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Discussion Starter #1
This wednesday, I decided to re-install my Jaws trail pipes and use them 'til the end of the season to see if I can run faster than my buddies' clutched '02 XC 800 VES, as he has been very hard to beat. My first test ride with the pipes on thursday, I didn't make it 4 miles from home, engine seized on a short straightaway. I was able to drive sled home after a 10 min. cooldown, but upon teardown, I found a defective pto crank bearing and the pto crank lobe that had split. First time I see or hear of this. Check it out ! So much for Bomb. synthetic oil and steel cage crank bearings. (about 2800 miles on these bearings, and mostly drag racing.)
 

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Discussion Starter #5
Krusty, I've used the Jaws trail pipes for 2 years and had no problems with crank. They are tuned for 8900-9100 rpm, which no doubt will wear bearings, pistons and rings faster than at stock 8100-8300 rpm. I've been using my stock pipes this winter to reduce rpm's and trail ride more, but my disease (drag racing) keeps kicking in and I'm not as quick as I want to be. Since I had my Jaws pipes sitting there (all lonely), I decided to pull all the stops and get the most power and start beating my buddies again. I'm pretty sure that the crank bearing was ready to go soon, but the extra h.p., torque and rpm's of the Jaws, made it go sooner. #### happens! We want to play, we gotta pay!
See Ya!
 

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Discussion Starter #6
dino, the blue that you see, is actually some leftover Loctite retaining compound 609 (that is a dark green) that I use on all my crank bearing outer races when I assemble the crankcase. This compound helps to keep bearings in place along with the pin in order to stop them from spinning in the case, should they start to wear.
See Ya!
 

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Limskii:  I'm not a big fan of using the cylindrical parts bonding your talking about, it tends to form a barrier between the bearing outer race and the case. The coolant does many things including drawing heat from the crank via the crankcase,in the past Rotax used '0' rings to stop rotation and for the past few years pins which seem to work for the most part very well. I don't mean to be critical of your method,I just wanted to give you something to think about. Dino.
 

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Discussion Starter #8
dino, does that mean that by using the retaining compound, I may actually be holding more heat in the crank bearings, as opposed to letting the heat dissipate through the crankcase and into the coolant? I have never thought of that, but it does make sense now that you mention it. The reason I started using the compound is because I had a bearing break the pin and spin in the case, which led to having the case linebored 2 years ago. I was hoping by using the compound, it would reduce the chance of a bearing spinning in the case in the future.
Thanks for the info.!
 

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Just my 2 cents.

Are you sure that the piston didn't seize first? That type of bearing failure looks like your crank is bent. When this happens, the balls no longer follow the grove in the inner race, but unstead try to climb out. I think the cage got pushed out because of this.

Looking at your crank, a split like that has to come from trying to peel the shaft from the lobe. This is common for a bent crank.

Just a thought - check your runout, its probably terrible.

A few points to check to determine if the root cause of failure was from the crank bent - or if the bearing failed first.

- Check the balls. do they look like there peeling? Do they all have this "peeling"?
- Do the balls look burnt?
- These 2 items would show a gradual bearing failure gone critical

On the other hand,
- Check if the balls look clean
- Are a few ball clean with pitted marks
-  Do some balls look good?

These thing would indicate that you had a forced failure of the bearing. They were running good and then started running out of thier groove in a helix patern.

Don't worry about using locktite. I instruct all my gearbox assemblers to do the same. - Helps elliminate creep and corrosion fretting on the outer race.
I don't think it will affect the heat disipation. After assembly there is barely a film a locktite.

Can you post a close up of the bearing?

Hope some of this is useful
 

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Discussion Starter #10
madsledhead, I originally thought that the seizure was my pto piston, as I had a little bit of aluminum on that plug. However, upon disassembly, there was no sign of my piston seizing, other than a faint sanblasted look to the top of piston and cyl. head dome (which I thought was detonation). When I checked crankshaft runout at pto end, it showed .040" out, which it should be a max. of 0.003". I then knew the crank was damaged and also then noticed the cracked crank lobe. I believe the crank bearings were worn as they have run at 9000 rpm for about 2800 miles. I'm just happy that the crankcase wasn't damaged. As for the info. that I get and read, I always appreciate it and learn from it. We can never learn enough about our interests.
Thanks !
 

