Check out this piston!

[Summit8]

I posted this here because of no Perf/Mod section anymore and don't know if Skidoo ZX section gets much looking anymore.
I sold my 02 800 to a buddy that wanted to try the mountains, was running fine end of last season, was stored with stabilized gas and started and allowed to warm up good several times over the summer and fall.
Jetting and clutching was set up for altitude, they rode a day and a half with no problems, egt's were running around 1150 deg., motor quit on him, pulled the plugs and found the PTO side plug gap closed, we pulled the head last night and found this. Notice the MAG side piston was plenty rich.
Whatta ya think? Never seen erosion like this on a piston crown and on the head, have seen a lot of torn up cylinders over the years but not this. Am not sure, may have been SPI Pistons.

 

[cascadesnowjunky]

Crank seal or intake boot leaking air and went lean on that side. That would be my guess.

 

[Summit8]

Didn't seize piston in cylinder, scored streak in the side but didn't seize, intakes are V-Force 3's only a few rides on them with anaerobic gasket sealant on sealing surface. Don't know how close temps were watched, would think if that cylinder was running lean long enough to do that, you'd notice it on the egt gauge right in front of you.
I don't know, got new MCB Piston set coming, replacing one cylinder.
Supose it wouldn't be a bad idea to take crankseal out and repack with Isoflex grease, see kits for sale pn MCB's website and Ebay.

 

[up-high]

Welcome to the world of detonation! Big time! Was doing this for a while. Did he notice a power loss? A rider who has experienced deto would have heard this. Something you don't forget. Don't know if it was detonation from bad/weak gas or from heat but it's definitely detonation. Could be plugged fuel line to that cylinder? I'd also check both rod bearings. Some how the piston came up far enough to close the gap on that plug. Unless someone thought it needed to be gapped that way? Don't see that happening though.

 

[plumnuts]

since there is a clean section on the head without destruction I would say water in the fuel or just crap fuel ... as funny as it may sound... if the cylinder and ports are okay, you can replace the piston and rings and ride it... carbon fills in the devits on the head

 

[Summit8]

My first thought was detonation too, I wasn't around the sled when it was being rode so I don't really know. The guy riding the sled is a true motorhead, autos, bikes, 4 wheelers. Was watching the egt's and wtr. temp while he rode it, they stopped and checked the plugs a ways into the ride and he said the plugs were a perfect chocolate brown.
I think the gas thing is a big factor anymore, my son lost a cyl. to detonation last spring after 3 days of filling out of the same fuel tank, I think I'm going to start carrying some race gas, I know diesel isn't worth a crap anymore.
Motor is going to get cyl. replaced and a new MCB piston kit, will be looking at intake and crank play but that all seems to be ok.
Thanks for the input guys, appreciate it.

 

[TVC 15]

Stabilized gas only means it won't plug a pilot jet the next season. But by the next season the octane is long gone. I left 4 gallons of "stabilized" gas in my sled one summer and first ride of the season added 6 gallons of fresh and it still would set off the det sensor. My opinion of adding 6 gallons of fresh gas to 4 gallons of old gas just makes 10 gallons of bad gas.

 

[Summit8]

As far as the piston hitting the plug gap, there's no way that dome can get to the plug gap with those bathtub shaped head chambers.

 

[up-high]

As far as the piston hitting the plug gap, there's no way that dome can get to the plug gap with those bathtub shaped head chambers.

Then what closed the gap on that plug? Was the gap closed or was the electrode melted off?

 

[mike_s]

If the plug gap was closed and not melted off, you need to be looking for what came apart. The ground on the spark plug cant be closed unless its struck by some sort of debris. Slim chance detonation dislodged a piece of piston crown that could have struck the plug, but i would still be looking for something that came apart. Detonation that bad should have stuck the piston long before it got that far, unless it had half a billion miles on it and had excessive piston clearance. Detonation superheats the piston crown and will usually stick the piston if its that bad...

 

[markoo]

That piston can't hit the plug. My guess is a piece of piston skirt or crank bearing made to the top to the piston and hammered away. No signs of deto on other piston, not bad gas. Maybe sucked in a small screw or rivet through the air box?

 

[Skidoox]

Check for a broken ring on the bad piston

 

[Summit8]

Then what closed the gap on that plug? Was the gap closed or was the electrode melted off?

There was a small piece of aluminun stuck to dome of head, suppose enough of that piston dome came apart and hit the plug electrode.
I dunno, only thing it could have been me thinks.

 

[Summit8]

Will look for a broken ring, buddy is waiting on pistons before taking jugs off.

 

[TVC 15]

I've seen turbo motors detonate and close the gap on a sparkplug.

 

[Summit8]

Was in my buddies shop last couple days putting a few goodies on my new sled, finally pulled clys. on 02's motor, found the wrist pin bearing cage had broke, bearings were still in connecting rod, but pieces of the cage had gone around in the case and knocked a piece out of the top case half, buddy is prolly just gonna go with a reman motor and keep the cyls and new MCB piston kit for spares.
Could just replace top case half, but crank should be looked at, no dealers for 200mi., so motor swap looks like best bet,
Could detonation have taken out the bearing cage, still can't believe condition of the top of the PTO side piston, and the mag side is plumb fine.

 

[ullose272]

DET will close plug gap. seen it plenty of times

 

[up-high]

Enough deto can also hammer the con rod bearings

 

[byeatts]

I posted this here because of no Perf/Mod section anymore and don't know if Skidoo ZX section gets much looking anymore.
I sold my 02 800 to a buddy that wanted to try the mountains, was running fine end of last season, was stored with stabilized gas and started and allowed to warm up good several times over the summer and fall.
Jetting and clutching was set up for altitude, they rode a day and a half with no problems, egt's were running around 1150 deg., motor quit on him, pulled the plugs and found the PTO side plug gap closed, we pulled the head last night and found this. Notice the MAG side piston was plenty rich.
Whatta ya think? Never seen erosion like this on a piston crown and on the head, have seen a lot of torn up cylinders over the years but not this. Am not sure, may have been SPI Pistons.

Air leak burn down

 

[Summit8]

Yeah I figured Det on the bearing cage also, never had that happen on seizures.
Air leak burndown cause that much of the piston crown to disappear? seized piston and stuck rings,tore up cyl. walls, yeah seen that.
No air leaks on V-Force3 reed boots w/ anarobic gasket sealant on the gaskets. Crank seal ?? Possible, anybody else see a piston top like that from a lean condition. Not saying it isn't possible.
Thanks for the feedback guys.