Redesigned 850 Crankshaft

[indydan]

In development for 3 years, Indy Specialty has designed and is now manufacturing a full Billet 850 Crankshaft.

This crankshaft was designed with one Major thought in mind...... ( dependable ) High Mileage

The most significant change is in the PTO - end ..... which can be used to replace the stock OEM PTO-end.

The 850 Patriot motor is one of the best designed High Horse Power to weight ratio motors I have ever seen.

However the 850 has the worst designed PTO-end, and worst PTO Bearing design for a 2 stroke motor with a press together crankshaft I have ever seen.

The stock PTO - end will haunt the 850 as it gets older, and when the drive clutch starts to wear badly.... when the drive clutch gets worn the PTO-end in many cases will slide hammer off the Rod Pin and it will run into the crankcase and the roller bearing at close to the same time.

And the motor will lock up..... it’s been happening already to the 900 Big Bores and some stockers as well.

The 850 Patriot has been one of the only motors we build with no crankshaft warranty...... And the reason we do not warranty it is because I do not trust the OEM PTO-end to stay on the Rod pin long Term.

That is the reason we built a full Billet Crankshaft is so we could offer a warranty......Our Crankshaft the OEM Roller bearing is no longer used.... It’s gone ( We do not use it anymore )

Dan

 

[el__gato]

So now that we pulled that scab off what would a person be looking at for cost if all the needed changes were added to a used 850 that runs ok, little hard to start sometimes?

 

[Reg2view]

The sheer number of 850 motors on the snow and increased motor hours, turbo and non-turbo, will increase dramatically in the next couple of years. Some pics of the failure will help everyone understand what they may be in for. If happening to stock motors still in warranty, will be interesting to see how Poo adapts, if at all.

 

[madmax]

So are you saying the problem is the main pto bearing not a press fit onto the crankshaft? Never seen a crank built that way where the bearing just slides on and off.

 

[kiliki]

So are you saying the problem is the main pto bearing not a press fit onto the crankshaft? Never seen a crank built that way where the bearing just slides on and off.

Arctic cat did that on the M7 and we all know how that turned out.

 

[indydan]

Good Morning, Great questions everyone.

Arctic Cat did take a big swing earlier at a roller PTO bearing.... ( Rod pin was incorporated into and was part of the PTO-end. ). PTO-end would not stay straight

Press fit is very important..... however the press fit needed to hold a PTO-end on the Rod pin if it doesn’t have a design function to hold the ( pressed together ) crank assembly together such as interference fit inner and outer races with bearings designed for side loading then there can be be big trouble.

I believe one Polaris Engineer in particular is to blame for the 850 PTO roller bearing design..... Let’s call him Larry for now.

i believe he took a Ski DOO 850 apart and saw a roller PTO bearing and thought is was ? cool.

So he went to work and took the easy road and copied it..... He didn’t just copy it he made it much bigger thinking he was safe.

Problem with copying instead of understanding he forgot to look at the big picture.

what’s different between the Ski-DOO 850 Crank and the Polaris 850 crankshaft that makes PTO-end design and PTO bearing design so critical?

The SKI DOO Crankshaft is one solid piece ( with split cap rods. )

The Polaris 850 Crankshaft is 7 separate components ( Rod Pins counted ) all pressed together ( With one piece solid Rods )

As for cost to convert a Stock OEM Polaris 850 Crankshaft to the similar design we have used in the 800 small block since 2008 is under $900 if you send in just the crankshaft.

a full Billet 850 Crankshaft assembly will be around $2200

At this Time we are focused on building mainly PTO-ends since most OEM crank main parts are in good condition.

Dan

 

[TRS]

Great job, Dan.
This is the fix we have all been waiting for.

 

[Sheetmetalfab]

Dan,
I’m guessing the patriot boost models will be more susceptible to pto end crank failure? (I have one coming)


Any speculation on the stop sale that was issued for early shipped 850’s this fall?
Maybe an update to the design?

Thanks for putting information and solutions out there. @indydan

 

[indydan]

Thanks Tony ??

As for the boost model S.M.Fab it’s actually the opposite Turbo sleds are much easier on PTO-ends then N/A sleds.

The turbo softens button end tongue just enough to make it much easier on cranks.

The stop sale had nothing to do with the Roller PTO bearing or the the center main bearings.

