Posts
6
Joined
9/8/2024
Location
USA
Edited Date/Time
9/8/2024 10:23pm
So i have a yz 125 from 2004. The thing is i have done a complete engine rebuild including a new nicasil in my cilinder and a wiseco piston. I have rode for 8h now including my heat cycles. I have done the start up exactly how i should have. The thinh is now i have it back open i see that i have some noticeable marks on piston and cilinder. What should i do? I have checked the ring clearance and that should be fine. It was 0.5mm as it should. Manual states .5-.7 so i’m good with that. Is there anything that i missed in my process? Did i use the wrong piston?
Did you check the piston clearance? Looks like it was too small or it has run hot for another reason.
How can i check the clearance? I did just use tap water not a specific coolant. Could that make a difference? I did already buy coolant when its back together.
You have to measure the bore and choose a matching piston. Typically after replating you should use an A-size piston which is 53.93mm.
Yes i have an a size piston thats the one i bought. I am going to send my cilinder back to powerseal to see what to do
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This looks more like the engine ingested sand or something. If you are going to have it replated, you can always send your intended new piston along and they will measure it up for you.
edit: And tapwater will cool the bike equally fine as coolant. You just can't run it in winter and will get calcium deposits over time.
That's why you use distilled water.
Don't run water. You'll eventually get corrosion. pre-mixed 50/50 Prestone from the auto store is fine.
Tell us what fuel, oil, and mix ratio you are using.
That piston looks like you forgot 2-stroke oil. I know... I know.. every guy that has ever forgot oil "I am absolutely positive I did not forget!!!"
Do the cardboard test on the fuel that is in the tank of the bike. Takes 2 seconds and tells without a doubt if there is oil or not. If you put pre-mixed gas on a clean piece of cardboard and let it evaporate it will leave an oil stain. Straight gas will evaporate 100% clean.
Full strength coolant and distilled water 50/50 mix is cheaper. That's why I said distilled water.
If it is tight for the Wiseco, avoid a Vertex. A Vertex only fit halfway into my re-plated KX125. Both pistons sold as same diameter, but the cylinder had been matched to a Wiseco.
Did you send the piston with the cylinder?
Doesn’t the water pump seal need lubrication?
I don’t think the hawk tuah is going to work for that. Water wetter from Redline, with distilled water I’d prefer over the expensive coolants.
That looks more like some sort of lubrication/grit ingestion issue.
Are you sure the air boot is properly attached to the carb?
My question is did you clean the cylinder throughly after getting it back from replating it? They need a good cleaning to get rid of the honing debris.
Looks like my kx piston after I ran a dry filter but the bore wasn’t so bad. Check for air leaks, otherwise lack of oil or forgot to clean the cylinder like others said.
Should be able to hone for next since piston.
Yes i will be sending it with the cilinder so piston piston ring and cilinder will be off to powerseal
I tested and i have oil in the gas so thats not the problem
Yes the boot is properly attached and has always been. Filter is also new with the correct filter oil
I was going to say this. The scoring looks like it came from dirt particles or sand. Check every connection from your reed valve backward to the air filter and make sure it's all airtight. (And obviously make sure you run a clean, oiled filter with no holes in it.)
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