Gen4 850 Down on Power? Here's how I fixed mine.

Feb 17, 2020
6
10
3
31
Minnesota
2017 Skidoo Summit 850 SP
1200 miles on it at time of problem

Story goes, I was riding deep snow in Northern WI all day pretty much full throttle. Halfway through the day after a long pull I let off the gas and went back on and it felt like a 440, no balls. No abnormal noises or anything, just power loss at the top end. I had fueled up that morning with fresh 91 non oxy and was 1/2 way through that tank. Checked plugs... they look good. hmmm Take it back home and park against a tree on ice and hold it wide open, it would only hit about 7500-7800rpm max and it would kind of fade in and out quickly, sounded almost like a rev limiter.

Being this is going on in March, I only had a few more weeks left of riding so I brought it to the dealer and picked up another sled to finish out the season on and keep as a spare in the future (2010 crossfire 800, 144, 2.6" powerclaw). The sled sat at the dealer from March until May when they said they re-clutched it and updated the ecu and now its running great, ok $750 later, I went and picked it up and put it in storage for the summer without even really testing to see if it was fixed I just took their word for it.

Fall comes and we get our first snow (Mid November 2019) so I pull the sled out of the garage and rip around the yard and wouldn't you know....SAME DAMN ISSUE. So I brought it back to the dealer and said they didn't fix anything and they said they would take another look free of charge. It sat there for another month before they called me and said they give up, they can't figure out the issue. So I picked it up and told them I'd let them know what the issue was as soon as I have time to look at it. Brought it back home and it sat until Mid January 2020 when I finally had a chance to take a look at it.

I am very mechanically inclined and have never had anyone else work on anything for me but I was finishing up multiple degrees at school, taking on projects at work and buying a house all at the same time.

I go completely through the electrical harness and sensors, probing, ohming and testing according to the service manual and everything looks great. Physically everything is in great shape and it still even smells like a new sled (1200 mi), I check compression and it give me a weird reading. 112psi on LH cylinder and 126psi on RH (mag). OK, service manual says 110psi is the service limit and I'm pretty close so I start tearing the engine apart thinking a skirt may have collapsed or something. I'm removing covers and parts and I get down to removing the rave valves and run into this (pictured) lo and behold a broken exhaust valve, I pull the rave bracket out and only one valve comes out. VIOLA! SOMETHING PHYSICAL, SOMETHING REAL.

I was so far into it I pulled the jugs while I was at it and brought it in for a quick re-hone. The cross hatch was gone at the top 1" of the cylinder so I figured it couldn't hurt. I called into BRP to tell them about my problem, I gave them the part number listed on their website Ski-doo.com (420954058 - Lower Exhaust Valve) the woman on the phone said those are discontinued and they now have a new part number (420954057) and I would have to go through my dealership to get them, So I gave her my dealers info and had her send 2 of them over. (I wasn't only going to replace 1, that would have been foolish). I went over to the dealer a couple days later and picked them up, they only charged me for 1. $49 out the door for 2 new exhaust valves. Upon inspection they were indeed a new casting, the new part number is made on different dies (New parting line on casting along with labels) (pictured). The new ones have a "19" on them, old ones had no labeling or marks.

Ordered a $90 SPI top end gasket kit off of ebay (SM-09530T) which came with fuel orings (harder durometer but I had no issues) and all top end gaskets except for the reed valves. This kit came with multiple base gaskets for the jugs so you can set your piston protrusion height. My sled came with a 7 hole gasket (.07mm) but I had to install the thinnest gasket to get the right protrusion height (5 hole) of .068-.072" , The thinner the base gasket the more compression you'll have as well. You may run into clearance issues so take caution. I installed the thinnest gasket and ended up with 122psi on each cylinder when I was done. (Still enough power to pull the ski's up for 200 feet while sitting down).

