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Old August 24th, 2022, 04:44 PM   #1
blackiredi
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Bad vibes

I have caught the ninjette bug and picked up a 2nd ninja 250R. Its a race prepped 2010 with a "fresh" motor with one race day on it. When I got it it ran real nice and smooth.

Took it to The Ridge in WA. Down shifted too far going into the carousel and spun it up real hard. At that moment it started to have a vibration. Not super terrible but enough to numb my hands after a while. It is present all the time, in whatever gear, stationary or not- but is strongest under load on the gas low in the rev range.

My guess is that I threw off the timing somehow, but really have no idea.

Any thoughts on where to start or similar experience is appreciated.

Thanks much.
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Old August 24th, 2022, 06:16 PM   #2
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Do compression test...
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Old August 24th, 2022, 06:59 PM   #3
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Do compression test...
Damn..... okay.
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Old October 10th, 2022, 06:35 PM   #4
blackiredi
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Do compression test...
Finally got to this.

210psi on left, 185 on right.

my understanding is that you subtract 14.7psi for atmospheric pressure? So...

195.3psi left and 170.3psi on right.

The right one seems a little low. Checking valves is next step yes?
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Old October 10th, 2022, 10:50 PM   #5
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Those compression results doesn't explain vibration levels.

Yes, do valve-clearance measurements...
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Old October 11th, 2022, 07:43 AM   #6
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Originally Posted by blackiredi View Post
my understanding is that you subtract 14.7psi for atmospheric pressure?
No, pressures specified in manuals do not have 14.7 subtracted from them. They are gauge pressure.

I'm trying to think of what could have disrupted the engine balance when it was over-revved. Is everything OK under the alternator cover?

Last futzed with by Triple Jim; October 11th, 2022 at 10:12 AM.
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Old October 11th, 2022, 04:04 PM   #7
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No, pressures specified in manuals do not have 14.7 subtracted from them. They are gauge pressure.

I'm trying to think of what could have disrupted the engine balance when it was over-revved. Is everything OK under the alternator cover?
What do you mean by ok? Is there something specific I should look for? Could timing being off throw off only one cylinder? Seems unlikely......
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Old October 11th, 2022, 05:05 PM   #8
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What do you mean by ok? Is there something specific I should look for? Could timing being off throw off only one cylinder? Seems unlikely......
I don't know of anything specific to tell you to look for, but if the overrev caused something to fly off the alternator rotor, for example, then it could be out of balance. I'm suggesting that it might be worth taking a look under there and just see if things look normal, without metal parts embedded in the cover, for example.

I don't know why the timing would have changed due to an overrev, and I don't know why valve adjustment would change either, but who knows at this point?

Now if a chunk of a piston skirt came off, that would cause an imbalance. I guess it would take removing the oil pan to check for that unless there were a way to get a small video camera (borescope) in the crankcase somehow.
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Old October 11th, 2022, 07:05 PM   #9
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That all makes sense. Im going to start with valves since that requires removing a ton of stuff anyway and then give everything a look see once its open. It's a "fresh" motor. People who have raced against it (previous owner raced it) say "that bike has a good motor" so hopefully it's something easy to spot. I would just do the top end but I don't want to lose the "good motor" magic unless I have to.
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Old October 20th, 2022, 07:44 PM   #10
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Quote:
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No, pressures specified in manuals do not have 14.7 subtracted from them. They are gauge pressure.

I'm trying to think of what could have disrupted the engine balance when it was over-revved. Is everything OK under the alternator cover?
Finally got into the alternator cover. Everything looks good. In fact it looks like it has a non OEM flywheel. I know this engine was put together to race so that's not surprising. Also did the valves. They were all on the tight end- this creates more top end yes- so that makes sense too. Now have the EX at .28 and IN between .18 and .20.

Water pump also looks good. Putting it back together and will check vibration levels. Going to check motor mount torques, etc as I do this.
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Old October 24th, 2022, 09:29 PM   #11
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So compression is the same (-5psi) with the valves adjusted. #1 205psi #2 180psi. Could this compression imbalance cause the vibrations? Could the imbalance be related to carb sync somehow?
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Old October 25th, 2022, 12:07 AM   #12
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nah, those compression numbers are good. Difference is around 10% and won't cause you that dramatic of vibration.

This point, I'd get USB borescope and take look in cylinders from spark-plug hole. Can also look at bottom of pistons with sidecases off.
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Old October 25th, 2022, 04:15 PM   #13
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Quote:
Originally Posted by DannoXYZ View Post
nah, those compression numbers are good. Difference is around 10% and won't cause you that dramatic of vibration.

This point, I'd get USB borescope and take look in cylinders from spark-plug hole. Can also look at bottom of pistons with sidecases off.
OK. Am I looking for broken bits or something else? And, what is the maximum out of balance in the compression department? Thanks.
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Old December 6th, 2022, 06:21 PM   #14
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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 !
....
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Old December 18th, 2022, 11:40 PM   #15
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You won't find your answer here, you need to just dig in deep. Might never find it because it might just be a bent part, like a bent connecting rod or crank. At that point you've replaced the engine or are already rebuilding, as measurements can't really be taken with the part installed
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Old December 21st, 2022, 08:16 PM   #16
blackiredi
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Chased down as much as I could without taking the engine apart. No clue. My racer buddy rode it and says just ride it. I'm going to just ride it. Maybe it will blow up bad enough I'll have to dig all the way in. Thanks for the help.
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