my bike starts to vibrate after 5000rpm. What could be causing this?

Question

I have a honda NV400 (shadow) with a vee-twin engine. It has been running smoothly until last week, when it started to vibrate. This doesn't seem to affect the ride but I can feel a serious vibration through the foot-pegs as soon as I hit 5000rpm.

I live in Vietnam, and my mechanic will always answer "no problem" unless something is actually falling off, and as I am reduced to miming and pointing, its quite hard to get any fine tuning done at all.

I would appreciate any possible diagnosis, so I can arm myself with a few things for the mechanic to check when I next visit him.

Thanks for any ideas....

just to me more specific, the vibration starts at 5000rpm, regardless of what speed I'm doing.

Answer 1

Always give year, make, engine size and model # when asking questions. We need all of that info to give an informed answer. How many miles on your bike would have been helpful.
I'd check the motor mounts. That model wasn't available in the USA so I don't know if it has rubber motor mounts.
A rubber mount could be worn or cracked. Or a motor mount bolt could be loose.
Or even the foot peg brackets could be loose.

Answer 2

Guardrailjim has the correct answer - check the engine mount bolts first.

Since the vibration occurs at a specific rpm, and is not affected by speed, it's definitely not a tire or chassis issue. It's either a loose motor mount or something internal.

We didn't have the NV in the states, so I don't know what redline is on this model - I think those folks nagging you about over-rev are basing this on a larger V-twin engine that builds power at lower rpms. Many earlier, smaller models revved to 7,000 and above.

If the vibration doesn't go away after checking and tightening all the motor mount bolts, then I'd drain the oil and look for sparkles. This would indicate a major failure of something internal (bearing, bushing, shim, etc).

Answer 3

Hi Nathan, if it is vibrating badly above 5000rpm in any gear you would have to assume it as an internal problem.
Something doesn't like the velocity that its travelling at and maybe its due to the fact that it is loose! Does it still have the same power characteristics you had before the problem? If it does then you might want to look at your balance shaft and the bearings at each end, If these fail or anything internal fails its going to cost you a lot more.
I would look there first mate.

Good luck,

Troy.

Answer 4

i would be very interested in knowing why u are holding enough throttle to get to this rpm range. this range is at almost 100% throttle. admit it...u are running at almost full throttle in all the gears arent u? of course ur gonna get a bit of vibration at this range when u get close to the redline. how bout backin down the throttle a bit to save the engine eh?

Answer 5

that's quite high of rpm's. i dont even get close to 4000 r's when shifting let alone when at freeway speed.
before this current cold snap, i took it on an interstate ride. at 65 mph, my rpm's didnt go over 3200. it didnt even get close to 3500 when bumped up to 70.
sounds like ur needlessly overreving ur engine. u dont need to be reving it that high with the clutch in. that's almost redline on my bike.

Answer 6

u are holding too high of rpm's on the throttle. u are close to or are redlining the bike.

Answer 7

What year is it?Clutch baskets getting bad could cause this and carbs in need of syncing also.You might want to check your swing arm bearings. I would start with engine mounts and make sure everything is tight?Could also be plugs in need of changing.A lot of things can make this happen.Depending on how old it is it might be time to clean the carbs.

Answer 8

wheel bearing