Why are 2 stroke 800cc motors so unreliable?

[TIM]

Lost my motor on my 2012 pro the other day.
Now before you go on a polaris bash, i have also lost alot of skidoo motors. So to me it is a 800cc 2 stoke issue.

However i will say no warranty becasue of a slp pipe and head. And polaris is out of pistons for the rest of the season.

But what i am not getting is why are these motors so unreliable. My doos went down every 1600 miles, this polaris motor at 2400 miles.

Is it just 2 strokes, or are we asking to much out of these motors?

anyway it sucks big time to always be wondering if and when my motor will fail agian.

 

[snowmobiler]

the different brands really are different.jmo

 

[Jaynelson]

The short non-brand-specific answer is because;

- In stock form, all the modern 800's are putting out somewhere around 185-205hp/per liter, naturally aspirated, on over-the-counter pump fuel, and are maintained and used in the consumer market. And it weighs about the same as a couple cases of beer fully assembled.

- For comparison, a Corvette ZL1 puts out 103hp/per liter, and needs forced induction to get there, and weights about the same as your entire sled, or more with a few of the accessories. It also costs $100K and roughly half of that is the engine and accessories.

- To put out that type of power/liter, a small block Chevy 5.7L (350) would need to pump out almost 1,100hp....without boost or nitrous....on pump 91 octane. And be started at 20 below 0 by drunk guys who will bitch on a forum if it takes more than a couple pulls.

Even in stock form, modern 2-stroke sled motors are full-on race motors, that get held wide-open longer than any other piece of recreational equipment. Not saying I wouldn't like them to last longer, but that is the general answer to your question. There is a little bit lost in the 2-stroke to 4-stroke translation of my example, but that is the root of the problem.

Also, the newer chassis' allow more people to ride them a lot harder, a lot longer than ever before. They have also attracted a lot of new people to sledding, who aren't used to owning recreational equipment with such a strung-out motor in it. It would be like someone replacing you wife's car's engine with a NASCAR V8 and expecting it to have similar reliability characteristics....ain't gonna happen.

 

[polaris dude]

Yeah, I don't get why this is such a problem either. The 500s, 600s, and 700s are all super reliable. My dad's 600xlt has 6000miles with only a chaincase being replaced. I've got 3k miles on my 600 and not even a hiccup not to mention a friend whose kids have all used his ol' 1994indy which has 9,000miles(and still runs).

 

[rmscustom]

Yeah, I don't get why this is such a problem either. The 500s, 600s, and 700s are all super reliable. My dad's 600xlt has 6000miles with only a chaincase being replaced. I've got 3k miles on my 600 and not even a hiccup not to mention a friend whose kids have all used his ol' 1994indy which has 9,000miles(and still runs).

Please refer to jaynelson's post above.

 

[INDEEP]

I think you just happen to buy the 2 most unreliable motors in recent history. The older Revs were notorious for having piston issues. The Pro is in the same category. It's been a consistent 0 since the 800 cfi 4 was introduced in the IQ chassis. They've tried to tweak this and that but it's basically the same 800 motor since 2008. It's really a shame that the best chassis in the industry is mated with this power plant. Just look at how many companies offer some sort of "fix" kit for these motors (Indy Specialties, RK tek, Power Addiction, PMS, Terra Alps, Northstar). These aren't big bore or performance kits, these are FIX kits. Also, every season Polaris has issues keeping pistons and cylinders off back order. Weird huh, that basically the same piston since the recall of 08 is backordered. I've been riding since 98 and I've never seen a motor get this much attention.

Imo Ski Doo has turned itself around with the Etec. It had some initial glitches but I think it's proving to be a winner. i think with the power all these 800's put out, new pistons every 2000 miles is mandatory. But the entire motor should be good for almost 4000 mountain miles. No crank issues, no cylinder issues, and nothing electrical. I definitely don't think the 800 category is the problem.

