Vibration troubleshooting

I've noticed a bit more vibration at low rpm this season on my 850 MKII. Last year the isolastics would quiet down at about 2500 but now I need to be at 3000 before it smooths out. I've already backed the adjustable isos off by a "hole" with no noticeable change.

There's also a strange new noise comming from the drive train somewhere. It's a low "rumble" when taking off in first gear when the clutch is released, also noticeable when running very slow speed like in a parking lot. It goes away as rpm comes up. Sorta sounds like chain noise, though both primary and drive chains are tensioned correctly.

I'm thinking that the two are related, but I'm unsure what to check for. Any thoughts?

Those drive train annoyances can be serious to life and bike. Rear wheel bearings to dummy axle giving up before failure. Chain links freezing up or crumbling in primary or drive chain and sprocket teeth folding over. Just loose isolastic end nuts have been reported to do this. Bent/cracking headsteady. Its also over laps with racers reports before they opened engine to find crank/rod faults about to blow up.
Tank or such fouling something. Generally I've found sloppy loose isolastic gap is a delight for smooth sailing just not hanging long sweepers under acceleration, UGH>
Some combustion imbalance can do this with horizontal imbalance isolastics and headsteady can ignore.

Hard to tell without looking at it, but check the easiest first.
Loose head steady, exhaust tightness, wheels bearings.
The alternater rotors can come loose causing a rumbling noise as you describe.
Loose clutch, clutch bearing.
Could even be main bearings, but have a look.

maylar said:

There's also a strange new noise comming from the drive train somewhere. It's a low "rumble" when taking off in first gear when the clutch is released, also noticeable when running very slow speed like in a parking lot. It goes away as rpm comes up. Sorta sounds like chain noise, though both primary and drive chains are tensioned correctly.

Click to expand...

There are a couple things that come up fairly frequently that can cause that noise. A good way to narrow it down is to find a big empty parking lot that you can have to yourself and ride without a helmet. Fire up the bike and leave it in neutral, lay a finger across the gap between the primary cover and the Z-plate. If there is some hitting going on somewhere between the engine/cradle and the frame you'll be able to connect it with what you're hearing and feeling with your finger. You can do the same riding the bike. You get a sense after a few tries if there's some contact between the engine/cradle and the frame or if there's something going on in the drive line itself but doesn't transfer to the frame, you can tell. Same goes for something loose on the frame. It helps narrow it down sometimes.

Top on the list for the driveline is loose clutch basket and loose swingarm. For the frame it's loose centerstand or sidestand.
As far as loosening the iso's to get a smoother ride, I recently tried it and got the opposite result. Went back the other way till it cleared up. I'm using a Taylor headsteady and it may be that rule doesn't apply anymore when there's a link involved.

The low frequency vibe is usually the Mk3 head steady spring thingy is too slack, though sometimes too tight.

The rumble, I had just that two years ago along with a rattle in neutral just off tick-over, and in my case I found the ignition was too advanced for this new crap fuel, and I'm sure that was the rattle. And the gearbox main shaft and clutch basket ball bearings were worn. Sorry to say I fixed all three at the same time the rumble and rattle went :?

Cash

A side note on Peel tri-links and iso gap, I had to get the gap pretty close to factory .01" or she shook if too lose and buzzed if too tight. Also buzzed if I did not set the rod ends to slack neutral. When dialed in though Ms Peel flat disappeared out from under me. I did have one bad buzz event on rodded Peel, when I put tank on minus some rubber discs to get it to lay a bit nicer so tank sat ~1/4" lower and the top rod fouled on tank tunnel. I cut the Al head plate and rewelded one rod mount 1/4" closer in to solve and some JBWeld to patch tank weep. All Peels rods are at least 5" long so clearances are close but I can't twist her frame up enough to bind them to notice by princess on a pea me.

I saved a collection of isolastic dial in instructions/symptoms I'll post later when at the 'puter I stored it on.

Here's some more on isolastic dynamics to loss sleep on formed in place concepts.
http://home.clara.net/captain.norton/cnn2sec33.html
From: John Pinkham
Date: Mon, 6 Jun 94 17:35:40 EDT

Diagnosis:
Vibration: up to 3000 RPM
o Rear engine mount tight- remove 0.005 shim
o Front engine mount O.K.

From 3000-5000 RPM
o Front mount tight- remove 0.005" shim

From 0-5000 RPM
o Both Mounts tight.

Don't support the bike on the center stand when servicing the isolastics.

From: Chuck Kichline
Date: Tue, 7 Jun 94 10:52:31 CDT

> Diagnosis:
I believe the best (and classic) method is the "night ride" where the analysis and adjustment requirements of the system is diagnosed thusly:

1) All tests should be made at 1000rpm intervals. Each interval should be tested for ~ 30 seconds.

