curious , for techies

**tanken2** · 29th December 2018, 16:27

why do bike cam belts need changing at 12-24,000k and car ones last 100,000k . is it an rpm issue?

**sidecar bob** · 29th December 2018, 19:37

No, it's a Ducati issue, same as those ridiculous clutches that sound like they are falling apart whenever they are disengaged.

**pritch** · 29th December 2018, 20:05

Originally Posted by sidecar bob

No, it's a Ducati issue, same as those ridiculous clutches that sound like they are falling apart whenever they are disengaged.

Ducati recommended a belt change every year even if you didn't run the bike IIRC. There was waffle about "set".

Anyhoo the recent models have done away with all that. Still, if I had an older one I'd be careful, if a belt lets go it's expensive.

And yeah those clutches! My 1954 AJS probably had a better clutch. Imagine what the magazines would say if a Jap manufacturer offered a dry clutch.

But I did like my Ducati: https://www.kiwibiker.co.nz/forums/a...hmentid=228690

**OddDuck** · 29th December 2018, 20:26

My guess: small pulleys compared to the ones on most cars. The belts have to go around a tight radius so there's lots of flexing, hence shorter belt life.

**tanken2** · 30th December 2018, 07:32

Originally Posted by OddDuck

My guess: small pulleys compared to the ones on most cars. The belts have to go around a tight radius so there's lots of flexing, hence shorter belt life.

i can relate to this.

**Grumph** · 30th December 2018, 07:44

To a certain extent it's torque load distribution. A single with belt driven cam has very distinct torque load peaks as each cam lobe opens a valve.
A car engine - usually at least four cylinders - has a lot of torque peaks as multiple loads hit and release. This does at least distribute the wear around a belt.
Combine the Ducati's high point loadings with what are rather small pulleys and you get short belt life....

**sidecar bob** · 30th December 2018, 07:59

Originally Posted by Grumph

To a certain extent it's torque load distribution. A single with belt driven cam has very distinct torque load peaks as each cam lobe opens a valve.
A car engine - usually at least four cylinders - has a lot of torque peaks as multiple loads hit and release. This does at least distribute the wear around a belt.
Combine the Ducati's high point loadings with what are rather small pulleys and you get short belt life....

So in brief, compounding stupid design.

**AllanB** · 30th December 2018, 08:17

Belt servicing is either 24 or 30,000 kms on newer model Ducatis or 5 years. The same as valve clearance checks on a Japanese bike.

Smaller pulleys than cars, so tighter radius and I think critically a much narrower belt than what is used in a car engine.

They are all wet clutches now and have been for some years - I suspect only to meet noise regulations. I think the 1000cc race version of the new V4 comes with a dry clutch.

**Grumph** · 30th December 2018, 10:20

Originally Posted by sidecar bob

So in brief, compounding stupid design.

I wouldn't disagree now. But when Ducati brought it in, on the first 500 Pantah, it was head and shoulders better than anything else they could have used.
The bevel twins were a cost nightmare - both to assemble and run. Italian camchain of the period had to be duplex to stand the pace - see Laverda twins.
The belt worked - and was affordable.

But as revs rose and DOHC heads came in, the limits were reached. It's hard to see what else they could have used at the time. The market had rejected the expensive bevel twins and a gear drive of some other kind would have been just as expensive. Yes, it's feasible now, CNC manufacture and the general willingness to pay for high tech at the top end of the market have allowed things like the new V4 Panigale.

**AllanB** · 30th December 2018, 13:03

Mmmmm gear drive with clear windows in the covers to see them whizzing around.

**sidecar bob** · 30th December 2018, 15:04

Originally Posted by AllanB

Mmmmm gear drive with clear windows in the covers to see them whizzing around.

Like watching Julian Clarry stand up comedy. Gay & predictable, but kind of fun to watch.

**pete376403** · 30th December 2018, 16:29

Originally Posted by Grumph

I wouldn't disagree now. But when Ducati brought it in, on the first 500 Pantah, it was head and shoulders better than anything else they could have used.
The bevel twins were a cost nightmare - both to assemble and run. Italian camchain of the period had to be duplex to stand the pace - see Laverda twins.
The belt worked - and was affordable.

But as revs rose and DOHC heads came in, the limits were reached. It's hard to see what else they could have used at the time. The market had rejected the expensive bevel twins and a gear drive of some other kind would have been just as expensive. Yes, it's feasible now, CNC manufacture and the general willingness to pay for high tech at the top end of the market have allowed things like the new V4 Panigale.

did the "market reject bevel drive" or did Ducati (up against the financial wall as usual) have to introduce a cheaper system to survive?

**husaberg** · 30th December 2018, 17:40

Originally Posted by pete376403

did the "market reject bevel drive" or did Ducati (up against the financial wall as usual) have to introduce a cheaper system to survive?

Second same as why they went to plain bearings.

**sidecar bob** · 30th December 2018, 17:48

Originally Posted by husaberg

Second same as why they went to plain bearings.

Desmo, bevel drive, dry clutch & roller bearing bottom end.
All ridiculous fancies that every 200 HP plus modern superbike manages to get by reliably without.
I'd rather shit on my hands & clap than own a Ducati.