Bad Vibrations please help
 

my bikes still vibrating to the point where i dont like going over 50mph for more than short bursts. the engine pulls strongly but my ankles and shins can't take the vibrations. that and my mechanically sympathetic mind

I've had a couple of old XT's & an XR before and yes they do vibrate but this is excessive.

All engine mounts & swing arm pivot are torqued up correctly. and I've checked all nuts and bolts are tight like crank balance shaft and flywheel/magneto. the Tank is sat on its rubbers properly.

the bikes fine up to about 45mph then it starts the vibes. pull the clutch in and coast and vibes go.

The bike - a 34L, has done 54,000 indicated miles although who knows what the true figure is.

the engine was noisy but since the top end rebuild it sounds really sweet.

could it be the bottom end even though it sounds OK?

what can I check??????

please help as the vibes are really stopping me enjoying the bike.


cheers

has it always vibrated or just started recently ?

If you're convinced the motor's fine then how about the running gear - has a balance weight popped off a wheel, or the chain developed a tight spot, for example?

i think if a weight had came off the wheel it would still vibrate with clutch in.
i was thinking maybe if its always vibrated there could be a tooth out on the balance shaft gear ?

what gear are you in it could be in the gearbox are the same vibes there at high revs in lower gears :confused1:

DOH! I should've read the post more closely - apologies - are there heavy vibes (blimey, i sound like a hippy...) up to the 45mph threshold? Wouldn't a balancer problem be at all engine speeds... this is a real head-scratcher :confused1:

yes, it does it in all gears:(

do you mean the balance shaft gear could be a tooth out? how do you check that?

You will have to take the clutch cover off and there is a punch mark on the balance cog it has to line up with the punch mark on the cog it's connected to

I would also of thought if it was that it would vibrate in neutral if you revved it as well but I could be wrong?

well, i've revved it when coasting with the clutch in and the vibes come with the revs.

now that puts it into the realm of balance shaft problem

Have you checked the engine oil for metal shavings? What happens if you rev the bike in neutral? Could the clutch basket be somehow loose or out of balance?


I know this is not what you want to hear, but I think you should open up the engine now. This sounds like something is taking a hammering, I think you should not ride the bike like this. I am not an expert in your bike, but my advice is to check the balance shaft as wolfzero said, and bearings in general, but also check if the clutch basket is wobbling, or if the flywheel is wobbling.

thanks for all the help on this,

balance shaft teeth line up OK

http://lh5.ggpht.com/_aJzSBN66Sc0/Sk...0/P4280230.JPG

but I do have a bit of movement on the clutch housing, presume there shouldn't be any play?
http://lh4.ggpht.com/_aJzSBN66Sc0/Sk...h%20basket.JPG

whats the best way (no special tools) to hold the clutch so that i can undo the nut and investigate

thanks
andy

I tried to take mine off without the proper tool and it cost me dear :( very easy to smash outer basket,windy gun is best option without clutch holding tool IMO

“A little” movement in the clutch housing is normal.

To loosen the clutch hub nut I usually put a bike in fifth gear and then put the rear brake stuff back on. Then I get someone to step on the brake, and then loosen the nut. If you are alone, you also can put a stick through the wheel and then rotate the wheel until the stick touches the swing arm… and then loosen the nut.. be very careful though and do not force it, if the nut is really stuck.

Sometimes though I have had to use some airtools…. Sometimes the clutch hub nut is really stuck and you can do damage if you are not extra careful..

Can you find some play in the balance shaft bearings?

