2012 Ninja 250R (EX250JB) Engine Harmonic

[SLOWn60]

2012 Ninja 250R (EX250JB)
Mid RPM (most notable): engine harmonic.

Anyone familiar with a twin engine boat or plane will know the harmonic vibration I’m referring to when the engines are not in sync. My 250 has an eerily similar harmonic: low frequency at lower rpm (5000; waaaawaaaawaaaa) with a steadily increasing frequency at steadily increasing rpms (9000; wawawawa).
Not speed related; its rpm related

Any suggestions what might be causing this and where to begin adjustments?

[csmith12]

Welcome Bill!

Could be
Dirty carbs
Carbs out of sync
Air filter
Debris in airbox
Debris in snorkel area

Believe it or not
Chain needs replaced or cleaned/lubed
Very messed up tires
Brake drag
Clutch out of adjustment

In my experience, patterned sounds are almost always drivetrain or rolling chassis related.

[SLOWn60]

Thanks Chris
The only thing not done on your list is the carb sync. I'll give that a shot and let you know how that works out.
Cheers

[jkv45]

Originally Posted by SLOWn60

Thanks Chris
The only thing not done on your list is the carb sync. I'll give that a shot and let you know how that works out.
Cheers

That would be where I would look. Seems like it could cause that type of thing. The smaller the throttle opening the more critical I would expect perfect sync to be.

My son noticed something similar the other day when out riding with a buddy on a pair of Ninja 250s cruising at the same RPMs.

[dcj13]

Originally Posted by SLOWn60

All these iron rings pumping up their tires and not one of them has addressed my technical issue! (I only have 3 posts; it's not hard to find).

Any suggestions what might be causing this and where to begin adjustments?

Hi, Bill! Welcome!

The cause of the apparent harmonic resonance are things rotating and/or moving up and down. That list Kentucky Chris put together looks comprehensive, although I can’t imagine how synchronizing the carbs would have much of an effect. But, hey, if it works…

You could acquire several 3-axis accelerometers and multi-input data logging device, glue the accelerometers at various points on the bike, run the engine at various RPMs and in different gears while searching audibly and tactilely for the harmonic resonance you’re interested in. Then look at the accelerometer data to see if there’s any correlation(s). You might have to move the accelerometers around and perform this exercise several times.

But then what will you do about it? Disassemble the engine and remove material from the pistons and connecting rods so they have identical weights and 3-axis mass moments of inertia? Put the con rods in a Tobin-Arp machine and make sure the big- and small-end holes are dead-on perfectly aligned and same distance apart? Have the clutch and flywheel dynamically balanced? And then there’s the transmission…

Another strategy would be to put speakers in your helmet and wire them to an mp3 player. Turn the volume up to drown out the wa-wa sensation.

Seriously, you might try tightening and/or loosening your final-drive chain slightly and see if the resonance gets better or worse.

These are inexpensive, entry-level bikes. To some extent, “They all do that.”

[csmith12]

^^^ true dat on the "they just do that"

Check the torque of the engine mount bolts if you haven't already.

[dcj13]

Originally Posted by csmith12

Check the torque of the engine mount bolts if you haven't already.

Good idea, too!

My pre-gen Ninjette had a wa-wa resonance. Thought it was the chain, but no...

[Motofool]

Originally Posted by SLOWn60

......... Any suggestions what might be causing this and where to begin adjustments?

I would verify the torque of the (3) bolts that anchor the engine to the frame.

[SLOWn60]

Thanks all!
That's what I thought the answers might be: generally a common harmonic with no go to fix.
The bike is cooling as I type: I did a carb sync; nice & even at idle (finicky to get there though!) but the right carb is consistently dominant cracking open and holding open the throttle until just past 5000 rpm going by the bike tach and then the vacuum drops to close to even.

[SLOWn60]

Originally Posted by Motofool

I would verify the torque of the (3) bolts that anchor the engine to the frame.

I'll try that! I had to use the ready rod bolts that came with the no cut sliders and there's no doubt they are not quite as robust as the stock engine mounting bolts. I may seek out some proper length grade 8 bolts that will have the tighter fit tolerance than the rod!

