One more hub.......
Posted October 08, 2000 - 09:39 PM
This week-end my hub went again.....
Only this time it was flat out in 4:th and it sent me in orbit around the moon.
It collected my sprocket, swingarm, spokes, chainguard, the rear frame, front sprocket and it even seems that the drive shaft is bent.
Before this happened I had lots of love for my 426 but now.....?!?!
I am totally out of it and thinking of switching this awsome bike I used to worship into a Honda 250.
As of right now I am talking to Yamaha Sweden ´bout warranty repair, but my confidence in this bike is lost.....
Posted October 09, 2000 - 10:22 PM
Did you recover all six of your sprocket bolts?
How many, if any, were missing?
And can you explain what sort of sprocket you were using and the condition of the sprocket after the failure? Was it torn in half, was it folded....etc.
Posted October 10, 2000 - 01:37 AM
Two of the bolts is still in my totally folded steel sprocket together with parts of the hub.
The rest is shattered around our local track I guess.......
The conditions was as usual at fall in the middle of Sweden, wet and half muddy (mostly water).
The most scary part is that after the next turn I was going to hit a 4:th gear flat-out table-top and whait if would have happened there....?
I will fill You in regarding the warranty issue as soon as I have got my answer from Yamaha !
Kind regards Numpsy
Posted October 10, 2000 - 05:05 PM
Oh, and you were about to hit a table top too, huh? Sounds familiar.
Posted October 10, 2000 - 10:38 PM
I used to be the optimistic one, and the first time I thought: "hey, what the heck... s**t happens ! Lets put a new hub on my bike and everything is back to normal "
But this time it really worries me.
There is too much what if, when and how going on in my head now and that is not good.
And since I have not raced mx bikes for over 12 years I do not think I can put my 426 on the limit !
It is a bit sad since I really loved this bike, it handles like crisp and the power is ..... hmmmm RAW !
Keep Your hopes up fellas, the 426 is still the most awsome bike I have ever ridden....
Posted October 11, 2000 - 05:47 PM
If you don't have all the bolts, and you still have complete bolts holes remaining on the hub, then you DON'T HAVE A HUB FAILURE.
Perhaps if you could supply me with a good description or picture of what the hub and sprocket look like, I may be able to conclude for you what really happened.
Posted October 11, 2000 - 08:09 PM
My hub is shattered, the sprocket is bent about 25-30 degrees.
One part of the hub is still bolted to the sprocket, two "bolt holes" is still on the hub and the rest is lying somewhere on our local track.
I mean the hub is dead !!!!
The sprocket was bent over the swing-arm, and it has smashed my chain guard.
In one of the hub "bolt holes" there is still a half bolt stuck and the strange part of that bolt is that it is broken in the middle of the hole. Not by the nut and not by the sprocket !!
I think that it is the bolts that broke first.
What do You think ??????
Posted October 12, 2000 - 11:18 AM
Thanks for the info. Perhaps this will help.
When I wrote "You don't have a hub failure", what I meant was that a weak or defective hub is not what caused your problem. Sorry if that was confusing.
Based on your description of the damaged parts, I would conclude that your chain was too tight, but perhaps not at your fault. Here's why.
When my hub failed I had three holes still in place on the hub. The other three hub holes will still bolted to the sprocket, and I was missing the hardware for three bolts, (bolt, nut, washer). Since I had just checked these before my ride, I knew for sure that I had six fully torqued bolts.
My sprocket was broken in half, and also bent over as if it was pulled out and away from the hub. It was curled! It was obvious that three bolts snapped, and the remaining pressure against the other three was too much for the hub. Hence it was the fault of the hub.
What caused the sprocket to curl out and away from the hub, thereby snapping the three bolts, was the tension of the chain when the rear axle height is equal to that of the swing arm pivot - its longest point.
Now here's the catch.
When you set chain tensioning on these bikes at or near the minimum spec, as stated by Yamaha, (40mm) the chain is too tight when the rear suspension gets compressed.
All you have to do to verify this is undo the linkage of the shock. Then install the hub, sprocket and chain, and set the tension to 40mm, then lift he rear wheel. Also if you hold the swing arm at its longest point, and adjust the tension bolts, you'll find that there is a big difference in tension between a spec of 40mm and 42mm - and an accidental setting of 39mm is unbelievably tight.In other words, 40mm is just too close for comfort.
This is what I think needs to get communicated back to Yamaha.
