JackShaft & Bearing Problems

rockinmranch · Apr 18, 2013

Pictures of jack shaft

These pictures should help to remove doubt to what is going on with the belt drive. This out out af a 2013 pro rmk use as a rental sled. It had 2500 miles when this shaft was replaced on the right, new shaft for comparison on the left. I ran the new shaft in it another 1000+ miles. The new shaft now looks like the old shaft. No doubt the shaft is turning inside the bearing, which is also causing extremely high top sprocket temps. Maybe regluing the bracket or bolting it is the answer. I have got to believe Polaris will be coming out with a fix soon. I bet there are many more sleds out there with this problem than are not recognized at this time. The problem surfaces with mileage and the sled will still run with the bearing in the shape as pictured, it just starts to clunk on hard excellerations.

Teth-Air · Apr 26, 2013

rockinmranch said:
These pictures should help to remove doubt to what is going on with the belt drive. This out out af a 2013 pro rmk use as a rental sled. It had 2500 miles when this shaft was replaced on the right, new shaft for comparison on the left. I ran the new shaft in it another 1000+ miles. The new shaft now looks like the old shaft. No doubt the shaft is turning inside the bearing, which is also causing extremely high top sprocket temps. Maybe regluing the bracket or bolting it is the answer. I have got to believe Polaris will be coming out with a fix soon. I bet there are many more sleds out there with this problem than are not recognized at this time. The problem surfaces with mileage and the sled will still run with the bearing in the shape as pictured, it just starts to clunk on hard excellerations.

We were aware of the QD failures early on and was one of the first to increase the torque on the upper pulley bolt. We still lost a shaft like this but the dealer said the replacement bearing from Polaris was different from original. Hope that is the end of this problem.

clamlake600 · Apr 27, 2013

rockinmranch said:
These pictures should help to remove doubt to what is going on with the belt drive. This out out af a 2013 pro rmk use as a rental sled. It had 2500 miles when this shaft was replaced on the right, new shaft for comparison on the left. I ran the new shaft in it another 1000+ miles. The new shaft now looks like the old shaft. No doubt the shaft is turning inside the bearing, which is also causing extremely high top sprocket temps. Maybe regluing the bracket or bolting it is the answer. I have got to believe Polaris will be coming out with a fix soon. I bet there are many more sleds out there with this problem than are not recognized at this time. The problem surfaces with mileage and the sled will still run with the bearing in the shape as pictured, it just starts to clunk on hard excellerations.

I think you found the root cause to most of the problems we are having with pulleys loosening up. Good detective work!!

Bushwacker1 · Apr 27, 2013

The top quick drive bearing is only a slip fit to the jackshaft and needs to be sandwiched tight to keep it from spinning on the shaft. Hence new bolts and higher torque on the fastener. The bearing on the driven side is pressed on to a predetermined fixed position requiring the width of the tunnel to be held to a very close tolorance to avoid side loading the bearings on the jackshaft. I dont see anything that makes up for manufacturing variations in tunel width to insure that the top bearing inside race, brake rotor, and drive pulley can be locked to the jackshaft and maintain precise placement of the driven side bearing. Any side loading of these bearings will cause heat and shorten bearing life. I would also think that this heat transfered into the top drive pulley may cause it to expand and contract enough that after many cycles the assembly that was once locked together is no longer, allowing the shaft to rotate inside the bearing race. If a locking type bearing (ecentric collar, setscrew collar, or skews lock type collar ) was used on the driven side it could be left loose until the pulley, brake, bearing assembly is locked together, then the lock collar locked down. This would result in bearing placement to the actual width of the tunnel with no side loading. Just my 2 cents worth.

rockinmranch · Apr 28, 2013

Would a jackshaft milled slightly larger where the bearing rides fix the problem? Just large enough that the bearing had to be tapped lightly onto the shaft with a hammer. Somebody said above that the tunnel/bulkhead has to stay very rigid to keep the adequate amount of pressure to keep the bearing and shaft spinning together. The current jackshaft bracket behind the brake rotor is very flexible, not rigid. I think this may be a difficult problem to remedy.

LoudHandle · Apr 28, 2013

rockinmranch said:
Would a jackshaft milled slightly larger where the bearing rides fix the problem? Just large enough that the bearing had to be tapped lightly onto the shaft with a hammer. Somebody said above that the tunnel/bulkhead has to stay very rigid to keep the adequate amount of pressure to keep the bearing and shaft spinning together. The current jackshaft bracket behind the brake rotor is very flexible, not rigid. I think this may be a difficult problem to remedy.

