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Bob KellyIII · December 6th, 2022, 06:21 PM

Could that dramatic downshift and overrev have caused a key way to sheer ? is there a key on the altenator ? even almost sheering a key can go unknoticed sometimes
....
at first I thought a skirt of a piston parted and is now in the oil sump causing the imbalance but now I'm not so sure.
I am assuming the vibration changes it's tempo with the RPM right ? (clutch in or out) meaning it is directly related to the crank some how, main shaft in the transmition holds the clutch basket and one of the pieces of the basket could have separated. but sense he had the covers off and no visible damage that's out.... that would be easy to see.
.... so my guess is the lower compression piston did a no-no perhaps a skirt half is missing but the rings are still holding fairly good compression... that would be very odd
but it has happened before.
.... the bore scope is an great idea ! through the spark plug holes and up the filter cavity should show the culprit !....
....
Danno is the crank pressed together or a one piece cut crank ? if it's pressed together it's possible that the crank has slipped and twisted ! ( I had a xs650 yamaha that did that)...and it vibrated and rumbled alot.... it ran great but the rumble was from the crank gear moving closer and further away from the clutch basket (bent crank)
and yes it sped up and slowed down with the RPM
......
I'm betting on a piston skirt regardless !
....
Bob......

December 6th, 2022, 06:21 PM	#14
Bob KellyIII Retired motorcycle Mc. Name: Robert Location: Weed, California. Join Date: Jul 2021 Motorcycle(s): 2012 Kawasaki Ninja 250R, 2021 CSC TT250, 1977 Triumph Bonneville 750cc,2001 Honda XR650L. Posts: A lot.	Could that dramatic downshift and overrev have caused a key way to sheer ? is there a key on the altenator ? even almost sheering a key can go unknoticed sometimes .... at first I thought a skirt of a piston parted and is now in the oil sump causing the imbalance but now I'm not so sure. I am assuming the vibration changes it's tempo with the RPM right ? (clutch in or out) meaning it is directly related to the crank some how, main shaft in the transmition holds the clutch basket and one of the pieces of the basket could have separated. but sense he had the covers off and no visible damage that's out.... that would be easy to see. .... so my guess is the lower compression piston did a no-no perhaps a skirt half is missing but the rings are still holding fairly good compression... that would be very odd but it has happened before. .... the bore scope is an great idea ! through the spark plug holes and up the filter cavity should show the culprit !.... .... Danno is the crank pressed together or a one piece cut crank ? if it's pressed together it's possible that the crank has slipped and twisted ! ( I had a xs650 yamaha that did that)...and it vibrated and rumbled alot.... it ran great but the rumble was from the crank gear moving closer and further away from the clutch basket (bent crank) and yes it sped up and slowed down with the RPM ...... I'm betting on a piston skirt regardless ! .... Bob...... __________________________________________________ Its too late when you've gone too far !