so i understand the basics like hydraulics have a preload and solids run a clearance but there's got to be more to it. someone told me solid lifters mean they are literally solid. if that's so, how do they get oil up the pushrod? why are solids supposed to make more power than a similarly sized hydraulic? is there any reason you can't run a solid cam with hydraulic lifters and vice versa?
these seem like such rookie questions but they're ones that don't seem to get answered in alot of books.

 

As always there's more to it, but in a nutshell:

1) The lifters are called "solids" because there are no springs or hydraulics in them - nothing that will compress. Solid lifters do have oil passages in them, and may even be made up of multiple pieces. In fact solid roller lifters have a wheel and needle bearings.

2) Hydraulic lifters are subject to this thing called "hydraulic intensity" which limits how quickly the cam can open the valve without "collapsing" the lifter mechanism (which would be detrimental in terms of performance). With a solid lifter, the cam profile can be more aggressive and can accelerate the valve off the seat and open it fully more quickly, resulting in "more area under the curve" (more valve opening during the same period) than is possible with a hydraulic. This is why solids will make more power, and you can turn them more rpms because the hydraulics can start to have problems at high rpms. Because of the difference in ramp rates on the camshafts, in general it's not wise to put hydraulic lifters on a solid lifter cam, and vice versa.

Dan

 

thanks dan,
so in a solid lifter, does it rely only on oil pump pressure to get oil up to the rockers?

 

Yes, there is no difference in solid vs hydraulic in the way oil travels or is supposed to travel.

 

o.k. now wait a minute. i thought in a hydraulic, the valve spring pressure as the lifter rotated onto the cam lobe caused the plunger to compress and that is what forced the oil up the pushrod. that isn't correct?

 

No, that is not correct. A hydraulic lifter is not a pump. Oil pressure is the only thing forcing oil up the push rod. And oil pressure keeps the plunger from sinking or compressing while the engine is running. The reason the lifter rotates is to reduce wear between the cam and lifter.

 

o.k. i was unclear on the rotation. i only meant the cam rotates and the lifter "rotates" onto the lobe ramp. i just thought the 'moment of inertia', i.e. the 'static' load on the plunger spring gave way to the inertia of the cam lifting the tappet. i thought that vertical acceleration of the lifter body and the subsequent lag reaction of the plunger to 'catch up' is what forced the oil up through the pushrod.
apparently, i'm overthinking things.

 

while i'm at it, i really have to test you on that. my assumption is backed up by observation.
i observe that while adjusting hydraulic lifters, they only squirt oil on valve opening event. by your description, an oil pump would provide a constant stream of oil through all 16 pushrods while the engine is running.
where/how am i wrong?

 

I don't know - maybe because that's when the oil hole in the pushrod is best aligned with the oil hole in the rocker arm??

Next time you have the valve covers off and the distriutor out, put an oil priming tool in the distributor hole and run it with a drill motor to drive the oil pump and you will see oil flowing, albeit slowly, out of "most" of the pushrods/rocker arms, if not all, without the engine running. Try it.

 

The oil comes out of an oil passage in the lifter bore. The sides of all types of lifters have passages to the top center where the push rod hole resides.

Of course as the lifter travels up and down it passes by the lifter bore oil transfer galley. So yes it does shut on and off to oil flow.

H-lifters also have a bleed off rate. I used to run the Crane Hi-Intesity H-flat lifters. Kind of like the Rhoads lifter that varies the cam timing with the RPM because of changing oil pressure.

The solid cam ramp is steeper and gets the valve open faster. try to use a H cam on a solid ram could exceed the lift rate and compress the internal plunger. So you would not be getting valve lift. H cams whether roller or flat are kind of RPM and total lift limited by the amount of spring pressure they can run before the internal plunger is actually compressed.

 

i will differ to more knowledgable people.
danno, your reasoning sounds logical although i think george is probably 'more' right.
well, i've learned something anyway so it was worth it.

 

Oiling: The lifters do not give and are solid, however there are oil ports on the side of the lifter and when oil under pressure enters, pressure causes oil to flow through the pushrod. I have one on my desktop at this sec. same way for stock I believe. my example is from a solid lifter i used on a 351(427) ford engine.