A press fit bearing will not solve the root of the problem, which is the distance from the clutch side bearing to QD side bearing is too far apart due to the upper half of the bearing plate not being held tightly to the tunnel. Thus the glue is thicker here and no amount of torque will pull it into alignment.

The only sure way to fix the ones that are wrong (Gapped away from the tunnel) is to remove and re-glue the bearing plate properly. I have done one so far and elected to add two bolts as "Geo" described in his post where the stock tunnel has two rivets. This ensures that the top of the bearing plate rests tightly against the tunnel as the glue cures. With this done the bearings are spaced correctly and the shaft works like designed. Allowing the upper bearing to be pinched between the jack shaft shoulder and the brake disk / sprocket stack.

So take a good look at the top of your bearing plate, if it is tight against the tunnel you likely have a good one. If not you should fix it, or buy stock in Polaris Parts, because your going to need to be changing parts on a frequent basis.

The other issue I've noticed is the clutch side drive shaft bearing, while it should be a press fit, it is not on most shafts. Resulting in stub failure in as little as 500 miles. I recommend getting a new shaft thru warranty and Loctite'ing (bearing retaining compound, there are a couple formulations depending on fitment) the new bearing in place to extend the service life a noticeable amount.

rockinmranch · Apr 29, 2013

Do you believe that what you have prescribed as the fix is going to become a service bulletin through Polaris or become the responsibility of the owner? Will polaris continue to replace Jackshafts until the sled is out of warranty?

LoudHandle · Apr 29, 2013

rockinmranch said:
Do you believe that what you have prescribed as the fix is going to become a service bulletin through Polaris or become the responsibility of the owner? Will polaris continue to replace Jackshafts until the sled is out of warranty?

I have zero insight into what the Polaris mentality is on the subject. Also living 300 miles from the nearest dealer, I put very little value on warranty and the dealer's service department. I personally would not take my sled to them for any work I can do myself, but that is just me. Living where I do, I just fix it for the piece of mind that I will get back home and not have to walk out ( because we all know you can ride further in five minutes on a sled than you can walk in a day, depending on snow conditions). If you want to deal with taking it back to the dealer every 1000 miles, so be it. With the cost and inconvience for me to do that, it is far easier to spend 2-3 hours and fix it right and to never worry about it again.

Anyway that's my two cents for what it is worth.

Hawkster · Apr 29, 2013

rockinmranch said:
Do you believe that what you have prescribed as the fix is going to become a service bulletin through Polaris or become the responsibility of the owner? Will polaris continue to replace Jackshafts until the sled is out of warranty?

Yes , I do believe that , they've proved it with the 800 . I am not being rude here but it does not cost them anything to have the failures as long as the sales and profits are up . That's what bean counters are for , why can't the majority of the people see the screwing the consumer is getting ? Or has society gotten so lazy that it's someone elses responsibility and the few that take it upon themselves to fix the problem are becoming a extinct breed ?

winter brew · Apr 29, 2013

Is there a reason they can't just put a bearing with setscrews on there like they ran for freakin' decades on the older Poo's?

diamonddave · Apr 29, 2013

I haven't torn into a '13 yet but would it be possible to machine a groove into the shaft and use a snap ring to help hold the bearing in place?

4Z · Apr 29, 2013

diamonddave said:
I haven't torn into a '13 yet but would it be possible to machine a groove into the shaft and use a snap ring to help hold the bearing in place?

Stress riser

LoudHandle · Apr 29, 2013

winter brew said:
Is there a reason they can't just put a bearing with setscrews on there like they ran for freakin' decades on the older Poo's?

You can do that also, on the clutch end (instead of the press fit bearing) to allow for the mis-fitment of the bearing plate, but then your upper bearing on the QD side is still slightly mis-aligned. Or you could put a shim in between the shoulder on the jackshaft and the bearing to account for the distance the bearing plate is away from the tunnel, but again the bearing is slightly mis-aligned. Why not just fix it correctly once and be done with it?

The one I did only took 2-3 hours, pull the rear suspension, remove battery and mount, QD belt and sprockets, drive shaft and track, brake caliper and disk, bearing plate. drill out two rivets and drill the two holes in the upper bearing plate. Re-glue plate, re-torque fasteners, and re-assemble. Easy to do and never have to think about if it is right or not again. Why wouldn't you?

Granted we shouldn't have to go this far, but you can't tell me you don't have one night after work to kill in the garage, and avoid all the headaches it might have caused if you hadn't.

Again this is solely my opinion for what it is worth, I believe this to be the root of the jackshaft bearing failures and my suggested proper fix. Quick easy and painless!

