Hello Everyone,

I was glad to find an active Olds forum site. I am building a 455 for my 68 Cutlass and am using a mechanical cam for the first time. I have a basic question regarding the operation of the lifter oiling piston...... How does the stroke of the lifter piston affect the valve lift as the cam rotates through one revolution?

I understand the lifter setup procedure for gap between the rocker and valve stem but dont have a firm understanding of how the mech lifter operates in relation to rocker oiling and clearance setup.

I have contacted the Mondello and Crane tech info lines but the answers these guys keep repeating over and over is only how to setup the valve clearance and I cannot make them understand my question in that I already understand the setup procedure as they have written it but want to understand the deeper question of how the oiling piston operates in relation to valve clearance?

68 Cutlass Supreme Coupe
70 Cutlass Convertible 4-speed

 

My understanding is that in a hydraulic cam lifter the oil pressure is what 'pumps' up the lifter and makes the plunger firm in the lifter. The plunger has little to do with how much oil gets to the pushrod and subsequently the rockers. The hydraulic lifter's purpose is to dampen the valve train shock when the lifter goes up the lobe...that is why you put a pre-load on a hydraulic lifter.

On a solid (mechanical) lifter the 'plunger' is fixed, it does not move. That is why you have to 'dampen' the shock to the valve train by adjusting the valves to the manufacturer's specifications (.018" - .020" as an example). The oil that goes up the pushrod is provided by the oil pressure in the lifter galley just like on a hydraulic lifter. The only difference is that the oil pressure is not used to 'pump' up the lifter like in a hydraulic lifter.

The short answer is that the oil is delivered by pressure in the lifter galley pushing oil into the lifter and up through the cup, and subsequently up the pushrod. The principle is the same for both types of cams. Hydraulic cams use oil pressure in the lifter to dampen the valve-train tension, and Mechanical cams use clearance to dampen the valve-train tension.

Clear as mud, right? Welcome to the forum

 

Hello and thank you for your response. Your answer was actually exactly what i was expecting to begin with when I started looking into choosing a mech camshaft. Here is my new problem however. The lifters I received from Mondello do have a piston action that I can compress and release against a spring, exactly like a hyd lifter. Would you confirm again that I should not be able to compress a piston at all in the top of my lifters for a mech anical camshaft? I have just rechecked my order info and shipping receipt from Mondello and confirm the correct part numbers were ordered and shipped but now I am concerned that the actual parts sent do not match the order info....

 

You should not be able to plunge the cup in a mechanical lifter...also, be careful dealing with Lynn Welfringer. In fact, my advice is to stay away from them completely.

For your reading enjoyment:

https://classicoldsmobile.com/forums...-mondello.html

https://classicoldsmobile.com/forums...-mondello.html

 

Mechanical cams = solid lifter cams. As above, the pushrod cup does not compress into the lifter; something in the valvetrain, pushrods or rockers, will be adjustable and the camshaft profile is ground with fairly long "ramps" to take up the clearance before raising the lifter. Hydraulic lifters have a movable plunger that the oil pressure keeps at zero clearance, and the cam profile has short ramps since there should be no clearance to take up. All the ramp does is smoothly start the lifter acceleration profile.

 

Much of the clearance in a mechanical lifter is there for heat expansion also. That clearance will tighten up as the engine gets hot. Without the clearance the valve would be open when it should be on the seat. The hydraulic system uses the oil to dampen the shock and take up clearance. Which reduces noise and wear.
Lift figures on mechanical cams don't take into account the 'lash' or clearance called for. So a mechanical cam rated at .500 of lift with .020 of lash is closer to .480 lift while cold and theoretically gets to it's advertised lift of .500 when hot.

 

I would see if you can return the lifters. Try to explain to them and see what happens.
I would use one of the Olds venders on this site. CutlassEFI is a dealer and will get you going in the right direction. maybe give advice on the cam you have, to make sure you have the best set up.

Gene

 

Actually the clearance with a solid cam loosens with heat. Cold, with an all iron engine, I set the valve lash .002" tighter than spec, so the lash will be correct at running temperature.

 

http://www.cranecams.com/pdf-tech-tips/mech-lift.pdf

Let this answer your questions

 

Thank you to all for the help, it is appreciated. I have now reconfirmed again that Mondello sent me the wrong lifters even though the order and shipping invoices all say the correct mechanical lifters, and until now I did not have the correct info to understand the difference.

I sadly am now part of the "Mondello Victims Group" as they basically said that they could not have possibly made a mistake. They did in fact send me hydraulic lifters. My order paper work clearly lists the mechanical cam part #MPV1-2 and matching mechanical lifters ML 235-sp. The lifters i actually received however are hydraulic with a compressable piston cup in the top of the lifter assembly.

Going to deal only with the reputable firms that so many have listed here for me.

Again, Thanks