 

[TIM]

sleds i have lost motors;
alot of 80's srx's, srv's yamaha
96 680 pol
98 700 pol
00 800 pol
02 800 90l
04 800 rev doo
06 800 rev d00
08 800 xp screwed up from the factory never right.
09 dragon but had turbo on it
2012 800 pol

The issue has been going on a very long time. Nothing new.

I guess i am bummed due to no warranty and polaris being out of pistons. And a blue bird day yesterday on my wifes sled that i am afraid to ride hard.

 

[Dogmeat]

I have 3600 miles on a boosted cat motor. Some mfgs make motors better than others.

 

[RobertTrivanovic]

sleds i have lost motors;
alot of 80's srx's, srv's yamaha
96 680 pol
98 700 pol
00 800 pol
02 800 90l
04 800 rev doo
06 800 rev d00
08 800 xp screwed up from the factory never right.
09 dragon but had turbo on it
2012 800 pol

The issue has been going on a very long time. Nothing new.

I guess i am bummed due to no warranty and polaris being out of pistons. And a blue bird day yesterday on my wifes sled that i am afraid to ride hard.

Dont trying to be rude but from the looks of it you have blown up almost is not every sled youve owned. My buddy has 4000mi on his 09 XP with somewhere around 2500mi on the top end. My 2007 M8 has 4000mi on the bottom end and around 2000 on the top end with absolutely zero issues on both sleds. My old M7 had 3000mi on the hole engine no rebuild and no issues. Yes you mentioned the polaris bashing but its not bashing, I personally think they have the best chassis, but the engine has issues. The new etecs like said above are all pretty damn strong and reliable engines from what iv seen. If you want an engine that will last forever (ok not forever but x3-4 what you poo lasted.) Get a cat, I love the M series chassis but personally the new pro climb chassis sucks IMO. I just rode a new XM and from the looks of it they are the ultimate mountain sled, chassis wise and also they have the least issues out of all the sleds iv seen recently. You need to think maybe you are doing something wrong, yes you have bought some of the least reliable sleds, but they should still last. Have you ever thought about just doing a simple top end change before the engine goes?

 

[89sandman]

high output engines with inconsistant oil fuel ratio's due to oil injection that are always running lean due to emmissions is part of the problem...

 

[snowmobiler]

the trick is to look on snowest before you buy and dont buy the brand thats currently blowing up.

 

[Jaynelson]

I think you just happen to buy the 2 most unreliable motors in recent history. The older Revs were notorious for having piston issues. The Pro is in the same category. It's been a consistent 0 since the 800 cfi 4 was introduced in the IQ chassis. They've tried to tweak this and that but it's basically the same 800 motor since 2008. It's really a shame that the best chassis in the industry is mated with this power plant. Just look at how many companies offer some sort of "fix" kit for these motors (Indy Specialties, RK tek, Power Addiction, PMS, Terra Alps, Northstar). These aren't big bore or performance kits, these are FIX kits. Also, every season Polaris has issues keeping pistons and cylinders off back order. Weird huh, that basically the same piston since the recall of 08 is backordered. I've been riding since 98 and I've never seen a motor get this much attention.

You obviously weren't lucky enough to own the wonder that was the 2007 Rev 800R. Mine needed 3 motors, a chaincase, a TPS, a primary, and a grocery list of small/medium parts/fixes....just to make it to the same mileage as my supposedly unreliable 2011 RMK. Which has needed....a set of clutch weights (wear item) and a motor mount.

So pick your poison. Finding a reliable 2-stroke 800 sled is like timing which stock to buy. Ya there's some science behind it, and if you catch the right one in the right year, and happen to have some money to spend in that year, you'll likely have some success. Still a risk component tho.

Bottom line is, since the motors are so strung out (and they are), if one little thing is out of whack, it can wipe out the whole shee-bang.

 

[TIM]

robert

I wanted to do a top end when i did the slp stage 3 kit. dealer said not needed. I am not going to deny pin it and run is the main way of riding. I love to sidehill and keep her pinned. I will also say it is a fricking machine, if i can go, so can the machine. run them hard, it is a snowmobile.


