Question about Honda 125cc piston ring

[bscull]

I am changing out the piston ring of my Honda 125cc motor for the first time. I am mechanically inclined, but I just want to make sure that there are no secrets I don't know about, or things that I MUST DO. Please help.

[Dale Seeley]

I'd go to the local Honda bike shop, the one that leans more toward moto than street, and offer to pay them twice their normal rate to do it for you while you watch and ask questions.

You'd know it was done right this time, and have a pretty good idea what it takes next time. I've found that learning the hard way is usually far more expensive....

[Noah Stark]

It is much simplier than it seems.

1- Drain the water by removing the 10mm drain bolt from the water pump cover.

2- Remove the head water lines and spark plug.

3- Remove the cylinder head (make sure the piston is at TDC incase there is any water left in the head so it doesnt go down into the bottom end and ports)

4- Remove the cylinder. Measure the base gasket thickness and make sure you have the correct thickness of gaskets avaliable to replace them.

5- Completely clean the head and cylinder with warm soapy water. It is only clean when you can take a clean white and slightly oily lint-free paper towel(like a wypall) and wipe the bore out and there is ZERO dirt and lint on the towel.

6- Insert the new ring into the cylinder and use a old piston to square it up to about 1/2-3/4 of a inch down from the top of the cylinder. Measure the gap. It must be at least .009". Anywhere from .009" to .014" is fine. Any more than that you will loose power.

7- Once gapped, put new ring on the piston and apply ample oil/lube to the piston, ring, and cylinder. Also put the new base-gasket on.

8- Carefully slide the cylinder onto the piston and ring making sure it is aligned properly and does not hang up anywhere. Torque the nuts to 16ft/lbs

9- Install a new head gasket or o-rings and install the head. Torque to 18ft/lbs. Check the squish to make sure all the clearances are good and peachy.

10- Re-attach the water hoses and add water and burp the system making sure there is no air anywhere in the system.

11- Fire up the motor, making sure the jetting is a few sizes on the righ side. Keep your hand on the motor(around the cylinder and head) making sure that the motor heats up just as quickly as the rad and hoses do. If the motor gets warm and the hoses and rad is still cold, then there is a air blockage in teh system. Shut down the motor and re-burp.

12- Run for 1 session with minimal or no load. Do not let it idle for more than 20secs at a time. Do not rev to more than 9,000rpm either. Run until the water temp gets to 130def F. Shut it down.

13- Let it cool down to room temp and re-torque the cylinder and head.

14- Warm it back up onto the stand and take it out onto the track. Take a few easy laps. After about 5mins of easy track time..... RUN IT! You are good to go!