RK TEK direct replacement pistons 2014 RMK Assault 155

[Turboegt]

I picked up a set of these on Friday.

Arrived at my house on Tuesday morning. Fantastic service, and a pleasure to talk with Kelsey on the phone to place my order.

I was under the impression from previous posts that I would be receiving a Wosner piston, and was a little concerned when I opened to box to find a set of wisecos staring back at me. Is anyone having any issues with the proprietary RKT Wisecos?

I tore down the top end this evening, and pulled the cylinder, and Pistons.

Out of the box I measured the Pistons and bores have exactly .050, and ring gaps came set between .19-.20

I only have 400 miles on the sled, and was disappointed to see the amount of wear already present on the exhaust side of the Mag piston. It wasn't horrible, but it is visible.

I'm honing the cylinder and assembling the engine Friday.

In addition to the Pistons while the engine is apart I'm turning up the oil pump, and installing a PCV-pti and a second y pipe i fanned up with an O2 sensor bung in each cylinder for individual cylinder auto-tune.

While going back together, does anyone have an tips for hits to ensure success? I don't want to miss anything.

Also... The little green o-rings installed in the injector bung on the cylinder.... What's up with those things?

I've never seen anything like them on any other engine I've ever worked on.

This is my first CFI-2 assembly. Hell its my first 2-stroke build. I've been messing around with 4 strokes for years, but I got hooked on sleds this year.

 

[Reg2view]

Regarding 02 sensors, on a 2 stroke, recommended to be at the fattest part of the pipe, 2 o'clock or 10 o'clock. I'm assuming you mean 02 sensor, not egt, but 02 sensors in the y pipe will get exposed to the pipe return flow and not give you what you're looking for. Heat issues, too. Nevermind if they are egts. Just my experience running both from the past 10 years. I've also used a heat sink with 02 sensors in the pipe to keep the sensor alive longer, improve accuracy. FWIW.


Think Kelsey had availability issues with Wosner, and now Wiseco is providing his design in a similar/same alloy as the Wosner. I had good luck with RKTs Wosner's and head myself, install to spec is very important to avoid issues. Wear on the OEM is likely lack of oil, especially if you hadn't had it turned up, added oil to fuel, checked ratio, changed cap, etc.

 

[volcano buster]

You might check your transfer port height with the new pistons.

 

[jhillam]

I'd recommend replacing the injector O-rings while down. Also check reed valve petals and clean the exhaust valves thoroughly, as well as the cylinder bleed hole venting to exhaust valves.

Use clean burning oil in higher quantity--like Polaris gold or redline. We've tried better corrosion resisting Petroleum oils and have had problems with exhaust valves sticking. Remember, exhaust valve sticking in the mid range causes lean burn downs or lean det on these Polaris CFI engines.

Call Indy Dan (Indy Specialties) about cylinder honing before re assembly. Stock cylinders and or pistons are sometimes out of round causing long term problems.

 

[Turboegt]

Put 100 miles on these this weekend.

They run noticeably smoother.

My hands don't go numb from vibration anymore.

 

[Turboegt]

UPDATE

Well...

The PTO cylinder burned down today...

I am pretty bummed... Of course there is 6" of fresh at the house, and 3' of fresh in the mountains.

168 miles...







MAG side



Intake side of mag piston


Exhaust side mag piston.


PTO side combustion chamber



MAG side combustion chamber.



PTO Side intake



Mag side intake



PTO side exhaust



Mag side exhaust

 

[rags319]

That sucks. Know why it did that.

 

[Turboegt]

I'm not sure. I double and triple checked every measurement going together, lubed every surface appropriately, and was very meticulous with my install. I've assembled more than a few engines, and there weren't any red flags going together. I am pretty bummed to say the least.

Hoping someone might be able to provide some insight as to what happened or has seen similar failures.

 

[dm04rev800]

was your oil pump turned up ? if so how many turns ?

and

did you add oil to your gas tank ? if so how much per gallon or what ratio ?

 

[Turboegt]

Oil pump was turned up 3 turns.

No oil added to gas.

 

[live2beel]

How did the stock ones look?

 

[Turboegt]

Like new. They only had 350 miles on them.

I'm gonna hone the cylinders and drop them back in.

 

[Turboegt]

Well... The stock Pistons are back in it, I honed the cylinders, and it runs as good as new.

First heat cycle is complete. Two to go. Looks like I'll be making it to Cantwell this weekend after all.

There was a small chip in the Nikasil in the PTO cylinder, but I'll be tearing the engine down at the end of the season anyways as I want to sleeve the cylinder in prep for the turbo that's in the mail. I'm not missing another day of riding this year.

Now I just need some forged Pistons... = (

I am disappointed that I didn't hear from RK Tek today, as I sent them both a phone call and an email yesterday.

Maybe Kelsey took the day off for ST Pattys day. Drink some green beer, happy St Pattys day.

 

[ProCat]

this makes me nervous I have 1600 miles on my stockers and was on the fence about throwing pistons in over the summer as preventative maintenacne

 

[The Bob]

Where you just running the stock map? Or had you tried using your auto-tune already? Just wondering if all the gas coming back into the engine made it read rich and leaned it down big time.

 

[briand]

I have a dropin kit i my 2012 pro with a rurbo. I have read lots of RKtec tech articles and here is one that i have followed since i did my kit. I have not had any issues by following this recommendation. Hopefully this helps explain the possible reason you had a failure. I want to be clear here that i am not suggesting that this is the reason for the failed pistons but only a possible explanation.

http://www.2strokeheads.com/POLARIS WARM UP.htm

He gives a good reason why we should add some oil to the gas.

 

[Turboegt]

Where you just running the stock map? Or had you tried using your auto-tune already? Just wondering if all the gas coming back into the engine made it read rich and leaned it down big time.

No, the map was not stock.

Autotune was only allowed to enrich, or lean the map I made by 3%.

 

[Turboegt]

Day 2 no response from RK Tek...

The two times I called to order something I heard back in a matter of hours...

Weird...

Maybe Monday.

 

[mtncat1]

that cylinder was very very lean , it was so lean it burnt the edge off the piston i would reconsider you tune numbers and you custom y pipe mod

 

[Turboegt]

The y pipe mod has never been run. The O2 sensor didn't fit with the steering.

The tune had 3% added to both cylinders, and a max it could remove of 3% and a max it could add of 3%.