what will do this piston scoring with rktec drop in pistons

[cbc24]

I don't know guys, maybe heat? you let it warm all the way up? I just did the rk tech kit.. to me the updated stock forged pistons look better than these cast ones and they are longer.

 

[purepolaris600]

rings

Sorry for the fussy pictures my wifes camera sucks, i double checked the rings and they where not installed upside down. The rings where installed correctly and the endgap set correctly, i am thinking it was a oiling probelm.

 

[ACTM7]

Piston

Snow / water sucked in engine washed lube away

 

[Torgenrud]

Possibly taking off before the engine is completely warmed up a few times? I have seen cold seized pistons and cylinders like that. I know yours didn't seize but maybe it was close a few times?

 

[sled_guy]

Yeah, not an RKTech piston problem like the title implies... and you might want to include all engine mod info in the original post, having a turbo on it is pertinent information.

Other's have given some good suggestions as to causes.

sled_guy

 

[markoo]

You have scoring all the way around piston, you have blue rod bearings, and you have vacuum in oil tank. Lack of oil is the problem. Most guys turn oil pump up two turns on stock sled never mind turbo. The oil tank gravity feeds into the pump so even a little bit of vacuum would be a problem. I would check crank bearings before putting back together. A seized rod can ruin an engine completely.

 

[purepolaris600]

thanks

I will check crank out thanks guys i think we narrowed the problem down to lack of oil or snow or water. I am going to vent the tank. Thanks guys

 

[mountainhorse]

Lets get some good, non fuzzy pics posted up of the pistons and ring ends with the rings mounted in the pistons.



.

 

[geo]

I agree. Blued rods would mean a complete bottom end check to me. Cranks like to live in a big puddle of oil. That puddle of oil lubes the rod ends. piston pins don`t show heat coming from the top.

It`s fun to be a detective but don`t get lost in it. Usually the simplest answer is the correct one.
Pop the top half of the airbox, wipe the plate with a paper towel. One thing will be discovered or eliminated.

One of my daily checks is oil use. Yank the sled off into the shop, pull and hang cover, pop side panels, quick look at sheaves etc. for something different or whatever, quick look at oil tank (mines graduated with a marker pen) for oil used.
If I used less than a liter of the cheap blue stuff I`m pissed because I need to figure out why. If it`s down where a happy 2 stroke likes I sip a shot of brandy while hanging the gear to be dry for tomorrow.
Thankfully that is the norm.

Some places fire an operator for not checking oil levels at the beginning of a shift. My dad needed to check the oil in the old car every day so he could go to work.
IMO the sled should be able to fire the owner if they can not answer the skill testing question of "what my ratio of fuel to oil use please" lol.

 

[geo]

Lets get some good, non fuzzy pics posted up of the pistons and ring ends with the rings mounted in the pistons.



.

MH. I don't know these pistons exactly but usually you can't put either ring on upside down and get the barrels on too (at least since CZed's and Bultacos, worn iron liners and a piece of 2x4 with a hammer, lol).
Either the bevel or the pin dictate how far the ring will enter into the land. In the pics it looks like an offset ring pin which would mean a minimum of 40 thou ring end gap to get the barrel to slip past the rings at the bottom.
At 40 thou ring gap and upside down, on this set-up, the ring pin would have left in the first 50 miles. At 60 thou ring gap it might have survived this long.

I don't know though, haven't seen everything yet but yes clearer pics when asking for input helps a lot.

 

[purepolaris600]

a

Are these any clearer i will need to go buy a new camera

 

[gman086]

Lack of oil. I don't know how the polaris is but I would definatlty switch to pre mix. Especially wth a turbo. All that fuel that gets added doesn't have oil in it. Bluing of rods means heat and that is a sign of not enough oil.

THIS! I was told to run at least an ounce of oil per gallon in tank with turbo!!! Carl's straightened me out on the "turning up the oiler" thing because it can't add enough once you get to a certain point!!!

Have FUN!

G MAN

 

[purepolaris600]

oil cap

It all could come back to the oilcap, i had oiler turned up and was running 100:1 oil in the ave

 

[bryceraisanen]

If memory serves me correctly you can't put the rings on upside down because they won't fit in the cylinder.

I think it's oil problem all the way and I wouldn't be surprised if at least 50% of the scuffed pistons over the last few years were an oil problem

 

[SledzRacing]

Looks like cold running man. Even after riding for a bit and stopping for a beer or what-have-you you need to let the sled warm up for a minute before you get on it.

 

[SXViper]

Can someone with more experience than me explain this? If it's an oil supply failure why is it that the crankshaft didn't lock up prior to the pistons? With the 100:1 fuel oil ratio id think the pistons could survive for a bit however the crankshaft at that point is getting no oil and i dont believe it gets a fuel supply in a cfi.

Just something I've been trying to figure out while reading this thread.

 

[sled_guy]

There is a lot more clearance in the bearings than there is between the pistons and the cylinder walls. And the pistons get a lot hotter than the rods do. Just because the pistons failed first doesn't mean you didn't hurt the rods too.

sled_guy

 

[bryceraisanen]

The bearings have steel balls or something in them for the races to ROLL on. Not a TON of resistance/friction to begin with. ((Sidenote:: a lot of high performance motors dont have any crank lube ive heard)) The piston/rings do not, its good old fashioned friction, metal on metal. Imo, the crank should have a good amount of oil splooging around in there all the time, the cyls not so much bc the gas is rinsing it off constantly. So when u run outta oil, the cyls get dry like RIGHT NOW.

Now, back when the gas went through the crank, thats where the "common knowledge" of "crank fails first in no oil situation" came from. Cause the oil would get rinsed outta the crank first and then lube the cyl on its way to the exhaust port. And even in that situation, the pistons were probably only a few seconds away from locking up anyway. Correct me if I'm wrong, but thats kinda my own self taught understanding.

 

[geo]

Presssssure lol and friction co-efficient.

 

[SXViper]

Thanks for the input! I get all that im just surprised to not hear there wasn't any apparent bottom end damage. Apparently 100:1 can't protect a cfi top end for very long as it's unlikely the oil vacuum lasted all 500 miles.