Fijnger Followers 1

[ubrben]

As a tyre guy my knowledge of engines is a bit sketchy, so I thought I'd post for some advice.

In MotoGP the engine capacity has been reduced from 990 to 800cc. It is already apparent that rev limits are being raised to recover some of the power.

To do this many teams are using pnuematic valve return systems. I understand that these remove any problems with resonance in coil spring valves at high revs, allowing higher redlines.

It has also been suggested that one team will be using finger followers rather than direct acting cams and retaining coil springs.

My question is; what is it about finger followers that might allow higher revs without switching to pnuematic return?

Regards,

Ben

 

[evelrod]

Lighter weight than a 'bucket' tappet, for one. Able to use more agressive lobe profiles for another. The old 'standby' DOHC system seems to have finally passed it's prime.

Rod

 

[Ataloss]

Could they be doing something like Ducati's Desmodromic system, where they not only use the cam to push the valve down, but also use it to pull it back up, instead of using a spring? They use finger followers to do it.

http://www.ducati.com/bikes/techcafe.jhtml?detail=article&value=technical&part=technical&artID=2

Bob

 

[evelrod]

I'm not too familiar with desmo, aside what I've read and the occasional Duck I have ridden in the past. I do have a bit of experience with high revving DOHC setups, depending on what you call 'high revving'. As it stands, 10K to 15K rpm, no problems, at least for my engines I've built (Lotus twincam, Kawa 650 and 1000). We even see NASCAR pushrod engines living for 500+ miles at 10K rpm!!! The problem these days is 'high revving' engines appear to be in the 20K range and that is NOT the range you will find a reliable long distance racing engine with bucket tappets, steel springs or, desmo, as I see it.
I just thought of another reason, perhaps for street engines, finger tappets are easier to adjust, OEM dealer maintenance, dontchaknow.

Rod

 

[TVP]

Lower friction for finger follower than bucket tappet. Some recent technical papers on this subject related to passenger car engines, not just racing engines.

 

[thundair]

One note is that the Ducati engineers agreed the Desmodromic head is just part of the sales mystic of Ducati.
The original concept was to replace poor valve springs of that era.
I will say that you can turn a Ducati cam in the head by hand (less resistance).

A major advantage of rockers is the ratio change I.E. a .382 cam lift with a 1.5:1 rocker ratio will lift the cam .573
and when you use a roller rocker some of the friction loss is cut down,leaving the spring resistance as a major energy loss.

Cheers

I don't know anything but the people that do.

 

[oab]

"One note is that the Ducati engineers agreed the Desmodromic head is just part of the sales mystic of Ducati."

Oh,Oh, how can you say such a thing:-D?

You really have to build a Desmo engine for racing, or race one, to appreciate the worth of the system. Valve durations and lift can be extreme, valve to valve clearances, valve to piston clearances, can be set to a minimum, knowing that the two, will never meet.
The rider can abuse the rev counter, miss gears, and over rev on the down change, knowing that the engine is not going to punch the valves into the head.

It is a big sales point now, but because it works. When a twin cylinder wins the World Superbikes, for as long as I can remember, against all the might of Japan.
Maybe the Desmo system is the difference.

Harvey.

 

[tbuelna]

Finger followers are typically used with pneumatic valve closure.

Check out Del West:

http://www.delwestusa.com/manufactured/pneumatic_valves.asp