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I have a 2007 CRF 250r that I've been working on it. When taking off the head, searching for possible places of a water leak, I happened to notice that there was wear on the top of the piston. It looked like the exhaust valves have been smacking the top of the piston. When the bike is running it does make a clack type sound, but I always thought something was wrong with the auto decompressor.

Here are some pictures of the damage:







What is outlined in the blue is the wear. The piston is a Vertex forged big bore piston and the valves are unknown. What could cause the valves to smack the piston like it is? I would assume maybe the valve clearance but I checked and its in spec. Another question I have is what to look for now that this has happened. Do I have to look for any wear anywhere else since this has happened? Your input would be very much appreciated. Thank You.

Hi,
Can you post up a full picture of piston top surface.

How deep are the impacts on the piston?

Are the base and head gaskets the same thickness as what came off?

Hi,
Can you post up a full picture of piston top surface.

How deep are the impacts on the piston?

Are the base and head gaskets the same thickness as what came off?

Here is the picture. I'm not sure it the base and head gaskets are the same thickness as what came off, I didn't really think about checking that when replacing. The impacts on the piston are probably about... A half a millimeter if that. Pretty minimal but definitely noticeable.

BTW: Sorry for the crappy photo. Was using the flash on my phone. If you need a better picture, I will be able to provide on tomorrow morning. My time of course lol.

Is the arrow on the piston pointing in the correct direction?
Normally to front but check paper work with piston and manual.
What is the Vertex part number on box.

Is the arrow on the piston pointing in the correct direction?
Normally to front but check paper work with piston and manual.
What is the Vertex part number on box.

This is what I have for the part number on the box. Unfortunately I miss placed the paper work, but I could've sworn it said the arrow faced the intake side. Also the piston looks pretty symmetrical on both sides but maybe I'm wrong.

Edit: But after doing further research, I might be wrong and it might face towards the exhaust side.

The arrow would be pointing in the direction of flow. Aft looking forward.

The arrow would be pointing in the direction of flow. Aft looking forward.

What do you mean by that? So the arrow should be pointing towards the exhaust side instead of the intake side?

Yes, aft looking forward. Arrow should be pointing in the direction of the air flow, which is out the exhaust side.
Note - that is true unless instructed specifically by the manufacture to not be so. Probably not in this case, but now days with so many parts coming from other countries that do not recognize US standards, you can run into directions giving the opposite of what most have used as a standard forever.
Think of airflow direction as the directive of what any indicators are given to you - like arrows. It's a standard in air flow descriptions.

Yes, aft looking forward. Arrow should be pointing in the direction of the air flow, which is out the exhaust side.
Note - that is true unless instructed specifically by the manufacture to not be so. Probably not in this case, but now days with so many parts coming from other countries that do not recognize US standards, you can run into directions giving the opposite of what most have used as a standard forever.Think of airflow direction as the directive of what any indicators are given to you - like arrows. It's a standard in air flow descriptions.

Ok so since the piston is not the right way, that could cause the exhaust valves to hit the piston?

It depends on the piston recessed clearance valve cuts. But there is certainly they have a directional arrow for a reason. Sometimes its the skirt has dimensional reasons others the valve clearance and many times both.

Before running off have cocked - I would go to Vortex site and look up some installation instructions and verify the piston arrow directional orientation. Those are good pistons so I would rule out a the piston itself as a defect problem. By the look of the piston picture with the valve hitting the edge of the valve clearance recession it does not look like a valve issue. Possible timing is off ? Not sure if the valves can hit the piston on your model if the timing is off or not? Even then they should hit down in the recession not the edge.
I do not recall if you said it was running good before this happened ?

Before running off have cocked - I would go to Vortex site and look up some installation instructions and verify the piston arrow directional orientation. Those are good pistons so I would rule out a the piston itself as a defect problem. By the look of the piston picture with the valve hitting the edge of the valve clearance recession it does not look like a valve issue. Possible timing is off ? Not sure if the valves can hit the piston on your model if the timing is off or not? Even then they should hit down in the recession not the edge.
I do not recall if you said it was running good before this happened ?

Yes it was running good before I found out this happened. It idled beautifully but did make a knocking sound. We thought it was the auto decompressor not working right, so when the exhaust rocker arm slipped off the decompressor and hitting the cam, we thought it was making the knocking noise. But maybe it was the exhaust valves hitting the piston the whole time... not sure.

Edit: Also when test driving it, it feels like I’m driving my dads 125cc Yamaha. It has absolutely no power. While in the middle of giving gas the bike lost power (it sounded like it was bogging) then regained it, but I don’t know if that’s because of the valves, the auto decompressor acting up or if the carburetor is not tuned for the big bore kit.

Wow, you have a lot of variables going on there. Start with verifying the piston orientation. Then the timing. The first issue is to determine why and how the piston was getting hit. With that hard of a witness mark I would be very concerned the valve could be damaged and very likely bent stem. If you figure out the problem and correct it that piston probably can be dressed out and reused.
After you determine the pistons orientation and if it is in correctly you are going to have to do as more slow bench testing with the head and cylinder to see how and why that happened. Clay works very well for clearance checks.
First figure out the piston & the arrow question.

Wow, you have a lot of variables going on there. Start with verifying the piston orientation. Then the timing. The first issue is to determine why and how the piston was getting hit. With that hard of a witness mark I would be very concerned the valve could be damaged and very likely bent stem. If you figure out the problem and correct it that piston probably can be dressed out and reused.
After you determine the pistons orientation and if it is in correctly you are going to have to do as more slow bench testing with the head and cylinder to see how and why that happened. Clay works very well for clearance checks.
First figure out the piston & the arrow question.

Ok I've been searching online and the conclusion I've come to is that the arrow on the piston is supposed to point towards the exhaust side. The timing was on point. I've had the timing off before and the bike wouldn't even attempt to start. Also what is this Clay thing your talking about?

That's good So is the piston in correctly now that you confirmed the arrow or backwards ?
General rule - Normal air flow always should be identified in the direction that the air will be flowing if an arrow or markings are used.

Clay can be used as a marker for checking clearance between two points where contact or clearance is a concern. Just like the strips used to check crank clearances but clay is for wider points you are checking. I use what is called modeling clay.