Doo go down just as much as poos. And yes the cat does seem the most reliable motor.

 

[INDEEP]

You obviously weren't lucky enough to own the wonder that was the 2007 Rev 800R. Mine needed 3 motors, a chaincase, a TPS, a primary, and a grocery list of small/medium parts/fixes....just to make it to the same mileage as my supposedly unreliable 2011 RMK. Which has needed....a set of clutch weights (wear item) and a motor mount.

"I think you just happen to buy the 2 most unreliable motors in recent history"

Um ya, I thought I covered that?

Tim, have the dealer or re plater double check that the cylinder skirts aren't cracked. It's pretty common for that milage.

 

[Jaynelson]

"I think you just happen to buy the 2 most unreliable motors in recent history"

Um ya, I thought I covered that?

LOL fair enough....but which 2 would those be? CFI-4? 2007-2008 800R? 900 Pol? Early 2000 800 Pol? Any 800 Cat from early 2000's? 1000 Doo?

There have been a lot of unreliable sleds built by all the manufacturers. The only one who can claim any sort of track record is Yamaha, and no one buys them (to ride stock) cause they're heavy and progress slowly.

 

[INDEEP]

In his original post he compared his Polaris to his older Skidoo. I knew he used to ride Revs and like you said they had a horrible history. Now the Poo 900's, thats next level unreliable. But he was lucky enough to dodge that bullet. Bottom line is the 800cc category isn't the problem. IMO

 

[Jaynelson]

Bottom line is the 800cc category isn't the problem. IMO

Correct, 200 hp/liter in a naturally aspirated light-weight application would have some reliability/longevity issues in the consumer market at any displacement. We see it most in the 800 class, because that is (by FAR) the most popular sled class on here, and the one we all have the most experience with.

A 2-stroke 250 dirtbike engine, for comparison, is ~40hp. So 160hp/liter, with basically no load compared to a sled, very limited WFO compared to a sled....and if you go by the book, it wants a top end job every 10 rides or so. My 450 4-stroke isn't much longer of an interval at maybe 120hp/liter. It's hard to find a great comparison, because you really can't buy much that's THAT racy direct from a large manufacturer....

 

[Coldfinger]

My 1999 Summit X 670 reportedly had 130HP stock and it had over 5,000 troublefree miles when I sold it. Never touched the engine and the clutches only needed a few sets of o-rings, 1 spring cup and I replaced the primary spring just because. The plastic buttons in secondary were replaced once.

1000cc/669cc = 1.4947
x 130 hp
= 194.3hp

1000/794cc=1.2594
x 160 hp
= 201.5hp

If it's that extra 7hp causing problems, I'll buy the lower HP version when it is offered.

 

[eddy]

Reliability

Valid points above, now what is the answer to the OP's question? One answer has to be the longer stroke (vs the super reliable 700's) and the cost savings Doo and Poo get by not balancing the cranks (and primary clutches). Cat (Suzuki) balances the cranks better in my opinion.

I think if you had a well balanced crank, maybe a 1.5 MM shorter stroke, a primary clutch that was well balanced and kept the peak power output RPM just below 7900 RPM reliability would be as high as ever.

If you had to pick one cause as the most likely it would have to be the combination of unbalanced crank and primary clutch as an assembly.

With good lube and a proper design 125cc motocross engines made 320 HP per liter and seemed like they blew up less than the 800 cc snowmobile engines. Now they also had very tight hourly replacement schedules for the top end components. Snowmobile engines have these top end component measurements specs in the shop manual but who tears down the motor to measure specs?

 

[backcountryislife]

Just sold my cat, and bought a doo... but I know guys with 10k+ on M8 motors without issues. Anyone who thinks this ISN'T brand specific is deluding themselves.
Poo is the only one building motors today with both low power AND poor reliability. Pretty impressive to nail both with such consistency though...

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