drain plug at the lowest point of the cooling circuit, usually near the pump.
Tip: the water drains better if you open the lid of the water tank.
Dismantling attachments
Remove the exhaust , carburettor and any coolant and oil hoses to gain access to the cylinder. This work should be done when the cylinder is still firmly screwed on.
Dismantle cylinder
Now all attachments on the cylinder should be removed and you can finally start dismantling.
Remove the screws or nuts from the cylinder head. Note the order and position of the screws as they may have different lengths.
The cylinder head is now loose and usually still sticks slightly to the cylinder. This is due to the seals. If necessary, use a lever made of plastic or wood to carefully “pry it off”. Make sure that the cooling fins are not damaged or bent.
After removing the cylinder head, thoroughly clean the exposed surfaces again. This will help you avoid dirt in the engine.
Excellent! The cylinder head is already down and you can see your combustion chamber and the piston crown.
Like the cylinder head, you can now also pull down the cylinder. The cylinder also tends to stick to the seal. Again, use a lever to help carefully. If you have had a piston seizure or your moped has been standing for many decades, this can be very difficult to fix. It can help to “soak” your combustion chamber properly with penetrating oil.
Replace piston
After you pull the cylinder down, you will see the piston mounted on the connecting rod and the open crankcase. If possible, no foreign objects such as dirt, tools, seal residues or screws should fall in here (beware of engine damage). That's why we pay attention to intensive engine and moped cleaning right from the start. Tip: cover the open crankcase with a clean rag. With the crankcase covered you can also best remove the old gasket residue from the engine block.
If you install a new cylinder, you always have to install a new piston. We therefore always deliver our cylinder kits with new pistons.
You can get tips and tricks for replacing pistons in our “HOW TO | this is how you install a piston”
Assembly of the cylinder
After the piston comes the cylinder. Lightly oil the cylinder base gasket supplied and place it on the sealing surface of the engine. If you placed a rag on the crankcase, you can now remove it. You also oil the cylinder bore with a nice film of oil. It's best to use 2-stroke oil for this. Now push the cylinder back onto the piston. This moment is a little tricky because you have to squeeze the piston rings together while pushing the cylinder on. Maybe you can find someone who can help you briefly. The cylinder must slide very smoothly onto the piston. Push the cylinder back until it rests cleanly on the base seal.
Now push the cylinder head onto the cylinder. To do this, install the cylinder head gaskets first. If these are rubber seals, you should grease them. This will help you fix the seal in its groove and it will sit better. Unless otherwise specified by the moped manufacturer, you should avoid using any other sealants.
Just attach the cylinder head with the appropriate screws or bolts. Make sure to tighten the screws according to the manufacturer's instructions and set the torque correctly. If possible, you should always tighten cylinder head screws crosswise.
Assembly of add-on parts
You have now successfully installed your cylinder kit. Before you set off, reassemble the add-on parts such as the exhaust, carburettor/ASS/diaphragm and any coolant and oil hoses that may be present.
Don't forget to fill in coolant otherwise you will only enjoy your new cylinder for a short time.
Test run
Double check that everything is tightened and there are no parts left.
Start your engine and check if everything is working properly. Your moped will smoke a little more than usual. This is because the cylinder bore has been oiled.
Once you have dismantled the fairing parts, it is time to reassemble them and put the new cylinder through its paces.
There are always myths and uncertainties about retracting cylinders.
Our recommendation for you: Slowly but quickly!
If you are unsure or have any difficulties, please contact us. Incorrect replacement can cause damage to the engine. Therefore, I would rather ask again.
We hope you have fun screwing!
