I'm 99% sure they're using hydraulic lifters, just like american pushrod V-8's have been using for the last 50 years or so.

Alittle more info here:
http://www.prime-mover.org/Engines/Marvel/tbo3.html

It's technically possible to do a hydraulic lash adjuster on a desmo.

 

Hydraulic lifters won't fit in an overhead cam engine; there's no place for them to go. They go into (or replace) the pushrod, and i'm sure they further increase the weight of the pushrod and therefore the valvetrain in general. They are good for low-revving pushrod engines that are otherwise low maintenance.

philb

 

Yup, no tappets on these motors, although it might be an interesting project for a graduating design engineer to do a thesis on. I, for one, would be very impressed.

 

Yup, no tappets on these motors, although it might be an interesting project for a graduating design engineer to do a thesis on. I, for one, would be very impressed.

I guess you'd have to fit them in the rockers somehow, and have them act torsionally to "bend" the rocker to take up the clearance, rather than linearly. Without increasing the weight of the rocker significantly. You could get rid of the "helper" springs, then, though. Who's game?

philb

 

Hydraulic lifters won't fit in an overhead cam engine; there's no place for them to go. They go into (or replace) the pushrod, and i'm sure they further increase the weight of the pushrod and therefore the valvetrain in general. They are good for low-revving pushrod engines that are otherwise low maintenance.

philb

Lots of cars with overhead cams have hydraulics, in fact, at this point most do. It is extremely easy to do on a bucket system. They are used on rather high revving European and Japanese engines, not to mention US hot rod applications. To use hydraulics on a Duc would require a whole re-engineering and probably add so much valve train weight and complexity and cost it just wouldn't be worth it.

 

only harley davidson could spruke on about the benefits of components of a pushrod engine and be serious about it. ducati = innovation and hi tech, desmo, fuel injection etc
H-D = low tech overpriced junk. :
just my 2c of course.

 

Lots of cars with overhead cams have hydraulics, in fact, at this point most do.  It is extremely easy to do on a bucket system.  They are used on rather high revving European and Japanese engines, not to mention US hot rod applications.  To use hydraulics on a Duc would require a whole re-engineering and probably add so much valve train weight and complexity and cost it just wouldn't be worth it.

Really? I was not aware of that (although I rarely deal with cars much anymore, and even more rarely with newer ones). I'll have to check that out.

Thanks,
philb

 

Ok, so rather than hydraulic adjustment... How about an eccentric rocker pivot shaft? At first glance it appears do-able on the Testastretta engines... Adjust it by a broached hex on the end of the shaft that is externally accessible under a tapped plug? A kinimatic anlysis would need to be done to verify the contact patches and varing motion as the eccentric was rotated...  It definately would make life easier... I suspect a better solution than shiming it is out there...

Regards,

 

Really?  I was not aware of that (although I rarely deal with cars much anymore, and even more rarely with newer ones).  I'll have to check that out.

Thanks,
philb

I think Jaguar had hydraulic lash adjusters in their bucket style DOHC I-6 motors in the late 60's...but I could be wrong.

Ok, so rather than hydraulic adjustment... How about an eccentric rocker pivot shaft? At first glance it appears do-able on the Testastretta engines... Adjust it by a broached hex on the end of the shaft that is externally accessible under a tapped plug? A kinimatic anlysis would need to be done to verify the contact patches and varing motion as the eccentric was rotated...  It definately would make life easier... I suspect a better solution than shiming it is out there...

Regards,

Yes, that would be possible. You could even actuate the eccentric shafts hydraulically.
It's just lots more parts than the existing setup. My S4 has 16 rockers...

 

You guys are already waay over my head.

 

Ok, so rather than hydraulic adjustment... How about an eccentric rocker pivot shaft?

Yep, Honda did that, in 1966. The Honda 450 I believe. Although it might have been the Honda 350 (1968) that first used eccentric rocker pivot shafts. It's been a long time since I took one of those apart.

Most of the Honda cruisers have rocker arms free floating on eccentric shafts and use a small hydraulic piston in the head to dynamically keep valve tappet clearance at zero. And these motors all are overhead cam(s). In fact the first of these motors (1982) was a three-valve 750 v-twin that could turn 10,000 rpms! But remember, Honda doesn't use extra rockers for "closers." Also, weight isn't a consideration on these motorcycles. A 600cc cruiser that weighs 600 lbs is acceptable. Do we want to see a M620 that has a 250 lb engine?

As far as Harley is concerned. Push rods work fine on motors where the torque peak is at 2,500 rpms

 

I believe hydraulic lifters first appeared on American engines around 1955. First thing hot rodders did was replace them with " solid " lifters to gain rpm. But by mid 60's there were hydraulic lifter/cam combo's that made good power to 6-7000 rpm...that is about where progress stopped..since no one really wanted to turn a street motor higher than that.

What happens with hydraulics..at higher rpm they can't cycle quick enough and you get " lifter pump up " ..which is sort of like valve float..motor just stops revving..usually doesn't do any damage...but sure does shut things down.

I thought most of the overcam car engines use non hydraulic lash adjusters..but since the amount of hardware is small, light...valve setting intervals are so long...like 50-75K that everyone forgets about it.

I thought all of the high rpm japanese sport bikes...14000rpm...used shim and bucket style adjusters..least amount of weight etc...

 

I'm going to repeat all of this to my 2 sons & make them think I'm really smart!!