questions re: solid & hydraulic

[jmp]

OK, this is mostly for curiousity's sake, but the whole solid vs. hydraulic thing kind of confuses me.

I'm not talking about which is better or why one is better, etc, but more of what are the actual, physical differences is setups. Some of my questions, I think, are going to boil down to terminology and definitions, rather than actual technical discussion.

Let me give some examples.

As far as I can tell, there's a "solid" cam setup and a "hydraulic" cam setup. Then there's the "roller" option which, I think, is available for both solid and hydraulic.

Now, we've got lifters, rockers, and the cam itself, right? Well, I can see how the rockers differ between "roller" and "???" whatever the non-roller term is. With lifters, there's solid lifters and hydraulic lifters, and I believe I understand the difference between the two. There also appears to be roller and non-roller lifters, which I'm guessing comes in both solid and hyrdraulic. Correct so far?

What about the cam? I've seen articles discussing "solid roller cams" and "solid cams", so I'm guessing that there are four different kinds of cams: solid, solid roller, hydraulic, and hydraulic roller. But where exactly do the hydraulics come in? What is "rolling" in a roller cam that is not rolling in a non-roller cam?

I'll probably have more questions after the first round of answers, so I'll leave it here for now!

 

[Stallion]

I'm not sure I understand your question, but if it's what I think it is, then I think I might be able to help you out.

There are two types of lifters. Hydraulic and mechanical. Hydraulic is the most desired. Less wear, less noise. But, I believe that hydraulic is only used in small blocks. Therefore, the big blocks need the mechanical lifters. I'm not sure why, but that's my understanding of this.

 

[jmp]

Well hydraulic lifters are the only thing the I know exist for sure, but going through the auto mags and articles, I come across terms such as hydraulic cams. Is the cam actually different? Does it have some hydraulic component? Or is it just meant to be used with hyrdraulic lifters?

 

[JohnZ]

There are four basic kinds of lifters, as you mentioned; solid and hydraulic, with flat-face and roller versions of each.

The cams designed for them are also different, in several ways. In the flat-tappet (lifter) cam designs, the lobe profiles are generally more radical (more lift and duration) for cams designed for use with solid lifters, they use stronger valve springs to enable higher rpm operation without "float", and solid-lifter cams also have "clearance ramps" at the very beginning and end of the lobe profiles that more gently accelerate and decelerate the lifter to take up the clearance ("lash") in the system. Hydraulic-lifter cams don't have clearance ramps, as the lifter maintains zero clearance in the system all the time, and hydraulics don't have the high-rpm capability of the solid-lifter types due to the dynamic limitations of the hydraulic system in the lifter and the lifter's added weight. Flat-tappet cams are machined from cast iron blanks to be wear-compatible with the cast-iron lifters, and the lobe surface is ground at a very slight angle (in side view) to promote rotation of the lifters to equalize lifter face wear; this angle also maintains a small degree of rearward force on the cam to keep it from moving forward.

Roller lifters require guide plates or links to keep the axis of the rollers parallel to the axis of the cam, and the cam lobe profile (in side view) is perfectly flat (no angle like flat-tappet cams) for full contact across the surface of the roller and the cam lobe. Lack of the slight angle leaves the cam free to move forward, so roller cams require a cam "button" or bearing inside the timing cover acting on the front of the cam to restrict its forward movement. Roller cams are machined from steel blanks (not cast iron) to provide a compatible wear surface for the steel rollers in the lifters; this causes a wear problem with the cast iron drive gear on the bottom of the distributor shaft (which is driven by the gear on the cam), so a special distributor shaft drive gear is required (usually a bronze alloy), whose life is limited. Some recent roller cams have pressed-on cast iron drive gears to allow use of the normal iron gear on the distributor shaft. This isn't an issue with modern OEM roller cams, as those engines either don't have distributors at all (computer-controlled coil-on-plug systems, etc.) or have distributors that aren't driven by a gear on the cam.

Use of flat-tappet vs. roller cams or solid vs. hydraulic lifters aren't tied to any size (SB vs. BB) vintage Corvette engines; solid and hydraulic setups, both flat-tappet and roller, are available for all engines in any combination you like, from many vendors.

 

[jmp]

Well, there you go then. Thanks, JohnZ!

 

[Stallion]

Yes, thank you, John!

Did you get my Private Message?

 

[JohnZ]

Missed it the other day - don't get many; just responded to you.

 

[Stallion]

Thanks, John! I just replied to that one you sent. Hehe .

TR