blown motors. help please

[Boreal]

My sled had one season on it and had low compression in one side. At the start of this season the dealer rebuilt the top end on the engine on the poor side. At the same time, I had the dealer install a sidekick turbo. Pull and go, pump gas.


I ran the sled for 3 rides in OK conditions and halfway through the 4th ride the engine seized. (around 100kms per ride) Difficult tow out of the mountains and back to the dealer. The same one side of engine was destroyed. I had to install a completely new engine. Dealer did the work and again installed the turbo. The new motor was put into break in mode.


This time I went safe and mixed added C12 fuel to make sure the fuel was good octane. I went for 3 rides in OK snow conditions and on the morning of the 4th ride the engine seized. Again, it was the same side of the engine that seized. Towed the sled out of the mountains and back to the dealer.


The dealer has said the injectors are working. They have gone to the turbo manufacturer and sent the fuel controller to them. The turbo co says nothing is wrong with it, same mapping in it as every unit they sell.


What do you think the problem is? My sled's injectors, the turbo fuel mapping, or other...? I am at a big loss this season now.

 

[Wood]

What model year and what side went down...PTO or Mag? Any pics? You will need to provide more details. Was the crank and/or seals inspected/replaced?

 

[Boreal]

It is a 2018 RMK 800. The PTO side each time. Yes; they were replaced on the rebuild. The last fix was a completely new engine. Sorry, I don't have pictures.

 

[Sierra G-Force]

I'm following this thread just for information. (My 17 axys just went down with 2000+ miles and just out of warranty).

Dealer says its the PTO piston. I'm interested in knowing whats the difference when one cylinder goes down or the other?



Sorry to hear about yours too...

 

[jim]

With an airleak with a turbo, the pressure pushes past the leak and you actually run rich and bog for that reason. So, I'd rule an air leak out.
You said you went C12...did you do that for every ride, including the time it seized? If so, that rules out detonation problem (unless not enough C12 for the elevation).

So, it sounds like you are either going lean for some reason, cold seizing or it is not getting oiled...at least for common issues.

The best way to rule things out after a burndown is to watch it closely. Look at piston top early for signs of detonation. Look at piston and cylinder surfaces for oil and/or scarring. Read the plug. Look at wash.

I also remember an issue with some sleds where the thermostat opens up suddenly and dumps cold coolant into the cylinders, causing cold seizes. Check thermostat too...but a failure there should trigger overheat sensor.

 

[Wood]

It is a 2018 RMK 800. The PTO side each time. Yes; they were replaced on the rebuild. The last fix was a completely new engine. Sorry, I don't have pictures.

Was fuel pressure/pump checked? Did your dealer have the injectors flow tested?

 

[Boreal]

It is definitely running lean. That is the symptom each time.


I don't know if the fuel pressure and pump were checked. Will ask.


My understanding is the dealer checked and saw that the injectors were working. I don't know if that included having them flow tested, or just a visual.

 

[Boreal]

With the rebuild, I only had av gas mixed into the first tank. On the new engine; I ran C12 every time.

 

[jim]

Fuel pumps can work just fine until wide open and longer pulls...sometimes they drop pressure. Pump might have issues or power, electrical things. My turbo likes 6 pounds. More and it starts to get lean on long pulls. Regulator can cause issues as well. Had a buddy with turbo...same issues. Turned out a new pump and careful power wiring fixes it...he would run out of pressure on long pulls. I take it you burned down on longer pulls? And very hard to verify at dealer. Guage is the only way to know.

 

[diamonddave]

Were the fuel injectors ever replaced? If not, I wouldn't consider running it again without new injectors. I'll save you my soap box reply on why but I replace them now on every rebuild. This motor design suffers from premature carbon build up in the injectors due to the placement on the motor. The injector's are okay electrically but not mechanically.


Are we sure there isn't a detonation issue? Locator pin okay? Some pics of this failure would be very helpful.

The other thing to know is: did the brass oil check valves get replaced/changed (or already on the replacement motor)?

May need to bench test the electric oil pump as well. Haven't heard of any issues but everything is going to need to be checked when this goes back together.

You're not running any combination of 94 pump fuel by chance?

 

[Boreal]

Yes; each time the engine seized was on a long pull. And on each seize, I climbed to the top, let off the throttle to stop or turn down, and the engine would stall. Game over.

 

[Boreal]

diamonddave; I'll have to check with the dealer on some of the specific items you mentioned. I don't know if those items were checked or replaced.


I was not getting det codes while running. The new engine I was getting a mid range bog on the first 3 days. Then got the chance to increase my weights for the 4th ride and it seemed like it went away. It was a short day though and only really just got into the riding area.


The fuel injectors I am quite sure were not replaced. Looking back now, I certainly agree I would replace them on every rebuild just in case.


On the first rebuild engine I did run pump gas 94 mixed in with 91. What are you thinking?