strange noise R.P.M. specific.

[wjw11teen]

my bike is an 81 special with right at 20.000 miles

i have done the service with proper oil on both the mid and final drive

also serviced drive shaft with moly lube

im certain that the u joint is getting sloppy and needs replaced

at 4000 rpm almost exactly,the bike makes a loud rattling noise,it sounds like a rattling heat shield on exhaust

it gets louder under acceleration ...especially hard acceleration

its quiet and smooth right up to 4000rpm

i removed the exhaust and inspected everything...that is definitely not the problem

could the u joint cause this effect?..possibly something in the mid drive?

thanks

[James England]

I'd inspect the u-joint, if I were you..... It's easy enough to do in situ and you would then be able to rule it in, or out, of enquiries....

[wjw11teen]

im sure the U-joint is a portion of the issues...just wondering if it or a bearing in the trans or the mid drive can cause this rpm specific issue

iv discovered that these bikes are kinda high maintenance...like super models...

if anyone has ideas or have similar experiences id love to hear em ...

[IanDMacDonald]

I would not consider them high maintenance at all. However, ur also talking about a bike that is is 35 years old.

[James England]

im sure the U-joint is a portion of the issues...just wondering if it or a bearing in the trans or the mid drive can cause this rpm specific issue

iv discovered that these bikes are kinda high maintenance...like super models...

if anyone has ideas or have similar experiences id love to hear em ...

No, these bikes aren't high maintenance. They never were when new. If they've been looked after in the past, they are bulletproof and immensely reliable. However, as Ian said, they are 30+ years old and many aspects of them have been neglected for decades. Your u joint is probably original and will have run for over thirty years with no maintenance whatsoever (unlike car ones which fail regularly). Although it is perfectly possible to strip, clean and regrease the bearing cups in the U joint, nobody will have done it, I suspect.

Many of the original rubber components are degraded through time and so on. But, when you think about it, how many modern bikes will last thirty years and more? And still run?

It's more likely to be the u joint in the transmission, rather than a gearbox bearing. It could possibly be your rear left wheel bearing. Noises are generally difficult to pinpoint, especially if the bike has to be moving to hear them. Sound transmits through solid things easily and it can be deceptive. Again, to rule it out of enquiries, I'd check it anyway. I still have a few of them if you need one.

Does the bike shake or vibrate at the 4,000 rpm level?

[wjw11teen]

yes james there is a slight vibration with the noise..not extreme though i mostly feel it in the handle bars when the noise begins

this is a list of what i have done to the bike


new cam chain and cam gears

set valves (approx 1500 miles since)

removed forks rebuilt,also did full triple clamp bearing service

rebuilt forks

removed front brakes,cleaned,serviced,new pads

did the carbs,,3 times, re built octy,and petcocks

cleaned up plug wire ends,checked everything with ohm meter

TC fuse block

new air filter

new rear shocks

removed cleaned,serviced, rear brake assy,installed new rear brake pads

completely cleaned inspected and serviced rear wheel drive assy..

serviced mid drive with new synthetic oil...

[TopCatGr58]

Hey WJW,

As has been worked out, most likely the U-joint. However, engine speed vibration specific noises can still be other things. You checked out the exhaust...I don't recall if it's OEM or aftermarket? The OEM's are double walled and can rust/come loose internally in the headers section. Secondly, if it's not mounted and isolated to the frame with the rubber mounts, it can also vibrate the frame and cause noises/vibrations. The engine mounts can be a little worn/loose allowing things to move under load.

You could ride the bike up to and a little beyond the 4K point and then PULL the clutch so that the engine rpms are low, but the driveshaft/u-joint will still be spinning at the same speed, and see/hear/feel if you can sense the same noise/vibration. IF NOT....then it may not be the u-joint...however pulling the clutch will also take the LOAD/STRESS off of the u-joint. You say 4k rpm, but is it the same no matter which gear as long as you're above 4K? If so, then again it may NOT be the u-joint because I would suspect it to be symptomatic more with road/wheel speed vs. just rpm.

new cam chain and cam gears

Did you mean cam SPROCKETS?? Do you still have the OEM cam chain tensioner or the ACCT mod??

