Machine shop may have found the belt problems

sledheadjake · Mar 21, 2017

Christopher not sure on how you ride, but have you stopped after playing in the trees for a good 1/2 hr and felt your clutches? Every 850 I have rode with the clutches are scorching hot. You might be partially right that it might have something to do with the rider(but the real issue is the snowmobile). I tend to ride for longer extended times between my breaks compared to the other 850s I ride with. I was hoping that this post by BRP was actually going g to give us hope that they found an issue that could be remedied, yet in all of that I read was that somehow this uneven clutch sheave is supposed to help keep the clutch temps down, really:face-icon-small-dis

mountainhorse · Mar 21, 2017

Balancing act.

Implementation of this new tech may take some time to perfect.... It certainly does add a new dimension and complexity to the puzzle.

Will this new tech, as BRP has show above in Christophers posts bear fruit... or be something that just doesn't work in the consumer sector on production built units??

That 80mm stroke has also been an issue for Polaris in the past... so much so that a fully tooled production sled, the 2007 Dragon 900 was scrapped months before production.... because of vibration. Polaris had HUGE money into the development of that engine.. and, in the end, had to let it go.

I think that Rotax/BRP is in this plant for the long term... but evolution can take time to perfect.

Plain and simple... a CVT with rubber belt that builds this kind of heat,IMO, is incompatible with long term durability... and rears it's head faster in sleds that are driven really hard or abused.

All of that energy that is heating the clutch system... is energy that does not make it to the track.... and is hard on the rotating assembly of the engine.

The lighter rotating assembly efforts that BRP/Rotax have made with this long stroke engine... are contributors to vibration

Causing BRP/Rotax to develop a Dynamic Vibration Reduction system in the clutches, a complex system, to hopefully minimize vibes. Light rotating mass with that long stroke makes dealing with this, without a counterbalance shaft (like on the 1000cc doo's) very tricky to pull off. I'd imagine that harmonics at diff RPM would play a role here as well.

With some true "belt eater" G4's out there...and some that have good belt life... It leads me to believe that this complex system may be difficult to execute with repeatable good results in a production environment as mfg. tolerances would have to be brought to +/- zero.... difficult to do.

Plain and simple, It is hard to make a long stroke, twin cyl 2-stroke engine smooth while keeping the rotating assembly light so that the engine is responsive to transient throttle use. :juggle: UGG.

Though the 850 eTec is only 50cc displacement larger than the previous models... there are many physical challenges to deal with in pulling it off well with that long stroke.

I'd personally like to see the 800 Etec offered as an option on the G4 chassis... IMO, this is a simpler engine design that makes great power.

.

Daag44 · Mar 21, 2017

BRP Engineering

Mountain_Man said:
Christopher, having been involved in international level manufacturing for 26 years I will offer my opinion. While it might seem that all products in a line are identical, there are occasional designs that are finicky about tolerances and operating parameters and in my opinion that can be considered a form of design flaw.

I read the information you posted from Ski Doo and I see the principles of what they have done. There can be no argument there are a lot of smart and capable people employed by them. While the actual problems people are having might be from other reasons, I suspect this new idea is somehow at the root of the issue. New ideas sometimes take time to perfect, or issues pop up that were not found in testing.

The sleds might vary more than you realize, it’s actually much harder ($$$$) to produce parts that are truly identical than you think. Sometime it doesn’t matter, sometimes it matters only a little, sometimes it matters a lot. In this case the technology might not be ready for prime time. Maybe I’m wrong and there are other issues instead. In any case, developing new technology and perfecting it takes time, it were easy to nail it every time we would have been riding much better sleds like these decades ago.

In conclusion I have little problem believing that sometimes issues are more design and/or manufacturing issues than operator issues, and of course some designs just won’t hold up to some types of use or abuse. It can work either way, depending of course.

On the bold you may have nailed it. In the video from RGM/SledPemberton (click here) we can see the primary has a wide and narrow belt prints at 180 deg apart. Also notice how high the belt was riding on the clutch. For all we know this could be a misalignment of the X for the type of load at high speed. The belt print on the other part of the clutch would also reveal a story of how the sled is being run and what may need changing for the owner's style of riding.

Christopher and Mountainhorse made very good points regarding where to look which I believe will be a big help.

Thanks for your comments. Very good points!

Mentzel · Mar 22, 2017

So much whining! Simple fix if clutch runout is off. Pop off the clutch get it machined and dynamically balanced. $200 at the most.. big deal

Sent from my iPhone using Tapatalk

SidewaysInto3rd · Mar 22, 2017

Mentzel said:
So much whining! Simple fix if clutch runout is off. Pop off the clutch get it machined and dynamically balanced. $200 at the most.. big deal

Sent from my iPhone using Tapatalk

a little late to the party, are ya ?

i'llDooit · Mar 22, 2017

SidewaysInto3rd said:
a little late to the party, are ya ?

Like a turd that didn't want to come out

Daag44 · Mar 22, 2017

0.6mm Clutch Offset can change Y-X Offset by 1.2mm

Here is a link to a good thread started by bcpowder84 who took his clutch alignment and posted pictures. I find it interesting how the manufactured offset can change the Y-X offset by 1.2 mm.

http://www.snowandmud.com/ski-doo-r...tec-offset-exploding-belts-2.html#post2385916

Reg2view · Mar 22, 2017

Back on point... the evolution from design to prototype to production can get ugly when the prototypes for new design concepts are handmade, and the actual production parts are later made by the lowest cost certified vendor. Vendors run multiple molds and tools, and tolerance differences between them can be acceptable in design - but not the field.

