RPM-related vibration

I have a 87 700. When I picked it up a couple of years ago it had ~18k on the odo. I now have ~45k. The bike runs fine, I do all the oil changes and chain maintenance, it has fairly new (less than 2K) sprockets and chain. I also adjusted the valves a while back.

To my issue:

I have a vibration somewhere. This is fairly new and doesn't seem final-drive related. I notice when I start it up cold it seems to vibrate a little more than it used to (just looking at things like my gloves sitting on the tank, no real science here). Also, when riding, especially in the 4k to 5k rpm range, there is almost a growl. I can't imagine it's a bearing issue because if it was I think the engine would have grenaded by now. Could this be valve-clearance related? Bad plugs? Any ideas? I'm very mechanically adept (pulled the carb assembly when I bought the bike, rebuilt everything, bench tested and installed and it ran perfect) but I'm not great at diagnosing this bike.

Thanks in advance

 

There are rare occasions that the springs on the split cam gear fail and make rpm related noise and vibration.

 

Vibrations can also be related to carb synchronisation, or spark issue.

 

All right. I think I'll take some time in the next week or so to pull the plugs and check them and make sure all my coil connections are tight. As for the split cam gear spring, what's the result of just letting this go? I can't see tearing down the engine unless 1. I know it's that for sure and/or 2. It could cause some serious additional damage.

 

The risk is chunks of spring or other hardware going somewhere bad. And it's not a tear down to verify.

 

So, finally getting back to this. My house got flooded recently and that has been a priority.

I have replaced my chain and counter-shaft sprocket. It almost seems like that helps, but it sometimes eases a bit. Overall, the vibration is still there, most of the time, and really bad a the 4k-4.k mark. What is involved to check the split cam gear spring?

Also, I will be checking vacuum lines this weekend, likely removing the CA smog canister. Seems like this could be an issue, and I'm trying to chase stuff down.

 

OK, I went through the entire VFR shop manual and I cannot find anything related to a split cam gear spring. The part is not listed on any parts fische systems I can find either, or listed on any site, nor does it show up on any google search. This is an 87, with cam gears, not chain, does that make a difference?

 

http://www.whitedogbikes.com/images/blog-img/vfr750-80813/cam/vfr750-cams-re-600x378.jpg
Here you can see the split cam gears. The thin side is spring loaded to eliminate gear lash and reduce noise. 86 and 87 have the same set up.

http://i.ebayimg.com/images/i/361638134167-0-1/s-l1000.jpg
https://i.ebayimg.com/thumbs/images/g/dIIAAOSwU-pXvfTS/s-l225.jpg

They are non-serviceable, that's why there's no mention of them in the service manual or individual parts on the fische.

 

So do I have to order a new split cam gear (set)? Or is there a DIY fix that someone has come up with?

 

They are part of the cams and long discontinued. And do you even know that that is your problem? People have disassembled them and removed the split gears and springs for racing. If it were me and it was my problem, I would probably patiently wait for the right one(s) on ebay.

I will say that every one of my 86 VFRs and my 2 buddies 86 VFRs all have a slightly different feel and sound. One my my friends has a pretty good sound coming from the front bank when I am over the gas tank, but disappears if I am off to the side a bit. Nothing out of the ordinary when he was in checking the valves. My track bike build is a little louder (noisier) than my other 3 and everything was perfect when I went through it.

 

Thanks for that Captain. In fact, I do NOT know that this is the issue. It's just something that was brought up by you and a buddy at work who used to work on these bikes. I am still planning on changing some other stuff up first: remove vacuum canister system and new plugs.
Also, I did find something last night. At work, while taking off my motorcycle cover, I heard the sound of something loose. Turned out to be the right-side chain adjustment plate. When I got home I noticed that there was a spacing difference from right to left. I decided to loosen everything up to re-adjust it correctly. Everything went well until I tried to tighten up the axle nut. Despite using a torque wrench, even when the nut was tight enough, it was easy to spin the axle bolt from the left side using a ratchet. I pulled everything apart and found what I expected, the nut was bottoming out on the inside end of the axle-bolt threads. I consulted the manual to make sure there wasn't some sort of shim/washer I was missing. There wasn't so I knew there had to be something else wrong. Turns out the right-side bearing is super tight, almost seized. It even looks uneven but I haven't pulled it yet to check. It's possible that I compressed the bearing one of the times I did NOT use the torque wrench and probably over tightened the nut.
When I started thinking about it, things started clicking. When I changed the front sprocket and chain a few weeks ago, it seemed the vibration got better for a while, then it returned. This could be because after replacing the wheel last time the axle was straight, causing less cross-chaining. I'm just reaching here, with no mechanical facts, but the rpm-related vibration could be from the engine working through a range with both a slightly crossed chain and extra drag (and vibration) from the worn rear wheel bearing. The vibration has always felt like a final-drive issue, but the RPM consistency seems strange.
Anyway, long reply but I have ordered a new bearing and seal kit and we'll see what happens. Keeping my fingers crossed. My $400 bike has been awesome so far and anything that has gone wrong has been minor.
Now it's time to research how to remove the wheel bearings. It may be pretty straight forward, but I'm thinking that right one might give me trouble.

 

Sounds like you probably found the culprit. Keep us posted when you get it apart.
And judging by all the posts by other people when trying to remove smog stuff, it may not be as straight forward as it seems for some people. Just remember to identify and remember what are vent lines and what are vacuum lines. And you can cut off and double fold/crimp the air injector lines to the front head until you are ready to do something prettier, did it to a buddy's VFR and he still hasn't touched them with zero issues 3 years later.

 

Tanks for the heads up on the vac lines. Yeah, I've got a DRZ400 and removing the smog can was a 15 minute process and well-detailed online. I'll make sure to do some research to find a step-by-step for that one. I know it's just a matter of time before I end up with vac line leaks so I want to be proactive.

I'll make sure to post a follow up when I finish the rear wheel bearings.

 

So, I'm cautiously optimistic that I have solved the problem. My bearing and seal kit from All Balls Racing arrived on Friday and I got everything swapped out. Though there is still a little vibration at the 4k-4200 mark, this "feels" normal. There is no more grinding sensation. I can't really figure out why the grinding was so pronounced at a specific RPM, but it may have had to do with torque at at that range???? Anyway, I really realized how smooth it was while commuting this morning. I noticed how smooth it was running and looked down to see I was at about 6200RPM and the bike felt great. I will still consider removing the vac lines, but for now I am once again a happy commuter.