07 Sprocket, Bolts, or Hub Failure

[RCannon]

How do you adjust the wrench btw? I am interested to know that.

No need to appologise...not a big deal at all.

The faastco wrench has a set screw, or "grub" screw, under the black, rubber cover on the end. Each "complete" turn on the grub screw changes the torque value 12 lbs. So if 48 is stock, 1 turn out will now give you 36 and so forth....

Its not completly precise, but it does allow a person to tighten each spoke evenly. Overall, I think the wrench is a load, but since I allready have one.....

I BELIEVE the old "ring the spoke" method was darn near as accurate. It does have very nice machined wrench sizes that dont round off the niples....

[Vibeguy]

Lots of good information here so I'll add my $.02 worth:

The previous post that stated the driving force from the sprocket to the hub is done via the contact face between the sprocket and hub and the friction they generate is correct. The sprocket bolts are the means in which these faces are held in contact, not as drive pins. I don't care if the have a grade 90 fastener made out of unobtaininum if they are loose, there by loosing the friction betwen the faces you will shear them or the mounting lugs on the hub.

Item 1) Remove the sprocket from the hub and look for relative movement between the 2 faces, fretting and/or shiny spots. Take a honing stone and lightly run it over the sprocket and hub faces to make sure there is no upset or proud material on either that would reduce the contact area between the 2faces.

Item 2) Clean both faces with a good clean evaporating solvent or contact cleaner. Inspect all fasteners for relative movement, fretting, witness marks or any other indication that the fasteners have been taking a side load, if they are not 100% throw them away. As Grey said about slef locking nuts, if there is still a reasonable amount of friction between the nut and screw then they can probably be reused. As a general rule of thumb if you can turn a self locking fastener all the way on by hand then it is shot and should be replaced.

Item 3) Install clean, dry fasteners with a suitable thread locking agent (I use Loctite red) and torque to the manufacturers recommended spec in a criss-cross pattern. After all this is done a little dab of a product used in the aviation industry called "Torque Seal" can be applied across the nut and threads. This product will harden and give you a visual indication if the nut has loosened up by cracking a part of the torque seal off.

[grayracer513]

The bolts are not "drive pins" just exactly, but niether does the clamping friction between the parts do the whole job independently of the fasteners. Just as the raised step at the center of the gear flange is used to locate the sprocket on center, the bolts prevent the sprocket from "creeping" rotationally, and that function is at least as important as the clamping force is. If the sprocket were held flat against the hub by a snap ring, or something similar, five 8mm steel pins could easily handle the drive loads. What could not, in that setup would be the aluminum of the sprocket around the holes for the pins, or the aluminum hub at the point where the pins were inserted.

By using bolts instead of pins, the rocking and battering between the parts is eliminated by the clampiing force, and the two work together in a cooperative manner. Occasionally, that's not enough, and in those cases, you will see precisely fit dowel pins in the hub flange to relieve the bolts of the shear loads.

[00YZ426FMRCD]

Not sure if this has been asked. If so I missed it. What is different if anything about the manufacturing of the 07 hub/rear wheel versus the 06, 05 or even earlier models?

Is the sprocket side bearing smaller or larger?

I believe the 06 and earlier models were 1 bearing on each side with a seal and collar. I assume the 07 is the same. Is the rear hub the same?

Just curious...

[aford541]

Not sure if this has been asked. If so I missed it. What is different if anything about the manufacturing of the 07 hub/rear wheel versus the 06, 05 or even earlier models?

Is the sprocket side bearing smaller or larger?

I believe the 06 and earlier models were 1 bearing on each side with a seal and collar. I assume the 07 is the same. Is the rear hub the same?

Just curious...

I don't think the bolts are as good on the 06 and 07, they seem to be softer than the grey ones.

[weldman]

we have a shop by us and a guy who got a yzf450 06 had his hub come apart also and yamaha gave him a new one because of a defect also another guy got a yzf250 06 that the frame cracked about 8" long down the front support the crack starts at the steering stem and runs down the side yamaha replaced the frame 2wks ago

[YamieRider411]

Yamaha replaced everything free of charge without hesitation… I was upset with the situation at first but I had a feeling that Yamaha would help me out on this deal.

I’ve read all the replies to my post and feel some of the criticism was a little harsh. I’ve been riding, racing and maintaining dirt bikes since 84. Besides seizing engines on my 2 strokes, I’ve never had a mechanical problem of this magnitude. Yes, I agree with all of the suggestions about checking the equipment and Loctiting the bolts, but these motorcycles are designed to handle massive loads of punishment without cracking up. Do you check the lug nuts on your truck or car before and after you drive it everyday? NO! Why, because it’s the manufactures responsibility to build the equipment to handle normal use. Normal use of a dirt bike involves loads of stress. They, the manufactures, know this and must build their products accordingly. I am very thorough when it comes to bike maintenance, and I don’t feel that my lack of maintenance caused this problem. I will however add new procedures to my normal maintenance routine so that this type of problem will hopefully be minimized in the future.

