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Tex

Cam chains?

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Tex

We don’t need no stinking cam chains! The timing gear of a Ducati Moto GP engine (1000 cc).

 

84590-C26-A2-F7-44-E1-946-F-7-ED802309-F

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alhendo1

The inside of an engine and what goes on within is a dark art to me...I will never take one apart and peer into it...I just rely on Honda to propel me to where I want to be😅....but that is a work of art....👍

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temp

It looks like a Swiss watch!

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Andy m

It looks like the designer was getting more that a bottle of Whisky from the gear manufacturer at Christmas! 

 

All that complexity and cost to add the last fraction to the performance because the rules limit the capacity. Adding 250cc and waiting for hydraulic valves to be available would work just as well. 

 

Andy

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Tonyj

Mate that’s the mechanical equivalent of Andy’s flag explanation... still baff’d. You defo want oil on that lot and I don’t think a pair of tights would get you out of jail if it started slipping:0)

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Tex
1 hour ago, Andy m said:

It looks like the designer was getting more that a bottle of Whisky from the gear manufacturer at Christmas! 

 

All that complexity and cost to add the last fraction to the performance because the rules limit the capacity. Adding 250cc and waiting for hydraulic valves to be available would work just as well. 

 

Andy

 

Ducati are caught in a cleft stick. The desmodromic valve gear (first invented by the French in the early 1900s under the name ‘desmodromique’ BTW) no longer offers them any practical advantage. It DID, back in the 1950s, when Taglioni used it on the single cylinder racers, because at that time valve springs couldn’t cope with the revs he wanted. Nowadays improvements in metallurgy mean valve springs can perform perfectly fine at all revs. But it’s become a ‘USP’ for Ducati, so they’re stuck using an expensive to manufacture system that’s actually worse than the cheaper system used by their rivals because it’s ‘what the customers expect’. ;) 

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Trev
8 minutes ago, Tex said:

 

Ducati are caught in a cleft stick. The desmodromic valve gear (first invented by the French in the early 1900s under the name ‘desmodromique’ BTW) no longer offers them any practical advantage. It DID, back in the 1950s, when Taglioni used it on the single cylinder racers, because at that time valve springs couldn’t cope with the revs he wanted. Nowadays improvements in metallurgy mean valve springs can perform perfectly fine at all revs. But it’s become a ‘USP’ for Ducati, so they’re stuck using an expensive to manufacture system that’s actually worse than the cheaper system used by their rivals because it’s ‘what the customers expect’. ;) 

 

Perhaps that explains the annoying and silly noisy dry clutch as well.

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fred_jb

The whole idea of valves opening and closing via either gear or chain driven cams seems a bit old fashioned to me.  Don't the F1 boys use pneumatic/hydraulic or electrically operated valves with timing directly controlled by computer?

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Rocker66
37 minutes ago, Trev said:

 

Perhaps that explains the annoying and silly noisy dry clutch as well.

Don’t think modern Ducati’s have that lovely sounding dry clutch anymore. For me it was part of the Ducati experience..

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SteveThackery
1 hour ago, Tex said:

 

Ducati are caught in a cleft stick. The desmodromic valve gear (first invented by the French in the early 1900s under the name ‘desmodromique’ BTW) no longer offers them any practical advantage. It DID, back in the 1950s, when Taglioni used it on the single cylinder racers, because at that time valve springs couldn’t cope with the revs he wanted. Nowadays improvements in metallurgy mean valve springs can perform perfectly fine at all revs. But it’s become a ‘USP’ for Ducati, so they’re stuck using an expensive to manufacture system that’s actually worse than the cheaper system used by their rivals because it’s ‘what the customers expect’. ;) 

 

Yes, that's exactly what my lecturers said.  In fact I think it was true back in the 1970s, as well.  My 250 Mk3 had an 8000rpm redline, and my mate's 250 Desmo had a redline of 8500rpm.  Absolutely not worth all the complication.  By then the Japanese four-strokes were revving as high or higher, and had comparable performance.

