2016 rc390, 12,000 mi - "Bumpiness" issue

[philipviana]

This is probably not a problem specific to the rc390, but this is my first bike and I could use an opinion diagnosing a problem I've been having this past week:

Bike experiences irregular bumpiness / chunkiness on all road conditions at almost any speed. Can't tell if this problem has always been there or if I have just noticed it, but I am pretty sure this is a new occurance. Feels like I am going over bumps on the road even when conditions are smooth.

Pretty sure it's not engine related because the engine feels and sounds totally smooth at all revs in any gear.

Things I suspect:
- Thought it might be chain slap. Slightly tightened chain slack per the manual spec so that when I press the chain upwards towards the bottom of the swingarm, it does not contact the swingarm itself (but does contact the plastic protector underneath the swingarm). Bumpiness has not gone away.
- Put a new front tire (Metzeler M7RR) on 2 weeks ago, just a little bit before I noticed the bumpiness. I properly balanced it with wheel weights and the tire (virtually) did not move on the balancer stand. Wonder if either the new tire is a harder rubber than my previous Pirelli Rosso II which is somehow causing me to feel more of the road than before. I have it at 29psi per the manual.
-A mechanic at Moto Guild in SF commented that my front suspension felt stiff - I asked him if that was bad; he said no, that's how you want a little sport bike. Can't tell if the suspension feels any different now than when I first got it.
-Have had a lot of false neutrals between 2nd and 3rd lately, wondering if perhaps I have damaged part of the gearbox or if the dog teeth on some gears may have shaved some remnants into the case which might be jamming things up. TOTAL speculation, though, I have no proof that anything is wrong with the gearbox. I adjusted my shifter lever linkage so that it is consistent and even going both up and down gears and havent missed any shifts since then.

Any idea what I should do to diagnose the problem and fix it? Going to have a friend who rode it once before ride it again for me this weekend to see if he notices it, and going to ride his ninja to compare to see if his bike is bumpy. Could all be in my head...

Thanks.

 

[isaac_]

If the ride is bumpy, I would be looking at suspension. Front and rear. I don't know the service intervals for suspension but I would go to your local suspension guru and ask.

I am not inclined to think it's internal. Missed shifts could be as simple as adjusting your shift linkage. Maybe at worst, needing a new shift detent but I wouldn't think so right away.

The tire pressure should be per the manufacturer recommendation. Not the manual.


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[philipviana]

Thanks. I'll have to show it to someone who knows suspension.

I'm still curious about the gearbox though.

Here's a video i took of the bike on the rearstand, engine running, 3rd gear, not touching the throttle at all (and making sure the bike doesnt hop off the rearstand). Notice the chain spasms at certain moments, and the racket the bike makes. This only occurs when the wheel and chain are in motion, not when the engine is just idling at a standstill. Am I right to think this is worrisome, or is this just how all bikes behave on a rearstand? https://www.youtube.com/watch?v=dylOMN0uP3w

 

[Fasteddy]

So this started just after having front wheel off, I wonder if front axle might not me aligned / adjusted properly causing fork slides to bind?

 

[philipviana]

Good question. I reassembled axle / spacers / nut carefully w the help of a mechanic at moto guild, but I plan on going back there soon anyway so may as well pop it off and check it out.

 

[Fasteddy]

There is a certain sequence and order to assembling the front spindle, it's the same on my SuperDuke. You have to "compress the front forks a few times firmly" with the brake caliper loose and before tightening the two pinch bolts to center the axle.

Your jumping chain looks like sprocket / rear wheel not aligned, never trust the alignment marks on the axle, I use a laser, you can also use a string to confirm front and rear wheels are aligned as seen via Google.

 

[Cords]

Check you have no frozen chain links and that your wheel balance weights have not come off

 

[Maddog Reynolds]

Thanks. I'll have to show it to someone who knows suspension.

I'm still curious about the gearbox though.

Here's a video i took of the bike on the rearstand, engine running, 3rd gear, not touching the throttle at all (and making sure the bike doesnt hop off the rearstand). Notice the chain spasms at certain moments, and the racket the bike makes. This only occurs when the wheel and chain are in motion, not when the engine is just idling at a standstill. Am I right to think this is worrisome, or is this just how all bikes behave on a rearstand? https://www.youtube.com/watch?v=dylOMN0uP3w

The idle speed sounds the same as mine (slightly slower than some 390s I have heard) and mine jerks randomly when I run it in gear to lub the chain. I'd call that normal on half the bikes I have owned. Transmission snatch just happens, although it's worth checking for looseness in the rear sprocket and cush drive rubbers.

Increase the speed and the problem goes away, yes?

But I wouldn't expect that snatching in normal riding. I guess that's a different problem. What sort of revs are you using when you get the problem while riding? If it's less than 5,000 rpm, change down and try again

It's worth a bit of lateral thinking an example, I had an occasional feeling of knocking on mine over small bumps. I eventually traced it to the bracket that holds the side stand. Took out the bolts, cleaned and used Loctite 243 on them. Problem hasn't come back

 

[philipviana]

Took it to moto guild in SF and had a few more experienced riders put their hands on it. They noticed the problem right away. Forks have zero rebound. They seemed surprised I was riding it. I think the problem might have occurred gradually over time and I just noticed it around the time I replaced the front tire, and superstition caused me to notice it.

Going to open up the forks, replace the fluid and seals to see if that works out. Glad it's not in my head and that it's likely just an issue with the forks instead of something more nefarious like a gearbox issue.

Maddog Reynolds, thanks for the comparison to your chain, makes me feel better.

I think i noticed the bumpiness less during acceleration because the forks have less load during accel. Once I stabilize speed or decelerate I notice the bumpiness much more.

thx for the help all.

 

[Maddog Reynolds]

Mine popped a fork seal. Someone here in the forums (I forget who--old age is like that) has suggested that the factory specify slightly too much oil in the forks, which builds too much air pressure when the forks compress.

The answer is to lower the oil level a bit and perhaps use fork oil one grade thicker, if that is your taste . . .

 

[Gxmazz]

Hey

Im in san francisco. Happy to help

 

[Bonarj]

Hi @Philipviana how did the experts find the way ur rear wheel spins in relation to the bumpiness of the chain while on rear stand? Coz i have the same issue here and i hope its just normal. The chain is racking up and down from time to time while its turning. Its not consistent and smooth.

 

[philipviana]

Bonarj, showed it to a few other people at a shop and they all thought it looked fine. Normal for a motorcycle chain to do that when it's on a stand and the rear wheel is unloaded.