Post by Mx Life286 on Sept 28, 2005 18:20:39 GMT -5
HOW TO: REBUILD YOUR TOP END (2Stroke)
Changing your top end or just your rings are one of the most important maintenance skills to have. If you ride or race a lot, you may be changing your top end often. To find out when you should be changing your top end, check the Maintenance Schedule.
THE PARTS:
-Piston
-Rings
-Gasket Kit
-Wrist Pin
-C Clips
STEP 1:
Remove the exhaust by removing the springs that hold the pipe to the cylinder. Then remove the bolts that hold it to the frame.
STEP 2:
Remove the radiator hose from the water pump area to allow all of the coolant to drain out of the system. While the coolant is draining this is the perfect time to remove the seat and gas tank.
STEP 3:
This is more of a reminder of a good practice than a step. Make sure you lay out all your nuts, bolts and hardware in an orderly manner so that reassembly is just as smooth as disassembly.
STEP 4:
Loosen the Phillips head clamps that hold the carburetor. I usually leave the sub frame in place and just work the carb out and lay it to the side.
STEP 5:
By this point all of the coolant should be drained so REMEMBER to remove the bucket you used to catch the coolant. Otherwise you will be following this step.
STEP 6:
Remove the six bolts (commonly 8 mm head) that hold the reed cage in. Inspect the Reeds for chips or cracks. Also check the rubber intake boot for cracks.
STEP 7:
Disconnect any external Power Valve Linkages that you may have. Yamaha owners will have to deal with this set.
STEP 8 :
Remove the motor mounts that connect from the head to the frame. This should be 3 bolts and 2 brackets.
STEP 9:
Loosen the six 12mm head nuts that hold the head on the cylinder. I only loosen them right now to make it easier to get off after we pull the cylinder, but we won't get any dirt in the moto if we leave the head in place. Remove the four nuts that hold the cylinder to the crankcase and slowly and evenly lift the cylinder and head off the motor.
STEP 10:
Check the Power Valve assemblies that are sticking down in to the exhaust ports. They should be clean and free moving to insure proper function.
STEP 11:
This piston shows some signs of wear but still is well within the service limits allowed. Remove one of the clips that hold the wrist pin in place. To do this you will need a pair of needle nose pliers. Slide the pin out and remove piston and bearing from end of rod.
STEP 12:
With the way that the cylinders are built today, unless you have an excessive amount of dirt go thru your motor, ring break, piston clip come out, or crank bearings go bad, you will not have to worry if the cylinder is wore beyond service limits.
Its Rebuild Time
NOTE: It is a very good idea to place a rag or paper towel over the opening in the engine while putting the bike back together. There are many small pieces and it is not fun when you drop one into the bottom end.
STEP 13:
Insert the new C Clip into one side of your new piston. This can be a bit tricky, so you will have to be patient. Use a pair of needle nose pliers, get one end in the groove, then twist the other end into the groove as well. If you put your thumb over the end that you put in the groove first, it will be less likely to pop out.
STEP 14:
Coat the wrist pin bearing with the same 2 cycle Pre-Mix oil that you put in your gas. Prior to putting the piston on the rod, slide the wrist pin half way into the piston.
STEP 15:
Place the piston over the end of the rod, oil the new wrist pin (Pre-Mix Oil) and slide into piston (Make sure you put the piston in the correct direction. Most have an arrow on the top that points to the front of the motor. The other means of identifying direction is that the intake side (back) of the piston will have a cut out in the skirt. Refer to piston pic above). Put in the other piston C clip so that the wrist pin cannot slide out.
STEP 16:
Put the new rings on the piston. Install the bottom ring first and then the top.(Depending on your bike, you may only have one ring.) In 2 stroke motors both rings are the same so you don't have to worry about which one is the top or bottom ring. To put the bottom ring on, put the end of the ring in the top groove and roll it onto the piston bypassing the top groove with the other end and placing it in the bottom groove. Continue to roll it around until it is completely in the bottom groove. Then install the other ring in the top groove on the piston. Refer to picture of rings above.
