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Old 02-22-2014, 08:13 AM   #1
Roland3 OP
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Help, diagnoses needed, should be easy

So i just did the valve shims clearance adjustment, when all reassembled, I was turning it over with the kick starter to check things over and noticed the rotor/ flywheel looked like it is wobbleling. It is wobbleling a lot. How could this be? Is the crank bent? Could it be on the shaft crooked? Ill have to investigate more tomorrow. The bike is new to me, 1997 yamaha xt350 low miles, everything is stock and unmolested, then this shows up? Are they supposed to be like this? Pics show the distance in gap change from the pickup

Update: checked things over the bolt in center is wobbleling also so either the shaft is off set or its bent.



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Old 02-22-2014, 09:02 AM   #2
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Does it vibrate when riding it?

Does the XT350 have a pressed up crank?
If the conrod bigend is roller bearing it will be and the crank pin may have shifted.
Just a guess.
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Old 02-22-2014, 09:15 AM   #3
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Does it vibrate when riding it?

Does the XT350 have a pressed up crank?
If the conrod bigend is roller bearing it will be and the crank pin may have shifted.
Just a guess.
No vibration that I've noticed. I dont know about the pressed crank. Just noticed it when I had cover off to align the t mark for TOp dead center.
It certainly doesn't look right.
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Old 02-22-2014, 09:21 AM   #4
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What you don't know can hurt you.

I'd take off the flywheel and hopefully it's just a sheared key or loose bolt.

Check for damage to the magnets and stator coils.

Good luck!

There may be a thread in Thumpers for the 350. Look for it and find people who have one they should be of more help!
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Old 02-22-2014, 02:24 PM   #5
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That's what I'm going todo as soon as I get the puller tool. I can see the threads in the shaft running out though. Wonder how long it will last
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Old 02-22-2014, 04:15 PM   #6
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That's what I'm going todo as soon as I get the puller tool. I can see the threads in the shaft running out though. Wonder how long it will last
The other poster might have nailed it.
Pull it and then check the end of the crank for run-out.

You do not want to find out how long it will last.
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Old 02-22-2014, 04:40 PM   #7
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The other poster might have nailed it.
Pull it and then check the end of the crank for run-out.

You do not want to find out how long it will last.
If it is the shaft that is running out, what is the fix? New crank shaft and bearings?
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Old 02-22-2014, 05:26 PM   #8
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I have a flywheel that's dicked up from some asshat using a two jaw puller instead of the proper threaded puller. ANYTHING is possible....
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Old 02-23-2014, 06:31 AM   #9
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Quote:
Originally Posted by Roland3 View Post
If it is the shaft that is running out, what is the fix? New crank shaft and bearings?
bent is probably a bad term for what's going on there, most likely nothing bent, just a little out of whack.

if the crank runout is bad: crank wheels could be tweaked (not parallel), or crank bearing could be bad, but you'd probably feel/hear that. or the stub is not straight in the crank wheel - you may want to check runout on the other side while you're at it - although the right side is a really short stub, and has a counterbalancer, so it maybe in spec....

it may not need new crank and bearings, it may just need trued. the specs are in the workshop manual.... it may have been apart at one time in it's life, and they tweaked the crank during reassembly.. or maybe the runout is within spec - you won't know till you measure it.

not that i wholeheartedly recommend it (never tried it...and could be hard on the bearings, depends on how much whacking is going on), but you could fix the runout with everything in situ - a rubber/plastic mallet, a dial indicator, and some carefully placed taps on the wheels or possibly stub could straighten it right out (pull cylinder and check crank wheels clearance spec to the cases and the rod - it's either the stub or the wheels that's out of whack..)... it's what your crank builder will do anyways (although out of the motor...).....

there is a tolerance spec for the pickup distance to flywheel - you're gonna need to measure that too..

or you could do nothing and hope for the best. it'll let you know when it's gonna come apart when it does come apart, it's gonna really start vibing, and ruin some bearings...

