Vibration

[pear0]

I have got my 66 scrambler engined cafe running. It is a one kick starter with the Powerdynamo ignition. The engine runs well but the vibration is excessive. Things are rattling off the bike. I have not been inside the engine other than to pull the head to look around.
Observations and advice appreciated. TomA

[DewCatTea-Bob]

[quote= pear0 ...
" It is a one kick starter with the Powerdynamo ignition. "

____ Care to add a little 'show-&-tell' about that system (as you have it installed) ?



" the vibration is excessive. "

____ Is the piston the stock 9.2:1 4-ring Motocross/Scr.type ?
__ Have you checked that all the motor-mounts are fully tightened-down ?


Hopeful-Cheers,
-Bob

[pear0]

Powerdynamo -- I did install a Battery. but a small one . Coil is under the tank and the rest of the boxes are under the saddle. Very neat system to install but quite expensive. $500 but does make many problematic things go away.
Only looked at the top of the piston when I had the head off. My first suspicion was that some previous owner did some cylinder stuff and a new piston and didn't do a re balance.. But I was hoping that there might be something less of a big pain in the ass than that.
I have to remove the saddle to show the PD install. Give me a day or so and I will post a picture.
Motor mounts are tight.
Winter is coming here in Montana . I Have never split a case on a Ducati and am not looking forward to it. I like doing the cosmetic stuff and hope that the engines just run. Alas.

[Nick]

The motor mount bolts should not only be tight, but also a snug fit! Over time the holes in the frame and mounting plates wear oversized/oval. A good snug fit makes a big difference.

Not good for originality, but slightly larger diameter bolts and everything round and sized for a snug fit can make a big difference.

Also, if you're running Scrambler gearing but riding on the street, the rpms may be too high. Try taller gearing. You can also make a metal base gasket (such as used on the 350) to shim the head/cylinder higher (say .020~.030") and thereby reduce compression and vibration.

[pear0]

I am running 17 front and 45 rear. Shimming the head would also require shimming the bevel too wouldn't it?

[Bevel bob]

If the piston is heavier than it should be (check against on old orriginal piston?) , you could lighten the piston by cutting off skirt at sides as per info on modifications for racing, also chamfer the inside bottom edge of the skirt.Fitting a compression plate under the barrel does not affect the gear shimming as the stepped joint in the cam drive allows for this. My 250 feels smooth enough to rev to self destruct ,but vibration still lost me my tank bolts somewhere on the TT course !, Don't feel sorry for me though, It was BLOODY FANTASTIC!.

[DewCatTea-Bob]

[quote= pear0 ...
" I am running 17 front and 45 rear. "

____ That's standard Monza gearing and should be tall enough to avoid excessive high-speed vibration.



" Shimming the head would also require shimming the bevel too wouldn't it? "

____ Well that would be true IF it were actually necessary to maintain the very-same amount of overlap-engagement between the upper & lower tower-shafts, however the top-end would have-to be lifted-up closer to near 3/8ths of an inch before such consideration became a valid-concern.



____ I really don't think you'd be concerned so much about your encountered vibration unless you had something rather SIGNIFICANT to overly bother you, (or-else perhaps you've been used-to riding something more modern that doesn't buzz as much as a n-c.250). _ But the only common thing I know-of that can cause such remarkably-notable vibration, is loose motor-mounts,, (as all other mentioned possibilities are quite considerably minor in relative comparison !).
__ Perhaps your clutch-drum has thrown-off one of it's leafs ?
But if not that,, then I can only assume that you haven't ridden any other n-c.250, so as to compare & realize how much they actually normally vibrate.
So are you really sure that your 250 actually vibrates excessively worse than most any other stock narrowcase-250 motored Duke ? - (I well recall the very-first time I ever rode [as a passenger] on a 250-Duke,, I thought something had to be very wrong with it and-that it was about to break or something, cuz I could hardly keep my feet placed upon the passenger-pegs and their vibration was quite disconcertingly alarming and very-much uncomfortable, [until I later became used-to it and realized that that rather extreme level of vibration was pretty-much accepted as being rather normal].)


Hopeful-Cheers,
-Bob

[pear0]

I had a 200 Americano in 1959 (new) and have no recollection of much vibration. But that is a long time ago.
The clutch basket mention reminds me that mine has a couple of pieces missing on opposite sides . looks like one broke and the other was cut off to match . I have a good basket but was spooked from installing it because I read something about the drive gear being matched sets.. Maybe I ought to try installing it and see if some of the vibration goes away. Thanks!

[DewCatTea-Bob]

[quote= pear0 ....
" I had a 200 Americano in 1959 (new) and have no recollection of much vibration. "

____ The 200-motor vibrates a slightly notable amount less but, the two n-c.motors aren't too awfully much different in that regard, and-so the difference isn't really enough to warrant your rather undue concern about (normal) vibration.



" The clutch basket mention reminds me that mine has a couple of pieces missing on opposite sides . looks like one broke and the other was cut off to match . "

____ Well then it seems that someone has already pretty-much fully addressed any vibration issue that THAT could've caused.

I've come-across a number of clutch-drum/baskets with a single missing leaf-tab and found them to still be useable without any real operating issues, by also breaking-off the leaf-tab 180-degess/opposite,, which usually brings the balance back to within a few grams difference and pretty-much cures any noticeable vibration (due-to such drum/basket mis-balance).
So in your case, even if the amount of mass of the leaf-tab that was purposely removed was rather poorly-equalized to the amount of mass of the portion of the broken-off leaf-tab, it would-not leave you with a notable vibration difference such as that which seems to have earned issue with you.
So going to the trouble of grinding-off any remaining difference (between the two opposed tab-stumps), or even replacing the drum-basket, really wouldn't be worth it to you (for the small gain, that you really couldn't obviously detect afterwards).



" I have a good basket but was spooked from installing it because I read something about the drive gear being matched sets.. Maybe I ought to try installing it and see if some of the vibration goes away. "

____ As I've already covered,, while your broken-basket likely hasn't been rebalanced as originally-new, the actual difference between it and your "good basket" is quite likely insufficient to make any noticeable-difference in motor-vibration.
__ It's true that the drive-gear & clutch-drum/basket originally come as a factory 'matched' primary-gear SET ! _ And a primary-set that's not well matched can either be rather loose & noisy OR (more likely) tight & power-robbing !
But there's a fair chance that your replacement-basket is fairly compatible with your motor's original drive-gear...
You'd just have-to try installing it and do about what the factory originally had to do, and make-sure that the two primary-gears mesh FREELY and without any notable slop.
But like I've said, it's not worth your trouble to go-through all the involved work just for the rather small gain (which you most-likely won't even be able to notice) !

____ I suggest that you try to get a ride on another n-c.250, to compare vibration for yourself,, before going-onward with trying to cure vibration that may very well be rather normal.


Hopeful-Cheers,
-Bob

[Scrambler]

On my 66 NC I had a similar vibration coming home from work one day. It was so bad is was hesitant to go over 45MPH for fear of damaging something. I had pulled over and looked for any obvious loose parts or broken something. I found nothing, checking all the nuts and bolts in the shop, I found the motor mounts snug. BUT the top rear was not really tight, it took a 1/4 ~ 1/3 of a snug and the vibration went away. It was a huge difference for such a small amount of torque/tightness. I have since sleeved the frame and case to maintain the original bolt size. Worth a double check............
I put 200 to 300 miles in on weekends and would not say the bike has any excessive vibration. Top end has the usual springer valve train noise, but nothing unusual.

Mike Mc