Let's revisit the broken bolt in the chaincase

yammi4ever

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Nov 26, 2007
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Ok, had my chain case apart and now my bolt is broken, so I had to get a new bolt (no time to order one from dealer) Anyway If I put in a bolt in the same length and same length threads it will run out of threads before tightening the shaft extension (or whatever they call it) and from the looks of the end of the driveshaft that this piece had obviously been spinning on the end some.

So with this set up it would never get tight. On the new bolt I shortened it up so it had to tighten the shaft extension to the axle and now will turn as one piece as I assume it is supposed to. I verified this by assembling without the big spring at first to see it did indeed tighten completely.

Hope this is clear as mud, but for those of you who have gotten the new bolt, did I do essentially what it now does.

Not really sure how it is breaking the bolt even like it is, but wtf do i know.

thanks
 

Swelly

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Tons and Tons of em break. You can put a harder grade in and it will help. Another thing is to be a little more gentle putting it in reverse. The bolt breaking should not cause any damage by running it. It just holds stuff in place for assembly.

Your fix should also work, as that is what many have done.

Good Luck
 

Mountaintech

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Tons and Tons of em break. You can put a harder grade in and it will help. Another thing is to be a little more gentle putting it in reverse. The bolt breaking should not cause any damage by running it. It just holds stuff in place for assembly.

Your fix should also work, as that is what many have done.

Good Luck
The driveshaft bolt is not there to merely hold stuff in place for assembly. It performs the same function as the driveshaft nut does in a non reverse chaincase. Its purpose is to secure the driveshaft in the chaincase, ie. keep it from walking out of the chaincase (towards the left side of the sled) and uncentering the drivers/driveshaft in the tunnel. Without the bolt the only thing holding the driveshaft centered is the two small setscrews on the left side driveshaft bearing.
 

ruffryder

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The driveshaft bolt is not there to merely hold stuff in place for assembly. It performs the same function as the driveshaft nut does in a non reverse chaincase. Its purpose is to secure the driveshaft in the chaincase, ie. keep it from walking out of the chaincase (towards the left side of the sled) and uncentering the drivers/driveshaft in the tunnel. Without the bolt the only thing holding the driveshaft centered is the two small setscrews on the left side driveshaft bearing.
Agreed. I was amazed when I had my drive shaft out, how flimsy those side castings are. I wonder if this has something to do with the bolts breaking?
 
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Mountaintech

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Good question. I wonder if the problem ever got figured out? Different bolt perhaps? Are the 2010's breaking?
 

ruffryder

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On my sled which has reverse I finally gave up....tried several combos and all broke. Last season I ran it all year with no bolt.....no issues so I'm not sure what to say:face-icon-small-con
The problem goes away the less you look at it? lol. This certainly is an interesting issue, as I don't think the bolt missing or being broke has caused any direct malfunctions..
 
Oct 18, 2004
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On my sled which has reverse I finally gave up....tried several combos and all broke. Last season I ran it all year with no bolt.....no issues so I'm not sure what to say:face-icon-small-con
Brendon the 2010's have a new drive shaft and related parts that cure this problem...When I changed out my track pre-season I of course found mine broken!! I looked at how the parts go together and with the help of my Father,a long time seld head and 25 plus yamaha owner in his time we came up with a cure!! When eveything is bolted up according to Yamaha's parts breakdown there is a space between the end of the drive shaft and the related parts when torqued up. I machined a spacer so everything was solid when torqued...Changed gearing near end of the season and bolt was still fine. Takes a little time to measure up the gap, but was an easy fix.
Hope that makes sense....
BC.
 
Oct 18, 2004
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so basically a thin flat washer thats the same diameter as the drive shaft....not allowing the collar to fully engage the shaft? ya for sure get me the specs..got a few in our group that could use this mod. thanks Man!
Not a problem Dude....extends the driveshaft inside that coller so there is no air gap between the end of the shaft and the coller....One solid piece when torqued up....Still same specs and assembly just dosn't allow that little bit of flex that we believe was breaking the stock bolt. The new shaft is longer and different coller to fix the issue.
BC.
 