"Desmodromic" is purely there for brand identity and a USP, as Tex says.  I'm glad the Japanese didn't waste their time going down that route.

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Tex
2 hours ago, fred_jb said:

The whole idea of valves opening and closing via either gear or chain driven cams seems a bit old fashioned to me.  Don't the F1 boys use pneumatic/hydraulic or electrically operated valves with timing directly controlled by computer?

 

Something like that, yes. They’re clever chaps those F1 people and can really make their engines ‘sing’.. 

 

 

 

 

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Tex

 

1 hour ago, SteveThackery said:


"Desmodromic" is purely there for brand identity and a USP, as Tex says.  I'm glad the Japanese didn't waste their time going down that route.

 

People (the paying customers, remember) can react harshly to manufacturers making changes to established practices. BMW found that out when it tried to phase out the boxer twin in the 80s. The customers deserted them in droves (we can buy a four cylinder bike anywhere, why buy a K100?). Harley Davidson got all ‘modern’ with the Vee Rod and the ‘faithful’ ran a mile (they called them ‘Damn Jap bikes’ which was ironic because the engine was a Porsche design!).

For that reason Ducati is stuck with the desmo, Triumph is stuck in a time warp making ‘Bonnevilles’ and Harley is stuck with ohv twins. But, it’s what keeps them alive! 

 

I have to confess I’m as bad as anyone. If I bought another Beemer (if only!) it would be a boxer. And I bought a Triumph rather than a W800 (wrong name on the tank, see?).

 

Peace and love boys!

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Andy m

Hydraulic tappets like the Enfield uses would make me like a design more. If the oil pressure is right the valves are adjusted. No shims or adjusters. 

 

Andy

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Rocker66
38 minutes ago, Tex said:

 

 

People (the paying customers, remember) can react harshly to manufacturers making changes to established practices. BMW found that out when it tried to phase out the boxer twin in the 80s. The customers deserted them in droves (we can buy a four cylinder bike anywhere, why buy a K100?). Harley Davidson got all ‘modern’ with the Vee Rod and the ‘faithful’ ran a mile (they called them ‘Damn Jap bikes’ which was ironic because the engine was a Porsche design!).

For that reason Ducati is stuck with the desmo, Triumph is stuck in a time warp making ‘Bonnevilles’ and Harley is stuck with ohv twins. But, it’s what keeps them alive! 

 

I have to confess I’m as bad as anyone. If I bought another Beemer (if only!) it would be a boxer. And I bought a Triumph rather than a W800 (wrong name on the tank, see?).

 

Peace and love boys!

I know what you mean as after having airhead boxers my 2 K100RS Beemers whilst being good bikes somehow just didn’t seem right.

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rjp996
3 hours ago, fred_jb said:

The whole idea of valves opening and closing via either gear or chain driven cams seems a bit old fashioned to me.  Don't the F1 boys use pneumatic/hydraulic or electrically operated valves with timing directly controlled by computer?

Maybe in a non interference engine - i would see a good business in bent value repairs

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neojynx
1 hour ago, Tex said:

. If I bought another Beemer (if only!) it would be a boxer.

plus they are nice and easy to work on - valve clearances, throttle body balancing all without major deconstruction.  BUT I wont mention clutch renewal..

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SteveThackery
4 hours ago, fred_jb said:

Don't the F1 boys use pneumatic/hydraulic or electrically operated valves with timing directly controlled by computer?

 

They don't, no.  They have what are called "pneumatic valves" but they are just air springs for closing them.

A lot of this is to do with the restrictive F1 regulations; I think (for instance) variable valve timing is banned, which greatly reduces the case for anything other than a camshaft.  There are companies working on camless valve actuation, but they are aiming at production cars to improve efficiency, emissions, etc.  When I get back home later I'll see if I can find a link.

 

 

Edited by SteveThackery
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fred_jb
24 minutes ago, neojynx said:

plus they are nice and easy to work on - valve clearances, throttle body balancing all without major deconstruction.  BUT I wont mention clutch renewal..

