[Johnmillner33]

Hi everyone. New guy to this forum. I have a 04 sx viper 700 that was my uncle gave me this year before he died. The sled has 426 miles on it and looks like brand new. When i got it i cleaned the carbs and changed the gas. It ran great. I put 200 miles on it on groomed trails with no issues at all. 2 weeks ago i went into a feild that was all fresh powder and now my motor has 3 melted pistons. Can someone tell me what happened and why?
Thanks in advance
John

 

[BC_Dan]

it's likely that the powder was ingested into the carbs and froze, causing a lean condition. Was the jetting adjusted for your temperature and elevation? it could also be an air leak at the PTO crank seal or in via the carb to engine adapters, but that would usually not fry all three. Bad jetting or all carbs icing up could cause it, though.

 

[Yamaha440]

All 3? That's impressive! Adding to Dan's post, a lean condition could have also been created from water in the fuel freezing and causing a restriction, or a failing pump. Make sure that there's no air in the cooling system as well. It still has a stock airbox and exhaust, right?

Low miles on a sled that old isn't always the best unfortunately, things tend to degrade when vehicles sit for extended periods, especially rubber parts.

 

[Johnmillner33]

Yes .stock air box with no mods to it. The whole machine is stock. I will pull the head off and post a photo. I would think that if it was a fuel issue there would be a lack in performance.

 

[Johnmillner33]

 

[Johnmillner33]

So the mag and center cylinder are the worst and the pto cylinder just started to eat the piston and leave deposits of aluminum on the cylinder. Also all damage is at the exhaust ports yet the exhaust system is clear. I used my bore scope to see inside the exhaust.

 

[Yamaha440]

I would think that if it was a fuel issue there would be a lack in performance.

When they run lean, they tend to run their best right before they burn down

 

[Johnmillner33]

Yes i know that. When a 2 stroke gose lean they tend to have more power until they melt. The power did not change nor the tone and rpm until i went into the deep powder. I drag race with a nitrous motor and read spark plugs all summer. The plugs were dark with a bit of oil on them before the ride that day. So with clean carbs and new fuel if it went lean it is usuely the pto or mag cylinder that goes bad from an old crank seal. I pulled the carbs and they are spotless.all the jets,air bleeds needels and seats are good. The crankshaft bearings are junk also. I can pull up on the clutch and all the rods move 1/8 to a1/4 inch. I pulled the oil pump and spun it with a drill and it works fine. As does the drive and water pump. Head gasket is not burnt or blown out . Put the cylinder head on my bridgeport and indicated . Its perfect.

 

[kccats]

Looks like a lean condition
Snow injection is possible
But that melted edge says LEAN!

 

[Johnmillner33]

Thanks for the replys. Can someone school me on snow injection ?

 

[BC_Dan]

When you are in fine powder, and the airbox is not sealed completely, some snow can get into the intake. If it's over the hood, some can even go into the airbox. If there is nothing to stop it, it ends up in the carbs. Some airboxes have a sort of filter to keep that from happening, others have a fine mesh screen that keeps the snow out of the airbox in the first place. Make sure that everything is sealed. On my 600 and 700, there was a problem with the seal around the headlight which would allow snow to get in. and another issue with the headlight adjuster knob opening. Both could let snow into the intake when in deep powder. Take a very critical look at any way air can get in and make sure it's sealed completely to prevent it from becoming an issue.

 

[Johnmillner33]

Thanks for your reply BC_Dan. I took a good look at the head light area and the seal at the air box. I can see how snow would get into the air box. The day it died i had snow coming up over the hood.
Thanks again for everyones help.
John

 

[tgsmartcows]

Yes .stock air box with no mods to it. The whole machine is stock. I will pull the head off and post a photo. I would think that if it was a fuel issue there would be a lack in performance.

Actually 2 cycle engines run really well lean just before they melt.
The only way to prevent this kind of thing is to check un8Der the hood very often until you're satisfied all systems are okay.
I hate when pistons burn. Makes good old sleds worthless because the parts can get too expensive to fix them.
Good luck with your sled.

 

[kccats]

A Piston only cost about the same as a tank of fuel!

 

[Johnmillner33]

I was shocked by the cost of repairing this motor. It needs the crankshaft rebuilt,three cylinders,pistons. Very expensive. I thought about swapping the engine to red head 700 . But then i spoke with friend and his 08 nytro got crushed by a tree this past storm. Will the 3cylinder 4stroke fit or will it be to tall? Just a thought.

 

[Coolhand]

That would take a ton of work to work properly if even possible and would be better off rebuilding or finding a used crankcase or engine.

 

[kccats]

You don't need all that OMG if so buy a new sled!
Most of the time you can just hone and put new pistons in $60-75 ea

 

[kccats]

By the looks I would bet you will find Plugged Pilot jets

 

[Johnmillner33]

I wish i could just hone the cylinders and replace pistons and rings. But the cylinders at the exhaust ports has missing aluminum. They would need to be bored ,sleeved and recoated. I also checked again and pilot jets are not blocked.

 

[kccats]

Never sleeve just send them and pistons to US Chrome in Wi
They will come back better than new about $175 ea