Hydraulic lifter bleed down

[David_viny]

Is it common practice to check hydraulic lifter bleed down rates when building a high performance engine? Maybe at minimum buy extra and match them to make a set of similar bleed down rates?

I've never messed with it before, but after reading a bunch about hydraulic lifters it seems lifter bleed down would be a pretty significant factor in how the engine runs.

[PackardV8]

The 1956 Packard V8 Shop Manual has a section detailing how to disassemble, clean, reassemble and test hydraulic lifter bleed down; there's a special plier-type tool to force the bleed down and how to determine if it meets specification.

If one builds a custom test bench and controls for oil viscosity, oil pressure, spring rate and RPM, then he might be able to produce a matched set which exactly meets the needs of a particular build.

In the real world, buying the best hydraulic lifters available is a better use of one's time.

(Can anyone else hear Joe Sherman calling from the great beyond, "Or just don't run a girly cam!"

jack vines

[CamKing]

Is it common practice to check hydraulic lifter bleed down rates when building a high performance engine?

No. Many people still mistakenly think the lifters are pumping up at high RPMs, and run anti-pump-up lifters, that actually have very high bleed rates.

Choice 1 for a high performance engine, is to not run hydraulic lifters.
Choice 2, is to run limited travel hydr lifters, so when they do bleed-down, they're only bleeding down .010"-.015".
Choice 3, is to lighten up the valvetrain as much as possible, so you can reduce the spring pressure, which will decrease the bleed-down rate.

[F-BIRD'88]

Hydraulic lifter are for da Gurlie-Man...

[ProPower engines]

Is it common practice to check hydraulic lifter bleed down rates when building a high performance engine? Maybe at minimum buy extra and match them to make a set of similar bleed down rates?

I've never messed with it before, but after reading a bunch about hydraulic lifters it seems lifter bleed down would be a pretty significant factor in how the engine runs.

What is the application and what engine is in question??

[cjperformance]

Is it common practice to check hydraulic lifter bleed down rates when building a high performance engine?

No. Many people still mistakenly think the lifters are pumping up at high RPMs, and run anti-pump-up lifters, that actually have very high bleed rates.

Choice 1 for a high performance engine, is to not run hydraulic lifters.
Choice 2, is to run limited travel hydr lifters, so when they do bleed-down, they're only bleeding down .010"-.015".
Choice 3, is to lighten up the valvetrain as much as possible, so you can reduce the spring pressure, which will decrease the bleed-down rate.

Exactly!

[BOOT]

^^^^^Ditto^^^^^

[RevTheory]

Does any one particular vender tend to do better than the others? I've been hearing good things about Johnson limited-travel lately.

[jed]

Just so I understand correctly a Rhodes lifter at idle and low RPM bleeds down guickly and the engine thinks it has a
Short duration camshaft.
Now As RPM increase to much higher RPM say 7000 the anti pump up lifter is actually
bleeding down even further making the engine think it has an even shorter duration camshaft and even less lift camshaft.

I don't know. I am one of those persons who "mistakenly thought that the lifter was pumping up at high RPM" simply
because that's what knowledgeable people told me.

[F-BIRD'88]

The lifter can pump up when there is valve float that creates valvetrain separation at rpm..( Lack of spring force for control.)

The hyd lifter can also collapse at rpm when oil is forced out faster than it can refill at speed. (Excessive spring force and excessive lifter parts cleance)

The lifter can also become compressive if when air gets into the oil at rpm. (Oil airation (crankshaft))
Once the engine oil is infected with air it can take a long time to recover. Eg: over night.

[PackardV8]

Just so I understand correctly a Rhodes lifter at idle and low RPM bleeds down guickly and the engine thinks it has a Short duration camshaft.
Now As RPM increase to much higher RPM say 7000 the anti pump up lifter is actually bleeding down even further making the engine think it has an even shorter duration camshaft and even less lift camshaft.

Completely inaccurate. Yes, the Rhodes, et al, have a calibrated orifice which at low RPM is sized to bleed off pressure as it is actuated by the cam lobe, thus minimizing the duration. No, you're not considering the time function. At 2,000 RPM, there's half as much time and at 6,000, 1/6th as much time per revolution. As RPM rises, the same orifice does not have as much time to bleed off pressure, so it more accurately produces the actual cam lift curve.

I don't know. I am one of those persons who "mistakenly thought that the lifter was pumping up at high RPM" simply because that's what knowledgeable people told me.

It's semantics, but important. Lifters do pump up and hold the valve open, but it's the springs which caused that to happen. When the valve springs can no longer hold the lifter against the cam lobe, the hydraulic lifter goes, "WTF, now we got slack here. It's my job to keep things tight; gotta pump up to take up that slack."

jack vines

[F-BIRD'88]

Jack Vines, as rpm increases there is also progressively LESS time for the lifter to refill with oil, from its leaked down, reduced valve duration- lift state when running at idle.

[MadBill]

I floated the valves a couple of times in my Mom's '56 Dodge wagon (43 MPH in 1st, AIR) and it pumped up the lifters so badly the car wouldn't start for half an hour afterwards...

[CamKing]

Like said above, a lifter will only pump up if you float the valves, and with today's spring pressures, that shouldn't happen.
As the RPMs increase, the forces pushing against the lifter also increase. At lower RPM's, the increase in oil pressure helps combat this, but as the RPM's increase, the added pressures start to collapse the lifter.
With Std Rhodes lifters, they bleed down even more at high RPM's then regular hydr lifters, that's why you need a longer duration cam with Rhodes lifters, to make the same peak HP.
The Rhodes V-Max lifters also bleed down, but since you set them .012"-.015" from bottomed out, they can only bleed down .012"-.015", and only lose a few degrees of duration.

[Stan Weiss]

Jack Vines, as rpm increases there is also progressively LESS time for the lifter to refill with oil, from its leaked down, reduced valve duration- lift state when running at idle.

Unless you have a constant speed oil pump the volume and pressure should increase with RPM.

Stan