I tried to take mine off without the proper tool and it cost me dear :( very easy to smash outer basket,windy gun is best option without clutch holding tool IMO

ahh the 'in gear with the back brake on' scenario.(much easier with a drum brake)
The nut wasn't particuarly tight. but wasn't loose.
http://lh6.ggpht.com/_aJzSBN66Sc0/Sk...0/P4290240.JPG

you say a little movement of clutch basket is OK, it is only a small bit of play and nothing looks worn. there is a slight bit of play from the shaft.

http://lh6.ggpht.com/_aJzSBN66Sc0/Sk...0/P4290245.JPG


http://lh5.ggpht.com/_aJzSBN66Sc0/Sk...0/P4290260.JPG

the idle gear for the kickstart is a very sloppy fit on its shaft, is that normal?
it looks OK though?
http://lh4.ggpht.com/_aJzSBN66Sc0/Sk...0/P4290267.JPG

http://lh3.ggpht.com/_aJzSBN66Sc0/Sk...0/P4290243.JPG

whilst its all open, what should I be checking and how?

cheers for all the help so far

.

...bump........

while you have it stripped down pop the balance shaft and crank timing gears off and check for any woodruff key damage especialy on the crank shaft it will also allow you to inspect the bearings for signs of damage and wear.

Its pretty bad if you can SEE damage on a bearing. You would most likely have heard it.

I remember my kickstart idle gear being a bit sloppy also so I guess it is normal?

Vando :innocent:

with those timing gears in place it would mask some of the normal signs of bearing wear and wont allow to check movement as the gears being meshed together would restrict the ability to check movement/play properly.

the posted problem is vibration so "noise" would not have been so obvious plus pitting. over heating and other damage to the bearing and its housing may not show as noises but mis alignment would give bad vibes.

i have worked on large electric motors and generators where bearings run quiet but vibrate like hell when the housings wear the xt has cast iron bearing housings cast into the alloy crank cases so should not suffer from mis alignment the main reason i said to visually inspect was to look at the woodruff key as mine sheared off ruining the engine not to visually inspect the bearings.

my two pence worth.it's a pain i know but i'd pull it apart and have a look.
you mentioned it had done at least 54000 miles, thats a fair bit, and then it's had a top end overhaul.
so you've got a nice full compresion top end running on a 54000 mile bottom end, not really surprising it vibrates!

gear wheels off and the keys are OK.

I saw this and thought they were cracks, but just imperfections in casting I think?
http://lh3.ggpht.com/_aJzSBN66Sc0/Sk...mera%20233.JPG

http://lh5.ggpht.com/_aJzSBN66Sc0/Sk...mera%20235.JPG

bearing on the balance shaft has neglible play, but on the crank there is a bit of play. the movement isn't the bearing, it is clearance between the crank and the inner race, is that normal? you can see the gap with the difference in these two pics
http://lh4.ggpht.com/_aJzSBN66Sc0/Sk...mera%20237.JPG

http://lh6.ggpht.com/_aJzSBN66Sc0/Sk...mera%20238.JPG


cheers

yeh those casting marks are pretty normal but the inner race should be a snug fit on the crank if it has too much play the crank can rotate in the inner race wearing the crank shaft after all thats what the bearings are for, any play/ movement will be exaggerated the faster the motor spins how much movement is there can you make it rattle?

i can get it to just about do an audible knock knock, and the bearing race spins freely on the crank, :(

thats not sounding to good i'm afraid it looks like it needs to have a bit more overhaul work :( hopefully just needs the bearings replacing.

Oh dear. I'd agree with Wolfzero.
If you can rotate the inner race on the shaft of the crank, that's bad, and is pretty certainly the cause of the vibration.

These two items should be an interference fit.

It's possible, if not highly likely, that the bearing has seized at some point, forcing the crankshaft to rotate inside the inner race. This will seriously damage either the inner surface of the inner race (repairable with a new bearing), or more seriously the outer surface of the crankshaft.

Depending what repair facilities/workshops you have access to, that might be repairable by metal-spraying the crankshaft and grinding to the correct diameter, or, exceptionally and maybe temporarily, finding a bearing with slightly smaller inside diameter and grinding the crankshaft to be an interference fit.
Either way, that bearing will certainly need repacing.

But returning to how you described the vibration, (it seemed pretty awful) other damage could have been done.
For instance, the outer race should be an interference fit in the crankcase, but may no longer be so. That will need fixing.
And in the extreme, the whole crank should be inspected carefully incase there is other unseen damage.

