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Tex

Cam chains?

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listener
19 hours ago, embee said:

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.

 

Reminds me of studying the OU course "T102 Living With Technology".

 

Stress ... Strain ... Young's modulus ... Plastic and elastic deformation ...

[ Head explodes ]

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Hickky

Now I thought that most modern Ducatis have dropped the Desmo system once they belt drove the camshafts. The fabulous looking gear train on the GP bike is probably only there for more accurate valve timing as they rev to 15,500 with a vastly oversquare bore/stroke and I'll bet the engine tolerances are tight regarding interference. But does anybody know if this, as well as the four cylinder road bike, is a desmo design? 

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slowboy
7 hours ago, Hickky said:

Now I thought that most modern Ducatis have dropped the Desmo system once they belt drove the camshafts. The fabulous looking gear train on the GP bike is probably only there for more accurate valve timing as they rev to 15,500 with a vastly oversquare bore/stroke and I'll bet the engine tolerances are tight regarding interference. But does anybody know if this, as well as the four cylinder road bike, is a desmo design? 

 

Both my Belt Drive Ducati's, GT1000 and 998S were desmo motors, the GT an air cooled 2 valve and the 998 a water cooled 4 valve. To be honest the GT was pretty simple to shim up, the 998 was more of a pain because to do it properly you really had to drop the engine, there wasn't much room round the rear cylinder for my sausage fingers😀

Im pretty sure the four is a desmo motor to. I don't think Ducati have made conventional valve engines since the 70's, when some of their bikes had "springer" engines.🤔

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Tex

 

1 hour ago, slowboy said:

Im pretty sure the four is a desmo motor to. I don't think Ducati have made conventional valve engines since the 70's, when some of their bikes had "springer" engines.🤔

 

That’s my understanding too, Brian. I think all Ducatis, road or race, twin or four, are desmo and have been for donkey’s years. 

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baben
12 hours ago, Tex said:

 

 

That’s my understanding too, Brian. I think all Ducatis, road or race, twin or four, are desmo and have been for donkey’s years. 

I'm dim. I thought cam belt changes were the reason Ducati servicing was expensive and that if they were not changed according to spec than terrible things would befall the engine and possibly the rider's trousers if it happened at speed.

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Tex
2 hours ago, baben said:

I'm dim. I thought cam belt changes were the reason Ducati servicing was expensive and that if they were not changed according to spec than terrible things would befall the engine and possibly the rider's trousers if it happened at speed.

 

No, it’s perfectly correct that the cam belts need very careful watching and regular replacement. And also true that a broken one will result in a huge bill.. :( but the desmo cams are driven by the belts, and a lot of the expense comes from the time taken to get both the opening shims and closing shims spot on.

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Hickky

Well, as Ducati are owned by Volkswagen, it's surprising they are holding on to an outdated valve mechanism when it just provides complexity. I was told that many Ducati's were no longer Desmo, but I must have been wrongly informed. I find it odd that they use belts on road bikes but gear drive on race bikes as a belt cannot be as good as a chain drive to provide accurate valve timing, and with the Desmo system requiring accuracy to open/close a valve. No wonder services are so expensive. The earlier bikes had a bevel drive for the ohc gear, then that was dropped for belts. 

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Rocker66

Just reading a road test on the Panigale V4S and one of the options is a dry clutch kit priced at £2808.

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Tex

Cam belts were, almost universally, adopted by cat makers in the 1970s/1980s because they’re cheap and (comparatively) silent running, which helps with the noise emissions. Motorcycle manufacturers were very slow in adopting them (although Honda used them on the early GoldWing and ST1100) and they never really caught on in the motorcycle world. Cars have moved away from them now due to reliability problems and I think Ducati are the only bike makers using them? Unless anyone knows differently? Horrible things. 

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