Polaris CFI-2 Engine and why you may NOT want to warm it up too long”
I have been holding on writing about this for some time because it is going to be very controversial..
But, I believe it is time to discuss this..
What I am talking about is this whole "idea" that letting your sled warm up until it hits "X" degrees before taking off on it is a GOOD IDEA!
This ,MAINLY, pertains to the Polaris CFI engines.
We all have heard and read about how the sled owner lets the sled warm up to 120+ degrees before ever getting on it and how this is a "good" thing..
I am going tell you that this is NOT a good thing and actually can be very bad for your engine.
I am not telling you to pull the sled off of the trailer and PIN IT!..
Hopefully, this article will clarify what I am trying to relate.
1) Without getting into Physics and the laws of thermodynamics (not the intent here), let's touch on the FACT that HEAT ALWAYS travels to COLD.. Hot "anything" will not seek out something that is hotter..
This is very important to remember when reading this article.
2) Your coolant temp is not ALWAYS a good indication of how "hot" the rest of your engine components are (see #1 above)..
Hotter coolant temps tell you that it has removed HEAT from your engine and transferred it to the cooling system.
It does NOT tell you that your engine is SAFE to run at high loads!
AGAIN… we are not trying to dive into ALL of the aspects to what is happening internally.. That would be far too vast and boring to capture anybody’s interest.
This article will be kept VERY SIMPLISTIC in its nature and, YES, any good physicist will, most likely, be able to find “holes” or “exceptions” within the content.
It appears that it is very common to pull into the unloading zone, start your sled, then proceed to get dressed while your sled is running.
Once dressed, you go to your RUNNING sled , check the coolant temp, see that it is at or above 120 degrees F, then jump on the sled and floor it out of the loading area.
With this particular engine design, this, IMO, is a very bad idea!!!
WHY??? OK, let’s try and break it down in very simplistic terms
1) See #1 and #2 above…
2) With this engine, AT IDLE, the oil pump is supplying little to NO OIL to the engine. So, all the time your engine is “warming up” it is near starved of oil.
THIS IS NEVER A GOOD THING… EVER!
3) The engine is heating up, the pistons are expanding, the internal temps are ,somewhat, stabilizing (trying to obtain a state of equilibrium with its surroundings) and the engine is transferring some of its heat energy to the cooling system.
Any oil that was present on the cylinder walls and the piston itself (to provide the NECESSARY oil film barrier needed for a 2 stroke engine to survive) has been completely removed or reduced to an un-safe amount to provide an adequate film protection layer/barrier.
In other words… your engine’s piston and crank-shaft are heated to a high level that is not desired for the amount of oil that is present.
NOTE--> The ONLY way ANY piston can seize in an engine is to have the oil barrier removed.
As long as the oil barrier remains fully intact, you can not seize an engine.
OK, back to the subject at hand…
4) The rider, “eye-balls” the temp reading, sees an acceptable number and “feels” that the engine is now in a “SAFE” state for WOT running…
With this confidence in mind, he/she grabs a handful of throttle and “peels out” of the loading zone heading to the “good stuff”
THIS IS WHERE THE PROBLEM SURFACES!!
5) The engine has just been subjected to HIGH RPM and possible pro-longed running with a cylinder and crank that have little to no oil barrier/film on themselves or the surrounding components…
NOTE--> This is the same scenario when new pistons are installed and the owner decides to let the engine do SEVERAL “Heat Cycles” in the garage after prolonged idling ... Not a good idea either! But that is a whole other topic!
Let’s break it down a bit further….
5a) The engine’s oil barrier is near depletion, the piston and crank are very hot . The cooling system is also at a high temp reducing its ability to successfully REMOVE heat from the engine.
The piston relies on this oil barrier to form a “coating” on itself and the cylinder wall. This oil barrier MUST be present to avoid Metal to Metal contact between the piston and the cylinder wall.
It may be good to note that the cooling system OFFERS the engine cooler running temps SOLEY by giving the engine an outlet to REMOVE its heat.
Many think that the cooling system is actually “COOLING” the engine by surrounding it with cold temps. This is not the case … The engine is removing some of its heat energy via the cooling system... see #1 above.
OK, on with the scenario....
5b) The throttle is “cracked” and the piston is immediately accelerated. Internal temps and pressures begin to elevate VERY quickly! With these higher pressures and temps (not coolant temps but engine temps), the oil’s function is of extreme importance!
5c) But wait… we are, severely, lacking in this oil dept!... NOT GOOD!!
5d) Due to the throttle lever being open past idle, the oil pump is supplying a higher volume of oil to the LOWER END ONLY! There is no direct oil supply path, in this engine, to the cylinder walls!!
This is another issue with this engine’s design.
5e) Oil supply is increased but, keep in mind, at 8000RPM the piston is making 133 revolutions PER SECOND!! And it takes time for this newly supplied oil to reach the cylinder wall and adequately coat it with the REQUIRED barrier (more than a few seconds worth of time).
So, the piston ,in say 3 seconds, has made near 400 revolutions with little to no oil between it and the cylinder wall.
5f) During this short time, the piston has grown even more because the heat of the piston has increased.
The piston is relying on the oil film and fuel to help cool it back to a better level and protect it from making aluminum to NikaSil direct contact.
BUT, the oil film is lacking and the hotter piston begins contacting the cylinder wall at small “points” along the cylinder wall TRYING to fuse itself to the cylinder wall.
This process continues until the oil can get in there to do its job.
The oil barrier is not able to form as easy on the intake side of the cylinder or piston… WHY? Because the piston and cylinder,at BDC, is such that the oil is scraped off the piston skirt via the cylinder skirt (another design issue IMO)
OK… What is the end result of all this??
The end result is that the intake side of the piston will become lightly scored due to its prolonged attempts (sometimes successful) to fuse itself to the cylinder wall.
NOTE: This intake scoring does not affect HP or reliability in any way, providing there is NO material transfer, ring stiction, or “scrapers” produced on the piston skirt from this experience.
OK, I know what you are going to ask... “Why is the stock piston not as prone to this intake scoring?”
That is a very good question.
Here is the answer: The Stock Polaris pistons suffer from skirt collapse VERY quickly. The intake skirts will collapse inward as much a .006” over a very short period of time. With this added piston to cylinder wall clearance, it is much more difficult to make contact to the cylinder wall for reasons that are apparent.
With this excessive clearance, the piston will develop “rock” and “lever” itself against the cylinder wall. This has been a known problem with the OEM pistons. This causes the cylinder to eventually crack and break causing catastrophic engine failure!!! It has also been shown to crack the lower intake CYLINDER skirt.
This is the main reason why Polaris thickened the cylinder skirt on the 2013 and newer cylinders.
OK.., How do you avoid this??
Here is what we suggest:
1) Run about a 200:1 premix of oil in every tank of fuel.
2) Install a better vented oil cap to assure a steady flow of oil to the pump.
3) Turn up the oil pump lever screw a couple of turns.
4) When you arrive at the loading area, start your engine, let it idle for about 2-3 minutes MAX. Your coolant temp will vary depending on the day. But, hopefully, it will be in the 80-90 F range after this.
5) Pull it off the trailer and SHUT IT OFF!!
6) Get dressed or do what you have to do before leaving for the day.
7) When ready to start the day’s ride, start the engine, let it idle for about 1 minute. Get on the sled and leave the area using VARYING throttle (NO Pro longed WOT running or hill pulls) until you get about 1 to 2 miles out of the loading area.
8) After #7--> Ride it as you see fit!!
Using the above method will make for a longer lasting engine.