Power: figure that for a hydraulic cam the lobe profile is "smoother" around the lobe. For a solid cam, you can have very little lift at small duration, but quickly increase the lobe angle very fast. The solid lifter, given the right valve spring pressure will stay on the cam lobe, the hydraulic lifter and lower valve spring pressure will bounce.
Ie, more power due to more cam lobe under the duration curve.
assumming the engine can use the area.

If you try running a hydraulic lifter on a solid cam, expect the cam lobes to get "artificially" reduced the first time you rev the engine.
The acceleration ramps of the cam are just to quick for the low tension valve springs and a hydraulic lifter. If you used a solid lifter on a regular cam, I don't think this is good either. Its been a while, but I believe the cams are hardened diff for the solids. ask someone like comp cams.

 

o.k. for my next question, let's switch to rollers.
given the more aggressive nature of solid vs. hydraulic cam specs,
1) could you interchange hydraulic rollers for solids and vice versa?
2) [the real question] can you 'make' hydraulic rollers solid?

 

[QUOTE=gkull]The oil comes out of an oil passage in the lifter bore. The sides of all types of lifters have passages to the top center where the push rod hole resides.

Of course as the lifter travels up and down it passes by the lifter bore oil transfer galley. So yes it does shut on and off to oil flow.

H-lifters also have a bleed off rate. I used to run the Crane Hi-Intesity H-flat lifters. Kind of like the Rhoads lifter that varies the cam timing with the RPM because of changing oil pressure.

The solid cam ramp is steeper and gets the valve open faster. try to use a H cam on a solid ram could exceed the lift rate and compress the internal plunger. So you would not be getting valve lift. H cams whether roller or flat are kind of RPM and total lift limited by the amount of spring
QUOTE] George you have just made the argument for why I run a rev kit with my hydraulic cam. More spring pressure without collapsing the lifter. Some will say that a rev kit don't help but that argument is not logical when you look at how the system works.

 

1) Wouldn't matter. The same logic applies as the tappet questions. Ramp rate/spring pressures can or will overrun the hydraulics ability to handle the pressures, tappet or roller.

2) Sure, I suppose it's just an engineering problem, but why spend $$$$ on engineering that no one cares about. You decide on the engine you want or the rules tell you what engine to run. Maintanance wise, solids aren't very difficult to live with. They're usually run by gearheads that like the tweaking aspect anyway. Of course you could just fill them up with JB Weld.

 

2) seems like it might just take a steel dowel roughly the same (installed) height and diameter as the spring. just thinking about doing that with my 4.3 for the track car.
just a thought...

 

Why???? I just looked at Summit, solid tappet vs hyd tappets & solid rollers vs hyd rollers. Within reason the prices are very close. $100 will buy tappets, $300+ will get rollers. Why try some mickey mouse crap when you can buy the correct parts. Gee, I saved $50 until the engine exploded doesn't make much sense!??

 

I remember reading that lifters have the closest machining of any part on the engine. There are even two different types of solid lifters to send varying amounts of oil up throught the pushrods.

 

well, the thinking is i already have perfectly good rollers for that motor that are hydraulic. just trying to think like a hotrodder.

 

Solids do have a tiny pump inside. In fact there a 2 types of pumps for solids inside. This is what lubricates the vlv train. Without it your rocker arms would be short lived. But there is no preload or collapse of the lifter plunger on a solid like the plunger does with a hyd.

Hyd lifters get confusing as they can pump up and actually keep the vlv off the closed seat at hi rpm - thus appears anti-pump-up lifters which are similar to fast bleed-down lifters but not quite the same. Forgive me as i can't recall why an anti-pump-up lifter is different than a fast bleed-down but there is a difference in design and function though they both control how the plunger cup pumps up. Actual anti-pump-up lifter use stronger plunger parts some how where fast bleed-down lifters have larger bleed orifices inside lifter.

As for an advantage, vlv always sees full lift with the solid. Personally i feel solid is more reliable with few parts though it still has an internal oil pmp. I have also read that the (hyd) lifter is the weakest and most delicate part of the entire vlv train. So unless the internal oil pmp quits for whatever reason the solid lifter will still do its job.

Ya know it does seem like solid cams have steeper rams but i can't explain why. Anyways my next/new cam is solid and i couldn't find a hyd to match the specs. Hoping the solid vlv's lash makes breakin succusful. Ruined my last hyd by turning on the starter while troubling shooting my ign. My guess/hope is a solid with vlv lash will be more forgiving to break in.

cardo0