450 scrambler to r/t desmo head

[Ventodue]

It was a marketing tool!

How COULD you say, even imagine, such a thing, George!

Go wash your mouth out ....

[blethermaskite]

Cheers, George

[Duccout]

I have to add a little shot of sauce to this discussion. I have never owned a desmo Single, but have owned a desmo vee twin for 40 years, and I find the desmo a big improvement over the springer twins for the following reasons: the valve spring engines suffer awfully high rates of wear on the valve rockers, bushes, pins and camshafts, which was a constant problem with my 750, requiring the replacement of the rockers and cams several times in the 60,000 miles that I covered on it. There is also the issue of bevel gear whine, which due to the loading and unloading of the gears as they push over the valve springs, makes an awful intermittent clatter. The desmo has none of these problems, and the rockers, cams and pins still look like new after 40 years and 48,000 KMS (I know that is not much!) and the bevel gears run much quieter. All of these points are the reason why Ducati went to an all desmo line-up in 1978, and this also carries over to the Pantah, because the desmo gave the belts a much easier time.

I know that the closing springs in the Twins are much lighter than the Singles, which is a big improvement, and that the Singles desmo set-up is a lot more complex (although I believe that they can be modified to the Twin system). I remember Vic Camp's mechanic Bert Furness saying in a magazine article that the desmo system was adopted for road use to give the valve gear an easier time, not for performance reasons. Given the choice, I would take a desmo Single over a springer.

Cheers,

Colin

[blethermaskite]

Colin I generally totally agree with what you are saying, I own both versions of the widecase single desmo and springer and while the wee 250 takes a bit of time experience and a full understanding of how the system actually works to set up, one must bear in mind that this is all within the constraints of the majority of desmo single heads being often far from mechanically perfect in the first place. Yes a desmo single well set up is quieter in operation than the springer, performance wise I would say its only the little 250 that can actually benefit simply due to its ability to rev higher, however having a valve control system that should be able to allow revs to 'nipon denso' in an engine who's bottom end will explode arround 12k is all a bit contradictory, I can only share my own experience on singles I have never owned a bevel V twin but again.... yes a well set up desmo should have considerably less loading on its valve gear which in turn should result in much less wear than on a springer.....in practice almost without exception every desmo single head I have worked on has been a long way from 'set up well' most needing new or recon rocker arms and pins and even sometimes a new cam as well! leaving me to believe the road going desmo single was all a fairly cynical marketing exercise on Ducati's part.......the machine in reality being a bit of a liability for most owners at the time having been sold by dealers who didn't have a clue how to service it for them. Yet all the desmo's were more exotic in spec. prettier to look at (depending on your opinion) more expensive (often equated with better quality) and even in their day quite rare in comparison to their springer stablemates, then there is the whole historic racing cache...... all adding up to a significant desirability factor in the mind of the customer.
I think we all know the desmo singles were at the end of production probably? more expensive to make than they could be sold at, making them something of a 'loss leader' but hopefully dragging all the (less glamourous) but cheaper springers along with them at the market place.
Personally I will always prefer my 350 springer head mk3 which I purchased new in 1974 over the little desmo (also long term ownership) which I always feel is a little fragile in comparison(maybe just in my imagination??) as opposed to the 350 which I have thrashed for nearly 50 years now with almost no mechanical issues (now that's a loaded statement where a Ducati's concerned ).
Now to an admission I have a complete rebuilt desmo head in a drawer in my workshop purchased a few years ago for my 350 mk3 I am probably never going to fit it until I am too old to ride the bike.......then I will fit the desmo head as a marketing aid to its sale .
Cheers,
George

[IanHood]

To echo George's admission (confession), I have 450 yellow desmo that was a basket case and didn't have a head at all. I have acquired a desmo head (for eventual marketing purposes) but I think the head that will actually live on it, in my ownership, is a springer head that Nigel Lacey is currently working on.

Ian

[LaceyDucati]

The later spring valve bevel twin engines didn't have any issue with valve component wear. The early spring engines had ridiculously heavy dual springs. It's worth noting that over the years the collet groove moved up the valve and the margin to the top of the valve shrank( someone knew there was an issue!). Hence the ever changing part numbers for valves of spring valve twins. Worse still try finding a valve spring on the seat height in a Ducati twin Manuel. By 78 someone at ducati had read a book on valve springs and promptly dumped the inner spring as well..... hence my 78 900 GTS covered many miles without issue and the cam and rockers looked perfect (even without straight 50 oil LOL). Fitting a Desmo head to correct poorly specified valve springs would be a bit over the top. I would go with a marketing gimmick/bar stool bragging rights. The fastest most reliable Bevel single race bikes are mostly spring valve and the Desmo ones are so in spite of being Desmo

I would add I have experience of as many atrocious Desmo bevel twins as singles, all with chewed rockers and badly ground cams. As far as I'm concerned the tooling they made the parts on was set wrong and it was a matter of luck whether the poor tolerancing corrected the errors

All that said a Bevel twin Ducati is a joy to ride, but the less you can measure and know about the engine the better the experience........

My fastest Race single I built was a Desmo, but I still stand by the above....I await the lightning strike

Nigel

[themoudie]

Aye George (blethermaskite),

the 350 which I have thrashed for nearly 50 years now with almost no mechanical issues (now that's a loaded statement where a Ducati's concerned ).

Indeed George, after what I went through on Monday this week, with a late Spanish 350 cylinder muff (same as yours) that appears to have been machined off-centre, I'll no be getting change from £500 to rectify the problem that requires some time on the lathe!

Aye Nigel,

but I still stand by the above....I await the lightning strike

I think it hit me instead, with this 350!

All being well the 450 will get a trouble free canter tomorrow and all will be well!

Good health, Bill

[Jordan]

What is a cylinder muff?

[Bevel bob]

A sheepskin barrel warmer for my 250 that takes an hour to warm up?, yes please !!.

[blethermaskite]

A cylinder 'muff' is the aluminium cylinder jacket the surrounds and supports the iron liner.
Cheers,
George