These engines seem to have a reputation for being pretty strong, so I hope it isn't as bad as this, but it could be.

If the new bearing isn't an interference fit on the crank, a cheap fix is to do multiple (50 or more)small (depending on the clearance) dot punch indentations around the crank to give a knurled effect, therefore creating an interference fit between crank & bearing inner race. And possibly some loctite during assembly for insurance. I'm not sure if these cranks are nitrided, if so this may not be possible due to the hardness of the crank.
Bob

Sorry to see this. Not good.


The bearing is probably made of harder steel than the crankshaft. It is more likely that the crankshaft suffered if the bearing temporary seized, causing the crankshaft to rotate in the inner bearing race. Sorry.

I would not rule out completely the chance of something else being responsible for the vibrations. Obviously you need to address this problem, but please take a good look at everything else to be sure.

Weird though… I would have expected the crankshaft to have welded itself to the bearing race by now. I have twice seen similar things, in one case the inner bearing race of a wheel bearing was welded to the axle after a temporary bearing seizure, and in the other case a primary sprocket had welded itself on a crankshaft after the key had snapped. Not the main bearings on a crankshaft in either case though. I remember that several years ago some of the GASGAS two-stroke enduro models had a flaw, the crankshafts could slide side-to-side in the main bearings, or at least one of them. I don’t think there was any noticeable play, but at least some of the flawed engines did run fine for a long time…. Guess the friction in the bearing itself was less than the friction between the crankshaft and inner bearing races given the pressure put on the crankshaft in a running engine...

yes, its not good is it

I need to take a look at the other side, I got the alternator rotor nut off (bastard tight as it should be) now all I need is a suitable puller, can anyone recomend where I can get one, or dimensions to make one

I'm in two minds what to do about the main bearings on the crank, obviously a full bottom end rebuild is needed but as we are in the middle of summer I may try a short term fix - get some very strong thread lock and squirt between the inner race and crank.
If glueing the bearing to the crank works then I'll leave the rebuild till the winter. it should also diagnose if this is where the vibration is coming from. it could be that the motor gets to certain revs then the crank starts oscillating in the bearing.

cheers for all the help so far from everyone

undo the 3 allen head bolts that hold it to the starter clutch and use them in the 3 threaded holes in the flywheel you might need to rotate the starter clutch so there is something behind all 3 of them threaded holes then tighten those bolts staggering the sequence so you apply even pressure put the main nut on the end of the crank a few threads and give it a tap when you have quite a bit of tension on those 3 bolts it should shock it free.

my bikes kick only....so no sprag clutch...can I still wind some M8 bolts through the 3 holes, what will they press against?

cheers

my bad thought you had e/start and kick :oops2:
post a pic and ill work it out from that :thumbup1:

looks like something like this is needed

http://lh5.ggpht.com/_aJzSBN66Sc0/Sl...800/001499.gif,
actually I think I have something like that buried somewhere....

i meant post a pic of your engine :innocent: :rofl:

i got a puller same as that from machine mart tho :cool4:

flywheel puller
 

I found my puller and have it on the flywheel, I've done it up 'kin tight but nothings moving.

any tips? I've tried a bit of heat, but don't want to resort to hammer.

cheers

as long as you protect the threads using a hammer is not a problem it probably just needs a whack to shock it free if your puller is similar to the one in the pic give it some torque and then give that center bolt a big 'kin whack i'd put the end nut loose on the crank so when it comes free it doesn't come flying off.

pulling flywheel off
 

I tried more heat whilst under tension from the puller and it flew off with a bang. -I didn't leave the nut on....doh

the bearing that side is seems OK, I'm gonna use the thread lock to hold the crank in the bearing on the other side and see what its like.

what about the big end - can it be checked without taking top end off.

cheers

only if you have a dial gauge with an extension rod but you might be able to knock something up with an old spark plug a rod and a ruler to measure any backlash.