Originally Posted by oldbogie
Wow this got long!
OK Dustin some basics:
1) Typical cam in block engines use a gadget called a lifter or tappet, one in the same thing. They can also be referred to as "cam followers" but this is more a Euro term and probably better fits some types of overhead cams where a follower is sandwiched between the cam and valve stem.
2) Lifter's/tappets/cam followers in definition are broken down into flat or roller. This defines what method is used to track on the cam lobe. Flat simply means the lifter is running a simple flat surface against the cam lobe. Roller means there is a wheel arrangement that is tracking along the cam lobe. Cams for flat lifter or roller lifters even if they have the same timing and lift at the valve have very different lobe shapes. Flat tappet cams come almost to a peak because in part some of their duration at the valve is in the time it takes for the lobe's peak to sweep across the width of the lifter's bottom. An identical roller liftered cam will have a wide peak because the roller of the lifter makes an instant contact, therefore, there is no sweep distance of the flat tappet so that amount of time has to be built into the lobe.
3) Because the valves expand more than the rest of the engine as they get a lot hotter, the valve train needs to accommodate this dimensional change with a distance called lash. This causes lifter's/tappets/cam followers to be further divided by how they deal with lash. This results in "solid" or hydraulic definitions. Solid lifters need a dimension of lash, or looseness, which the valve stem takes some away as it expands but never all of the lash distance as if the valve were to hang open it will burn away. Hydraulics are set up at zero lash dimension and accept the changes in the valve stem length with an oil filled plunger. Solid and hydraulic mechanisms can be applied to either flat or roller tappets.
A) Solid lifters aren't really solid pieces of metal, that would be really heavy so they are hollow inside. They have a cap that sits on a register inside the body making for a solid connection between the bottom and top of the lifter. The cap will have a retainer usually a wire bale or a Cir-clip. They may be full of oil as some engines like the Chevy pass oil into the lifter to flow up the pushrod and lubricate the rocker arms and cool the valve springs. Others like the Ford FE do not lubricate the top end thru the lifters and pushrods. So as you get into engines you'll see differences like this. When a solid lifter is disassembled there will be no mechanism inside, unlike the hydraulic which is full of stuff.
B) Hydraulic lifters maintain a zero lash once set up. They, also, have a cap in which the pushrod sets like a solid lifter, but this cap is not seated into the outer body of the lifter. Instead it is the top of a mechanism that is supported by oil pressure. The mechanism is retained by a wire bale or Cir-clip just like a solid lifter, so just looking at them isn't a visual aid as to which is a solid or a hydraulic. These work by timing the cut off of the engine oil supply into the lifter's piston and the back force of the valve spring along with some degree of internal leakage. There is an oil supply hole in the body which floods oil to the underside of a piston assembly inside the lifter which has a check valve on its bottom side. As the lobe begins to raise the lifter, the valve spring pushes back shoving the piston into the spring loaded check valve. This allows the plunger to both stay in contact with the pushrod and to allow a dimensional lash, which in measure is about the same as that lash of a solid lifter but contact, while light, is never lost between the parts of the valve train so no noise. As the lifter's body continues to rise on the lobe, the plunger closes the check valve shutting off the plunger's oil supply hole. At this point the plunger is hydraulically locked and can move no further downward. The hydraulic lifter then acts as if it were a solid lifter. As the lifter descends off the cam lobe, the plunger rises from inertia which opens the check valve allowing engine oil pressure to keep the plunger in constant contact with the pushrod maintaining zero lash. The engine oil pressure is less than the closed valve spring pressure so the presence of engine oil pressure on the plunger is not strong enough to force the valve open as the lifter goes around the back (heel) side of the cam lobe.
4) So to find out if you have solids or hydraulics, just get 16 clean towels. Take the retainer clip from each lifter and dump out the insides on a towel. If there's a bunch of stuff in there its a hydraulic. Put the parts back in and lock them with the clip, the less the guts are handled the better.
Now it isn't a good idea to mix cams meant for flat tappet solid lifters with hydraulics and vise versa as the ramps for these two systems are different and cross pollinating parts will lead to increased wear on them. Of course in terms of flat tappet and roller cams, mixing these cams with the wrong lifter will lead to sudden destruction as roller cams have abrupt profiles a solid lifter can't track without digging into the lobe and the wide lobe under a solid lifter would put so much duration into the valve event that if parts didn't collide in the upper cylinder, there would be no compression from the simultaneous opening of intake and exhaust valves. For a roller lifter on a flat tappet cam, it would also be a disaster as flat tappet cams are typically made of cast gray iron which does not have enough surface strength to resist the roller's extreme contact forces. The roller would soon surface fracture the lobes till they ceased to be. Because of the peaking lobe shape, the timing would be really short as the intended sweep across bottom of a flat lifter by the lobe would instead just instantly shove the roller lifter up and then drop it closed with damn little duration.