Why DOO SKI-DOO motors blow up at such a low mileage?

[M1ryguy]

They can be one of the trickiest sleds to get the mapping figured out - that would be my guess as to why she blew at a grander - I'm loving my aurora box - 12.5afrs at 8lbs - flat lined there - runnin off the 02 sensor - runnin flawlessly

Right on, I gave up after that one and swore I would never do a two stroke turbo again. I am sure I will be eating those words one day though.

 

[RGM]

Others have touched on design aspects of the 800 vs 850 ETEC, but I'll share my thoughts.

Background; 2-stroke engines utilize a total-loss lubrication method to lubricate the crankshaft bearings and piston. As 2-stroke engines don't operate on pressurized lubrication, traditional journal bearings are not permissible, necessitating ball and roller bearings for the crankshaft and rod bearings. Generally all or some portion of the fuel is injected through the crankcase in a 2-stroke engine, diluting and washing the oil film from the bearings and cylinder surfaces. Dilution of oil with fuel reduces the oils viscosity and reduces its lubricating effectiveness at best, at worst it washes the fuel completely from the surfaces allowing metal to metal contact and engine wear and possible engine seizure. Given that 2-strokes don't have an oil sump to collect and circulate oil, a continuous feed of oil is required to maintain lubrication in the engine, but this oil consumption must be kept to a minimum to meet emissions regulations.

The 800 ETEC was designed with a very key feature that I believe is a major cause of it's extended reliability. The 800 relies solely on direct injection to supply fuel to the combustion chamber of the engine. (BRP acquired the assets of OMC which was undergoing bankruptcy in early 2001, one of these assets was Evinrude, which held patents for 2-stroke direct injection). None of this fuel travels through the crankcase, almost guaranteeing fuel dilution will not occur, and with proper fuel injector nozzle design and injection timing minimizes fuel wash on the cylinder keeping the piston properly lubricated. The non-diluted oil film can also serve as "padding" for the piston as it rocks back and forth in the cylinder during every crank rotation, this oil film also acts to transfer heat to the cylinder walls which keeps the piston cooler. A piston that rocks less in the cylinder, and does so at lower temperatures suffers much less cyclic fatigue, which greatly improves piston life and reduces the chances of skirt breakage. The lack of fuel in the crankcase also ensures the crank bearings are well lubricated, and are much less prone to failure from oil starvation.

The 850 was designed as a more powerful version of the 800. Except with the future intention of adding boost. The 850 has smaller fuel injectors installed than the 800, necessitating adding fuel by another set of injectors, BRP decided to do this through auxiliary injectors in the throttle bodies. There are benefits of adding fuel this way, including better mixing of the air fuel mixture prior to combustion, for better emissions and performance at high rpm and high loads (Ford has even added secondary injectors to the 3.5 ecoboost for similar reasons). The 850 relies heavily on the auxiliary injectors above mid throttle to supply enough fuel to the engine. The downside of this is oil dilution in the crankcase and lower cylinder, greatly reduced oil viscosity in the bearings, and the decreasing the oil film strength on the piston. Inevitably decreasing the service life of the crank bearings and of the piston by removing the oil cushion for the rocking piston. Both of which have been seen as failure points on the 850.

BRP didn't design the 850 without knowledge of the oil dilution issues that throttle body injectors creates, BRP has created a very innovative 2 piece forged crankshaft, with well placed oil galleries to delivery oil to the lower rod bearings. On paper it looked good, from what I've seen though on the snow, and other failure reports I've read, crank failure is still more prevalent than the 800 ETEC.

The extra injectors on the 850 were for the turbo and to help cool it . The 850 has pressurized oil in the crank

 

[ABMax24]

The extra injectors on the 850 were for the turbo and to help cool it . The 850 has pressurized oil in the crank

Not as per BRP, the throttle body injectors were also used in the naturally aspirated version at high loads, as the main injectors are too small to supply all the fuel.

It's not really pressurized, just enough to get it to the bearings. No different than any other current 2 stroke.

Even if it was pressurized it doesn't really matter, my reference was to journal bearings that require pressurized oil to "float" the crank on. The 850 still uses ball and roller bearings.

 

[RGM]

When skidoo first put the extra injectors in the 850 NA it was obvious that they did it with the turbo in mind.

 

[Caper11]

There are no greased bearings in a 850 engine, the oil is supplied by the oil pump to the crank gallery, and centrifugal force Lubes the rod bearings, and the oil pump supplies oil to the crank bearings.

The rods on the 850 are similar to a 4s with a rod cap.
In 2019 the oil system for the bottom end got a update.

 

[struglin]

Had a 16 biggest pos ever thing ate 3 motors bone stock my buddy on the other hand just blew his up at 7500km all boosted running 10 lbs it’s a crap shoot….

 

[Longhairfreak]

The 800 etec swallows up 8lbs of boost all day long - I've got 8000kms on the chassis - I put a new crank in it at 5000kms just to be safe - 3000kms now of 8lbs - I'm running it till the rods leave the chatroom then she's gettin parted out

Running more than 5 lbs of boost drastically reduces the life of these engines. And they were bad stock.

