OK ... education time for Ed.

What is the operation difference between solid and Hydraulic lifters? I know what a lifter does, how it works with the pushrods and valves and things ..

Also how does this relate to the cam?

Thanks for all the help. This place is GREAT!

Ed

 

because the lifter is actually solid the cam can have more aggressive lobe profiles. The sides of the lobes can much steeper giving higher lift earlier in the rotation. Also solids wont 'pump up' so they can rev well above hydraulic lifters.

 

Ed,

Both lifter types ride on the oblong lobes of the camshaft at the bottom. As the camshaft rotates (driven by the crank + timing chain), the lifter actuates the pushrod...and so on. The difference lies in their internal design.

Think of a hydraulic lifter as a shock absorber that uses internal valving to regulate its stiffness and dampening ability. Comparatively, a solid lifter is a rigid, non-adjustable piece of metal instead of a shock absorber. Accordingly, mechanicals require exact rocker to valve stem clearance (adjusted with feeler gauge) to function properly while hydraulics are adjusted by loosening or tightening the rocker arm nut so as to seat the lifter plunger (which is pushed down by the pushrod) somewhere in the middle of its travel.

Until recent years, solid flat tappets (lifters) were more synonomous with racing and high performance applications because they produced more precise performance characteristics and required periodic adjustment. Hydraulics were the standard in low or moderate performance engines due to their troublefree nature and more forgiving design. Recent cam and lifter design advances now allow hydraulics to compare favorably with solids (i.e. Comp Extreme) in performance applications. The main problem for hydraulics in the past was lifter "pump up". This is where the lifter piston would rise up within the lifter body at high RPMs to a point where it would adversely effect valvetrain operation.

Hope this helps!!!

Mark


[Modified by mdsmith, 9:00 PM 11/6/2001]

 

The reason solid lifters are used in racing engines is that they allow for higher revving. Hydraulic lifters, whether roller or flat tappet weigh more. Because of that, they create more momentum. The increased momentum makes it more difficult for the valve springs to push the lifter back down so that at higher revs, you will get valve float over 6,000 to 6,500 rpm's. This is a bad thing. Hydraulic rollers, because of the roller, will allow for steeper lobe profiles, and therefore you run higher lift while maintining a smoother idle with hydraulic rollers. However, you still can't go much over 6,000 rpm's with them before you run into valve float. Hydraulic flat tappets will allow you to run high lifts, but the ramp up has to be more shallow, so you will get a rougher idle with a high lift flat tappet cam. And again, valve float at > 6,500 rpm's. Mechanical rollers are lighter, there fore less momentum and no valve float, allowing higher revs and steeper lobe profiles. The problem is that they require more frequent adjustment.

 

Excellent replies...

To clarify- "in a nutshell"- from a purely mechanical perspective-

Solid lifters are solid. They do not have any internal hydraulic parts. Therefore, they must be manually adjusted to the proper clearance. As time passes, and things wear, they must be (periodically) re-adjusted to maintain the correct clearance. You don't adjust them to zero primarily due to heat expansion.

Hydraulic lifters have an internal hydraulic system which compensates for wear and maintains -0- clearance. Once adjusted into their operating range, you should be able to forget about them.

Hydraulic lifters were the answer to the constant maintenance requirements of solid lifters. Mom & Pop cars all had solid lifters when I was in diapers... solid lifters were not a performance prodcut, they were the only game in town.