Vibration

[blethermaskite]

This is all a bit subjective......but....my 1974 350mk3 is without doubt the smoothest 350 single(without a balancer) that I have owned or ridden, it has always felt very good to me right up to (my max) 8500 rpm. My 1975 250 desmo is also pretty smooth too, however once the revs get above 8500 the vibration starts to get intrusive and worse rising up to (my max) 9500 rpm.
I think it is generally accepted that the widecase 350 is the sweetest running Ducati single, I have owned and ridden dozens of the singles and without wanting to upset anyone I have always found the more sporting narrowcase 250s to be worst vibrators, any more than 15 miles and its numb bum and filings falling out of teeth . I can't comment on 450s I have never ridden one.......but their reputation seems to proceed them.
Cheers,
George

[Eldert]

Nigel did try a headsteady on de Ducati racers .

i dont think it was a succes so no more headsteady on his racebikes .

Eldert

[Bevel bob]

Hi George, My 250 M3 NC does not seem to vibrate enough to notice. I have ridden it all day and yes numb butt , caused by narrow hard seat. Its very happy to rev off the clock if I don't keep an eye on the RC . It does have an orriginal Borgo piston that I have worked on and lightened a bit. I do remember the Mach 1 used to vibrate if engine mounting bolts got loose, which they did as I was often racing with the big bikes !.

[Ventodue]

I can't comment on 450s I have never ridden one.......but their reputation seems to proceed them.

For just this reason, I was a bit hesitant when I bought my 450 SCR - at the time, I had a choice between a 250 and a 450.

Long story short: took the 450, had the engine rebuilt by John Wittman, never had the LEAST concern about vibration, including a week in the saddle on the MotoGiro.

Morale? I suspect the amount of vibration is intimately linked to the quality of the engine build ...

[Duccout]

Yes Craig, I owned a 450 and I can't say that the vibration bothered me. The worst Ducati in that respect was my Sebring, which had high-frequency vibration which used to loosen all the nuts and bolts, so that a journey had to be punctuated by stops to tighten something that had come loose. If I owned one now I would fit nylock nuts and Loctite everything.



Colin

[blethermaskite]

I said above I considered one's perception of how much or little or in what way your Ducati single vibrates is subjective to your own experience, however I think there is an X factor in this equation......Ducati's own level of quality control during engine component production and subsequent assembly. As an example when I rebuilt my first 250 desmo disc (and believe me I am a seriously fussy and careful engineer) I shortly after did exactly the same job on a friends 250 desmo disc.....and I mean EXACTLY the same job.....all bearings replaced with the correct spec, new rod and big end (genuine Ducati) crank trued to within 1 thou of runout, new borgo forged piston, and head overhauled to factory spec. Same carb and settings, same exhaust, same ignition,........so what were the two bikes like to ride? performance..... identical!, vibration......one (like my present one) was smooth up to really high rpm, the other had vibration through the entire rev range (not really bad but there). I could only put this down to original manufacturing precision.(or lack off)
Cheers,
George

[Jordan]

I've noticed that too - some singles vibrate more than others.
But we want more info than just putting it down to how well or not they were assembled.

Could it be related to balance factors? Were they the same in both engines you built, George?
Someone named Henry stated these as:
450 cc - 68 to 69%
350 cc - 66%
250 cc - 72 %

As usual with a vertical engine, these are around two-thirds of reciprocating weight.

Something that could be fun to try is clamping a weight to frame tubes to change resonant frequency.

[graeme]

Same engine, in a different bike vibrates differently.
74, 450 Desmo balanced at 55% has little vibration in the 74 Desmo frame (this is a 250 frame without the 450 gussets)
This engine in a 450 Scrambler frame vibrates lots more.

Would like to hear Eldert’s and Nigel’s recommend balance factor they use for a 450.

(the above 450 engine has a 1mm longer Honda XL500 rod)

Graeme

[Harvey]

Once on my 450 I was riding along, when vibration rapidly became severe.
I stopped to see what might have caused it, and there it was - one of the long rear mounting bolts was sticking out by some inches, having lost its nut.
Check the simple things first.

Jordan’s post reminded me of the 72 Desmo Special that I had. I had a 74 Desmo first that didn’t do anything in the way of vibration or go.

When I got the 72 I was going to a rally about 500k away with my friend on a Paso, I just follow him when he took off to pass, I clicked 4th and went WFO after him, about 350k out, went to do the pass when the vibration was extreme, backed off to feel something against my ankle, looked down to see the bottom rear bolt falling out and the top one against my ankle. Walked back down the road found the bolt but no chance of the nuts, so removed the two nuts off the front brake stays to bolt the engine back in.

I had a 76 750SS at the same time,, and believed that the 450 should have the same type of engine performance, so decided to rebuild the engine to improve it. Bored it to 88mm, got Brooke Henry to do the big end, fitted the V2 12mm lift cam.
As the pin in the new big end had a smaller hole through the center (so heaver) and the bigger piston it had to be re balanced.

Now with the balance of a single you either balance for high or low speed, you can’t have both perfect, if you used 100% of the reciprocating weight of top half of the rod, and all the piston bits, the vertical balance would be perfect at high speed, but the heavy bob weights would produce a huge horizontal out of balance, so you take your choice. I wanted it to be able to run at around 6000rpm for peak torque, and up to a max of 8000rpm. I did a lot of work on the piston to remove us much mass as I could safety do, I think it ended up at about 470gms, so I used 70% of the reciprocating mass.

The end result was a very smooth engine at speed, I could ride for long 1000k trips with out anything breaking or falling of, but when stopped at stop lights, I had to hold the front brake on to stop the forks from jumping back and forwards from the horizontal out of balance.

Like I said you make your choices one or the other.

[blethermaskite]

Jordan, (name drop alert ) towards the end of his amazing life I became great friends with the late Stanley Woods, so sometime in the late 1920s / 1930s (not sure exactly) when he was a works rider for Velocette his TT machine was suffering from severe vibration problems, his solution was to get a lump of lead and fix it to the front downtube ........cured!. I know when you fitted a Triumph twin engine into a Norton featherbed frame you needed to change the balance factor to cure excessive vibration,
Re the two 250 desmo engines....I can't answer that for you....which is my point.....factory build tolerances, one crank may well have had a slightly different factor???
Cheers,
George