Cadillac V-16 hydraulic lash adjuster

[bob horgan]

I'm not a mechanic and I will never need to know this. But... Can somebody GENERALLY explain in layman's terms, what the heck is a hydraulic lash adjuster and was it the first time Cadillac developed it, just for the V-16?

Thanks.

[Guest]

RE: question about "valve lash adjustors" and the Cad V-16

The "bottom line" is that the metals of a motor expand as the engine warms up, and shrink when the engine cools down. Therefore, the connection between the valves and the cam-shaft that operates them expand and contract, resulting in the "clearances" between these parts changing. When the engine really cools down, the excess clearances would result in noise. To eliminate this noise, engineers developed hydraulic mechanisms that automatically compensate for the changes in metal "size" due to changing temps., by automatically "taking up" these clearances.

There are two ways to do this. Lets dispose of the simple modern way first...known as hydraulic valve lifters. These are essentially minature hydraulic pumps that provide an oil cushion between the cam-shaft and the valve stem. Cadillac used the "modern" style hydraulic valve lifter on the SECOND of its two V-16's - introduced in 1938 (as well as its V-8 from roughly '35 on). Although a "flat-head" engine, the "SECOND SERIES" Cad. V-16 was VERY modern in its lower end design, which was a "square" bore/stroke relationship, its much shorter stroke making it smoother than the longer-stroke Packard Twelve.

Now...an important difference in "clearance take-up" technology. Valve "lash adjustors" are not hydraulic lifters! They do use the principle of hydraulics ( which does sound confusing - let me explain).

Valve lash "adjustors" are found on the FIRST Cad V-16, a long stroke overhead valve engine (and its "partner" the Cad V-12) introduced in 1930, and discontinued at the end of the 1937 production. They are also found on the 1932-1939 Packard Twelve ( which got more torque and raw power out of its larger displacement). They differ from hydraulic valve lifters in an important respect...in that the valve "train" is SOLID. Changes in clearance are taken up by an off-set roller that is hydraulically operated.

The concept of the hydraulic lash used by both the FIRST SERIES Cad V-12/V-16 and the Packard V-12 is similar. But, for those of us working on these fine engines...there is one important difference.

The Cadillac can be adjusted AS IF IT WERE a hydraulic valve lifter, but the Packard adjustment is fixed at the time of assembly - can only be changed by adding to or grinding off the valve stem. Incidentally, both of these fine engine designs used a roller cam follower.

Hope that answers your question !

Pete Hartmann

[bob horgan]

WOW! Is this a great forum or what? Thank You Pete for the expert information. I'm grateful for your time.