Can someone please explain what lifter bleed down is? What happens to the adjusted valvetrain in that 20 minute wait period before adjusting the second cylinder? When hydraulic lifters are set on a Gen 1 small block Chev as an example , I don't see people waiting to go to the next cylinder. I have the dealer do my work but would like to know the why's.

Thanks
Jerry

 

Hydraulic lifters are filled with oil from the oil pressure system of your motor. When the bike is running and the pressure is over zero the lifters are filled with oil. Since fluids can't technically be compressed they assume the variable distance between the cam lobe and pushrod that comes from cylinder height changes due to engine heat (amongst other things). They also allow a little bit of cushion when the valve actuates and puts downward pressure on the lifter, but that's a side effect of their operation.

When your engine is off there is no oil pressure so the spring pressure from the valve spring pushes down the pushrod and makes the lifter collapse. Since lifters are made to contain hydraulic pressure this doesn't happen quickly, hence the duration of time to bleed down. Once you fire the bike back up the oil pressure pumps them back up and you're back in business.

The oil that's pressurized inside them also flows up the pushrod to lubricate the rocker and valve tips.

 

when the engine has been run the lifter has been pressurized with oil, pumping it up. (hydraulic function as intended) when you remove the pushrods they expand a little more. when re-installing the pushrod or installing new ones, the adjusting of the pushrod is to find the center of the lifter travel. in the process of tightening the pushrod, the lifter does not immediately collapse, the valve usually comes off it's seat. the spring pressure on the pushrod pushes down on the rod, then the lifter until the oil has vacated the lifter and (if your adjustment is correct) the center of the lifter travel has been reached. it is the factory recommended method of doing the job. once the pushrod spins with your fingers, you know that the lifter has bled down, therefore the valve is back on it's seat again, and it is safe to rotate the engine.
as far as doing the small block chevy, we always did it with the engine running,(or b the manual) to the predetermined number of nut rotations.
m

 

Okay, thanks.
So when a cam & lifter upgrade is done, would you then have to submerge the lifters in oil to fill the chamber before adjusting.

Thanks

 

That often times doesn't work. I have a dedicated syringe with a plastic tip that I used to pre-oil lifters but even still the oil doesn't get everywhere until it's under constant pressure while being used in action. At least it helps the initial noise though being 75% oiled up already.

 

Guess it has already been said but lifters have a bleed relief. (Sort of like a car floor jack when you open it a little to let it down slowely) It is either thru a slot with a ball sitting in it, a flat disk with a + stamped in it that bleeds around the raised disk or an external groove in the plunger it's self. That bleed is designed to be overcome by the valve spring. The lifter without the bleed would go past letting the valve close since it has a good .150 of travel to allow for all the stacked up tolerance in the valve train. (length of valve and how deep it is in head, cam profile at low point, clearances worn. ect. So what happens is it pumps up and take all the lash out. If it goes too far, as the cam allows the valve to close. the valve spring will shut the valve even it needs to push the lifter (bleed) down some.

If you push hard on the lifter, you can collapse it but it is a pain. Then it will clack like it's going to blow up till the oil pump pumps up the lifter. I set hydraulics with no oil in them other than on the surfaces. if you pump them up, it is real easy to leave them too loose when finding no clearance with adjustable pushrods) I find it amusing when people say they here lifter when usually it is something else. If they have ever heard a bleed down lifter in a Harley, they would stand back a few feet.

 

I'd like to clarify a few things about lifer bleed down and function. To do so, I need to post a picture. This one comes from http://www.crankshaftcoalition.com and is OK to use copyright wise as this is for educational purposes.


This lifter is very close to a stock HD lifter with the exception of the check valve seat is countersunk into the plunger and the lifter body has a roller on the bottom.

1. The check ball cavity is what needs to be filled is with oil for the lifert to reduce lash on the valve train. When installing the lifter into a motor with the punger cavity and check ball cavity filler with plunger is extended all the way out so that the socket is up against the circlip. As the pushrod preloads the lifter the plunger needs to move downward in the picture. It's common to say that the lifter needs to collapse for this movement.

2. Assuming the check ball is sealing well, the only way for the plunger to move downward is to allow oil to bleed between the lifter body and the plunger. Setting the lifter to body clearance is what sets lifter bleed rate.

3. Lifter body movement does not pump oil up the pushrod. Looking at the picture, the pushrod cup gets its oil directly from the plunger cavity which gets it oil through an oil hole in the lifter body and another hole in the plunger. Pressure from the oil pump forces oil up through the pushrod tube.


When it comes to bleed down time, 20 minutes is a bit excessive on certain lifters. Woods lifters with stock oil might take that long. Most new lifter use lightweight machine oil which manage to bleed within seconds of placing a load on the lifter. Lifters that have been run in a motor will bleed longer as the motor oil is thicker.

It's worth noting that time the motor stops with a valve open the lifter collapses to lip shown in the check ball cavity. As soon as the force from the pushrod on the lifter plunger is released, the plunger spring pushes out the plunger, oil from the plunger cavity fills the check ball cavity and valve lash is restored.

Pumping oil into the side of the lifter only fills the plunger cavity. It does not fill the check ball cavity. Plunger movement is need but happens on first startup.

Here is a short video of a lifter pumping up for the visual. It's not quite correct as the lifter plunger action aids in lower cavity filling.

 

Max, what do you mean by this? It appears you are saying the bleed rate is adjustable.
2. Assuming the check ball is sealing well, the only way for the plunger to move downward is to allow oil to bleed between the lifter body and the plunger. Setting the lifter to body clearance is what sets lifter bleed rate.

In your example picture which is a close Harley except for no roller, where exactly is the bleed off. I assumed it was a channel where the spring loaded ball set?

 

It is but only by the manufacturer. The tighter they set the clearance between the lifter body and plunger the slower the bleed rate. IMO it has it's own set of issues. The tighter it is, the slower the plunger can extend. IIRC Woods gets his lifters from Johnson HyLift and they set then up specially tight. Those lifters cam rattle some up until the motor oil is warm.

What typically makes lifter rattle is thinner oil and higher bleed rates, The lifter collapses enough during valve lift that the setdown ramp is missed.

 

Know on a multi valve engine typicial in cars, when they stop leaving a valve in the open position, you can get some valve clatter. One of the worst ones I have ever had is RIP's new Subie Outback. I just shake my head when she starts it up when I am out in the shop.

Another interesting one is the Jeep I have been restoring for the last year. The engine was a factory rebuild that the previous owner let set and a freeze plug rusted thru and lead to overheating.
I went thru engine since the valves were coked up from oil going by the frozen rings and lifters were frozen I though.

I put everything back to spec including mismatching shell bearings to be mid tolerance. However, I still have a valve idle tap. It's the 1.5 AMC 4 cylinder. Torque non-adjustable rockers. All but a couple have a turn after no clearance. Two have 1 1/2 turns before bolt bottoms. That is only about .007 . Hard to get the valves length that close. Is it possible that extra turn would cause a click? Have not checked compression or leak down since overhaul. Only have about 300 miles on it. I have replaced the lifter now for the second time using
Federal-Mogul Motorparts Sealed Power when I checked the turn after no clearance.
I did not replace the rockers and the fulcrum looked good and still had the oil slots in them. However, they seem to have a lot of side to side motion but I could find no spec for that. Tick goes away with a little RPM but sounds like a diesel at idle. Idle oil pressure is 55 and running is 75. 75 seemed crazy high for a small four but that is to spec. Jeep 1993 has 299K on it and only had to rebuild AX5 five-speed, reseal the transfer and one universal on the front axle. Always heard Jeeps are trouble prone but YJ was built to go.