LoudHandle · Apr 29, 2013

diamonddave said:
I haven't torn into a '13 yet but would it be possible to machine a groove into the shaft and use a snap ring to help hold the bearing in place?

4z nailed it.

If you were to cut a snap ring groove into the shaft it creates a stress riser. In essence it makes a weak point for failure to start, especially in this design where you already have a large overhung load. With the snap ring groove at the base of the last support (bearing), the shaft will flex at the snap ring groove and eventually break off there. Additionally the snap ring will not ensure that the inner bearing race will not turn. The race needs to be held between the shoulder and the brake disk / sprocket stack with torque from the fastener. If you want additional insurance use a retaining compound, but that will slow any future maintenance, as the compound will need to be heated to loosen and remove the shaft from the bearing.

diamonddave · May 26, 2013

Yeah I guess you are right. When the NV4500 gear boxes used to blow off the 5th gear retaining nut the fix was to either use a special nut with set screws or machine a groove in the shaft and use a snap ring. The snap ring fix was the real fix and has worked for years.

There are tens of thousands of applications with much higher loads than this that use a snap ring to retain a bearing. Pull apart any manual Trans or 6 speed behind today's diesels.

rockinmranch · Nov 7, 2013

Has Polaris fixed this yet?

I just found my post from this spring. Has anyone found a solution to this problem or has Polaris offered a fix. After this spring's post, another Jackshaft was put in my sled. This is the third shaft. Sled has somewhere in the 4000 mile range. I expect to replace another shaft soon 500-1000 miles. No solution from Polaris or my dealer.

rockinmranch said:
These pictures should help to remove doubt to what is going on with the belt drive. This out out af a 2013 pro rmk use as a rental sled. It had 2500 miles when this shaft was replaced on the right, new shaft for comparison on the left. I ran the new shaft in it another 1000+ miles. The new shaft now looks like the old shaft. No doubt the shaft is turning inside the bearing, which is also causing extremely high top sprocket temps. Maybe regluing the bracket or bolting it is the answer. I have got to believe Polaris will be coming out with a fix soon. I bet there are many more sleds out there with this problem than are not recognized at this time. The problem surfaces with mileage and the sled will still run with the bearing in the shape as pictured, it just starts to clunk on hard excellerations.

LoudHandle · Nov 7, 2013

I'm assuming you have the minimum wage mechanic at the dealer doing your work. Is it any wonder you are having issues. I would check your bearing plate to tunnel fit. I would bet money it is gapped at the top. When it is; no mater how much you torque the sprocket bolt it will not stretch the jack shaft enough to pinch the bearing between the shoulder on the jack shaft and the brake disk upper sprocket stack.

The only real way to fix it is to re-glue the bearing plate properly. I also add two bolts at the top where there are two tunnel rivets. so it has no choice but be against the tunnel when the glue sets. Check everything as you go back together.

I've posted this fix in detail in other posts if you want more info. Search my posts in the drive train section. Or if there is interest I could search and re-post it in it's own thread.

Update: I see that I already posted that / this info last spring, sorry for the re-post but if you follow my suggestions it will fix your problems.

rockinmranch · Nov 10, 2013

What type of glue do.you reccomend for the fix?

LoudHandle · Nov 10, 2013

rockinmranch said:
What type of glue do.you reccomend for the fix?

Either the OEM Lords 406 or the more readily available Fusor 111, the Fusor you can get at most body shops and NAPA stores. As I am in Alaska The Fusor was easier and far cheaper to get than paying the hazardous product UPS fee.

pura vida · Nov 17, 2013

Tore into my sled yesterday to see if any of the above issues were possibly contributing to me going through my first 3 QD belts in less than 250 miles (I have over 200 miles on belt #4 with no change in riding style??). I didn't find any of the above issues, there doesn't seem to be any gap between the QD plate and the bulkhead, the bearing was turning with the shaft when I spun it by hand, and the jackshaft did not show any signs of wear after I removed it. There did seem to be some slight coloring on the shaft but I'm not entirely surprised with this considering the amount of heat my top pulley seems to always carry.

As others have noted the QD plate above the bulkhead did not seem very rigid with everything removed. Which leads me to be concerned if I can cause flex with just my fingers, is the entire system flexing under load causing slight belt misalignment leading to QD belt failures over time? Or is this really not a concern once everything is torqued to spec as this should help to overall system rigidity?

So... any thoughts or suggestions as to why my top pulley seems to always carry a significant amount of heat (too hot to touch for more than an instant) and what might be causing my QD belt failures? Right now I still feel the two are related???

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JackShaft & Bearing Problems

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