STEP 17:
Align the rings to that the end gaps are over the locating pins in each ring groove. Compress the rings with your fingers and slide the cylinder over the top of the piston. Once the piston and rings are up into the cylinder continue to slide it downward as far as possible. You can also slowly move the kickstarter to bring the piston up so that you can seat the cylinder back down on the crank case.
STEP 18:
It is simple from here, Begin replacing the nuts for the cylinder and torque to proper specs. Now put the head back on and torque the nuts in the proper sequence and to the proper torque. The Torque spec is very important! You can get these from your owners manual or local dealer.
STEP 19:
Reinstall the reeds and intake boot. Remember to Torque properly.
STEP 20:
Reinstall the carburator and tighten the clamps that hold it in place.
STEP 21:
Reinstall the radiator hoses, fill coolant to proper level, seat, gas tank, and exhaust. Put in a new spark plug.
STEP 22:
Double check your work, make sure bolts and nuts are properly torqued and everything has been reinstalled.
STEP 24:
Now you are ready to start your machine. Allow it to run until warm, shut it down and allow it to cool fully and recheck all nuts and bolts for proper torque.
STEP 25: BREAK IN
There are many different theories on break in procedure, so here is ours. Basically, when breaking in an engine, you do not want to strain it in anyway, never go above 3/4 throttle, don't ride in sand and try to keep it on flat ground:
Note: You will be riding the bike at half throttle. To avoid fouling the plug, you may want to install a hotter one.
1) Start the bike and warm it up. Ride for about 10 minutes at half throttle. Shut it off and allow it to cool.
2) Check for any leaks and noises and pull the plug to check it.
3) Start the bike, warm it up and ride for about 20 minutes. Shift through the gears, but do not use more than half throttle. Allow the bike to cool. Check all components of the bike, look for leaks and check the spark plug.
4) If the bike looks good, not making any funny noises and is not leaking, you are good to go and the bike is ready to be put through its paces.
Changing your top end or just your rings are one of the most important maintenance skills to have. If you ride or race a lot, you may be changing your top end often. To find out when you should be changing your top end, check the Maintenance Schedule.
THE PARTS:
-Piston
-Rings
-Gasket Kit
-Wrist Pin
-C Clips
STEP 1:
Remove the exhaust by removing the springs that hold the pipe to the cylinder. Then remove the bolts that hold it to the frame.
STEP 2:
Remove the radiator hose from the water pump area to allow all of the coolant to drain out of the system. While the coolant is draining this is the perfect time to remove the seat and gas tank.
STEP 3:
This is more of a reminder of a good practice than a step. Make sure you lay out all your nuts, bolts and hardware in an orderly manner so that reassembly is just as smooth as disassembly.
STEP 4:
Loosen the Phillips head clamps that hold the carburetor. I usually leave the sub frame in place and just work the carb out and lay it to the side.
STEP 5:
By this point all of the coolant should be drained so REMEMBER to remove the bucket you used to catch the coolant. Otherwise you will be following this step.
STEP 6:
Remove the six bolts (commonly 8 mm head) that hold the reed cage in. Inspect the Reeds for chips or cracks. Also check the rubber intake boot for cracks.
STEP 7:
Disconnect any external Power Valve Linkages that you may have. Yamaha owners will have to deal with this set.
STEP 8 :
Remove the motor mounts that connect from the head to the frame. This should be 3 bolts and 2 brackets.
STEP 9:
Loosen the six 12mm head nuts that hold the head on the cylinder. I only loosen them right now to make it easier to get off after we pull the cylinder, but we won't get any dirt in the moto if we leave the head in place. Remove the four nuts that hold the cylinder to the crankcase and slowly and evenly lift the cylinder and head off the motor.
STEP 10:
Check the Power Valve assemblies that are sticking down in to the exhaust ports. They should be clean and free moving to insure proper function.
