[joe4702]

Just did my 15K service and the engine is now exhibiting a high-frequency
buzz that I can feel in the bars, pegs and tank. Engine starts and idles fine.
Power and gas mileage same as before.
Only diff is the buzz, which is very annoying when cruising on the backroads or freeway.

I had the front cams out for a shim swap.
Could the cam chain be off by 1-tooth?
I tend to think this would create more symptoms than just vibes, but am not sure.

Could bad carb sync cause vibration at speed? 
I'm hoping that's the cause, as it would be much less work to correct than a cam timing issue.

I also changed the coolant, air filter & spark plugs, but I don't see how those
could cause engine vibration. The AF is stock and the plugs are the same
NGK iridiums I had in before.

Any info appreciated.

Thanks.

 

[nc_sv650]

I f the cam timing was off by a tooth I think you would notice the difference in performance. I've done this on a vertical twin and it will barely run; one less cam chain obviously, but I think you'd feel the difference.

In my experience, carb sync can make a huge difference in how a bike feels. I would re-check that first.

 

[andyauger]

Recheck your carb synch at 3,000 RPM. Sometimes when the mechanism is sitting on idle the two throttles aren't at the same spot. Sometimes when you synch in this condition the engine is actually out of synch when off idle.

 

[joe4702]

Carb sync is good at idle & 3000.
After another ride today, I can say the buzz is only at 5000 RPM and above.

Could it be the CCT? The motor certainly seems more noisy (as in whiny) now, too.
I didn't remove CCT, only held it backed off with a screwdriver while I had the cams out.
Perhaps it didn't tension up fully when I removed the screwdriver. I should probably
back it off and let it re-tension, just in case.

 

[Randy S]

How far did you retract each tensioner? At what point did you release the arm? Did you check the tension before you put the valve covers back on?

 

[joe4702]

I backed it out enough so I could get the cam chain off the sprockets. Actually,
I assumed it was backed out all the way - perhaps not. I didn't release it again
until the cams were back in and the chain back on. The chain definitely tightened
up when I released the CCT.

Talked to a few people and can't get any consensous as to whether 1 tooth off
could cause the buzz. Looks like I'll be opening her back up to re-check the cams.

Thanks for the info.

Joe

 

[andyauger]

One tooth off on cam timing would be dramatically bad. The engine would do worse than just buzz.

 

[Randy S]

If it were me I would re-synch the carbs, and if that didn't do it, I would re-set the cam chain tensioners before I re-opened the valve covers.

Did you, by chance loosen any of the engine mounting bolts during your maintenance? I have occasionally had a bike where I incorrectly torqued a critical fastener (left too loose) that introduced a vibe into the bike.

 

[joe4702]

Thanks Andy. As I mentioned, I've gotten conflicting opinions on that, but I trust your opinion
and tend to agree. I think the engine would misbehave more than just a buzz.

I'm going to re-tension the CCT and check for loose bolts as Randy suggested & also
check the spark plug gap (supposed to be pre-gapped, but I should have checked anyway).

If that doesn't fix it, I'll open her back up and re-check my work on the front cylinder.
While I'm in there, I'll probably bring all 4 valves to mid-range clearance just in case that
has anything to do with it. The right side IN and EX valves are at the tight end of the range,
while I adjusted the 2 left valves to mid range since they were too tight. I should have just
adjusted them all to mid-range the first time.

Thanks!