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New top end and powervalve questions.

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we just changed the top end on my step brothers 2003 yz125 but have yet to start it up. we put a wiseco pro-lite piston in. im wondering, do new pistons require some kind of break in period? if so, how are they broken in? what do you torque the cylinder base screws too? i read for a 97 its 23ft/lbs and for an 01 its 30 ft/lbs, but i dont know if its the same or different for an 03. also, while we were had the cylinder off i opened the powervalve assembly and it was full of black sticky goop. i assumed that was sludge from the 2-stroke oil and cleaned it out best i could with brake cleaner. was that the right thing to do?? the old piston was a crispy black color, what exactly does this indicate? to rich of a jetting? i know it should, idealy, be a like a light brown. lastly, what worried me was on the piston there were some scuff marks that line with some slight scuff marks on the intake side of the cylinder. it seemed to just discolor the cylinder wall in that area of the scuffs and not leave any visible scratch or depression. is it anything to worry about? thanks in advance.

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we just changed the top end on my step brothers 2003 yz125 but have yet to start it up. we put a wiseco pro-lite piston in. im wondering, do new pistons require some kind of break in period? if so, how are they broken in? what do you torque the cylinder base screws too? i read for a 97 its 23ft/lbs and for an 01 its 30 ft/lbs, but i dont know if its the same or different for an 03. also, while we were had the cylinder off i opened the powervalve assembly and it was full of black sticky goop. i assumed that was sludge from the 2-stroke oil and cleaned it out best i could with brake cleaner. was that the right thing to do?? the old piston was a crispy black color, what exactly does this indicate? to rich of a jetting? i know it should, idealy, be a like a light brown. lastly, what worried me was on the piston there were some scuff marks that line with some slight scuff marks on the intake side of the cylinder. it seemed to just discolor the cylinder wall in that area of the scuffs and not leave any visible scratch or depression. is it anything to worry about? thanks in advance.

Yes they require a break-in, this seems to work great. From Moto814

1) Assemble the engine properly and torque all fasteners to specs.

2) Start the engine with the bike on a stand and allow the engine to come up to operating temperature (top of the raidator hot to the touch). Do not allow the engine to run at one RPM at all. Constantly vary the RPM and do not allow the engine to idle. When then engine reaches operating temperature (about 3 to 5 minutes of running time), shut it off.

3) Let the engine cool completely (at LEAST one hour). You want the engine to be dead-stone cold. Longer is better.

4) Start the engine with the bike on a stand and allow the engine to come up to operating temperature (top of the raidator hot to the touch). Do not allow the engine to run at one RPM at all. Constantly vary the RPM and do not allow the engine to idle. When then engine reaches operating temperature (about 3 to 5 minutes of running time), shut it off.

5) Let the engine cool completely (at LEAST one hour). You want the engine to be dead-stone cold. Longer is better.

6) Start the engine with the bike on a stand and allow the engine to come up to operating temperature (top of the raidator hot to the touch). Do not allow the engine to run at one RPM at all. Constantly vary the RPM and do not allow the engine to idle. When then engine reaches operating temperature (about 3 to 5 minutes of running time), take the bike off the stand and put it in gear. Take it for a ride. During this ride you want to keep the engine under a load at all times. Do not coast. Do not let the bike idle. Do not allow the engine to stay at one RPM. Riding on a mild slope is fine for this, as is slightly dragging the rear brake the entire time. Do this for about 15-20 minutes. Then shut the bike off.

7) Let the engine cool completely (at LEAST one hour). You want the engine to be dead-stone cold. Longer is better.

8 ) Re-torque the head and base nuts.

9) Go ride.

The cool-down steps are crucial to this operation. You must let the engine cool completely for the break in process to work properly.

Also, do the warm up procedure I outline here before EVERY ride. Your top ends will last much longer if you do.

-Steve

torque specs vary so i couldnt tell you, yes cleaning the powervlave is good, brake cleaner worked great for me as long as it was moving easily. yes it could be running rich or just old and lots of carbon deposit. the scuff marks could have occurred if the bike was near seizure, usually happens when the bike is held wide open for too long. As long as there was no damage or mishaping to the cyclinder it should be fine. I think that about covered all your questions. Good Luck hope the bike runs great! :thumbsup::ride:

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wow thats a longer process than i thought. thanks for the info!

one question tho. you can't run wide open to long or it scuffs the cylinder? whys that?

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IMHO...........having no load on an engine is far worse than not breaking it in. An engine idling has no load on it, even if you rev it up. The best way to get a piston/ring to seal is to have some load on it so the force places equal pressure over the top of the piston and causes it to slightly expand under the presure.

I just install the piston/ring dry (but lube the bearings) and ride it easy (after a complete warm up) for about 5 laps then let 'er fly! :thumbsup:

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theres alot of different ways to break them in, thats the one that i thought was the easiest to understand. IF I am recalling this right, the oil doesnt have time to lubricate properly before it is burned up, thats why most engines seize when the are held wide open for too long. I have done that once on a rm125. It was a very long push home. Tell your bro to not hold it wide open for 10-15 min at the most. that was about how long mine lasted before it went :ride: . keep me updated on how it goes!! :thumbsup:

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