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Yamaha Tech Originally the Yamaha XT600 Tech Forum, due to demand it now includes all Yamaha's technical / mechanical / repair / preparation questions.
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  #1  
Old 9 Nov 2011
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xt550 - who wants to have a go at knock troubleshooting!!

long story of course ....

this is the sound of my 83 xt550 - not all that pretty.

it started to sound like this just after I had a really bad kickback incident due to a faulty pickup coil. - solved that one. but inherited this knock.

xt550 engine knock - YouTube - this is just after is started about a year ago.

XT550 - persisting knock - YouTube - this is a few months later.

I first diagnosed this as cam chain, so i went in and replaced the cam chain, checked the tensioner and replaced one slightly worn cam chain guide. put it back together and re adjusted the valves and yet it still persisted.

the knock is only at idle, and the lower the idle, the worse it gets. But sometimes, the knock will stop and the engine will run smoothly ... and quietly ... just like it is supposed to, then ... a moment later the knock will start up again. (pretty infrequent that this happens, once in a blue moon really.)


it is a knocking noise that appears to be coming from the right hand side of the crank case, although it is quite hard to spot, even with a stethoscope.

I have had the clutch side apart and there wasn't anything that jumped out at me as being wrong or too out of wack. Also showed it to a couple mechanic friends of mine, they said everything looked about right and said they couldn't really tell unless they took everything apart measured all the tolleranced and compared it to the manual.

well I am trying to advoid taking the crankcase apart. Although I am taking the head off to do my rings next week and thought I could tear into the clutch side a bit more if I knew what I was looking for -
Any ideas would be helpfull.

sheared woodruf key on the main gear?

anyone??
anyone??

Thanks in advance.
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  #2  
Old 9 Nov 2011
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Don't know the xt550 engine at all but if your lifting the topend off do yourself a favour and strip the bottem end aswell and check the rod bearing,mains and balancer bearings.in my experience a knock nearly always comes from 1 of these on a big single.sorry i cant be more specific to your motor.cheers
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  #3  
Old 9 Nov 2011
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i currently have the same exact problem on my '93 xt600 and i do very much agree with dodger on the bearing issue. i feel its a bottom crank bearing for mine but the inconsistency of the noise points out the fact that it would be a bearing. if it were a more steady knock id say valves, but it definately sounds like a bearing to me. ill upload a clip of my bike and let you hear it.
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Old 9 Nov 2011
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Something as simple as some sort of auto decomp clacking ?

A bottem end bearing going bad should also knock above idle....Atleast, thats the way I see it.

What is the idle supposed to be at from the factory? I would guess a couple hundred rpms faster?
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Old 9 Nov 2011
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Might be a loose nut - primary drive, clutch or balancer.
Makes sound on low revs, gets balanced on higher revs and sound almost disapears.

No idea how "deep" you have been into your clutch side - but I would
recommend to check all three of these nuts - as well as damping springs in
primary drive.

just my two cents
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Old 9 Nov 2011
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I think if it was a bearing it would get worse as the revs rise.
Nuts are worth checking, it sounds like the cam chain tensioner is not working erratically?
Have you used it over the last year and has it developed in anyway?
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Old 9 Nov 2011
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not necessarily on higher revs the bearing gets hotter which in turn makes it quieter. i had a buddy who had a spun bearing that would wine everytime he started his bike but it wouldnt make a sound the whole day afterward once it was warmed up only the first start of the day
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Old 9 Nov 2011
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Weatcoastrider is not online at the moment but might I point out, if you look at his you tube there is a third vid with the clutch cover off, where he points out one or two lose gearings. But I don't think this is his problem.
I would strip down the engine bit by bit, eliminating each part as I did so.

Whatever it is ain't going to get better, without help.

Socks
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Old 9 Nov 2011
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It's the erratic coming and going, not in time to the strokes, that swerves my judgement away from bearings. That's not to say it's not.......I've changed a wheel by text but diagnosing engine knocks via you tube........Take it apart, giving everything a good push-pull, up-down as you are doing it.
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Old 9 Nov 2011
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Id say you hit the nail on the head the first time, worn woodruf key in the balance shaft? or a worn 3mm washer next to the main bearing RH side.

This sounds like a similar problem Danny is having, read this.

Mezo.
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  #11  
Old 9 Nov 2011
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I'm no mechanic but I remember an old XT once sounded like this, it had been sitting around for a while and the fuel had got contaminated.
Is the kick start disengaging properly ? that seemed to be the start of this problem.
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Old 10 Nov 2011
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i guess i've finally come to the right place.

hey unbelievable! i never expected so much feedback in one day! thanks so much.

I have been riding the bike like this all summer this year, even did some 200 - 400 km trips. Basically the noise is exactly the same. Its hard to say but the noise may even get a bit better once out on the highway for a 1/2 hr or more.

I think i will split the bottom end just out of curiosity, the weather here is starting to suck anyways and i have the time to dedicate to it so why the heck not right.

oothef - I am pretty sure the tensioner is working properly and as i said i did replace the cam chain already. also noise is really coming from the rhs in the middle near the top - as far as my ears can place it.

bubbla - where do i find these damping springs you speak of.

Jens Eskildsen- decomp is adjusted to spec and appears to be working properly.

Pboko2388 - would love to hear your bike, especially if you think you have found the problem. I am quite handy with a wrench but this is definitely as far as i have ever gone into the motor so i'm a learning noob but very curious, any feedback or hints welcome.

Mezo - thanks for the link to Danny's build - real nice BTW. i think my 550 is in need of some black wheels too - looks great. those vids are certainly going to come in handy once i open up the rhs.

I am not familiar with what bad bearings should look or feel like - if anyone has a good description of a bad bearing I'd be keen on hearing it.

thanks again for all the help, - I'll post my results after i get into this weekend.

cheers

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Old 10 Nov 2011
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A good bearing should have no play radially and be smooth turning, no notchiness or grating. Take your time, be methodical and label stuff.
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Old 11 Nov 2011
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results

update:

A+ for Bubbla and Mezo ! - balancer shaft woodruff key was almost completely sheared in half and the tab on the lock washer that sits in the groove was also missing. after removing the clutch i noticed the balancer nut was just spinning around loose.

The only thing I just can't figure out is why i didn't see this before. I had already checked these nuts and they all seamed fine. Hopefully this will be the source of all of the knocking and once re-assembled will purr like a kitten again. good news is that all the bearings appear to be in good condition, no real play anywhere as far as i can tell.

some piscs that are not great. I always get so excited to find something broken that I am too busy to stop and take great photos. at least it gives the idea.





i noticed a small amount of play on the primary gear as well coming from the way it fits over the key, not the bearing. Should i just replace this key as well, for good measure? I can't imagine this is a bad idea.

will get some video tonight and post again with some better images etc.
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Old 11 Nov 2011
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Good to hear it's something that's easily remedied,you must be relieved.Is the keyway still in good shape?
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