Scorched piston?

[Burns1980]

I pulled out my piston and found a hole on the top. It must be from running too lean and the heat melting the top of the piston. The other piston only has a small hole compared to the one in the photo below. Would the APV have anything to do with the fuel mixture? Any input would greatly appreciated.

 

[Killerk]

Detonation for sure.
Not sure what your ? about APV oil is.
Are you running premix or injection?
That is not an oil related failure IMO.
If you premix and are rich with oil, you have less fuel, but the oil is not the issue.
What sled and mods do you have?

 

[Arctic Thunder]

Looks like the standard lean burn down to me.

Detonation maybe but the exhaust side of the piston always look like that when you burn the top off the piston.

Thunder

 

[2deep4u]

Imo almost to hot of a spark what plugs are you running Maybe detonation, but my knowledge of lean burn down i would say you were just too lean if that is the case

 

[Burns1980]

I don't have any mods on the engine. My question was about APV was about the valves. I noticed that the cable connected to the servomotor that was controlling the valve on the piston in question was way too loose. Would that have an affect on fuel/oil mixture? And what do you all mean by detonation?
Thanks for the input so far.
I was using BR9EYA plugs.

 

[RickM]

lean condition

just looking at the only photo you supplied, piston has no signs of piston wash on top of piston, top of piston is showing lean burn area where your seeing the pitting in the center of piston and also looks like its burning off the exhaust edge of the piston. ( its hard to see clearly in photo) I think it is lean on fuel and probably caused by hard long pull causing the problem.
tell us what the conditions were that you were running. that may help explain your problem.

 

[Arctic Thunder]

I don't have any mods on the engine. My question was about APV was about the valves. I noticed that the cable connected to the servomotor that was controlling the valve on the piston in question was way too loose. Would that have an affect on fuel/oil mixture? And what do you all mean by detonation?
Thanks for the input so far.
I was using BR9EYA plugs.

Typically I would say the APV cable isn't going to do crap with your air/fuel mixture. But on an efi I suppose your ECU could have you running lean just prior to it opening and with it not coming open you might have a bit of a lean spot. But again I doubt the APV cable had anything to do with it. Honestly I would bet money this isn't it. Look somewhere else for the problem.

Not your plugs running hot. BR9EYA's are pretty darn standard.

Again like others said. Long pull running lean burned it down. Melted the exhaust side of the piston off. Pretty simple. Rebuild it, jet up and run it.

As for detonation. If it is a bone stock sled then detonation isn't the problem. Detonation is really a factor when running a head, turbo, pipes that add running compression, etc. On a stock sled running 91 oct this isn't it.

What sled, what is your jetting, what were the conditions, Cold weather. etc.

They all play a part.

Good luck.

Thunder

 

[m8magicandmystery]

I don't have any mods on the engine. My question was about APV was about the valves. I noticed that the cable connected to the servomotor that was controlling the valve on the piston in question was way too loose. Would that have an affect on fuel/oil mixture? And what do you all mean by detonation?
Thanks for the input so far.
I was using BR9EYA plugs.

yes the loose power valve cable will make that cylinder heat up..!!!...on my STM valves on valve had a hole in the bellow and the other was opening as it was supposed to and my egt guage was indicating the cylinder with the valve failure was 300 degrees hotter..!!!!..a person would be better off with both failing i think the having on working and one not because with both failing you would really notice an issue but when one cylinder partly carries the other with a closed valve at high rpms and heat...then voila..

 

[superfast]

How loose are we talking because if the valve was not opening because of the cable the sled would run like crap. Like it would feel like it is running on one cylinder. I had a cable come off and the sle just wouldnt run for crap hard to believe that it isnt opening properly and not be able to tell

 

[Burns1980]

just looking at the only photo you supplied, piston has no signs of piston wash on top of piston, top of piston is showing lean burn area where your seeing the pitting in the center of piston and also looks like its burning off the exhaust edge of the piston. ( its hard to see clearly in photo) I think it is lean on fuel and probably caused by hard long pull causing the problem.
tell us what the conditions were that you were running. that may help explain your problem.

I figured out that the edge of the piston being shaved was from the APV valve because the valve also has rounded edges that correspond to the edge of the piston. I think that the valve was falling into the cylinder.
I was riding in 55 degree weather in about 30 inches of snow on flat land at about 1400 feet. Would the warm weather have an effect with EFI? I was riding hard for a while, then I would ease up for a while. I did hit trails for about 15 minutes but wasn't riding hard except for out of corners. And come to think of it, the engine blew about 2 minutes after I hit the ditches from the trails.