It's interesting that doo is just announcing this new design now - perhaps they had to perfect the patent. And/or, they were moving so fast, they became blind to the acceptable production tolerances. They didn't build and test the impact of slight deviations in handmade layups of the prototype design adequately.

Could be some finger pointing going on between design and manufacturing engineering right now. They'll figure it out, eventually...

mountainhorse · Mar 22, 2017

What would be interesting to find out... is... does the ACTUAL high spot coincide precisely with the factory mark on the sheave... and is the amount of "offset" truly within the factory designed parameters (is is more-than or less-than)... casting process...even the precision ones used in clutch mfg... can be less than 'exact' and/or susceptible to mfg variation more than a machined process... and yes, I realize the sheave is machined...but the mark is cast.

.

mountainhorse · Mar 22, 2017

With the new clutches being machined on the backside for cooling... and a whole new process/molds/tooling for the production of the 850-pDrive... there is a high probability that the 2018 850-pDrive has tighter tolerances and production monitoring.

sledheadjake · Mar 22, 2017

So last night I checked both my fixed and movable sheaves on my primary. On the stationary sheave the high spot is where the factory mark is at.(I cant get my video to upload)
The moveable sheave had .008" out. I talked to my dealer today and Skidoo is sending them out a recalibration for the clutching. Im going out with them for a ride this weekend to compare my sled to their new setup. Ill post up more when I get more info.

mountainhorse · Mar 22, 2017

Upload it onto youtube rather than facebook.

What was your run-out measurement exactly?

Having a sled or two in you group WITHOUT the recalibration for comparison to the sled(s) WITH the re-cal ... AND a IR temp 'pistol' and crew ready to check temps is what would be needed to have an accurate picture of what is going on.

Have a "pit crew" ready in a spot at the bottom of a hard pull course... and another course of WOT-off-WOT-off-WOT sidehilling ... at the ready to pull the side panel and cover to take temp readings would be most handy to see if a "re calibration" makes much of a diff... and what exactly is that difference.

.

sledheadjake · Mar 22, 2017

The Fixed sheave had .027" of variation, the movable had .008".

That is the plan for this weekend, the dealer is going to set up their demo with the new clutching that they receive, not sure how many they are going to bring but with mine and theirs we will definetly get a good comparison with me and the dealer being able to both ride each sled and compare the differences if any.

mountainhorse · Mar 22, 2017

Go to NAPA/Orielly/CarQuest and buy a cheap IR thermometer ... Just sayin

(If you don't already have one)

christopher · Mar 22, 2017

sledheadjake said:
Christopher not sure on how you ride, but have you stopped after playing in the trees for a good 1/2 hr and felt your clutches? Every 850 I have rode with the clutches are scorching hot. You might be partially right that it might have something to do with the rider(but the real issue is the snowmobile). I tend to ride for longer extended times between my breaks compared to the other 850s I ride with. I was hoping that this post by BRP was actually going g to give us hope that they found an issue that could be remedied, yet in all of that I read was that somehow this uneven clutch sheave is supposed to help keep the clutch temps down, really:face-icon-small-dis

I think it is time for me to install a CLUTCH TEMPERATURE GAUGE and get some REAL WORLD INFO to log and share...

Daltech · Mar 22, 2017

The question now will be, who will be the first to offer a "TRA 7" conversion for the 850?
I bet it wont take long before we see the first beeing remachined if possible.

christopher · Mar 22, 2017

Just a note of clarification on this post I made on behalf of BRP about the "Clutch Wobble".

This BRP Bulletin was NOT intending to address the BELT ISSUE. This was made solely to address the video suggesting people have their clutches machined to remove the wobble.

FYI to my fellow 850 Doo Riders..

BRP is still very much investigating the "Blown Belt" issue and has NOT made a final determination on either its cause or how it can be remedied. We will have a wait a bit longer for that statement to come forth. And it may well be after this season has come to a close..

salmonbum · Mar 22, 2017

christopher said:
BRP is still very much investigating the "Blown Belt" issue and has NOT made a final determination on either its cause or how it can be remedied. We will have a wait a bit longer for that statement to come forth. And it may well be after this season has come to a close..

I think it would be in their best interest to offer some type of solution plan that will be implemented into the 2018's before April 15th. My group of riding buddies that are wanting to snowcheck have put that thought on HOLD until I hear more positive changes so I feel warm and fuzzy that all is going to be OK. One guy already jumped shipped for a Poo. But hey, its only a few of us so if we don't get doo's this season, no big deal. However, the "other side" brand may be the brand for us to continue to buy for yrs to come.

sledheadjake · Mar 22, 2017

Yes, I have a heat gun I am going to bring with to be able to get more accurate readings. After each session we do I am going to record each sled temps (primary, secondary)also have each sled start and stop with the same amount of time ridden. I am going to get as much detailed info as possible and as close as I can comparisions to rule out rider influence

gopherchoker · Mar 22, 2017

Now the question is what is doo going to do to fix it. If I snowcheck a '18 is it going to arrive late because they are going to have to Micky mouse a updated design together, test ,tweak, retool, and manufacture in a 6 month window. From the sounds of it Doo riders are blowing belts too, so there IS going to be upcoming changes. It's just going to be a good question of is the cure worse than the poison and will the cure arrive before everyone is to sick to to care. But that's just my .02

Machine shop may have found the belt problems

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