Piston Failure Diagnosis.

[xTonyCRx]

Guys,

My 2012 Switchback Assault recently went down with 3200 miles. The motor locked up solid but after it cooled down it freed up and I was able to limp it home which will likely complicate any diagnosis. The engine just lost power and died. It did not make any loud noises.

The both pistons appear to have “broke” above the top ring on the exhaust side. In some areas it looked like they broke but some of the edges looked like they may have been melted due to a lean condition. Lots of exhaust side scuffing.

The dealer replaced the entire top end except the head. He assured me that the bottom end was clean in in great condition. The fuel pressure checked out as normal so the dealer couldn’t explain why it went down.

Could this failure been avoided with aftermarket pistons? I have no problem replacing the OEM pistons after my warranty is up in Feb 2014. Any help is greatly appreciated.


Additional Background

Fuel filter was replaced in the fall at approximately 2000miles.

Sled wasn’t pulling top RPM (~7700) but I had attributed it to a worn belt. It let go before I could replace the belt and now that I have it back it is pulling RPM (8100-8200) on the same belt.

The sled has had the periodic “bog” but comes out of it as soon as the throttle is lifted. This doesn’t happen often. The dealer has adjusted the TPS but I suspect only the idle setting was adjusted.

 

[Old Scud-doo]

1. Was oil consumption extremely low?

2. Is the damaged part of the pistons on the intake or exhaust side?

 

[skibreeze]

They are lean to start with, I ALWAYS vary the throttle.

 

[xTonyCRx]

I knew I was forgetting something!

The damage is all on the exhaust side. Unfortunatly I forgot to take pictures of the intake side. I was too alarmed at the exhaust side damage while I was at the dealer. Apparently after so many days the dealer can throw them out (or give them to me). When I get them home I'll get better pictures with a real camera.

Sled always runs Premium 91 non ethanol fuel w/ the Prem Resistor. I do not mix oil in the tank. Oil consumption around 65:1 which is low but not as low as some. I did not want to take any chances getting denied warranty if I turned up the oiler but I will be running some pre mix for the remainder of the season.

 

[xTonyCRx]

They are lean to start with, I ALWAYS vary the throttle.

As do I, I was riding a fast trail and was on off the throttle hard. The water temps were normal around 125-130.

 

[skibreeze]

65 to 1 is nuts IMO, turn it up.

 

[mutti_wilson]

I'm gonna say oil ratio is a major problem at 65:1. I run my cat at 32-40:1. It's not a Polaris, but I can't imagine them being that much different.

 

[xTonyCRx]

IMO the oil is not the primary cause of this failure. I cannot see how lack of oil is going to "remove" the top part of the piston.

 

[skibreeze]

I wouldn't say "primary" but these motors have lots of small things, that when added together, cause the failures.

1. very lean air fuel ratios
2. very lean oil ratio
3. very loose piston clearances from new
4. cast pistons

 

[winter brew]

Assuming no air leak, it needed more fuel and oil....it's just lean from what I can see. Bad fuel/detonation?

 

[xTonyCRx]

Assuming no air leak, it needed more fuel and oil....it's just lean from what I can see. Bad fuel/detonation?

I have never experienced DET with this sled. The fuel tested OK at the dealer but I assume that is just an ethanol test.

The piston on the right looks to be more broke than melted. I am not sure which piston is the PTO nor am I sure which side went down first.

 

[sledhead1]

Bad fuel. Looks like detonation to me. Unfortunately i have seen it before, repeatably, before i found out what it was.

 

[geo]

IMO the dealer should have taken two more steps and explained those to you before shrugging their shoulders.

One is a quick leak down test to prove the bottom end seals and the other is a visual or flow check on each injector.
I would want to know those things before reassembly even if warranty didn't cover checking for them it.

 

[xTonyCRx]

Bad fuel. Looks like detonation to me. Unfortunately i have seen it before, repeatably, before i found out what it was.

There was no DET codes thrown. Unless the system didn't pick it up. I got the fuel from the same station same as always. So did everyone else.

IMO the dealer should have taken two more steps and explained those to you before shrugging their shoulders.

One is a quick leak down test to prove the bottom end seals and the other is a visual or flow check on each injector.
I would want to know those things before reassembly even if warranty didn't cover checking for them it.

I agree! I figure it will be right back up there for more new parts in short order if its an injector/bad seals.

 

[flying frenchman]

Wow!!! This is exactly how my PTO side looked like when it went down at 2100 miles.

To me it's detonation, but does detonation act like it's lean when this happens as the inside of my exhaust was alumacoated. The other piston was good, but everything else had ate aluminum on the bottom end from the piston blowing apart. It was all trashed, crank, cylinder, piston.
Never seen DET on gauge. I always run fresh 91 fuel. I thought these sled had this DET feature to prevent this.
My Vertical Escape was a little lean a few years ago, it melted the piston NOT blow it apart.

I'm like xTONYCRx down time sucks but would like to find out why it happened.

 

[2XM3]

99% of the time when the area that failed in your pictures lets go its detonation/heat related...one tank of crappy fuel will do it. and yeah 65-1 ratio is just insane, I go for 35-1 and 2oz oil per 5 gallons for the heck of it

 

[snowmobiler]

65/1.LOL

 

[xTonyCRx]

I had thought that the DET protection on these CFIs were so sensitive any little blip or hint of DET would set the system into limp mode. How would DET be so severe to damage the pistons like that without throwing a code?

I ran 150 miles the previous day on the same fuel. The sled let go approximately 40 miles into the ride the next day on the same fuel.

Snowmobiler: What ratio do the etecs run?

 

[mutti_wilson]

Found this on Dootalk.

http://www.dootalk.com/forums/topic/442216-800-etec-fuel-oil-ratio-1001/

 

[2XM3]

Remember how a det sensor operates, it is nothing more than a sensor to pick up noise in the motor at a set frequency they have determined to be "detonation" like any sensors dont bet the farm its working properly,if at all, or its picking up any little noise the motors making inside it.....ie a piston could and has melted to the wristpin without settin off a sensor.


Oh and as far as oil ratio goes, look its pretty simple in ANY high performance 2 stroke motor be it motorcycle,racing outboard or sled, you want to keep pouring the oil to it till it bascily fouls plugs...oil is GOOD it makes more power on more oil (proven on dynos for years) and the only reason in the entire world to run less of a mixture is because of the stupid emission rules, we ran 20-1 in my mercury drag 2.5 motor at 13,500 rpm, zero issues.........end of story.