It's my opionion, the Yamaha's chain tension spec should be reset to 45 to 50mm.
Posted October 12, 2000 - 11:20 AM
I meant to say "Hence it was NOT the fault of the hub".
Posted October 12, 2000 - 12:02 PM
Posted October 12, 2000 - 03:17 PM
Posted October 12, 2000 - 07:55 PM
Posted October 12, 2000 - 08:23 PM
My heart goes out to you! You've been bitten too many times. I thank God you didn't hit that jump before she went. I really hope Yamaha helps you out with this latest issue.
All I'm saying here, is despite all the technical and years of riding experience that everyone is putting together, one fact remains: THERE IS AN ISSUE WITH THE HUB.
I pray no one gets in a jump and is struck with this issue. Y'all ride a lot more aggressively then I do. Lets all collectively come together and try to obtain a solution before someone gets seriously hurt.
If I can help in any way Numpsey, let me know.
Til then, take care!
Posted October 12, 2000 - 10:18 PM
Numpsy - I don't mean to question you, but double check your setting as it is stated in the manual (top of rear screw head on the chain guide to the bottom edge of the chain).
You can also try reconstructing the bike with the old hub, and a new sprocket and chain, and then check the tension on the chain when the swing arm is raised (assuming you have not moved the adjuster bolts).
Next, investigate the possibility that the rear axle may have slipped back in the swing arm during your ride. Was the axle torqued to spec? Is the head of the adjuster bolt on the right side of the bike damaged or is the bolt bent? Are there slip markings against the swing arm and the axle holders left by any movement? Check the inside of the swing arm as well. And check to see if the rear axle is bent.
If none of this shows up, the other possibility would be that the sprocket bolts were over torqued. (I really doubt that, but it's a possibility). This of course assuming that all the bolts were there in the first place. Right?
And look at the inside edge of the sprocket where the chain edge makes contact. If this is severely thrashed, as if the chain had ground down into the sprocket, then the changes are even greater that the tension was too much before the break occurred, (the chain digs into the sprocket before it rips it off).
Lastly, examine the broken hub. Look at the areas along the castings where the fractures run. If all the fractures look dull and rough, then it was not a poor casting. If any of the fractures have any shining areas, then the casting had a bad spot (the shiny areas are caused by poor casting areas that rub together before they break). This does not apply to any surfaces that are machined or areas that were hit by other parts. Only on the fresh cracks.
Other than this, there is the possibility that the hub failed, which then ripped out some of the bolts without damaging some of the hub holes. It's possible, but if that was the case, that could only happen if you had a bad hub. Again, you can gauge that by looking at the breaks. And I would assume that such a failure would leave the sprocket in better shape. Depends on how fast you were going.
The only other thing that could cause this would be a sprocket bigger than 52 teeth, which I'll assume you're not running.
I have abused both my old and new hubs with so much force that if these hubs were really under-designed, I'm sure I would be replacing them after every ride, so this is really not making much sense. And I also see fellow riders pushing these bikes hard as well.
Numpsy - let me know what you find and don't take any of my remarks as though I question your workmanship. I'm just running through all possibilities with you so to help get this resolved.
Let me know what you find.
Posted October 13, 2000 - 01:19 AM
The rear axel is straight and torqued, no problem what so ever with the tensioning bolts, the sprocket bolts torqued acc. to the book.
To explain my self: Last year was my final one as cheif race mechanic of a road racing team....
Certanly everyone could make a misstake, but I am, and has allways been, the tye of guy that first checks the book and then double check if that seems to be good enough.
It seems that the bolts went first and the rest is history.
All I know is that when all is back together the bolts will be replaced with better quality steel ones (and not 8.8) since the stock ones seems to fragile.
Could be too hard ?!?!
The thing that beats my mind is how the h**l my countershaft could have been bent ?????!?
Any idea anyone ?
Posted October 14, 2000 - 06:05 PM
Here's the verdict.
Your chain ripped your bike apart.
There's no way that you can have a broken hub, (with remaining bolt holes), a bent over sprocket, and a bent main shaft without the chain somehow getting overly tight. End of story.
Now you need to go out and figure out how that happened.
This would mean that the tension was set at or below 40mm, or your rear wheel moved, or the chain got caught on something during suspension compression, or the swing arm moved from it's position.
You may want to determine this before you attempt to the ride the bike again with all new hardware.
Best of luck.
Posted October 14, 2000 - 06:33 PM
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