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Post by tippo on Aug 12, 2013 18:07:31 GMT 1
Hi, just rebuilt my 250LC and am running it in at the moment. Took it up to 7k for the first time last night and the vibration was terrible. Bike rides Ok up to 6k and then starts to vibrate and gets progressively worse.
Anyone have any ideas what the problem may be?
Cheers
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artie
Thrash Merchant
Posts: 341
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Post by artie on Aug 12, 2013 18:13:54 GMT 1
Could be an out of balance crank  I was thinking the same thing mine gets smoother over 6000. |
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Post by cb250g5 on Aug 12, 2013 18:23:13 GMT 1
Start with the easy stuff. Are the engine mounting bolts tight? Are the exhausts free to move at the rear mounts? Tie bars tight, if fitted?
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Post by tippo on Aug 12, 2013 19:14:49 GMT 1
Cheers for the replies, looks like an engine strip to investigate further. Engine is running great, all bolts tight etc....
Thanks for the replies
Cheers
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Post by arrow on Aug 12, 2013 19:40:00 GMT 1
Check the sync. of the carbs, could be a dynamic imbalance.
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Post by seahorse83 on Aug 13, 2013 8:15:59 GMT 1
double check all engine mounts including torsion bars underneath and axles and swing arm are all tight. I had a similar problem with a Mito years ago, went over the bike three times, it had a terrible bone shaking vibration come in at about 5k.I pulled the engine to pieces no obvious problems found. Turned out to be the front engine mount was not bushed up, and had worn enough to shake the motor about a mill. Food for thought before you pull and re index crank
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Post by Delbert on Aug 13, 2013 21:37:24 GMT 1
Also check engine mount damping washers ,, exhaust rear mounts and that they are tight in the barrels , not wobbling about
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Post by simon5264 on Aug 13, 2013 22:17:36 GMT 1
Try revving past 7k and when vibration starts de clutch is it a drivetrain issue?
also is clutch plates stacked correctly? you could also de-clutch while free wheeling and see if you can play with the throtle and see if it is an engine rather than transmission problem.
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Post by tippo on Sept 21, 2014 7:43:54 GMT 1
Gents, should have posted this a long time ago. Problem solved when I had the crank rebuilt.
Thanks for the replies
Cheers
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Post by tippo on Sept 21, 2014 14:30:26 GMT 1
Crank was an unknown, I took a chance and it backfired.
I guess the crank was twisted.
Moral is to 'clock' the crank prior to fitment and to not cut corners.
Taking no chances with the 350 I'm building, crank is being rebuilt regardless.
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