Actually the clutch is not a problem on the LC boxers as it is now a wet clutch under the front engine cover, unlike the old dry clutch hidden away between engine and gearbox.  However, you don't want an alternator problem on your LC as that is now where the clutch used to be!

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Trev
6 hours ago, Rocker66 said:

Don’t think modern Ducati’s have that lovely sounding dry clutch anymore. For me it was part of the Ducati experience..

 

Yes my mate had a couple and he always said the same but I never got how something sounding like it was about to fall apart was much of an experience :D

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Rocker66
3 minutes ago, Trev said:

 

Yes my mate had a couple and he always said the same but I never got how something sounding like it was about to fall apart was much of an experience :D

It’s not something that I can explain you either get it or you don’t much the same as the sound of a 2 stroke which some people love yet does nothing for me.

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listener
On 15/05/2019 at 11:44, Tex said:

Something like that, yes. They’re clever chaps those F1 people and can really make their engines ‘sing’.

 

That sounds worse than a Stylophone ... and a helluva lot more expensive! :whistle:

 

Mind you I don't think a Stylophone could win an F1 race ... unless you threw it very, very, very hard. :lol:

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embee

There have been a lot of advances in spring technology over the years. The old carbon steel wire had relatively limited stress range, and suffered relaxation so you always started off with higher preloads than really necessary, bad for friction, wear etc.

Modern alloy steels can be stressed over a much greater range and retain a satisfactory fatigue life, and don't suffer anywhere near the relaxation of the old materials. See https://www.suzuki-garphyttan.com/en/technical-information/oteva/oteva-70-sc/

The thing which really dominates a spring design is the "Goodman diagram". It can take various forms, but essentially gives the stress range versus the mean stress for an infinite life, the higher the mean stress the less stress range you can use, so the fitted and full lift conditions for the spring have to be considered.

Goodman.png.166c11c5ae2353a0fe70213ef4478998.png

The next significant factor is the natural frequency. If the spring is forced with certain frequencies it will develop internal vibrations which both increase the stress range and reduces the available force for controlling the valve, plus it tends to generate noise when coils clash. The tendency for a spring to develop serious surge can be to a large extent be designed out by using either progressive of more often now dual rate springs. When the valve is closed there are more active coils free in the spring, this reduces the rate and increases the effective mass so the natural frequency drops. When the valve is opened some of the coils close up completely, leaving a reduced number of free coils and less effective free mass, so the natural frequency increases. Higher natural frequency permits use at higher rpm but some internal vibration always results, but when the valve closes again the natural frequency of the spring suddenly drops to the lower value again and the vibration gets damped out very quickly, avoiding it getting amplified on the next cycle.

I did a development exercise a couple of years ago at a consultancy for a car manufacturer. Their new engine was dropping valve heads at high speed. We measured the various parameters in a running rig, valve motion, forces in the various parts, spring stresses, hydraulic lash adjuster movement etc, and did a design analysis and correlated the results. Our design actually used a lower spring load using a dual rate design, with a revised cam profile which reduced the problem forcing frequencies and the breakages were eliminated. On the rig you could actually hear the problem region with the original design, there was a very harsh peak sound at the problem speed due to spring coil clash. The changes were quite subtle, but that's often all that is needed.

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SteveThackery
5 hours ago, embee said:

I did a development exercise a couple of years ago at a consultancy for a car manufacturer. Their new engine was dropping valve heads at high speed.

 

Fascinating account.  I envy you your career - automotive engineering is much more interesting that telecommunications, which was my field.

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Mr Toad
On 5/15/2019 at 13:43, neojynx said:

plus they are nice and easy to work on - valve clearances, throttle body balancing all without major deconstruction.  BUT I wont mention clutch renewal..

 

Ah yes, the stuff of nightmares................

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Mr Toad
On 5/15/2019 at 11:55, Tex said:

I have to confess I’m as bad as anyone. If I bought another Beemer (if only!) it would be a boxer. And I bought a Triumph rather than a W800 (wrong name on the tank, see?).

 

Peace and love boys!

 

I only ever rode the K series when my boxer was in for service and never really liked them. Nothing wrong with them but for me BMW means boxer.

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