| Author | Message | ||
     Hoppalong |
Since my Ulysses has hydraulic lifters, it got me to thinking about mechanical valve adjustment (shims) vs hydraulic valve-lash take-up. Suppose there were two very similar motorcycles: moderately tuned 650cc, parallel twin, OHC. One had typical mechanical valve adjustment (shims) and the other had a typical hydraulic valve-lash take-up. What kind of differences would there be in rpm red-line, peak horsepower, and weight, etc? | ||
| Desertjeff |
You might be able to compare a 81 or 82 honda 650 with a 83 honda 650 nighthawk. They had a couple other differences the former being a single overhead cam with chain final drive. The latter had double overhead cams and a shaft drive. But the truth is rpm at red-line, peak horse power and weight in a moderately tuned engine would not be affected in any way what so ever by the type of valve lash adjuster.  | ||
| Hoppalong |
I'm asking about hydraulic valve-lash take-up. Something comparable to OHV engines' maintenance free hydraulic lifters (like on our Ulysses), but on more modern OHC motorcycle engines. I would gladly trade a little rpm, peak horsepower, etc, for no required valve adjustments (shimming) at regular intervals. As I understand, it's not all that uncommon for modern automobiles to have maintenance free valves on OHC engines. Is it too complex for motorcycles? Too heavy? Too expensive? One reason I don't consider owning a Ducati is that I do my own maintenance and I don't want to deal with Desmodromic valves. | ||
| Mark_weiss |
Tiny parts with even tinier oil passages are prone to oil-flow failures. Honda had a few OHC engines with hydraulic valve lash adjustment. One was a 650cc single cam, the other a 700cc double cam. One of the reasons for low redline on our engines is that the valve lifter/lash adjuster is a moving part (and is heavy). The lash adjusters on high rpm engines do not move. | ||
| Ratbuell |
Your typical car cylinder head, for an OHC engine, is about four inches tall from head gasket to valve cover gasket. Lifters are typically about 1.5" tall. My CR has a cylinder head that's about 2.5" tall, I think. And the rocker box stack is less than that. There's just not enough real estate in there - height wise - to stack a lifter, rocker, and cam - so the "lifter end" of the rocker arm gets shimmed. And the lower redline isn't necessarily the lifter...it's the pushrod. THAT'S the heavy piece, and it can only change direction so often before stuff bends or breaks. Hydraulic lifters are RPM limited not because of weight, but because of "float" - they can only empty and refill so quickly, before they start to sit at "half-full", letting the rocker arm come loose - and when that happens, it gets ugly. DAMHIK. Wedging a rocker under the cam in a turbocharged 2.2 engine is a good way to break the cam, bend the valve, and tweak the cam support. | ||
| Hoppalong |
I appreciate everyone's responses. Today's motorcycles commonly have: EFI multiple engine tuning maps ABS traction control with multiple settings automatic transmissions dual clutch transmissions constant variable transmissions electronic suspensions with multiple settings tire pressure sensors etc I would think maintenance free valves on a modern motorcycle would also be a selling point. Maybe not on a sport bike, but not everybody wants a sport bike. When I got interested in the Ulysses I considered the maintenance free valves and belt as pluses not minuses. | ||
| Arcticktm |
Not sure I would call CVT, auto trans and dual clutches common. At least not yet. | ||
| Parker16 |
There is a lot of slack and flex in a push rod engine that changes with temperature. The hydraulic lash helps take this up. Other valve gear styles can eliminate/reduce much of the problem with moving all of that metal. However continued high speed running an engine with hydraulic lash adjustment can lead to "pump down" where you start losing lash. Eventually you could run out of lash and the valves would no longer seat. When I was involved in OE valve train, high engine speeds and hydraulic lash adjustment were not typically seen together. | ||
| Froggy |
Why not ditch traditional valves all together? http://www.coatesengine.com/csrv-system.html
I guess you didn't see the maintenance schedule in your service manual. This thing needs more attention than my ex girlfriend. (Message edited by froggy on July 10, 2012) | ||
| Teeps |
Hoppalong Posted on Sunday, July 08, 2012 When I got interested in the Ulysses I considered the maintenance free valves and belt as pluses not minuses. As did I. As well as no points or carb to tune. And, don't get me started on "no bling" to clean... |
