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Discussion Starter #1
Hi Folks;

Did a bunch of work to the bike the other day, new tires, clutch, Ohlins rear shock, chain and oil change etc. When I test rode it I noticed a vibration. Also, fuel economy sucked and the engine appeared to be laboring. Long and short was it got me thinking something is wrong in the transmission and there is friction there reducing power and economy.

It seemed to occur after the work so I went in today and checked the clutch thinking maybe in my rush I messed something up. Clutch is great, steels are great - no issue. The engine was a bit over-filled with oil, thought that might cause it, drained some off - same thing.

The more I think about it the more I'm coming back to a transmission bearing. The rivet on the chain is great, the entire chain is supple - it's not coming from there. It's not coming from the clutch. It's not wheel bearings - it's either engine or transmission.

Is there any easy way to determine where it's coming from or to pin it down? I'm thinking the engine is going to have to be pulled :crying:
 

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so everything was fine until you did the work, and now you think that the engine has spontaneously ruined itself?

i think you need to take a more logical approach to this.



go back over absolutely everything you touched when you did the work, and double check for something you might have messed up. if it was good before you messed with it, chances are it's something you did.
 

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Discussion Starter #3
Been there done that (as mentioned). I ordered up all new bearings and a countershaft. I'm about as certain as can be that the issue is a bad bearing. As for it happening after the work, I started to wonder about the length of the shock. If the shock is longer it will change the geometry and could put tension on the countershaft bearing on a different angle. It's about the only thing I could come up with that could possibly have a 'bearing' on it. I then lowered the shock considerably and took it for another drive, it seemed to be better. My guess is that that shock highlighted an issue that was already present.

The person I got the bike from had ridden it with the chain very tight (zero play) for a protracted period before I saw it and addressed it. That had always had me concerned but the decision's been made - it's getting a new countershaft and all appropriate bearings/seals as well as new shift forks etc.
 

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with a properly adjusted chain, the length of the shock is irrelevant.

a bold move to order parts already. but it's your money.
 

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It really can't be anything else that I can think of. If it was engine related it would have scattered very fast at 15k. There is no knock. Chain is new, riveted link is sound, I just checked the clutch, it's good. Even if approached through the process of elimination I'd say we're down to the tranny/bearings. For all I know it could be nothing more then coincidence with respect to the timing. Either way, it's getting done and I also have a spare transmission in the event that there's some wear there. I just want it back to normal and ready for use at any time.
 

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i just feel that if a bearing were absorbing enough horsepower for you to describe the engine as "laboring", then it would have blown the hell up.


is your rear brake dragging? are your wheels installed correctly?



i just can't imagine a transmission bearing destroying fuel economy without a complete failure in very short order.
 

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Discussion Starter #7
I thought the same but...that countershaft bearing is huge and I bet it almost can't blow up unless it gets really, really bad. Wheel bearings are new OE, I pulled in the clutch at speed and let it idle with the bike coasting at freeway speed - no vibration. Brakes are also relatively new and they are not dragging. Wheels are correct as are rotors and rubber.

It's really hard to describe/diagnose over the Internet - if you drove it you would probably think along the same lines. Easiest way to describe it would be that it's a vibration from the engine, you can feel it through the pegs and bars, and it appears to be directly related to coast/drive loads on the throttle. Ie, if it's sitting still in the garage and you rev it, it won't do it. It has to be under drivetrain load.
 

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Did you check for some kind of suspension binding under load? Just a thought as it sounds like an off axis binding type thing.
 

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Did you check for some kind of suspension binding under load? Just a thought as it sounds like an off axis binding type thing.
The rear wheel is aligned perfectly, the chain is new, the riveted link is free and the freeplay is correct. Having said that, you mentioned an off axis binding - I think that could easily be one of the bearings in the mainshaft or countershaft. Reasonably sure that's all that's left. Parts are on order and once I get in there I will certainly post up pics about what I find. My best guess is countershaft bearing. That's the one that would take the biggest hit knowing that the previous owner had the chain too tight (zero slack on the tight side of the chain).

One thing about this bike though, it has always had a tight side of the chain and a loose side of the chain. My understanding is that this usually means the chain is shot. However, I had seen new chains pretty much do the same thing. I just replaced the chain with a DID X-Chain and it's got maybe250 miles on it, and when I checked it, it also has a tight side and a loose side. So I always adjust it when it's on the tight side of the chain but here's the thing - why would there be a tight side and a loose side with a new chain?

Perhaps a sprocket that's just a little off?
 

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With those kind of things on dirt bikes at least it binds the rear wheel bearings long before the transmission along with the shock linkage and the like would slacken before the trans. Just seemed to make more sense as the 'tight chain' pressure is no longer there the bearing in the rear comes to play binding. Try wiggle the rear left to right and see if when you bounce up an down any side motion kicks in. No expert but for me I would as wibbly says go through what I messed with before cracking open a case.

My two cents worth from a more a solid dirt bike/Supercross background.

As far as sprocket you can spin the tire and see that. What you are talking with a loss of power is a physical restraint on the round and round motion. Since its not stop go stop go bind I doubt the sprocket or warped rotor. You are having a torque induced full bind kind of thing that would explain vibration as well. At least that's what it sounds like.
 
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