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All Opinions Needed (piston troubleshooting)

I installed the RK Tek drop in dual ringers a little less than 600 miles ago in my '06 X Power Tek. 440 main jets, V-Force 3 reeds. Since new I have had no problems with them, until Saturday. I was making a climb @ WOT when she broke loose. Pulled the pto side plug and had 10 pounds of compression. Pulled the head and this is what I found. I was only 4-5 miles away from the trailer where I had just changed out my BR9ECS plugs and put in two new Denso W27ESR-U plugs. As you can see from the pictures, the outside of the piston appears like it melted, but the pic from inside the piston skirt looks more like a break. This is all on the front of the engine where the exhaust port is. Also, the top of the piston and head have tiny marks on them. Is this from detonation or from the pin that keeps the ring from turning breaking loose and getting on top? I would appreciate everyone's opinion so I can fix the problem so this doesn't happen again. Also, would you split the crank case and check for pieces of piston, or clean it out good from the top and put it back together? Thanks
 
I've never seen the locator pin come out as a whole like that before and do that much damage. As for the piston I would not guess all of that happened all of the sudden. Looks to me like you have detonation or water issues and it just finally burned all of the way through on that climb. Sure wish the guru's would not have left this site, it would be nice too see what they say about this. Good luck
 
Now the next question is WHY did I get so lean so fast. Obviously I already have my top end tore apart so I cannot do a leak down test. My carb boots look perfect. My base gasket appeared to have no problems when I lifted the cylinders. Tore apart my carbs, drained fuel into a clear bowl, and found nothing dirty or clogged or any water separation. I have been told it is possible to change out the pto side crank seal without splitting the crank cases. Is this a good idea and do you have any advice on how to do it?
 
Well it sure looks like those imprints are from one of the ring pins just based on the fairly consistent shape of the imprints, probably bits of the ring too as it broke up and then got spit out the exhaust port. I agree that doesn't look like something sudden happened there but probably the catastrophic end of a process that was going on for some time.

I'm guessing that you have sent these pics to Kelsey over at RKT... what did he say?

How was the sled running on the last couple of rides before the ride on which this happened, had you been checking plug color/burn after your top end rebuild? (I know it was 600 miles ago).
 
I did send the pics on here along with multiple others to Kelsey at RK Tek. He replied "Looks like a VERY lean condition that melted the piston... Possible bad gas or air leak" .... and ... "I think it is the chicken or the egg scenario.. What came first?? The spinnig ring will surely ruin your cylinder but it will not cause melting like your piston shows.. So I suspect that you had a meltdown that loosened the pin and then it spun.. I am not familar with the Denso plugs so I am not sure what issues they can or can not cause." I agree with Kelsey and surely will heed any advice he is willing to give me. Over the telephone and almost solely blamed it on my HPS can which has been on the sled since I bought it new. I changed the plugs previous to this ride (6-7 miles previous) and thought the old ones looked great. I changed them because I thought it was running a little poorly. I changed from a BR9ECS plug to the Denso equivilant. I also borescoped the piston previous to this ride and noticed no damage on the piston dome and thought my piston wash was totally acceptable. I do think this problem started on a previous ride and I was unable to tell by looking at the piston from the top down. Now, back to the subject of changing a pto side crank seal without splitting the crank cases. ANY advice is welcomed! thanks
 
more pictures

Here are pictures which clearly show where the top ring locator pin once was (about 120 degree from where my piston melted by the exhaust port)...how it worked its way to the piston dome (you can even follow it's trail like a worm in the mud) .... and also my MAG side piston. What do you guys think?

DSC00966.jpg DSC00968.jpg DSC00963.jpg
 
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Don't screw around with the wrong plugs. Bad news, can cause detonation.

as far as the seal goes. remove clutch, remove seal retainer, remove seal, pack bearing with expensive grease, lube seal, install seal, install seal retainer, install clutch. That being said, my motor was out when I did mine.
 
With that amount of damage on both pistons,i wouldn't put it back together
without splitting the case.If there is something in the crank bearings it won't
be long before it goes to.As for what happend i'm thinkin bad fuel with to hot of plug.Good luck
 
I would say detonation, possible and probably from bad fuel, caused the locator pin to bust loose, and then melt down. Kind od fluky that it melted down AND you lost the locator pin. If you hadn't lost the pin I would say that it would have just burned down. Looking at your MAG, looks like detonation to me.

Like you said, JMO.
 
There's alot of missing metal there. As much as you hate the extra work of splitting the cases, it really needs to be done.
 
With that amount of damage on both pistons,i wouldn't put it back together
without splitting the case.If there is something in the crank bearings it won't
be long before it goes to.

Excellent advise. I was given the same advise with far less damage and followed it. Ended up I needed to replace both outer PTO side bearings. Cost me 200 bucks but would have been way more when the crank failed shortly after reassembly if those parts had not been replaced.
 
Thanks Everyone

I am going to take all of your advice and go ahead and split the crank cases. Do you think I need to press my crank apart and replace the inner bearings? How about the rods? I do not want to have to tear it apart again so how far do you guys think I should go? Possibly even considering RK Teks 830 kit....any opinions on that?
 
Failure Clues

1) 440 main jets: Seems lean, unless using Kelsey's head. 480 is stock.

2) Denso W27ESR-U plugs could be an issue as the negative electrode will heat up and act like a glow plug accentuating detonation. The "ECS" short recessed electrode specifically is to avoid this issue.

3) Locating pin getting loose is classic result of detonation.

4) The exhaust side was real hot and melted the aluminum. The combustion pressure just finished off the hole in a hot spot.

5) Detonation can take out crank bearings even if the pistons do not fail.

6) Top of the piston and head look very clean with no soot which may be a symptom of lean and/or advanced ignition timing.

Something as minor as a plug change, temp change, fuel change can take a marginal condition and put it into failure condition by finally finding the weak link. The way to avoid this is to give yourself more safety zone in the set up in the future. Fattening the jetting is the easiest way to give a little bigger safety zone.

Ski Doo is very close to the edge of the safety zone in their stock tuning parameters from about 2004 to present. There is little to be gained by making more aggressive settings because the stock set up is so close to the edge as factory delivered!

It is now more important than ever to make all your tuning parameters as an engineered system. These variables have to work in concert with the performance parts added. The ski doo motors made since emissions compliance started are as close to the ragged edge as they can be. And many are almost not reliable as they come in an effort to gain this compliance. It is very easy to get in trouble because the factory has used up some of the safety margin to get emission compliance! Your individual motor's knock sensor may be just barely not able to sense enough to detect the detonation that took out the piston in this case. Each one has a personality and they are not all the same.

IMHO fatten the jetting some after the crank rebuild just to be safe. Replace all jets and the knock sensor as well. With the ECS plugs installed and as long as the jetting is OK (and you have some oil in there) the engine will live to fight another day!

BTW we have learned this doing failure analysis of too many situations just like this one. Denial of the tuner is the biggest enemy of a long engine life.

Or you can just blame it on the oil and go on to have the same failure next time with different oil!
 
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Thanks Eddy

I appreciate your advice and opinions tremendously Eddy. I will keep you all informed on how the rebuild goes. My shop manual states I need to reset the TPS because I unhooked the throttle cable....any opinions and/or directions on that?
 
Cable

If you did not change anything more than likely its OK. I would check it anyway just to be safe. Shop manual is always a good guide!
 
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