[csmith12]

Originally Posted by SLOWn60

the right carb is consistently dominant cracking open and holding open the throttle until just past 5000 rpm going by the bike tach and then the vacuum drops to close to even.

Both my 2fiddys do this. I have played with it a bit, and gave up. No harm, no foul.

[Motofool]

Originally Posted by SLOWn60

I'll try that! I had to use the ready rod bolts that came with the no cut sliders and there's no doubt they are not quite as robust as the stock engine mounting bolts. I may seek out some proper length grade 8 bolts that will have the tighter fit tolerance than the rod!

Any update?

[SLOWn60]

Lol! I forgot about it!
But I haven't been on the road with it since the carb sync. I've enjoyed two track days since the sync but there's no steady throttle or rpm on the track! I certainly didn't notice it while on the track. I'll have it back on the street later this week so whether it's still there or solved should be known then!
To be continued!

[csmith12]

Well then... if it didn't do it at the track, then try a different road surface and then go back to the road where you noticed the resonance. Fact is, certain tires on certain surfaces are just that way.

Lastly, get the rear in the air and get it up to the same rpm and gear where the resonance occurs and see. If not, check your top and lower rear shock bolts, bones and other bolts in that area.

[SLOWn60]

So....
I sync'd the carbs, rode hard on 2 track days (one with rain tires, one with DOT's) and the last 4 days riding on the street including 8 stretches of steady highway droning and 20 minutes on the track stand; no signs of the harmonic! So no answer to the riddle except one of the changes made must have been the source! Keeping in mind the harmonic was RPM dependent, not speed or gear selection: I don't have a clue as to the cause! Lol!
To the best of my limited carb knowledge; syncing the carbs affects low RPM, not midrange.
Thanks for everyone's input! I'll let you know if it reoccurs or if I solve the mystery!

[dcj13]

Cool!

[xXecuterXx2]

Nice!! i wonder if the correct word is "Sunk" the carbs, no, that doesn't sound right at all, hmm guess "sync'd" will have to do...

[greg737]

The EX250's engine is a pretty big compromise.

On the plus side: the EX250's parallel twin, with its 180 degree crankshaft architecture, is the most compact, lightest weight and highest revving 2 cylinder engine you can build.

On the bad side: the 180 degree crankshaft makes the EX250 a "big-bang" engine. The two power pulses occur only 180 degrees apart then there's nothing for the remaining 540 degrees of crankshaft rotation.

This big-bang firing order subjects the entire motorcycle to a whole lot of vibration (compared to other, smoother engines like inline 4 cylinder engines). That's why, for example, the EX250's engine mounting bolts have a habit of loosening up. Other fasteners on the bike are similarly affected, like the fairing fasteners.

Once a fastener or bolt somewhere on the bike loosens to anything less than the manufacturer's torque specification you can end up with a resonance.

[xXecuterXx2]

Originally Posted by greg737

The EX250's engine is a pretty big compromise.

On the plus side: the EX250's parallel twin, with its 180 degree crankshaft architecture, is the most compact, lightest weight and highest revving 2 cylinder engine you can build.

On the bad side: the 180 degree crankshaft makes the EX250 a "big-bang" engine. The two power pulses occur only 180 degrees apart then there's nothing for the remaining 540 degrees of crankshaft rotation.

This big-bang firing order subjects the entire motorcycle to a whole lot of vibration (compared to other, smoother engines like inline 4 cylinder engines). That's why, for example, the EX250's engine mounting bolts have a habit of loosening up. Other fasteners on the bike are similarly affected, like the fairing fasteners.

Once a fastener or bolt somewhere on the bike loosens to anything less than the manufacturer's torque specification you can end up with a resonance.

Dude, i didn't even know that, thanks for the lesson, I'm gonna go spend hours learning more about my engine, i bet it'll save my butt one day

[greg737]

Originally Posted by xXecuterXx2

Dude, i didn't even know that, thanks for the lesson, I'm gonna go spend hours learning more about my engine, i bet it'll save my butt one day

Know your onion.

[xXecuterXx2]

They make me cry when i open them...so does my engine