Tuesday

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Not a problem Dude....extends the driveshaft inside that coller so there is no air gap between the end of the shaft and the coller....One solid piece when torqued up....Still same specs and assembly just dosn't allow that little bit of flex that we believe was breaking the stock bolt. The new shaft is longer and different coller to fix the issue.
BC.
Interested as well, the bolts just keep breaking.
 

yamahaboy701

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Just for the record I put 1200 miles on the new 2010 bolt and it was fine at the end of the year and did not break. Part #90105-10368-00
 

Motleyone

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Ok, a little long winded probably but may clear up some confusion. The reverse gear assembly bolt is just for that,"assembly" and maybe a slight preventativ measure in case other things fail in the system. If you have tried to put the gear case cover on without the bolt it is near impossible. That is the reason the bolt is in there, it compresses the spring inside the collar that holds the reverse gear assembly together on the drive shaft. The reason it does not cause damage when it breaks is two fold. First when it does break there is nowhere for the pieces to go, they are contained. Second, the space between the collared retainer and the gear case is very very small so when the bolt does break and the spring releases the collar laterally into the chain case it does not puncture the case. You might ask if the collar is rubbing against the case why does it not rub through it eventually. It's because the collar is not spinning with the shaft. This is why when the bolt breaks it does not cause damage, it just rests in place up against the case. I know 2 guys that run without them and have for 2 years without any damage. What is interesting to me is WHY the bolt is snaping off in the first place. Everyone I have seen snapped in half did so internally and left about 1/2-3/4 of an inch of the bolt attched to the head. This happens because you are putting a bolt that is 9.7mm in diameter through the hole in the collar that is 10.7mm wide. There is 1mm in play. There is also a gap bewteen the end of the collar and the driveshaft about 7.5mm wide. So when you tighten down the assembly you have the bolt head tight against the collar which is pressing the two reverse gears against the bearing housing with side to side play. What happens is the collar has a little play in it side to side and this (under load of the track turning over) causes stress on that bolt that is not fully supported inside because of the 1mm gap between the bolt and the wall of the collar and the 7.5mm gap from the collar end to the drive shaft. The easiest fix is to insert a collar that has a wall thickness of .5mm, a diameter of 10.7mm and is 22.5mm long (the length of the exposed bolt inside the collar). This will support the bolt and should stop it from snaping off because you will eliminate almost all of the side to side play. The best fix would be for Yamaha to send out updated collars that have a narrower bolt hole and are extended 7.5mm and butt up against the drive shaft.

As for holding the drive shaft in place that bolt has nothing to do with it. On the drive shaft on the chain case side there is a permanant bearing guide fixed to the shaft that turns with the shaft. This fit into the bearing housing that is fixed to the chain case side bulkhead piece with three bolts. The shaft cannot move laterally towards the chain case unless that housing were to fail and the bolts gave out.

On the clutch side the drive shaft is stopped from running out laterally towards the clutch by the bearing housing on the outside of the bulk head. There are 6 bolts on this side for a reason. They needed extra strength on this side. As for the set screw assembly on this side it is not the only thing or even the primary system to keep the shaft in place. It would be impossible because the plastic piece fits inside the bearing housing piece that bolts to the bulkhead. The plastic piece sits against the inside of the actual bearing not the housing or the bulkhead. The job of this little plastic and metal piece with set screws in it is singular. Once you have your drivers on and both sides of the shaft bolted up into the bulkhead and all is snugged down you simply reach under and and pull that set screw piece laterally against the bearing then tighten it down. It's job is to be there as a back up to prevent the bearing from walking back and forth in it's little spot between the two bearing housings and causing them to fail. Your clutch side bearing is encased and cannot move in either direction more than an 1/4 of an inch even if the pressed on bearing were to move and the set screw assembly were to move. This is because on the outside is your speedo sensor gear and it is slightly bigger than the inside diameter of the bearing so the bearing cannot slip over it. On the inside your shaft tapers out within a 1/4 inch or so on the backside of the retainer with set screws. There are alot of things in place to prevent such a catastophic thing as loosing you drive shaft out the side of your sled from happening.
 
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