bad vibration above 4000 rpm

Hi All.

I have a 1995 ST1100, owned for 3 years now. bike currently has 43,000 miles. I have always had a small vibration that would numb the hands, it was tolerable. last year after new tires it was gone till about half way through the season then came back. New tires this years and now its even worse, can feel it in my teeth. This vibration seems to come on at 4000 rpm, at any speed and any gear. because of that I lean toward it being an engine vibration

have read the forums and lowered oil level, no luck. Check the center stand and found it rubbing on exhaust. Fixed that and still have it. While riding I pushed down on center stand and its still there and I notice I really feel the vibration on the stand.

Any ideas where to look next?

thanks!

dbuck44 said:

Hi All.

I have a 1995 ST1100, owned for 3 years now. bike currently has 43,000 miles. I have always had a small vibration that would numb the hands, it was tolerable. last year after new tires it was gone till about half way through the season then came back. New tires this years and now its even worse, can feel it in my teeth. This vibration seems to come on at 4000 rpm, at any speed and any gear. because of that I lean toward it being an engine vibration

have read the forums and lowered oil level, no luck. Check the center stand and found it rubbing on exhaust. Fixed that and still have it. While riding I pushed down on center stand and its still there and I notice I really feel the vibration on the stand.

Any ideas where to look next?

thanks!

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How do you balance the tires? Do you add beads?

he says its RPM dependent, not road speed dependent, which would suggest its not tires.

OP, does it vibrate when the bike isn't moving at all, and you rev the engine to 4000 RPM in neutral ??

If so, then experiment with it more, but I have no idea what could go out of balance internally to cause a lot of vibration. (maybe water pump bearing going bad, but I doubt that would vibrate)

If not, then the only other thing I can think of is the U-joint, but you'd think that would be speed dependent, not RPM dependent. But, maybe its torque dependent, so that might align with certain engine RPMs, just guessing.

Balance is weights on center seam of rim, clamp on.

It doesn't seem bad rev in neutral but I only tried on center stand, will check just sitting up. A friend and I both seem to agree it's not speed dependent, he has an ST1100 also, we traded on a ride.

Is there any kind of harmonic or crank balance that could go wrong?

Here a W.A.G. possibly a torn carb diaphragm causing one cylinder to come out of synch with the other carbs.

If its a engine vibration it will vibrate at 4000 rpm on the center stand. If it is the engine vibrating, that would eliminate the drive shaft. What else spins? Doubt if the water pump would cause that with out making noise from a bad bearing. Clutch drum or alternator possibly. Try using the clutch while on the center stand nd see if there is any difference. This could be a tough one to figure out.

I had a vibration on the '01, only after it progressed to *really bad* did I pull the rear wheel pumpkin and find little pin bearings on the ground.
The swing-arm bearings had fried.
You might want to borrow the 'swing arm' tool and inspect them.

Replacing them wasn't a lot of fun; but, fixed the problem.

You may think I'm crazy.... but if you fill the engine oil all the way up to the top mark, it can cause the engine to vibrate. Try dropping the level to the middle of the window and then drive it. When the oil is at the high mark, the crankshaft hits the pool of oil very hard and causes the vibration. It did this on my '99, I lowered the oil level to approx middle of the window or the lower mark and put almost 50k miles on it with no problem... Remember there is about 4 quarts of oil in that beast, and it only takes about a pint to lower it to that level... so there is plenty of oil.

vinny said:

You may think I'm crazy.... but if you fill the engine oil all the way up to the top mark, it can cause the engine to vibrate. Try dropping the level to the middle of the window and then drive it. When the oil is at the high mark, the crankshaft hits the pool of oil very hard and causes the vibration. It did this on my '99, I lowered the oil level to approx middle of the window or the lower mark and put almost 50k miles on it with no problem... Remember there is about 4 quarts of oil in that beast, and it only takes about a pint to lower it to that level... so there is plenty of oil.

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This is one on of the first things I tried, seen someone on the forums recommended it. Didn't help in this case. got me very puzzled.

I am not mechanically inclined, at all. I re read your message, though, and am not sure if you did say it only happens when the bike is in motion or, also, or ,does it happen at 4000 rpms in neutral. (?) Curious too…did you replace your tires with the same as before.
I had a similar problem with a Road King, once. In my case, the bike was fine until I had a punctured tired replaced with a new one. The vibration was immediate. Very annoying and obvious…..had the bike checked on a couple of occasions (for safety) and nothing was wrong. It was concluded that the new tire was the probable cause. I had the opposite happen as you, although, it worked itself out.

