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Old 02-25-2014, 01:40 PM   #1
Roland3 OP
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Question about crank stub runout on 350 thumper

I noticed the mag wobbleling when rotating by hand doing a valve adjustment. Pulled mag and crank stub is running out somewhere around .030" at the seal.
Its a 1997 xt350, 2100 miles, excellent shape. No sign if a accident, does no apear to ever have been taken apart. Not sure if it left factory this way or something happened, at this point it doesn't matter.
There is no unusual noise or sign of this, i happen to stumble upon it.
It seems to me this will certainly lead to crank failer in the very near future, maybe not i dont know. I have tried tapping on it with a block of wood and hammer a little to see i it moves, hasn't moved from what I can tell by eye. I will set a indicator on it to get a number of total runout and attempt tapping one more time but i dint think this will work.

Any thoughts, input or advice is apreciated.
I am a toolmaker by trade and am considering attempting to remove and repair/straighten crank and install new bearings myself. But I have never done that in depth of a engine job before
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Old 02-25-2014, 03:37 PM   #2
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.030" is a SHITLOAD. No way it has run like that since new. I'd guess she's suffered some trauma... like a sudden stop. Such as, sucking in water while wading, hydrolocking the engine, flywheel inertia could have tweeked the crank. Don't plan on running it that way, it needs dismantling. Sorry, dude.
As for straightening the crank, as a tool maker you CAN do it, but having someone who has done hundreds, has all the fixturing for pushing, pulling, pressing it into compliance is my recommendation. I use www.northerncrankshaft.com and have always had good results.
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Old 02-25-2014, 03:39 PM   #3
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+1 on the shitload. You will find bent parts inside.
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Old 02-25-2014, 03:55 PM   #4
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For reference the max runout spec, at the very end of the crank, for my 640 is .0016" - so I would concur with Concours about that being a shitload

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Old 02-25-2014, 05:02 PM   #5
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Sorry to hear this Roland.
As stated by some one else, you may have bent pieces inside... like the connecting rod.
After taking it apart and estimating repair, a used engine from a motorcycle breaker may be more attractive than repair of this one.
Or use the best of this low mileage engine in the used unit. Like the transmission and clutch.

One spec that comes to mind on crank run out is for the Twin Cam Harley(friend has one).
The spec used to be .003" but when Harley went to chain driven cams they increased it to max. .012", probably as a cost savings in cheap labor.
Some fellas that want to upgrade to gear drive for better valve definition must remove the crank to get it to the older/better .003" spec.

Please post pics in this thread of what you discover.

Good luck
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Old 02-25-2014, 05:46 PM   #6
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uhhhhhhhhhhhh the crank is pressed no? that means the cheeks are pressed on the shaft. the crank is trued during assembly. as above, I would guess it had a sudden stoppage causing one of the cheeks to slip. anybody that builds 2 strokes, snowmachine engines, racing 4 stroke bikes, etc, should be able to re-true. problem is the crank needs to come out of the case to do it. actually, you can do it yourself with a few of the right tools & some patience. v blocks and a dial indicator. you just hit the right spot with a big brass hammer & then check. a good wack or two in the right spot will do it.

edit.... I just looked at a pic... appears to be all press fit, no pinch bolts, etc. that probably means the cheeks (wheels) aren't concentric. on some other designs, especially tapers, there is also a tendency for the wheels to tip in or out so the cheek faces aren't parallel.... either condition will cause runout. I did a few with my lathe. chuck one end into a collet, dial the runout, mark the spot, remove crank from the lathe & hit the wheel.... repeat

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Old 02-25-2014, 06:42 PM   #7
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Quote:
Originally Posted by Beezer View Post
uhhhhhhhhhhhh the crank is pressed no? that means the cheeks are pressed on the shaft. the crank is trued during assembly. as above, I would guess it had a sudden stoppage causing one of the cheeks to slip. anybody that builds 2 strokes, snowmachine engines, racing 4 stroke bikes, etc, should be able to re-true. problem is the crank needs to come out of the case to do it. actually, you can do it yourself with a few of the right tools & some patience. v blocks and a dial indicator. you just hit the right spot with a big brass hammer & then check. a good wack or two in the right spot will do it.