it's not expensive to tear it apart and fix it, just time consuming, and you're gonna need to replace some gaskets....a crank true on a single is cheap.
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Old 02-23-2014, 01:50 PM   #10
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Originally Posted by stainlesscycle View Post
bent is probably a bad term for what's going on there, most likely nothing bent, just a little out of whack.

if the crank runout is bad: crank wheels could be tweaked (not parallel), or crank bearing could be bad, but you'd probably feel/hear that. or the stub is not straight in the crank wheel - you may want to check runout on the other side while you're at it - although the right side is a really sort stub, and has a counterbalancer, so it maybe in spec....

it may not need new crank and bearings, it may just need trued. the specs are in the workshop manual.... it may have been apart at one time in it's life, and they tweaked the crank during reassembly.. or maybe the runout is within spec - you won't know till you measure it.

not that i wholeheartedly recommend it (never tried it...and could be hard on the bearings, depends on how much whacking is going on), but you could fix the runout with everything in situ - a rubber/plastic mallet, a dial indicator, and some carefully placed taps on the wheels or possibly stub could straighten it right out (pull cylinder and check crank wheels clearance spec to the cases and the rod - it's either the stub or the wheels that's out of whack..)... it's what your crank builder will do anyways (although out of the motor...).....

there is a tolerance spec for the pickup distance to flywheel - you're gonna need to measure that too..

or you could do nothing and hope for the best. it'll let you know when it's gonna come apart when it does come apart, it's gonna really start vibing, and ruin some bearings...

it's not expensive to tear it apart and fix it, just time consuming, and you're gonna need to replace some gaskets....a crank true on a single is cheap.
Great info thanks a lot. I'm pretty sure it's never been apart, 2100 miles and screws heads look new still. I would have never noticed if i didn't happen to see it. I was thinking of attempting to straighten in assembly but not by hitting it as that would be bad for the bearing but trying to bend or jack it straight. I have to get the mag puller tool this week and get it off to get a good look. I'll put a indicator on it. I have the clymer manual, the only spec for runout is .001. I see the parallels call outs and a size between the wheels. I am a toolmaker by trade so if I have to go this rout i can probably doo all of it myself.

About the gap for the pick up to flywheel, by eye the gap goes from about .020" at smallest to .060" at worst. It is closest at the magnet piece mounted on outside of wheel. I cant find a spec for this gap however

Also, even if the crank wheels were tweeted, wouldn't the bearing true up the end of the shaft sticking out that the magneto goes on?

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Old 02-23-2014, 07:38 PM   #11
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Quote:
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Also, even if the crank wheels were tweeted, wouldn't the bearing true up the end of the shaft sticking out that the magneto goes on?
not necessarily . the bearing could be cocked in the cases. the stub could be bent, that's really unlikely, unless it took a hit of some kind... and i'm pretty sure it's a c3 or looser bearing which gives enough play for the runout to be apparent.. i'm assuming that .001" runout is spec at the bearing, not at the end of the stub... you could spend a long time fiddling with it to get .001" runout at the end, while keeping everything else straight..
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Old 02-23-2014, 08:08 PM   #12
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It could be a key shearing or walking out of the slot. Remove the rotor and inspect. Don't wait for it to break.
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Old 02-23-2014, 08:16 PM   #13
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. i'm assuming that .001" runout is spec at the bearing, not at the end of the stub... you could spend a long time fiddling with it to get .001" runout at the end, while keeping everything else straight..
The book says That spec is for the runout/concentricity of both ends of crank shafts out of the assembly on v blocks. Thanks for the info good to know. I'm getting the mag puller tool this week to start there.
Thanks for the help

ETA; i see what what your saying, ya they show tge indicator on the diameter that mounts in bearing

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Old 02-24-2014, 06:14 PM   #14
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Well i ordered the tool online today then got impatient at work tonight and made the tool, hopefully it fits. 27mmx1 left hand with a 1/2-13" thread inside
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Old 02-24-2014, 07:20 PM   #15
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Nice job.
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