Compression before, tested with engine warmed up at 900' elevation, no added oil to cylinders or anything. Stock pistons and rings with 1200miles
112psi LH, 126psi RH
Compression after, same testing environment just with new exhaust valves, thinner base gasket and fresh cylinder hone. All done with a cheap compression tester, I never did a dead-weight test to calibrate the gauge so It could easily be off 10+psi for all I know, I just want consistency. Runs like a raped ape on "122psi".
122psi LH, 122psi RH


TLDR
I had no top end power and had a bog/rev limit scenario. Turned out to be my exhaust valve stem had sheared off on the LH, clutch side cylinder. No damage done to engine.
Had BRP send new updated PN exhaust valves to my dealer, where I picked them up, installed them and I'm out ripping around full power again.
For a quick check, stick your fingers in your exhaust port while pulling your rave cable to make sure they both move *CAUTION, *can lose finger if engine turns over* Disconnect power first and stick a bar through primary clutch to keep engine from turning over

Took a couple video's the day after the rebuild. Ski's up, no problem.
 

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c_sharp

New member
Lifetime Membership
Jun 2, 2016
13
2
3
Thanks for the great write up.
Did you have an rpm issue?

My sled was running fine, 1500 miles on the stock plugs. Has a jaws can, occasional pops and crackles. Halfway through the day it decided that 7100rpm was all it wanted to give. And it sure felt under powered.
Messed with clickers, no luck.
Changed the plugs, it was definitely time.
Put the clickers back to 3, and now im hitting 7400. Doesnt feel like its got the normal power it had.
Also at one point it was stuck at 6400 climbing, blip the throttle a bit and then it decided to kick it up to 7400 and had more power like it should.

Thinking maybe its time for a compression test..
 

c_sharp

New member
Lifetime Membership
Jun 2, 2016
13
2
3
C_sharp, sounds like

Your problem sounds very similar, does it still have power down low? Mine did, until it gets above about 6000rpm then the power would fade out.

Yep, it seems to have the normal power at the bottom end.but the top sure doesnt seem right. Just checked compression last night 160psi on both cylinders.
 
Feb 17, 2020
6
10
3
31
Minnesota
Pull off your exhaust and stick a bore scope ($10 on ebay/amazon) into the Y-pipe and pull your rave valve cable to make sure both exhaust valves move fully open and fully close. If you don't want to wait for a camera, remove your Y-pipe (Heat bolts first as they are blue-loctite'd in) and stick your finger in there to feel. Unplug your battery, push your kill switch, unplug your tether, just whatever you do, don't turn your engine over or you could lose a finger.
 

julians

Member
Lifetime Membership
Nov 28, 2010
67
9
8
39
Park City Ut
My 17 did the same thing after they replaced the wiring harness. Turned out the clip that holds the rave valve actuator connector together was gone or not reinstalled after the service. Wouldn't go above 7400 RPM. Once the dealer figured that out she's run good ever since.
 
Dec 11, 2012
53
23
8
50
2017 Skidoo Summit 850 SP
1200 miles on it at time of problem

Story goes, I was riding deep snow in Northern WI all day pretty much full throttle. Halfway through the day after a long pull I let off the gas and went back on and it felt like a 440, no balls. No abnormal noises or anything, just power loss at the top end. I had fueled up that morning with fresh 91 non oxy and was 1/2 way through that tank. Checked plugs... they look good. hmmm Take it back home and park against a tree on ice and hold it wide open, it would only hit about 7500-7800rpm max and it would kind of fade in and out quickly, sounded almost like a rev limiter.

Being this is going on in March, I only had a few more weeks left of riding so I brought it to the dealer and picked up another sled to finish out the season on and keep as a spare in the future (2010 crossfire 800, 144, 2.6" powerclaw). The sled sat at the dealer from March until May when they said they re-clutched it and updated the ecu and now its running great, ok $750 later, I went and picked it up and put it in storage for the summer without even really testing to see if it was fixed I just took their word for it.

Fall comes and we get our first snow (Mid November 2019) so I pull the sled out of the garage and rip around the yard and wouldn't you know....SAME DAMN ISSUE. So I brought it back to the dealer and said they didn't fix anything and they said they would take another look free of charge. It sat there for another month before they called me and said they give up, they can't figure out the issue. So I picked it up and told them I'd let them know what the issue was as soon as I have time to look at it. Brought it back home and it sat until Mid January 2020 when I finally had a chance to take a look at it.

I am very mechanically inclined and have never had anyone else work on anything for me but I was finishing up multiple degrees at school, taking on projects at work and buying a house all at the same time.