STEP 11:
This piston shows some signs of wear but still is well within the service limits allowed. Remove one of the clips that hold the wrist pin in place. To do this you will need a pair of needle nose pliers. Slide the pin out and remove piston and bearing from end of rod.
STEP 12:
With the way that the cylinders are built today, unless you have an excessive amount of dirt go thru your motor, ring break, piston clip come out, or crank bearings go bad, you will not have to worry if the cylinder is wore beyond service limits.
Its Rebuild Time
NOTE: It is a very good idea to place a rag or paper towel over the opening in the engine while putting the bike back together. There are many small pieces and it is not fun when you drop one into the bottom end.
STEP 13:
Insert the new C Clip into one side of your new piston. This can be a bit tricky, so you will have to be patient. Use a pair of needle nose pliers, get one end in the groove, then twist the other end into the groove as well. If you put your thumb over the end that you put in the groove first, it will be less likely to pop out.
STEP 14:
Coat the wrist pin bearing with the same 2 cycle Pre-Mix oil that you put in your gas. Prior to putting the piston on the rod, slide the wrist pin half way into the piston.
STEP 15:
Place the piston over the end of the rod, oil the new wrist pin (Pre-Mix Oil) and slide into piston (Make sure you put the piston in the correct direction. Most have an arrow on the top that points to the front of the motor. The other means of identifying direction is that the intake side (back) of the piston will have a cut out in the skirt. Refer to piston pic above). Put in the other piston C clip so that the wrist pin cannot slide out.
STEP 16:
Put the new rings on the piston. Install the bottom ring first and then the top.(Depending on your bike, you may only have one ring.) In 2 stroke motors both rings are the same so you don't have to worry about which one is the top or bottom ring. To put the bottom ring on, put the end of the ring in the top groove and roll it onto the piston bypassing the top groove with the other end and placing it in the bottom groove. Continue to roll it around until it is completely in the bottom groove. Then install the other ring in the top groove on the piston. Refer to picture of rings above.
STEP 17:
Align the rings to that the end gaps are over the locating pins in each ring groove. Compress the rings with your fingers and slide the cylinder over the top of the piston. Once the piston and rings are up into the cylinder continue to slide it downward as far as possible. You can also slowly move the kickstarter to bring the piston up so that you can seat the cylinder back down on the crank case.
STEP 18:
It is simple from here, Begin replacing the nuts for the cylinder and torque to proper specs. Now put the head back on and torque the nuts in the proper sequence and to the proper torque. The Torque spec is very important! You can get these from your owners manual or local dealer.
STEP 19:
Reinstall the reeds and intake boot. Remember to Torque properly.
STEP 20:
Reinstall the carburator and tighten the clamps that hold it in place.
STEP 21:
Reinstall the radiator hoses, fill coolant to proper level, seat, gas tank, and exhaust. Put in a new spark plug.
STEP 22:
Double check your work, make sure bolts and nuts are properly torqued and everything has been reinstalled.
STEP 24:
Now you are ready to start your machine. Allow it to run until warm, shut it down and allow it to cool fully and recheck all nuts and bolts for proper torque.
STEP 25: BREAK IN
There are many different theories on break in procedure, so here is ours. Basically, when breaking in an engine, you do not want to strain it in anyway, never go above 3/4 throttle, don't ride in sand and try to keep it on flat ground:
Note: You will be riding the bike at half throttle. To avoid fouling the plug, you may want to install a hotter one.
1) Start the bike and warm it up. Ride for about 10 minutes at half throttle. Shut it off and allow it to cool.
2) Check for any leaks and noises and pull the plug to check it.
3) Start the bike, warm it up and ride for about 20 minutes. Shift through the gears, but do not use more than half throttle. Allow the bike to cool. Check all components of the bike, look for leaks and check the spark plug.
4) If the bike looks good, not making any funny noises and is not leaking, you are good to go and the bike is ready to be put through its paces.