You can't see from the photo but the piston, along with the cylinder, have some pretty nasty gauges. The second piston was also damaged but not as bad. It sounds like most of you agree that it was running too lean. If that is the case, how would I change it so it doesn't happen again.
Thanks again for all the input so far.

 

[Burns1980]

How loose are we talking because if the valve was not opening because of the cable the sled would run like crap. Like it would feel like it is running on one cylinder. I had a cable come off and the sle just wouldnt run for crap hard to believe that it isnt opening properly and not be able to tell

It was pretty loose. Also, when I tried removing the valve, it was wedged in the cylinder pretty good. It took a lot of work getting it out. My guess is that it was bent from the piston hitting it. I didn't hear anything unusual before it died. It didn't seem to have as much power as it had the previous time I went riding, but that was 2 months ago in sub-zero temperatures so I figured it was just me along with the warmer temps. It was only hitting 7700-7800 RPM's max.

 

[m8magicandmystery]

How loose are we talking because if the valve was not opening because of the cable the sled would run like crap. Like it would feel like it is running on one cylinder. I had a cable come off and the sle just wouldnt run for crap hard to believe that it isnt opening properly and not be able to tell

when one is operating properly and one not ...the good cylinder carries the other just enough where your suspicious of something but just cant pin it down to failed powervalve right away cause we anticipate really poor performance with power valve failure ...which is the case with them both not opening..that was the way mine was..don;t know if the torque of the bigbore makes it any differant then stock..??

 

[m8magicandmystery]

I figured out that the edge of the piston being shaved was from the APV valve because the valve also has rounded edges that correspond to the edge of the piston. I think that the valve was falling into the cylinder.
I was riding in 55 degree weather in about 30 inches of snow on flat land at about 1400 feet. Would the warm weather have an effect with EFI? I was riding hard for a while, then I would ease up for a while. I did hit trails for about 15 minutes but wasn't riding hard except for out of corners. And come to think of it, the engine blew about 2 minutes after I hit the ditches from the trails.

You can't see from the photo but the piston, along with the cylinder, have some pretty nasty gauges. The second piston was also damaged but not as bad. It sounds like most of you agree that it was running too lean. If that is the case, how would I change it so it doesn't happen again.
Thanks again for all the input so far.

i cannot imagine that the power valve is hitting the piston.??..there should be slide stops making it near impossible ...the only time its a concern is when going bigbore and then matching is required

 

[m8magicandmystery]

It sounds like most of you agree that it was running too lean. If that is the case, how would I change it so it doesn't happen again.
Thanks again for all the input so far.

if staying stock run egts/koso...adjustable fuel pressure reg..
possibly higher octane fuel below 3000 ft

 

[rcr1978]

What sled is this? Sorry if I missed it somewhere you said stock but what is it EFI?

 

[Burns1980]

What sled is this? Sorry if I missed it somewhere you said stock but what is it EFI?

06 M7 EFI Engine is completely stock. Only mods are non engine related.

 

[Burns1980]

i cannot imagine that the power valve is hitting the piston.??..there should be slide stops making it near impossible ...the only time its a concern is when going bigbore and then matching is required

If the piston is not hitting the valve, what else could cause the valve to be unable to open all the way? I was thinking the valve got bent from hitting the piston, but if that's not the case, what else might have caused that.
Thanks, Burns.

 

[Hirevtuner]

I pulled out my piston and found a hole on the top. It must be from running too lean and the heat melting the top of the piston. The other piston only has a small hole compared to the one in the photo below. Would the APV have anything to do with the fuel mixture? Any input would greatly appreciated.

Looking at that piston things are bad. Not from the power valves. Skirt looks ok in the pic so no overheating from what I see. Sandpaper pitting on the pison top like that from a stock motor...seems like there is a piece to the puzzle missing.

 

[Evolution Powersports]

We had two identical 06 M7's go down with 100 yds of each other. Mag piston only. Looks just like this one. Ours had 15:1 heads on them. We ran them for 2 seasons that way with no problems. Then one day, kind of warm after a cold spell (so the snow was like concrete). We were all racing back to the parking lot after a day hard riding. All I can figure is not enough snow gets onto the heat exchangers in those kind of conditions. Engine overheated and mag side started detonating. Since ours were modified, our margins are surely narrower than yours, but my belief is that if we had scratchers, they would not have burned down.

 

[TREE_MAGNET_777]

I say its fuel. Is your oxygenated fuel wire unplugged??? If you ran with oxygenated fuel and it sat for a month it went flat and you need to unplug the wire. We will see more of thus as fuel quality goes down....Garry