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Saint Marys, OH
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eric513anderson
10/9/2017 5:57pm
10/9/2017 5:57pm
Edited Date/Time
10/12/2017 7:35am
What's best to do with this cylinder? I pulled it off the bike that broke a piston skirt. Some small scratches and nicks in it you can barley feel with your finger nail. Do you guys recommend a re-plate process, hone it or bore/hone if needed. Im guessing this cylinder has the nikasil playing? If I'm correct? First time messing with a cylinder like this. I need to clean up some of the oily residue off the walls and get better pictures maybe but this what I took wuick last night
They'll swap your broken one for a refurbished one for quicker turn around times, and then repair yours for someone else.
You can opt not to I'm sure.
Paw Paw
The Shop
If the squish is set too tight you will be reducing the fuel mix from the edge of the piston where it is needed for cooling. The result is that the piston top and the head start to erode and pit which then makes the problem get worst and finally the piston either fails or get so hot that it deforms and caused the ring to get stuck in the piston causing a loss of compression.
If the squish is set too loose than you get an incomplete fuel burn and a loss of power.
So be sure to have it checked and rest after the cylinder is reworked as some cylinder reworking involves the cutting of the top of the cylinder to make sure it is true. The result can cause the squish to be reduced.
Paw Paw
Paw Paw
I would just replate it. Only costs around $200 from millennium...
Have you checked the timing?
Here's how it looked when I got it back
The reason the piston broke is because it was ran to long and the cast stock pistons always bust the skirt off them when ran to many hours. Put a wiseco back in it and have piece of mind that wont happen again unless something catastrophic happens.
When you get it all back together you need to check the ignition timing.
Paw Paw
I would send the cylinder to Millennium or Power Seal USA and have it replated.
Here is a head I did for a customer and I do this as a hobby, not my full time job. I would have at least polished the combustion chamber as this has shown on my flow bench to be an improvement in gas flow.
I tried some different velocity flow on this head during my machining, this is on a KX112 and showed some improvement on the dyno, but the rider likes it better on the track and shows better burn pattern.
If you can afford to run 50/50 race /pump gas, get the head cut for race fuel run good gas and you can leave the timing advanced and it will run perfect.
Also if your looking for something else that makes a huge difference in top end power and over rev. Look up HP Race Development STIC for your carb. It might seem like a gimmick but it truly works. I was given one to test when they first came out and couldn't believe the difference it made on my yz295.
Pit Row
I normally use Millenium for re-plating but decided I would give PowerSeal a try this last time. I used them to plate a KX112 cylinder and they did a great job.
Like you said I don't think you will go wrong with either, the re-plating by both companies is far superior of the OEM plating.
The advanced timing cost me an OEM cylinder and top-end back in 2005. Aaaargh! The power was also too abrupt for a lot of the riding a did back then. I nearly had the same issue in 2012 on my 2006 YZ250. Fuel, timing, jetting and head are all essential things to figure out on the YZ250.
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