The main reason I posted this message was to get advice from others on this situation and to alert others so it wouldn’t happen to them. I love motocross, and the people who participate week in and week out are some of the best people I’ve ever known. I don’t know a single motocrosser in my area that wouldn’t give you the shirt off there backs when the need arises. I did not post this with the intention of disparaging Yamaha’s good name. I just wanted to open a line of communication to help me and inform others. Peace!!!!

[Fastest1]

Great to hear they fixed you up! I only wish FORD heard that!

[Ga426owner]

Did yamaha fix this and and others because there is a technical bullentin out and they admit some failures? This is what I want to know....can anyone confirm that there is a Technical bulletin out for this ???

[brian389]

I've had both an '04 and an '06 hub fail, both cases locktite was used, and it was extremely difficult to remove the bolts from the pieces of the hubs that were remaining (because of the locktite). There are too many of these failures going around to blame it on maintenance. I'm extremely careful about chain and spoke tension also. They need a re-design on these hubs. Talk to the guys at Rad Manufacturing. They will tell you the YZ hubs and KTM hubs are the most often-failing hubs they see.

[joe346cbmx]

you are not alone. I went thru this twice on my previous bike, an 04 Crf450. I should note I raced it for 2 years 20+ times each year. I maintained it regularly. I had too.

The first time my hub failed i noticed when lubing my chain between practice motos that I started breaking sprocket bolts. At first I thought it was fatigued bolts. So I checked them on each ride. I'd replaced all of them and they kept breaking. So I then pulled the sprocket off and saw the hub sprocket bolt holes had gotten egg shaped. Got a new hub and new bolts, lock wahsers, loc tight etc. and all was good for a long time.

Near the end of the next year I was practicing on some pretty rough terrain. I was breaking hard into the corners and accelerating out of a corner it locked up the rear wheel. I looked down ad saw the rear hub broke off an ear and trashed my chain guide, chain, sprocket, etc. This time I had not broken any bolts and had just cleaned the bike, checked the bolts/nuts, adjusted the chain to spec, lubed it and went to ride.

In my non expert opinion, sometimes it comes down to how hard you ride them and how much torque they have. Every manufacturer is trying to shave weight off the mx bikes. The bolts and hub fatigue a little more every time you ride and eventually give out. think about how much stress is put on those little bolts and hub ears when you are full throtle to full breaking 100's better yet thousands of times. sooner or later something is going to give.

that said I also think some hubs, like the thread owners here , are just lemons and have faults in them. It happens sometimes. I am glad to hear Yamaha fixed it, just like they did on the 250f valves when that was a problem, they do stand behind the product and take care of customers. Not that common anymore.

joe

[CISCO]

Did yamaha fix this and and others because there is a technical bullentin out and they admit some failures? This is what I want to know....can anyone confirm that there is a Technical bulletin out for this ???

Yamaha fixed it because it is under factory warranty. There is no tech bulletin. There instances of this occuring to a Yamaha installed sprocket are nearly non existant. Take a deep breath and go ride your bike:thumbsup:

[THORFXMX]

After Landing Of A Easy Double My Honda Cr450 Rear Hub Came Apart,the Sprocket Broke In Half Breaking Off The Chain Guide Mounts Off The Swing Arm. At About 5 Hours Of Ride Time I Just Serviced The Bike Checking Spokes Sprocket Bolts Included I Had To Tighten The Sprocket Bolts Twice Before, This Is Not A Maintence Problem It Is The Weak Streching Bolts The Factory Uses Perhaps A Bad Batch.

[THORFXMX]

After Landing Of A Easy Double My Honda Cr450 Rear Hub Came Apart,the Sprocket Broke In Half Breaking Off The Chain Guide Mounts Off The Swing Arm. At About 5 Hours Of Ride Time . I Just Serviced The Bike Checking Spokes Sprocket Bolts Included I Had To Tighten The Sprocket Bolts Twice Before, This Is Not A Maintence Problem It Is The Weak Streching Bolts The Factory Uses Perhaps A Bad Batch.

[todds924]

Did yamaha fix this and and others because there is a technical bullentin out and they admit some failures? This is what I want to know....can anyone confirm that there is a Technical bulletin out for this ???

GA, I have seen no bulletins at work for the YZ hubs. I think the most common cause is loose bolts. And once the holes get egg shaped it is almost impossible to keep them tight or the hub from breaking. I check mine every race.