The issue is Rod bearing roller separator

Dan

 

[indydan]

So are you saying the problem is the main pto bearing not a press fit onto the crankshaft? Never seen a crank built that way where the bearing just slides on and off.

Yes Madmax ( The stock OEM PTO bearings floats ) not a press fit.

poor design

 

[Teth-Air]

So I know of these motors with 3000 miles on them. (2019 even) At what mileage are they expected to fail?

 

[el__gato]

depends on a lot of factors, how close the tolerances are when it comes out of the factory, how the owner rides it..... the stop sale i heard it was liek close to 100% failure rate on those bearings. Get Dan's parts to rebuild yours and not have to worry about how long it will last out in the deep snow.

 

[indydan]

Yes as mentioned by ( el_gato ) It has to do with a lot of factors....... With Rod pin more towards the ( + ) side of the tolerance and the PTO-end more towards the ( - ) side most likely never come apart.

Many many will be fine..... keep in mind most mountain sleds ( from the Midwest are very low mileage ) a few hundred miles a year max.

The People that live near the mountains that put a few thousand miles per year will see the failures first.

it depends a lot on quality control..... And with a slip fit roller bearing tolerance is creepy important

With a PTO designed with conventional Press fit bearings quality control parameters are much less critical

The roller bearings was a really poor choice for a press together crankshaft

Dan

 

[TRS]

So I know of these motors with 3000 miles on them. (2019 even) At what mileage are they expected to fail?

Yes there are engines with lots of miles. What would be interesting is a digital wrench check on where those engines have spent their life. DW has TPS and RPM history stored in the ECU.
Personally, the third engine just went in my ‘19. I lost one in ‘19, ‘20, and ‘21. Polaris takes weeks to authorize warranty. You must have multiple sleds if you want an uninterrupted season.

 

[volcano buster]

Yes there are engines with lots of miles. What would be interesting is a digital wrench check on where those engines have spent their life. DW has TPS and RPM history stored in the ECU.
Personally, the third engine just went in my ‘19. I lost one in ‘19, ‘20, and ‘21. Polaris takes weeks to authorize warranty. You must have multiple sleds if you want an uninterrupted season.

Tony,

Is there a common denominator in the engine failures on your '19?

 

[Teth-Air]

Tony,

Is there a common denominator in the engine failures on your '19?

Tony is the common denominator. He must hold er pinned when he rides Actually my 19 has been flawless and has 3600 kms on it. I may put on 2 more years of extended warranty on it this year before the factory warranty ends. I did this on my 2015 and it worked out very well for me. In 2018 when I added it to the 15 it was only $1400 (CDN) for 2 years for bumper to bumper coverage. The motor it paid for would have cost much more than that. Yes it took a couple weeks to get it fixed but as a second sled it was acceptable.

 

[shattuck]

I love Indy dans stuff have one of his long rod motors and clutching on two sleds but in my experience the axys chassis is pretty well done at 1,000 miles of hard mountain riding. The trail guys might get better bang for their buck with the fixed crank shaft.

 

[TRS]

Tony,

Is there a common denominator in the engine failures on your '19?

Yes. The locating pin migrates in, the ring spins on the piston and catches the exhaust port.
I have had this issue on 800’s and 850’s.
All from 300-800 miles per engine.
The last 850 engine made it just under 1100 miles, but failed a leak down test around 750 miles. We kept dropping fly weights until it went down. Polaris moved from a historic 5% leak rebuild to 10%. I think the bean counters made this decision to get past warranty claims before they pass it on to the insurance company.
You can tell when a ring starts it’s migration, you will get a audible pop and the engine shuts down. It will start up, but the inevitable has started.

 

[Teth-Air]

Yes. The locating pin migrates in, the ring spins on the piston and catches the exhaust port.
I have had this issue on 800’s and 850’s.
All from 300-800 miles per engine.
The last 850 engine made it just under 1100 miles, but failed a leak down test around 750 miles. We kept dropping fly weights until it went down. Polaris moved from a historic 5% leak rebuild to 10%. I think the bean counters made this decision to get past warranty claims before they pass it on to the insurance company.
You can tell when a ring starts it’s migration, you will get a audible pop and the engine shuts down. It will start up, but the inevitable has started.

So what shuts the motor down?

 

[TRS]

I think the ECU doesn’t get a proper signal from the flywheel when rotation is interrupted for that micro second.