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2000 Yamaha Kodiak 411 4x4 Ultramatic
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Discussion Starter #1
Hi, I bought this machine for $100 and it was not worth much more at the time but it is a Yamaha and these Kodiaks have a good name, especially this vintage. It was and still is a Father-Son project that will get us riding together. Working on this project has really helped bring us together. I could type for hours and not tell the whole story of the resurrection. There's a local history to this particular machine that I hope to one day learn more about (where did all the plastics go?). When we got it, it was sitting outside in an overgrown local backyard looking pretty rough and neglected. It had no seat (well, it had a Suzuki Quadrunner seat that I later sold for $100), a busted grille, bent bumper, no battery, no fuel tank cover, no plastic engine side covers, four flats, bald tires, rusted out muffler, torn CV boot, busted shifter, bent racks, faded plastics, and did I mention the engine was seized? Not exactly what you would call pristine condition. So we pumped up the tires, found neutral, and pushed it onto my utility trailer for the short trip to its new home. Covered it with a tarp in the backyard, the poor thing must have thought it was at the spa.
First order of business was getting the top end apart, luckily? water had gotten into the airbox due to the missing seat, and flowed through the carb and the open intake valve, so the piston rings rusted to the cylinder wall. No water or rust in the base. Showed the boy a few tricks for getting frozen stuff apart. Cylinder sent out out to the local speed shop, bored to the second oversize to clean up the rust, and a Wiseco piston kit, its a 411cc now!
Found all the plastics on eBay or Kijiji, replaced and serviced a lot of things, basically went through everything, all new fluids throughout.
Cleaned and painted a LOT!
Got a set of near new takeoff tires from a friend.
Reassembled the engine and then the rest of the machine. A few glitches along the way but now it runs and has been used about five hours without incident (well, almost)
Two issues outstanding:
1. The electric start quit working after a couple of hours of riding, it would just make a buzzing noise from the starter solenoid. Luckily the pull start works! Back at home I traced that concern to a broken positive brush holder in the starter, did a temp solder repair and reinstalled, ordered a brush kit, now that's the son's latest task: remove and recondition the starter and reinstall. Easy fix.
2. Gear Whine: This one I'm hoping for some input from the experienced Yamaha folks before I tear into anything. It's got an audible gear whine noise at any speed above 10 mph, seems like it originates from either the middle or rear of the machine. Sounds a lot like the classic rear end howl from an old vehicle, which usually indicated worn pinion bearings. The whine gets worse when accelerating or decelerating, its not nearly as bad under light throttle, no load on level ground, but still noticeable. The noise might be coming from the rear diff, or possibly somewhere in the transmission. I'm thinking of blocking up the rear end and running it in gear and listening with a stethoscope to help isolate the source of the whine.
Back story on this is that when we picked up the machine, the rear diff breather tube fitting was not pressed into the top of the diff housing where it belongs, it was dangling loose on the vent hose and the diff had oily dirt stuck to the outside around the vent fitting hole. There was some oil in the rear diff but not the factory amount and it was pretty dark. No water, a little fine metallic glitter was in the oil. the ring gear teeth looked ok when looking through the oil fill plug hole. I'm wondering if the pinion and or side bearings are known to fail on these diffs, even with regular oil changes? Rear diff bearing and seal kits seem to go for around $110 CDN and are for sale everywhere. Any tips on getting or fabricating the special tool for removing the rear diff pinion bearing retainer? This seems like a pretty simple job otherwise. We've already had the rear suspension completely apart to replace the rear axle bearings which were pretty worn. Do the bearings in the middle gear often fail? I believe they are lubricated with the engine oil. and the engine looks to always have had good oil pressure, and the crankcase oil was clean. I'm really not excited about splitting the cases to replace the internal middle gear bearings, but it looks like the middle gear output shaft bearings can be replaced without splitting the case? Any advice appreciated, I realize this thing is 20 years old but it will get my son out on the trails once we've got these last details sorted out.
Thanks in advance for the help.
 

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The noise is most likely a failing pinion bearing. Especially since the differential oil was in such bad condition. The differential midy likely has rusty bearings inside.
It could also be a failing u-joint on the rear driveshaft.

The middle gear bearings rarely ever fail. And yes they are lubricated by the engine oil.
 