As James said, have you checked the wheel bearings??

T.C.

[James England]

yes james there is a slight vibration with the noise..not extreme though i mostly feel it in the handle bars when the noise begins

this is a list of what i have done to the bike


new cam chain and cam gears

set valves (approx 1500 miles since)

removed forks rebuilt,also did full triple clamp bearing service

rebuilt forks

removed front brakes,cleaned,serviced,new pads

did the carbs,,3 times, re built octy,and petcocks

cleaned up plug wire ends,checked everything with ohm meter

TC fuse block

new air filter

new rear shocks

removed cleaned,serviced, rear brake assy,installed new rear brake pads

completely cleaned inspected and serviced rear wheel drive assy..

serviced mid drive with new synthetic oil...

Mmm... I'd check re front wheel bearings first, then the rears. Just to rule them out. Or in.

As TC has pointed out, you need to determine whether the vibes and noise are coming from the engine (including headers and exhaust system) or from the drive train, wheels and stuff that continues to rotate at the same speed with the engine disengaged. Yes, the load will be off the UJ if you pull in the clutch but, as I mentioned before, it'd easy enough to check that right now and find it's the problem...or not.

[wjw11teen]

definately not front wheel bearing..

i put it on the center stand and idled it in first...sounds ok

however in neutral if i rev it to 4000 rpm it makes the noise...it sounds like its coming from the clutch area...or rear lower engine cases

while riding if i run it to say 5000 then pull in clutch the noise goes away

definatley throttle related

i have not reset the cam chain tension in 2000miles...is that an issue?

also it has the stock tensioner and stock exhaust

there is a little excessive play in the drive train but im certain that that is not the cause of this noise

it sounds like possibly a bearing in the cases....is there a bearing in the mid drive that is engaged while the trans is in neutral?

[TopCatGr58]

Cam chain tension adjustment is usually every 6K miles. However, this is the reply I gave to MrBill in another thread regarding WHEN he should replace the cam chain.

As stated, depends on how well the bike was maintained or beaten upon. The indicating factor is with the OEM cam chain tensioner, it has a certain amount of travel to take up the slack that occurs as the chain stretches from age/wear. When the tensioner is fully extended while in place, then the chain has worn/stretched far enough to require replacing.

The chain can be changed WITHOUT splitting the cases. We highly suggest installing a different type of cam chain tensioner vs. the OEM due to it's propensity to wear out/ loose it's tension allowing the plunger to move and too much chain slack to occur, which leads to the chain hopping cam sprocket or crank sprocket teeth, putting the valves out of time, which leads to pistons meeting valves=bent valves or worse!

Either install the ACCT, or perform the mod to the OEM with the carriage bolt, a search should reveal the threads complete with photos and info on how to make the MOD yourself, and thoughts/pros/cons for both types.

The Xs11 engine is notorious for top end noises that are otherwise normal!
With your bike having only about 20K miles, it's probably not beaten up too much, so I doubt that the PRIMARY DRIVE chain is what you're hearing.

Also, with the middle drive, then driveshaft, then final drive, there's several places for drivetrain slack to occur.

There are bearings on the ends of the primary shaft and countershafts, but they are bathed/flow with oil provided the galleys haven't gotten clogged.?

T.C.

[TADracer]

Similar symptom happened to me about two years ago. Around 4,000 a buzzing started and I chased it all around with a stethoscope but could not find anything. Turned out to be the clutch cable touching the tank on the inside tunnel. Hit the right RPM and the buzzing started. Sounded like it came from inside the motor.

Before you get too deep in maybe first do a quick check for anything loose that could be harmonic with the motor.

[wjw11teen]

lol that would be awesome if its that simple.....i will start looking into it

thanks

[wjw11teen]

just wanted to give an up date..i found the noise to be the left side exhaust heat shield...i fixed it once already but it was touching the pipe and that was it

still some slop in drivetrain so thats next

thanks for the help fellas