Re: Some details of the 2AZ-FE engine

Dyno wrote:

> Actually, the reason to go to mechanical lash is not for high speed 
> valvetrain control but rather to reduce engine friction. The hydraulic 
> lash adjusters exert a significant amount of force on the cam base 
> circle, increasing mechanical friction. This IS both measureable and 
> does contribute to fuel savings. If you examine the base circle of the 
> came you can even see the lobe is narrower and flairs out to a wider 
> surface (Ford Zetec).

That would be a lot more palatable explanation if not for two factors:

1) Lash adjusters (unlike hydraulic lifters) are generally located at 
the valve-stem end of the follower. They're about the diameter of a 
valve stem, not a lifter. Therefore, the plunger inside them is about 
the diameter of a valve stem, not order-of 5/8 inch like a lifter. 
Taking the oil pressure and multiplying it by the surface area of the 
lash adjuster plunger produces a TINY number.  When lift begins the 
valves in the lash adjuster close and the entrained oil is 
incompressible so they don't collapse, but the BASE CIRCLE pressure is 
solely due to engine oil pressure multiplied by plunger area, and is 
miniscule.

2) With roller followers cam followers, adding base circle pressure 
doesn't increase friction much at all. That's one big reason they're 
used- far far lower friction than flat lifters from base circle all the 
way to full lift. And of course they can follow a lobe profile with a 
much sharper ramp rate so that you can get long duration without 
excessive overlap.

> 
> With modern oils and their additive packages, the need for frequent lash

> adjustment is very rare. Most will make it thought the mandatory 100k 
> emissions durability requirements with no adjustment.


No argument there, but I still think eliminating auto lash adjusters is 
more cost-driven than engineering-driven. And I don't even disagree that 
its a good idea to go ahead and save that money IF the engine can run 
200k miles without opening the overhead, as we've come to expect from 
cars with hydro lifters or hydro lash adjusters.