Difference between hydraulic and mechanic Valve Lifters

[Stallion]

I was looking at the specs of the '69 and the engine types originally in them, and the first four engines (Base 327, L46, L36, and L68) they have hydraulic valve lifters and the L71 and L88 have mechanical valve lifters.

What are the exact differences in these two methods? Are there any advantages/disadvantages to hydraulic/mechanical? Is mechanical the best?

Thanks!

 

[Ken]

Valve Lifter:

1. The cylindrically shaped component that presses against the lobe of a camshaft and moves up and down as the cam lobe rotates. Most valve lifters have an oil-lubricated hardened face that slides on the cam lobe. So-called "roller lifters," however, have a small roller in contact with the cam lobe -- thereby reducing the friction between the cam lobe and the lifter. Also called "valve follower" or cam follower.
2. A tool that compresses valve springs for removal and replacement. Also see hydraulic valve lifter

Also known as...

Valve Tappet:
An adjusting screw to obtain the specified clearance at the end of the valve stem (tappet clearance). The screw may be in the top of the lifter, in the rocker arm, or in the case of the ball joint rocker arm, the nut on the mounting stud acts in place of a tappet screw.

There are two types as you have already discovered...

1. Hydraulic Valve Lifter:
   A lifter that uses hydraulic oil pressure to maintain no clearance between metal parts so that valve noise is reduced. Also it reduces wear on the valves and eliminates periodic valve adjustments.
   
2. Mechanical Valve Lifter:
   Mechanical, or "solid" lifters have no hydraulic mechanism to pump-up. Mechanical lifters should be used when hydraulic cams reach their maximum RPM potential. Theoretically, with the correct cam and engine components, a mechanical lifter cam has an RPM potential of 8000 to 8500 RPM. Mechanical lifters are noisier than hydraulics. The engine must have an adjustable valve train system. Valve lash must be set, periodically checked, and maintained. (Mechanical lifters CANNOT be used on a hydraulic design cam.)

As for which is best, well...

_ken

 

[Stallion]

Thanks for the information, Ken! So, I guess that the "desired" type is a hydraulic, but it can't handle the higher RPMs so the mechanical lifter is necessary.

Question, you were talking about how there was, for mechanical, more noise and more friction, so would the mechanical lifters (as it said, to be checked frequently) need to be replaced more often due to being worn down?

Thanks again!

 

[Ken]

Wear is not necessarily a factor, and as for constantly having to adjust the solid valve lifters, that is pretty much a thing of the past as well. Today we have poly-locks to keep the rocker arm adjustment set and rocker arms from chattering.

_ken

 

[Stallion]

Yes, but if you don't have a Vette that has a recent engine and it using mechanical lifters (such as an L88), would it be a lot of maintanence (sp?) on the lifters from the wear?

Thanks!

TR

 

[sscam69]

See the lobe of the cam and the lifter are actually offset a little less that half way.

In other words the "Tappet" "lifter" or whatever you want to call it does not sit directly on top of the lobe. The reason for this offset is so that as the cam pushes the lifter up the "tappet" rotates and evenly wears the bottom of the tappet.

If it does not spin thats bad news. That means that the tappet will get worn down with time and start to make a funny ticking noise. Yeah I know the whole engine makes a lot of ticking noises :L but its distinct. and also wear down the actually cam lobe reducing the amount of lift of the valve.

Thats why when you install a cam its extremely important to run the engine up to 2500 rpm for at least 15 min to get those tappets to spin and get the lobs broken in.

Unless your spinning the engine up to 8K rpm just stick with hydraulic. Typically mechanical tappets are for all out racing. So unless you are doing that don't sweat it.

Are you getting an L88? Because thats an extremely RARE VETTE and believe me I would not be driving that car in the street.

 

[sscam69]

That's right! The cam floats in the block. Actually all the lobes on the cam are ground at an angle to keep the lifters rotating to reduce wear. This angle forces the cam rearward into the block using the cam gear as a stop.

Just found this response from Stingray6974 to another person, hope this helps some.

 

[Stallion]

See the lobe of the cam and the lifter are actually offset a little less that half way.

In other words the "Tappet" "lifter" or whatever you want to call it does not sit directly on top of the lobe. The reason for this offset is so that as the cam pushes the lifter up the "tappet" rotates and evenly wears the bottom of the tappet.

If it does not spin thats bad news. That means that the tappet will get worn down with time and start to make a funny ticking noise. Yeah I know the whole engine makes a lot of ticking noises :L but its distinct. and also wear down the actually cam lobe reducing the amount of lift of the valve.

Thats why when you install a cam its extremely important to run the engine up to 2500 rpm for at least 15 min to get those tappets to spin and get the lobs broken in.

Unless your spinning the engine up to 8K rpm just stick with hydraulic. Typically mechanical tappets are for all out racing. So unless you are doing that don't sweat it.

Are you getting an L88? Because thats an extremely RARE VETTE and believe me I would not be driving that car in the street.

I'd love to get an L88 D), but I don't know yet. I haven't set my eyes on one specific Vette yet. I'm not going to be too particular, but I would like at least an L82. I would also be happy with an L48 and then I could mod it to get more power.

TR