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Limskii, nice picture.

You can tell alot from this pic. First off - you were right. That bearing is beyond allowable tolerences. When you lose the mirror look of the balls it is because they are getting rough. They get rough because they are loosing surface material. If you were to compare that ball in the picture to a new one using a powerfull microscope it would look like huge crators are forming. Another indication is the dark color of the groove in the inner race. This is because of the poor surface quality of the balls. If the balls were perfect, that surface would be mirror like.
Looking at this picture, it is defenetly not a failure due to the cage or cage material. The cage is damaged because the crank let go under load - forcing the balls the run out of their groove.
The bearings were installed properly because there is no indication of a shoulder forming on the inner race. If the bearing was cocked you would feel a ridge at the edge of the groove.

My guess is some type of cyclic stress on the crank, due to excessive axial/radial play in the bearing.

Just my 2 cents, hope some of this is usefull

Thanks for the picture, and I'm glad you don't need to line bore.

Good luck next season
 

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Discussion Starter #12
madsledhead, that is quite informative, you must work with/or around equipment that uses bearings and have experience in reading different types of failures and their causes. That is definitely an asset when troubleshooting mechanical failures, as there is always a cause for a failure, and to find the cause will allow you to properly fix a failure and to possibly eliminate another. Thanks for the info., and hopefully I can re-install a rebuilt crank and break it in before the end of this season. As for the closeup of the bearing, I tried the macro setting (for closeups) on my digital camera, and it worked well.
See Ya !
 

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madsledhead, not stepping on your toes. i am not a bearing expert, but have taken a few skf bearing training coarses for a maintenance job i work at.
Its hard to tell from the last pic, but if you look at the lowest ball in the picture, it looks like a blue ring right beside it to the left.
is that not caused from over heating?
could that be from the balls flaking on the surface do extra heat caused fron the loctite as dino mentioned??
The other thing causing heat is the bearing being torqued down to tight. this causes stress on the balls beause they are being compressed between two races and the balls start to flake then the race heats up and wears out causing that blue ring.
just my 2 cents
 

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These are good facts that you mention ski-dood.I aggree the bearing did overheat I don't think anybody disagrees. Overheating causes bearing wear and failure. The wear on the balls and the inner race is definetly  from heat. But I don't think it comes from the lack of coolent contact or coolent efficiency.
When the balls become worn like the ones in this picture, it creates an increase in surface friction. This heat from friction has a much bigger impact than improper cooling. And is degenerative, which means that the more you run, the more heat is created, which means the more wear is created, which means the more heat is created and so on, and so on.

This wear is what I think cause the crank failure. Because eventually the looseness caused flexing in the crank.

Thats another good point on the outer race being compressed. This causes the balls the run harder/hotter and fail. But I don't believe that this type of application can cause this. You sound like your familiar on this type of failure probably because you work on split bearing cartridges that need to be shimmed, or on the taper roller bearings that you need to tighten up the locknut on the taper sleeve in order to achieve proper clearences. And we all know what happens when they are improperly installed. You run the equipment up to speed, measure the temp, and watch as the temp keeps climbing to critical.
But on the type of bases on sleds, I don't think it would be possible to compress the race enough. The only way I could see this happen is if the groove where the bearing sits in the housing was damaged and had a high spot or not properly cleaned. Then I could aggree that this could cause the bearing wear.
Using locktite only creates a film, the excess gets pushed out plus I don't think it has the strengh to compress the race.
As far as the locktite goes for heat transfer, it does not have the "R" value to insulate. So basically if the bearing is hot, the locktite is hot, so heat will still be removed.

Interesting theories, but in the end, we both may be wrong. These are just our 2 cents and don't actually have the bearing in front of us to study.

Just my opinion
 
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