Royal Enfield Motorcycles > Bullet with the UCE engine

How do Hydralic Lifters work. ?

<< < (2/3) > >>

ace.cafe:
That's a good diagram of how typical hydraulic lifters work.

Basically, a hydraulic lifter is a self-adjusting type of lifter, that is designed to take up any lash in the valve train which might occur from heat expansion or for any other need.
This is set by "pre-loading" the lifter to be able to have enough distance to make the necessary length adjustments to cope with any lash changes during normal operation.

When I look at things like this, I don't only look at "how they work".
I look at what happens when they don't work.

One of the limitations of a hydraulic lifter design comes in high performance applications.
In theory, any amount of pre-load that you have adjusted into your hydraulic lifters can be "pumped-up", causing the lifter to be too long, if certain things occur during the higher rpms of your rev range.  If there is any pushrod flex, or momentary valve float in the valve springs, which can occur in high rpm conditions like racing, then the hydraulic lifter treats this the same way as it treats normal valve lash, and takes up the distance by becoming longer. This "pump-up" then makes the lifter longer than it should be, and it holds the valve off the valve seat, losing alot of power and potentially burning a valve.
As you reach near your limits of valve train stability, it doesn't all happen at once. You may start to see some pushrod flex or momentary valve spring float at rpms lower than your theoretical maximum rpm. And the hydraulic lifter will take up this distance and them become too long, and you'll then lose power from compression leakage at the valves.

Most people generally consider hydraulic lifters to be suitable to 5500-6500 rpms. Above those rpms, there are some "anti-pump-up" types of hydraulic lifters that can be used, or most people then switch to a solid tappet, and if they have roller tappets they switch to a solid roller tappet. This solves the rpm limitations that are seen at higher rpms in hydraulic tappets.

In the UCE, the rpm range is well within the ability of a hydraulic tappet to handle. it's a good quiet system, and is not going to have pump-up problems in this normal application.
For a racing application in which rpms higher than 6000 rpm are contemplated, it would be prudent to switch to a solid roller tappet to avoid "pump up" issues with the hydraulic ones.

This is a well-known issue that is discussed often in racing communities. The rule of thumb is hydraulics are ok under 6000 rpm, and use solids at higher rpms. There are ways to modify hydraulic tappets to "act" like solids, but that's another topic. At that point, you may as well just install solids.

chinoy:
Thanks guys.
Good find there Ric.
With the Bullets 90MM stroke. I see no point in reving it out to more than 6000 RPM.
Unless you can somehow reduce the stroke.

WKinNJ:

--- Quote from: ace.cafe on February 03, 2010, 08:47:53 AM ---
One of the limitations of a hydraulic lifter design comes in high performance applications.....
Most people generally consider hydraulic lifters to be suitable to 5500-6500 rpms. Above those rpms, there are some "anti-pump-up" types of hydraulic lifters that can be used, or most people then switch to a solid tappet, and if they have roller tappets they switch to a solid roller tappet. This solves the rpm limitations that are seen at higher rpms in hydraulic tappets....
... The rule of thumb is hydraulics are ok under 6000 rpm, and use solids at higher rpms. There are ways to modify hydraulic tappets to "act" like solids, but that's another topic. At that point, you may as well just install solids.

--- End quote ---
Honda Motorcycles has been using hydraulic lifters in their engines for years, granted they are Overhead Cam designs - but red-line is much higher than 6,000 RPM.  I have a 1985 Honda Nighthawk with hydraulic lifters that red-lines @ 9,000 RPM and has 25,000 miles on it with no issues.   Also in the "stable" is a Harley Davidson XR1200 with hydraulic lifters and push-rods that red-lines @7000 (HP / 67kW @ 7000 rpm).

ace.cafe:

--- Quote from: WKinNJ on February 14, 2010, 11:25:23 AM ---Honda Motorcycles has been using hydraulic lifters in their engines for years, granted they are Overhead Cam designs - but red-line is much higher than 6,000 RPM.  I have a 1985 Honda Nighthawk with hydraulic lifters that red-lines @ 9,000 RPM and has 25,000 miles on it with no issues.   Also in the "stable" is a Harley Davidson XR1200 with hydraulic lifters and push-rods that red-lines @7000 (HP / 67kW @ 7000 rpm).

--- End quote ---

Great!
Your Honda has anti-pump-up lifters. They have a rapid bleed-down feature.
Your Harley might too, being that it is a sport model which has a higher redline than a typical Harley would encounter.

That doesn't help engines which don't have them.
Most Harleys don't have them, and the UCE doesn't have them either.

motomataya:
a 1985 Honda doesn't have hydraulic lifters they have hydraulic valve adjusters. Its very different.

Navigation

[0] Message Index

[#] Next page

[*] Previous page

Go to full version