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2000 Yamaha Kodiak 411 4x4 Ultramatic
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Discussion Starter #3
Thanks Dezz, It's good to hear from someone with experience. I'm 25 years into the automotive trade, just started working on these machines for a new challenge, lots of similarities, but I don't have the experience base. The U-joint was not worn or binding, we checked it for play and stiction before reassembling the rear suspension. Looking at the bearing set, that little Torrington bearing that supports the small end of the pinion shaft looks vulnerable, and it runs directly on the shaft, I'm hoping that if it has failed, it hasn't trashed that bearing surface. Could be the side bearings too I guess. I've rebearinged a few truck diffs, can't be that much different.
Thanks for the advice.
 

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Discussion Starter #4
UPDATE: Starter is now rebuilt and installed, test started several times today, all good. Gear whine noise diagnosis next...
 

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Discussion Starter #5
Our rear brake rotor for the quad finally showed up today, so its time to pull things apart for that replacement task (20 year old Allen head bolts, and probably Loctite on the threads so this might be interesting...), and carry on with the rear diff removal and teardown for bearing inspection. Still haven't figured out how I'm gonna get that bearing retainer nut off yet either. Not a lot of info on YouTube for a DIY tool, but they are available for sale.
 

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Discussion Starter #6
OK, removed the rear diff, tore it down, everything looks like new inside so I guess the old oil wasn't as bad as I thought. Bearings are all good, no play or roughness. No evidence of water or even dirt contamination, which is a relief. Contact pattern on the gear tooth faces looks normal for the type of gear. Removed the rear swingarm and then the output shaft of the middle gear hoping to find worn bearings, but again bearings are all good there? Really I can't see anything visually wrong with the gears or bearings, everything looks to be in great condition. I don't have all the facory tools to measure middle gear lash, but i'm going to try removing shims from under the middle gear output shaft bearing carrier,spin it all to be sure I'm not running with zero lash, then see if the noise changes. The shims are easy to put back in with everything completely reassembled, if removing them makes things worse.
 

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I am beginning to wonder if you are chasing a ghost (a problem that does not exist).
What kind of whine are you hearing?
Since everything is checking out back there, I think the noises your hearing are normal. It's how it operates.
If you can post a video of what your hearing that would help.
 

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Discussion Starter #8
It's a possibility that I am just hearing a normal noise. I really figured I'd find the smoking gun in the disassembly yesterday but nothing horrific has popped up. Thing is I've ridden a friend's Yamaha, it's a bit newer, but runs basically the same drivetrain, and it's not as noisy. After dinner I went back out to the shop and had a really close look at everything. The rear axle is bent quite a bit more than the .060" allowed. As best I can tell without a good set of centers, the bend is isolated to the right hand side of the shaft, maybe at the point where the shaft exits the diff housing (this would be logical since the bearing supports the shaft there). I'm dropping the axle off at my local machine shop to see if he can straighten it.
 

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Discussion Starter #9
Dezz, to answer your question about the kind of whine I'm hearing, it is the classic automotive rear end type gear whine or howl usually associated with excessive gear lash caused by worn pinion bearings. It is noisy under load, pretty quiet at light throttle running on level terrain with no load, and noisy on deceleration when using engine braking. When its all back together and if the noise is still there I'll try to get video or audio of it.
 

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Discussion Starter #10 (Edited)
So my machinist was able to straighten the axle the same day I dropped it off, he said it was .165" out, well in excess of the .060" allowed, and it was bent exactly where I suspected, right at the spot where the axle exits the diff housing. He got it sorted out and down to .008" overall, which is not going to be noticeable. He mentioned that the axle is not tempered or hardened as he had initially suspected, so it was fairly easy to bend back to straight. I also replaced the middle gear shaft output seal at the yoke, it was leaking engine oil and had probably contributed to the demise of the bellows we replaced between the transmission and swingarm. After 20 years I guess that is to be expected. The seal is a metric one, dimensions are 52 x 35 x 8 mm and is dual lipped (old seal was single lipped, new one will keep crap out if the bellows is compromised), if anyone wants to avoid buying the Yamaha seal for three times the price. Total charge for labour to straighten the axle and the new seal was $30! Can't beat that same day service. I'm going to put everything back together today less the shims I mentioned earlier, and see if things get better. If there's no change I'm just going to run it like it is, there's no damage being done that I can see.
 
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