Have you tried bringing the bike up to the speed where you feel said vibes and then pulling in the clutch to allow the bike to coast while you let the rpms drop to idle? If you and your buddy both feel it is engine related, you must have done this.

We ASSUME you've driven in all gears at 4,000 RPM. If it's engine dependent, then you'll get the same vibration at 4,000 RPM regardless of the gear you're in. If you find the vibration only in 5th gear (i.e., your speed is very high) then I'll take a bet on the tire or u-joint. Also, if you're getting vibration in 4th gear at 4,000 RPM (fairly high speed) but the vibration increases when you're in 5th gear - also at 4,000 RPM - then I'll take a larger bet on the tire. More interestingly, if you're vibration is higher at 4,000 RPM when in 2nd or 3rd (or 4th) gear, than the vibration you experience in 5th gear (at 4,000 RPM) then you may have a more challenging opportunity to resolve. Let us know.

Johnny Canuck said:

then you may have a more challenging opportunity to resolve. Let us know.

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Lol. Translation from Canadian into American English: then I don't know what the problem is. Good Luck!.

Thanks for all the advice. The vibration seem to soften a bit during the season but is still present, just endured it through the season. Life got in the way of much riding this past year or to work on it. My next step is to pull swing arm and check driveshaft while upgrading to 40 amp alt.

I will let you know what I find.

I re-torqued the engine mounts, renewed the HT leads, ran carb cleaner through the system, finally pulled the carbs to check floats and diaphrams. In fact it was pilot screws were mis-matched. Much better at 1.5 turns open and a good carb balance...

dbuck44 said:

Thanks for all the advice. The vibration seem to soften a bit during the season but is still present, just endured it through the season. Life got in the way of much riding this past year or to work on it. My next step is to pull swing arm and check driveshaft while upgrading to 40 amp alt.

I will let you know what I find.

Click to expand...

Get in the open air, run the engine and check around the exhaust joints - cylinder head, the single collector joint and the two silencer joints. Also check for slight leaks elsewhere.

I once fitted a new exhaust system which had two inlets for the exhaust downpipes and two outlets for the silencer (ie not an OEM part). The down pipes were a simple push fit into the collector (no clamps). It was excellent, except when it got disturbed by a dealer when doing some work on the cylinder head. The seal around the down pipe on one side had been compromised. I couldn't tell from the exhaust note, which I thought was odd, but I got terrible vibration through the pegs and bars. I put some exhaust sealant into the joint where the downpipe slid into the collector - very watered down, so that it just flowed in and let it dry. Result - no more engine vibration.

Just for info in case you're interested - it was a Motad stainless steel exhaust, and I took photos at the time. There are still here http://www.jfheath.co.uk/st1100/st1100-exhaust.shtml

Carb balance, carb isolators leaking, fuel valve not fully opening (punctured diaphragm) thus engine starving for fuel, etc... sometimes as stupid as a partially clogged air filter...

As ST1100Y initially stated........carb sync IS likely the vibration issue....BTDT.

Brant said:

As ST1100Y initially stated........carb sync IS likely the vibration issue....BTDT.

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Does carb sync have much affect at higher rpms? I don't think it does because the butterflies are open much more at 4,000 rpms, thus the small carb to carb differences at idle are not noticeable at higher rpms. Essentially, small opening changes at 1100 rpms are a much larger percentage of the overall opening than they are at 4000 rpms.

paulcb said:

Does carb sync have much affect at higher rpms? I don’t think it does because the butterflies are open much more at 4,000 rpms, thus the small carb to carb differences at idle are not noticeable at higher rpms. Essentially, small opening changes at 1100 rpms are a much larger percentage of the overall opening than they are at 4000 rpms.

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Very true to a certain extent. Idle mixture settings are still in effect thru all rpm ranges. That circuit, when maxxed out, main jet circuit is added according to venture velocity. So, therefore idle mixture settings correct and all four carbs pulling same amount of fuel/air mixture IS critical for engine to run smoothly through ALL rpm ranges......in other words, all four cyls. doing same amount of work. After which a re-sync NEEDS to be done in order for all four venturis to create same vacuum and velocity. Idle mixtures are done using 'lean drop method'. Pick a carb to start with. With motor warmed up at operating temp, back out idle mix screw(pick one) a few turns, then slowly start back in with mixture screw till exhaust sound changes and stays constant with that change. Now, back fuel mixture screw out 1/8th turn and no more than a 1/4 turn. Now, do other three the same way.....THEN sync carbs, but not before idle mixture screws are set correctly FIRST.