Ducati Monster Forum

For those of you who have done the 14T mod, did you notice the bike felt like it vibrated more?  I seem to notice a spot around 4k rpm where there seems to be a rhythmic vibration.  I thought at first it was speed related, but instead it seems to be an rpm range.   I checked my chain tension and wheel alignment twice and all looks good.  I'm wondering if anybody has noticed similar behavior after the mod, as this didn't start happening until after I put the 14T on.

Set your chain so that it is a bit looser than spec and see if it helps.  I can't seem to run my chains at factory settings without the sort of vibrations you're describing.

Right now it's set at about 27mm, so I will try loosening it up to about 30mm. 
I find measuring the tension a bit weird since the chain hits the underside of the swingarm when pushed up so I don't really know the full travel upward, just downward.

even more critical if you have raised ride height.

I realigned my rear axle and checked the chain tension and I'm still getting the vibration.  Later today I will loosen up the chain even some more to see if it takes care of it.  Those axle alignment plates are so useless it's a joke.  I don't know why they even bother putting them on when they bend the first time the axle nut is loosened. 
I'm going to measure the axle from the pivot point on the swingarm this time to make sure it's straight. 
I'll post up after this adjustment.  For the ride home today....vibrations...

no change going from 15t to 14t in my case.....you did check the tension in several positions, right??....sometimes the sprockets are out of round and can make chain tension vary considerably which can cause vibration

Instead of getting to do the adjustments, it rained 40F hell all afternoon and night yesterday.  Hopefully, nature will give me a chance to work on it today.  I'm not fortunate enough to have a nice garage to work on the duc in.

No vibrations on mine,i will try to feel for it next time i ride though.

You would feel it pretty obviously if it was I am talking about.  It's audible, rhythmic and has a vibration associated with it.  Noticed most in 2nd gear 3k-4k rpm then in 4th and 5th same rpm range.  Usually more noticeable when in a turn or under steady uphill acceleration, not fast hard acceleration (that takes it right past the rpm zone that causes the vibration and the bike feels pretty normal).
I'm wondering also if it could be a tuning thing...but have no idea.
Since it just popped up when I put the sprocket on, I really think it's somehow related.

Why not put the 15 tooth back on temporarily and see if the concern goes away? At least then you would know if you are headed in the right direction...

I thought about it...the 15T just...sux.  I would hate to have to ride it with that on.  More teeth on back, sure, but the stock setup is bad.
But yea, maybe I might have to do that...

I've used 14t fronts for over 45,000 mi. now and never noticed a problem of any kind. Love em. And I've always kept the rear ride height an inch taller than stock.

LA

I just switched to the 14T, and I too noticed a hum or vibration at speed.
Mine doesn't seem to be rpm/engine related..it is still there when I coast.
I think mine is the rubbing of the chain on the swing arm guide.
It has been about 3 weeks I don't really notice it now [moto]

If in doubt, loosen the chain a little more.  A chain a little too loose will not hurt, a chain a little too tight can cause damage, and may even damage the output shaft bearing, which is a major repair.  It is common for do it yourselfers to make stuff too tight.

I spent my spare time exhaust can chopping tonight.  I didn't loosen the chain yet to see if it helps.
Will report back tomorrow after I git r don.  I'll be aligning the rear axle from the swingarm pivot.

Yeah, the alignment marks are always off.  I get better alignment just by eyeballing from the rear sprocket down the chain to the front sprocket than by using the marks on the adjusters.

Swingarm pivot works.  Or you can just lay a straightedge (I use a piece of bar stock) flat on the rear sprocket and see if the chain follows it.  I generally eyeball and then use a straightedge to confirm. 