 

[SUMMIT TREE]

Running more than 5 lbs of boost drastically reduces the life of these engines. And they were bad stock.

You must be getting your info from CNN. The 800 Etec is an amazing Engine. Between mine and friends we’ve ran 8 or 10 of them all were flawless. Just pulled the reeds out of my 15’ with aerocharger on it and engine still looks pristine inside. A guy bought my last one with 4500 km on it to replace the engine in his with 15,000 km before it failed. It was untouched, as in ran for 15K without issue. Meaning it was not opened up. Outside of maybe external parts like reeds and belts etc.

 

[snopro]

I wonder how long those mid 90’s motors lasted that the Freak ran all his life on snow?

 

[kingcat162]

You must be getting your info from CNN. The 800 Etec is an amazing Engine. Between mine and friends we’ve ran 8 or 10 of them all were flawless. Just pulled the reeds out of my 15’ with aerocharger on it and engine still looks pristine inside. A guy bought my last one with 4500 km on it to replace the engine in his with 15,000 km before it failed. It was untouched, as in ran for 15K without issue. Meaning it was not opened up. Outside of maybe external parts like reeds and belts etc.

Personally I think doo shoulda just bored the 800 to an 850 and kept that same engine in the gen 4 - it handles boost just fine - only thing I don't like is the 2 part wedge reed design other than that it's tuff as concrete nails

 

[maxwell]

Personally I think doo shoulda just bored the 800 to an 850 and kept that same engine in the gen 4 - it handles boost just fine - only thing I don't like is the 2 part wedge reed design other than that it's tuff as concrete nails

again, i am SO thankful you dont have any input with BRP R&D

 

[ABMax24]

I think the 850 is a great start, I think if they moved the throttle body injector into one of the transfer ports it would be a whole lot better though.

 

[kingcat162]

again, i am SO thankful you dont have any input with BRP R&D

And I'm thankful your behind a keyboard and I don't see you in person - so many design flaws in the gen 4 - it only took them 5 yrs to figure out that a motor mount on the side of the mono jug is a terrible idea - but wait let's mount a ground strap there and mount a big stupid plastic wiring harness there too - genius - maxwell you should apply at brp in quebec you'd fit right in

 

[catrutt]

I also wondered about a little bit of oil in the gas. However the 850 uses more oil than my 800.

 

[lilduke]

I wonder how long those mid 90’s motors lasted that the Freak ran all his life on snow?

The 670s were dam near bullet proof.

 

[snopro]

The 670s were dam near bullet proof.

They were good for their time. I was a dealer then. I could rebuild one of those to this day with my eyes closed. Lol

 

[maxwell]

And I'm thankful your behind a keyboard and I don't see you in person - so many design flaws in the gen 4 - it only took them 5 yrs to figure out that a motor mount on the side of the mono jug is a terrible idea - but wait let's mount a ground strap there and mount a big stupid plastic wiring harness there too - genius - maxwell you should apply at brp in quebec you'd fit right in

ive dealt with ALOT of skidoos Old and new. i have had substantially less issues with the 850 vs the 800. Both are good. The 850 is better, there isn't anything wrong with the design. There are people at rotax alot smarter than you and i designing these things. They aren't designed in Quebec sorry. If there was major issues with this powerplant we would be seing changes made to it regularily.

 

[ABMax24]

I could rebuild one of those to this day with my eyes closed. Lol

That's how I feel about my Polaris 800....

 

[kingcat162]

ive dealt with ALOT of skidoos Old and new. i have had substantially less issues with the 850 vs the 800. Both are good. The 850 is better, there isn't anything wrong with the design. There are people at rotax alot smarter than you and i designing these things. They aren't designed in Quebec sorry. If there was major issues with this powerplant we would be seing changes made to it regularily.

Wherever the f*k they are designed - I took it for granted that it was in Quebec because of the few things that are 180 degrees out - the motor mounts on the gen 4 is and always will be a bad design - the reason for the gen 5 motor mount changes - I consider the gen 4 850 motor a GEN 1 through the n/a yrs - now the boosted 850 is Gen 2 and now the revised motor mount 850 engine is a gen 3 - every one of them has design flaws - all it takes is someone like me to run it in real world conditions and make changes accordingly- same thing I've done to my T3 over the years - maybe one day I'll see you in person and stuff your head under my hood and show you what r&d really is - till then eat

 

[tmo1620]

Wherever the f*k they are designed - I took it for granted that it was in Quebec because of the few things that are 180 degrees out - the motor mounts on the gen 4 is and always will be a bad design - the reason for the gen 5 motor mount changes - I consider the gen 4 850 motor a GEN 1 through the n/a yrs - now the boosted 850 is Gen 2 and now the revised motor mount 850 engine is a gen 3 - every one of them has design flaws - all it takes is someone like me to run it in real world conditions and make changes accordingly- same thing I've done to my T3 over the years - maybe one day I'll see you in person and stuff your head under my hood and show you what r&d really is - till then eat

Did you just tell maxxy to give you a BJ? It is 2022 so maybe he’s gone with the trend but I’m pretty sure he’s not into dudes