edit.... I just looked at a pic... appears to be all press fit, no pinch bolts, etc. that probably means the cheeks (wheels) aren't concentric. on some other designs, especially tapers, there is also a tendency for the wheels to tip in or out so the cheek faces aren't parallel.... either condition will cause runout. I did a few with my lathe. chuck one end into a collet, dial the runout, mark the spot, remove crank from the lathe & hit the wheel.... repeat
Well, I guess i have a new project on my hands. Ya I'll get it apart and see if i can do anything with it. If not i have a reputable engine guy know engine guy in my area i just spoke with and he will take it if i cant get thru it.

eta; gues i didnt get such a good deal on the bike either. Seller will be hearing from me!
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Old 02-25-2014, 10:16 PM   #8
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Quote:
Originally Posted by Roland3 View Post
Well, I guess i have a new project on my hands. Ya I'll get it apart and see if i can do anything with it. If not i have a reputable engine guy know engine guy in my area i just spoke with and he will take it if i cant get thru it.

eta; gues i didnt get such a good deal on the bike either. Seller will be hearing from me!
IF it hydrauliced, the sudden stop may have bent the rod and caused the runout. The flywheel wouldn't want to stop as fast as the crank, and probably twisted a bit. As it twisted, it didn't stay centered. TDC on the crank may be different from any marks on the flywheel--which would be slightly advanced from the crank.
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Old 02-26-2014, 04:08 AM   #9
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Quote:
Originally Posted by Roland3 View Post
Well, I guess i have a new project on my hands. Ya I'll get it apart and see if i can do anything with it. If not i have a reputable engine guy know engine guy in my area i just spoke with and he will take it if i cant get thru it.

eta; gues i didnt get such a good deal on the bike either. Seller will be hearing from me!
Make sure it's an engine builder with 2-stroke expertise... (Yes folks, I know it's a 4-stroke) automotive machine shops are not equipped to do pressed crankshaft repairs.
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Old 02-26-2014, 04:59 AM   #10
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Make sure it's an engine builder with 2-stroke expertise... (Yes folks, I know it's a 4-stroke) automotive machine shops are not equipped to do pressed crankshaft repairs.
He is, and many years expierance. Just does snowmobile/atv/bike engines.
TDC lines up withh mark, bike runs fine you would never know it
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Old 02-26-2014, 08:39 AM   #11
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Look for "seaweed" (bits of grass/mud) in the airbox, always present on ATV's driven in the water... there may be some in that bike. Just may be a clue..
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Old 03-01-2014, 02:07 PM   #12
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Well its completly torn down. I haven't had a chance to take it to work and set it up and indicate it but I can see it definatly must have slipped on the pin. If I put a straight edge on the outer diameter if the thicker wheel ther is about .050 difference from one side to tge other. I'm just going to take it to the engine guy from here.

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Old 03-02-2014, 09:41 PM   #13
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Was it running ok before this?
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Old 03-03-2014, 03:47 PM   #14
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Yes it ran fine, would have never known unless I saw the run out. It appears the crank spun the wheels on the crank pin. The wheels have a heat spot around the pin hole where it got hot. The rod play is in spec, and rod bearing seems fine, so I'm following the clymer manuals method for truing it up. Brass hammer the wheel until the centers are within .001. It's out about .060"! I cant believe it ran this way this long, the main bearings dont even look bad but i ordered new ones
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Old 03-05-2014, 07:50 AM   #15
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Update: just incase anyone doing a similar job wants to reference this, i'll use this thread as a documentation of what it did.

the crank rebuild specialist looked over what i did and said its good, .0015 total indicator runout is more than acceptable. only thing he said he would do, which i will is tig weld the crank pin, he does this on cranks that have slipped the pin or are prone to slipping. He uses a special filler rod that will resist cracking, something similar to a 300 series stainless.
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