Measuring from the swingarm pivot was a bit off because my DSS is asymmetric, it forced the tape measure to bend out of straight.  I measured from the rear end of the swingarm to the axle and loosened up the chain.  The vibrations were less noticeable, but maybe still there, or maybe I'm just kind of expecting to hear it.
I think I may have killed my chain on the first 50mile ride after the sprocket change when it was just waaaaaaaaaay too tight. [bang]

    Let me see if I can help a bit here. I myself run a 14 on my S2R800 (15tooth really does suck) and i did notice a vibration with the same rpm range you mentioned. I had my VERY trusted tech look at (20plus years as a Duc wrench) the chain and it was fine in stock required tension. I see this sometimes in my job as well....I work in the cycling industry as a race mechanic for a drive-train component maker. The vibration we get is smaller gears (11-13 tooth) under low to medium torque and then goes away as the rpm rise or you go higher in the gear ranges.
   The reason we feel is that the chain is wrapping around the cog in slightly tighter angles (possible more chain noise and vibration from such frequencies in a small area) and mix that with the fact the cog is now smaller in diameter (from the stock 15) so there is less mass on the end of that rear axle  (drive shaft-out put shaft of the engine) but it has to handle the same amount of engine frequency, torque and vibration.....The noise can be felt and heard. Change the belts on your Monster and they will whine and vibrate a tad when breaking in especially if you run open or no covers.
   My Monster has run most of its life on the 14 (my first mod after 500 mile service)and after a few rides you get used to it.
    Chain lube can play a huge factor as well. Thicker lube isolates noise and vibration just like sound dampening material in a car...i use spray wax type lube and my drive-train is all but silent and doesn't sling off. (an issue we see as well in cycling)
   I would also say is that if your chain had time on it and then you switched to the 14..your chain stretch may be just enough to cause conflict. Try the 15 again and make sure its the 14 making the fuss. I run a Ducati steel 14 and its fine...if yours is after market else where then maybe a pitch conflict in the new cog and your used chain.  Hope this helps and wasn't too long winded...and made sense  [moto]
   

Alienfocus is on to it.  The stock gearing for your bike is 15/42, which gives you a fractional ratio (2.8).  You changed to 14/42 which is a whole ratio of 3.  You try to avoid whole ratios because you want to spread the wear over different sprockets.  With a whole ratio, every few revolutions the same chain link will hit the same sprocket tooth.  With a fractional ratio, it takes many more revolutions.

Besides the periodic wear, the whole ratio will make it more susceptible to set up periodic vibrations or harmonics in the chain/sprocket system.  I'm running a 14/42 also, and besides making sure everything is aligned, tightened to spec, and chain in good condition and loose,  not much else you can do. 

14 tooth sprockets are talked down because they can wear the plastic spacer in the front of the swingarm, and in extreme angles, even the swingarm.  Here is a condition where the plastic spacer can work as a vibration damper as it gets worn down.  Make sure you have some plastic there.

How old is your chain?

I have about 5000 miles on my chain now.  I'm sure the chain isn't too tight, I triple checked.

I really appreciate the lengthy explanations, I agree this seems to be the issue and it makes perfect sense.  It's nice to know some others have experienced the same thing and that it might not be my newbie user error.

I'm thinking I'm just going to get used to it for now and get a new chain and sprockets eventually and go up a few teeth in the rear sprocket instead this time.  I'd like to get as much life out of my current setup as I can before I spend the $$$'s to replace everything, though.

5K mile old chain and a new sprocket can be the problem, particularly if you change sprocket size.  What battlecry is referring to is hunting, partial hunting and non hunting gears.  A hunting gearset is when any tooth on the smaller gear will come in contact with  all the teeth on the bigger gear, considered best for wear.  This ratio, for example, 42:15 cannot be reduced to an even number.  Partial hunting  is when one tooth on the small gear will contact some of the teeth on the bigger gear, but it will take more than one revolution of the bigger gear, for example, 42:14, which would take three revolutions of the big gear.  Non hunting is when one tooth of the small gear comes in contact with some of the gears on the big gear in one revolution of the big gear, for example, 60:15.  Add a chain into the equasion and it is unlikely you would wind up with any combination that would be a non hunting or a partisal hunting of any consequence.

To specify more, I changed the sprocket to 14T at 4500miles and have about 5000 total now.  I might put the 15T back on if I can't take it, but I hate that stupid sprocket so much.
I can usually avoid the vibrational section of the rpm range in the lower gears, but up in 4,5,6 it becomes more noticeable.  If the chain is dead, I'm thinking it's not going to get better in a hurry.  If that is the case, I'd rather wear it down until I take the bike in for the first service and change it then...