Down after only 2k miles, stock pistons are better?

[keller772]

My 2014 Pro RMK (Lola) has been my favorite sled I've ever ridden I love her. She has taken care of me and I've taken care of her, or so I thought. Hearing that the pistons in these motors liked to "abort mission" after a few thousand miles I decided on a rebuild to try and get ahead of the issue and gain some reliability. So at about 2000 miles I rebuilt the top end with new RKtek forged pistons, along with the rings, wrist pins, wrist pin bearings, and the necessary gaskets. After a couple shorter 20-30 mile test rides at op-temp and using some very restrained throttle input (it was the beginning of the season I wanted to rip) I felt as though the engine was ready to rock, and it was! Yeah no the engine didn't burn up after I rebuilt it, unlike my ever supportive father told me it would.

So, Lola and I soldiered on for a couple years. I kept her full of 91 and oil, I kept her greased up, I cleaned the valves twice a year, I thankfully only went through one a-arm somehow, and I replaced the primary clutch at 3400 miles. I thought life was good, the lighter forged pistons seemed to help keep the throttle response snappy and everything was running just peachy. Until the end of March this year when I had just passed 4100 miles on the clock, I was following my dad up a hill and she let go on me. The engine gave out and there was all of the sudden a lot of angry noises coming from under the hood.

I'm not a mechanical failure forensics expert so I honestly have no idea how the engine failed but if I had to guess the skirts started collapsing and then got caught on my exhaust port stopping the piston dead in its tracks and the rod pulled itself right out of the bottom of the piston. I've attached some pictures I took and I can take more if needed because I'm sure someone more knowledgeable than me would be able to paint a better picture... with some better pictures? Either way I'm disappointed because these pistons were supposed to be stronger and more reliable than stock but they barely made it over 2000 miles. Meanwhile in "I'm always rightville" my dad's sled, which is the same exact sled as Lola, is bone stock with 3000 miles and still pulls like a freight train all the way up the hill. RIP Lola 2014-2020.

Also all jokes aside about my dad and I we get along great and he's been gracious enough to give me his sled since I'm in school. Plus he's going to finally pull the trigger on an axys so I'm happy about that and I know he will be too, can't thank him enough for always having my back.

 

[NapaMatt]

Idk. but looks like a pinched oil line.. or shortage of oil!!

Ouch!!!

Did you ever turn up the oil pump??

Always warmed up to temp?

 

[keller772]

Yeah I had the oil pump turned up before I even put the new pistons in, and the reservoir was full of oil too that day. I guess it could have been a pinched line? I could maybe look for it if you had an idea of what line it would be let me know and I'll take a look next time I'm in town.

I think what contributed to it was the fact that even though it wasn't an overly warm day it was real heavy snow, the sleds were working hard that day to make it up the hills. I honestly was probably too hard on the motor that day, well obviously I was because it blew up lol, but I can't imagine I was that hard on it because my dad's sled did everything mine was doing and then he was the one who pulled me 30 miles back home.

 

[AdrenalineAddict]

I can't speak for the reliability of RKtek pistons, but I can speak volumes about OEM pistons. Since 2011 I have had 8 or 9 motors go down (lost count) on account of ring retaining pin failures, they were all with stock pistons right at the 2,000 mile mark (+ - 100 miles or 100 hours) I have always had warranty so I just rode them until they gave up. I have several riding buddies who have also never seen 2,100 miles on the stock piston. In a non-warranty situation I would positively replace my pistons around 1,800 miles in an effort to avert pending disaster. I went on my last ride for the year last weekend on my 2018 Axys 800 and was thrilled to make it to the trailer, it just turned 2,200 miles as I road up the ramp, personal record over the last 10 years. I'm just guessing that in destructive testing if they hit the 100 hour mark they met their reliability criteria. I would happily re-piston on my own dime if they wouldn't gouge me for ~$825.00 for two pistons, gaskets, 0-rings and needle bearings.

 

[Reg2view]

Regarding oil starved, stock oil cap? Tank collapsed at all?

From the pics, my guess is similar to yours - cylinder or piston skirt broke and hung piston within a handful of strokes, pulling off the bottom of the piston. It's those damn strong connecting rods...

 

[keller772]

Yeah I am going to have to look at the whole oil system a bit closer when I get home as that seems to be a common theme in the replies. As far as I could tell the oil tank and all that was good but like I said I'll have to take a look again. I should probably look closer at the second cylinder and piston now that I think of it.

I agree with you on the connecting rods though because that rod slammed into the bottom of the piston quite a few times before I was able to get the engine shut off. Couldn't believe how straight it was! If only the pistons were that strong lol

Thank you for all for the replies so far though they've given me some ideas to look into for the source of the failure.

 

[NapaMatt]

About 2 inches from the tank..

the hose makes a right 90 deg.. i have put a brass 90 elbow in..

I have had great luck with the upgraded polaris pistons

 

[Teth-Air]

I have had a 2014 go down twice. First it was the lower con rod bearing and then a crate motor went in and the second motor had the same failure on the same side so I expected it was an oiling problem. Got about 3000 kms out of both though and oiler was turned up. Piston fragments could have taken out the bearing too as they were warranty so I didn't get to see inside the motor.

 

[diamonddave]

What’s the condition of the rod bearing?

 

[xpturbo600]

I would stop speculating. You may end up being wrong and blame the piston, leading to another failure. Call the owner of RKTek and ask him if he has seen this type of failure. He did the R&D and knows what the piston will handle. My suspicion is a rod bearing failure.

My brother in law locked up two motors, lost riding time, and wasted money because of incorrect diagnosis. His was a hairline crack in the cylinder he could not see. Under boost it would open up, lean out the engine, and over heat the piston until the point it locked up.