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Chasing a vibration problem


Blowtie316

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I have been chasing a vibration for a while now on my banshee.  When I bought it I didn't really notice it, was my first banshee, but upon riding other banshees I figured out mine was pretty bad.  I removed the stator cover and flywheel and checked crank rounout and found it was .008", pulled it further apart and found a loose rod bearing. So I called up FAST and they hooked me up with a welded 4 mil hot rods crank, new pistons and a spacer plate (due to not having time for the proper port job).  Runout on new crank was around .001".  Put it all together and it vibrates the same.

 

I did some searching and found that the motor mounts are supposed to have 2 dampers, so I bought new ones and installed them per the book, also torqued mounts per manual.  No change.

 

The flywheel had some idiot marks so I bought a mint used one off of ebay.  It looks perfect, same as old one except it doesn't have what looks to be 8 balancing holes drilled into it from the outside radius.  Are drilled holes normal? Anyway, I tried the mint one and it didn't help.

 

I installed the clutch clocked the way the manual calls it out, am I missing something else?  Where should I look from here?

 

Thanks for any help.

Edited by Blowtie316
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what kinda handlebars do you have vs other bikes? fixing a vibration on a banshee is like trying to tighten up a vagina on a prostitute. aint gonna happen.they viberate. higher compression, pipe choice etc can also amplify it. pipe hanger choice can also increase vibration.

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For comparisons, I have ridden or felt 3 other banshees here local, one high compression trinity ported t5 pipes, one stock with lrd pipes, and one other ported with 18c heads and t5s.  Mine has easily 2-3 times as much vibration as these others.

 

Also, my other ride is a big bore (330) trx250r, and it doesn't vibrate as much as this banshee. Should I take another look at the clutch?

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Could have a detonation issue

Could be a tuning issue and it isn't running smoothly.

Hard to tell over the computer.

 

Yeah I'm just looking for ideas.  It has 21cc domes, cranked 165-170 compression, squish was right around .045.  I have tried 110 and 91 pump gas with no change.  It runs good, sounds clean, doesn't bog or miss, idles fine, etc.  27.5 pilot and 300 main.

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I'm just putting this out there because I just went to the Hotrods L/R 4mil from a shortrod 4mil, and I noticed a big change in the amount of vibration.

I just figured its a balance issue with the crank, longer rods, and the pistons. I know for sure the crank was never balanced with the pistons I got. Can't say for sure if they even balance the crank and rod assembly.

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Not really anthing else done to it.

 

4 mil long rod hot rods crank, welded

65.5 pistons, no porting

Spacer plate

21cc domes-coolhead

170 compression

.045 squish

Stock carbs with 2-1 k&n type filter

CT racing/power pros midrange pipes

+4 timing

 

Engine runs quiet, no rattles or pinging.

Edited by Blowtie316
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I wonder if the crank is not trued up? Did Jeff say he checked the trueness of the crank?

 

I didn't talk to Jeff, but Cody said they check them all, and won't send them out if they are not within spec which I think was .0015 or .002.  I checked the stator side of this one only and it was real close to .001, maybe just a little over like .0012 or something.

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Is this felt at idle, or when riding? You're sure it's the motor, not loose hubs, loose chassis bearings, junk exhaust hangers, sloppy axle, etc?

 

It is most noticeable Idling and revving, but it does it during riding too, probably just masked by all the other bumps and vibes.

 

I think Atomic Monkey may be right, I have read that the stock 350 cranks are balanced for 250 pistons and it gets worse with longer strokes, longer rods, and bigger pistons.  I'll call FAST and see what they say.

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