I go completely through the electrical harness and sensors, probing, ohming and testing according to the service manual and everything looks great. Physically everything is in great shape and it still even smells like a new sled (1200 mi), I check compression and it give me a weird reading. 112psi on LH cylinder and 126psi on RH (mag). OK, service manual says 110psi is the service limit and I'm pretty close so I start tearing the engine apart thinking a skirt may have collapsed or something. I'm removing covers and parts and I get down to removing the rave valves and run into this (pictured) lo and behold a broken exhaust valve, I pull the rave bracket out and only one valve comes out. VIOLA! SOMETHING PHYSICAL, SOMETHING REAL.

I was so far into it I pulled the jugs while I was at it and brought it in for a quick re-hone. The cross hatch was gone at the top 1" of the cylinder so I figured it couldn't hurt. I called into BRP to tell them about my problem, I gave them the part number listed on their website Ski-doo.com (420954058 - Lower Exhaust Valve) the woman on the phone said those are discontinued and they now have a new part number (420954057) and I would have to go through my dealership to get them, So I gave her my dealers info and had her send 2 of them over. (I wasn't only going to replace 1, that would have been foolish). I went over to the dealer a couple days later and picked them up, they only charged me for 1. $49 out the door for 2 new exhaust valves. Upon inspection they were indeed a new casting, the new part number is made on different dies (New parting line on casting along with labels) (pictured). The new ones have a "19" on them, old ones had no labeling or marks.

Ordered a $90 SPI top end gasket kit off of ebay (SM-09530T) which came with fuel orings (harder durometer but I had no issues) and all top end gaskets except for the reed valves. This kit came with multiple base gaskets for the jugs so you can set your piston protrusion height. My sled came with a 7 hole gasket (.07mm) but I had to install the thinnest gasket to get the right protrusion height (5 hole) of .068-.072" , The thinner the base gasket the more compression you'll have as well. You may run into clearance issues so take caution. I installed the thinnest gasket and ended up with 122psi on each cylinder when I was done. (Still enough power to pull the ski's up for 200 feet while sitting down).

Compression before, tested with engine warmed up at 900' elevation, no added oil to cylinders or anything. Stock pistons and rings with 1200miles
112psi LH, 126psi RH
Compression after, same testing environment just with new exhaust valves, thinner base gasket and fresh cylinder hone. All done with a cheap compression tester, I never did a dead-weight test to calibrate the gauge so It could easily be off 10+psi for all I know, I just want consistency. Runs like a raped ape on "122psi".
122psi LH, 122psi RH


TLDR
I had no top end power and had a bog/rev limit scenario. Turned out to be my exhaust valve stem had sheared off on the LH, clutch side cylinder. No damage done to engine.
Had BRP send new updated PN exhaust valves to my dealer, where I picked them up, installed them and I'm out ripping around full power again.
For a quick check, stick your fingers in your exhaust port while pulling your rave cable to make sure they both move *CAUTION, *can lose finger if engine turns over* Disconnect power first and stick a bar through primary clutch to keep engine from turning over

Took a couple video's the day after the rebuild. Ski's up, no problem.
That is absolutely pathetic your dealer couldn't diagnose the problem.
 

Wapow

Well-known member
Premium Member
Dec 4, 2007
487
340
63
Nice work! Agree that the dealer should have been able to figure it out. Why did you go with the SPI gasket kit? Was the Doo gasket stupidly expensive?
 
Feb 17, 2020
6
10
3
31
Minnesota
Nice work! Agree that the dealer should have been able to figure it out. Why did you go with the SPI gasket kit? Was the Doo gasket stupidly expensive?
Yeah, pretty pathetic I was charged $750 for nothing... I'm not one to bitch and whine so I didn't bother trying to get any money back. Powerlodge in Ramsey, MN is my dealership btw

As far as the gaskets go - I have a habit of checking Ebay first for everything. Didn't even look for a factory gasket set. I put 150 hard miles on it yesterday and today. No leaks or problems, she rips. Too much though, wanted to keep flipping over backwards on me in the hills. I have to dial in my suspension next time I take er back out.
 

c_sharp

New member
Lifetime Membership
Jun 2, 2016
13
2
3
Yep, it seems to have the normal power at the bottom end.but the top sure doesnt seem right. Just checked compression last night 160psi on both cylinders.

Update on my issues:
It was the rave valve motor, the actuator had stripped out inside and was stuck closed.
When you install a new one you will need the dealer to reset the rave valves with the computer*
 
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