2) All tests should be made in appropriate gear for use at that rpm.

3) Rider will position himself in front of an automobile who has turned on their headlights and is driving at an appropriate speed.

4) The rider will examine the pattern made in the rearview mirror(s) by the headlights for diagnostic wave patterns.

5) Diagnosis:
Figure 8 below 3000rpm
o Rear engine mount tight- remove 0.005 shim

Figure 8 above 3000rpm
o Loose front engine mount.

Horizontal line 3000-5000rpm
o Front mount tight- remove 0.005" shim

Vertical lines 2000-4000rpm
o Loose rear engine mount.

Squiggles at all rpms
o All mounts loose.

Handlebars squiggle at all rpms
o All mounts tight.

Two rock-solid spots above 5000rpm or all goes lightening bright then dark...
o Blew your engine or flying off road d/t eyes off path too long.

Thanks for that, hobot. My lousy memory told me to loosen the front for under 3000 buzzing. I'll put that back and try a bit more clearance on the rear.

As for the funky noises, I was unable to ride this weekend (damn rain) but Bob's advice to roll through a parking lot sans helmet sounds like a plan. One other piece of data is that it only happens after warmup, not when cold.

My biggest fear is that something's amiss in the cranckcases.

Ugh, I hope the collected iso summary is realistic, but I'd sure check primary tension when hot. i've had cam tensioner get torn off and it still ran ok w/o any unusual sounds-vibes, just no power after 5000 rpm d/t ignition over advance and valve timing skewing. At these Cdo are pretty to look at outside and inside. ugh.

maylar said:

. One other piece of data is that it only happens after warmup, not when cold.

My biggest fear is that something's amiss in the cranckcases.

Click to expand...

Could be a main bearing is loose, I've seen this only twice before and each time it was the timing side.The only clue was end float would come and go, strangely there wasn't any of the usual signs of the bearings turning in the case. Both times loctite saved the day.

I hope this isn't your problem.

Best of luck,
Cash

Both times loctite saved the day.

Click to expand...

SAY WHAT Cash!!??
Are you saying that locktite actually functioned in a hot engine area????!!!!
I ask bluntly at risk of offending you to get to the truth of the mater.
JUST WTF do you think locktite save? You state You Did Not Find bearing bore
damage??? So to me that's like saying I almost cut my finger but a
band aid later saved it.

Well I was expecting something like this, no offence taken.

There was no bearing bore damage that we could see, no polish, no rubbing, nothing. From memory the bearing bore was roughly 0.0005" over size, measured with an un-calibrated bore mike, the bearing was tightly held while cold but boiling water expanded the case enough to let it fall out. I borrowed the bearing lock from RGM, I forget the grade of Loctite nothing you can't buy and stuck it back in, that motor is still running sweetly. The other motor was done ages ago, was hardly used and I haven't a clue where it's at now.

I reckon the rattle was caused by the momentary loss of end float ?? I could be wrong, anyhow it worked for me and my mate and at the end of the day that's all that matters.

Cash

PS. Are you back on the road yet ? my bike is but not me, though I did 15 miles painful miles last week and she's going like stink, it's doing my head in.

Ok Cash, your clearances may just be at the threshold to get away with locktite. Hope it just wasn't better assemblely the 2nd time around. Remember to ping back if you ever open up and look again. Crank end float sounds suspicious to me as rods should self center crank, even thought its advised to shim pretty tight. Until then will take your word for it.

Trixie is still dead d/t ignition failures yet to be diaganosed before replaced. But I did feel a buzz so found head steady in a bind and tweaked it back to N but not riding yet to know how it feels.
Tweaking Trixie Headsteady.
tweaking-trixies-head-steady-t9873.html

hobot said:

Ok Cash, your clearances may just be at the threshold to get away with locktite. Hope it just wasn't better assemblely the 2nd time around. Remember to ping back if you ever open up and look again. Crank end float sounds suspicious to me as rods should self center crank, even thought its advised to shim pretty tight. Until then will take your word for it.

Trixie is still dead d/t ignition failures yet to be diaganosed before replaced. But I did feel a buzz so found head steady in a bind and tweaked it back to N but not riding yet to know how it feels.
Tweaking Trixie Headsteady.
tweaking-trixies-head-steady-t9873.html

Click to expand...

Zero end float COLD. This will grow over .004 when hot...Main bearing bores: over time with a few cold drifting, well they get big, Problem with steel rings in alloy they need to be .001-.0015 tight cold which if the bearing as less than this in roller clearance will bind when cold. and "slack" when hot..and will rumble when hot! Thats why water cooling was derived...air cooled engines died with the discovery of H2O :lol: Some times i wonder why i own a Commando..it's what i call a condiction..or addiction!