Some details of the 2AZ-FE engine
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From: Steve on 24 Jul 2008 10:41 Scott Dorsey wrote: > > This means hydraulic lifters, but it also means sealed chassis components > that don't need regular greasing with every oil change but which fail > before 80,000 miles is up. It means "sealed for life" transmissions, where > that life is about half what it should be. Here here! Eliminating the dipstick on automatic transmissions has to be the single most unnecessarily STUPID thing car makers have done in the last 50 years. Maybe since the dawn of the automobile.
From: Retired VIP on 24 Jul 2008 13:28 On Thu, 24 Jul 2008 08:58:29 -0500, Leftie <No(a)Thanks.net> wrote: >Retired VIP wrote: >> On Wed, 23 Jul 2008 16:26:59 -0400, "C. E. White" >> <cewhite3(a)mindspring.com> wrote: >> >>> "Steve" <no(a)spam.thanks> wrote in message >>> news:AM6dnZjsFev_EhrVnZ2dnUVZ_vednZ2d(a)texas.net... >>> >>>> Shims-in-a-bucket cam followers for valve adjustment is positively >>>> stone-age (the last car I had so-equipped was a '78 Plymouth Horizon with >>>> the VW-based SOHC 4). Rocker-tip mounted hydraulic lash adjusters that are >>>> common now don't carry enough mass penalty to worry about and are commonly >>>> used in engines with 7500+ RPM redlines. That said, I never had to adjust >>>> the valves on that VW engine either. Everything else about it sucked, but >>>> the valves never needed adjustment! ;P >>> Numerous modern engines from Toyota and Nissan do not use hydraulic lash >>> adjustment. The most modern Camry V-6 does have hydraulic lash adjusters, >>> the older Camry V-6 and 4 cylinders do not. The engines without hydralic >>> lash adjustment do require routine valve clearance checking (if not actual >>> adjustment). I think this requirment is widely ignored. Interesting, Fords, >>> newest V-6 also does not have hydraulic valve adjustment - I guess they have >>> learned from Toyota. >>> >>> Ed >>> >> >> I guess I'm just to stupid for my shirt. How is increasing the amount >> of necessary routine maintenance as well as increasing the cost of >> operation a step forward? >> >> Jack > > > There are two problems with hydraulic lifters: they are more >expensive to build and, more to the point for us, they tend to fail long >before the rest of the engine. Who wants to have to spend $1k on new >lifters on a car with 150k miles on it? The shim & bucket type setup >rarely needs adjustment when properly designed (and it is as used by >Toyota and Volvo in their older engines) and it doesn't fail. I've had >two cars and one motorcycle suffer from hydraulic lifter failure. I'd >much rather have the valves adjusted every 5 years or so. Ok, I'll grant that hydraulic lifters are more expensive to build but 'they tend to fail long before the rest of the engine'? Maybe for people who don't change their oil but in over 35 years of car ownership, I've NEVER had hydraulic lifters fail. I have heard a lot of cars with solid lifters clicking and clacking down the road sounding like an old Singer sewing machine and punching holes in their rocker arms. This would seem to me to be another example of why bean-counters should be kept in a locked room. They should never be allowed to attend management meetings or review mechanical drawings. Jack
From: Dyno on 24 Jul 2008 14:50 Steve wrote: > 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. > Not all hydraulic lash adjusters are that small. Some are actually nearly the diameter of the bucket itself minus the wall thickness. Nevertheless, I have seen the friction measurements and the mechanical lash systems DO have lower friction. How minuscule are we talking about here? Sample base circle load calc: Oil Pr : 60 psi Adjuster Dia: 0.30 in # Valves: 16 (4 cylinder) 60 psi x pi*(.15^2)*16 = 68 lbs is small? Maybe it is, but it certainly is more than ~0. I don't think this is negligible. And detailed engine friction studies have verified the reduced friction using mechanical lash systems. > 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. Agreed, roller followers are in a different category and do have low friction. But, they are costly and tend to be relatively bulky. Because the roller assembly has to be controlled by the valve spring, they tend to weigh more and are not as stiff as a direct acting bucket. Valvetrain stiffness is critical when you have aggressive acceleration rates in the opening/closing ramps. > >> >> 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. No doubt cost is a driving factor. But, if one can get equivalent durability at a lower cost with some fuel savings, why not do it? I know the simple mechanical valvetrains do pass the manufacturers 300 hr durability tests.
From: N8N on 24 Jul 2008 15:28 On Jul 24, 2:50 pm, Dyno <d...(a)null.torque.net> wrote: > Steve wrote: > > 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. > > Not all hydraulic lash adjusters are that small. Some are actually > nearly the diameter of the bucket itself minus the wall thickness. > Nevertheless, I have seen the friction measurements and the mechanical > lash systems DO have lower friction. > > How minuscule are we talking about here? > Sample base circle load calc: > Oil Pr : 60 psi > Adjuster Dia: 0.30 in > # Valves: 16 (4 cylinder) > 60 psi x pi*(.15^2)*16 = 68 lbs is small? Maybe it is, but it certainly > is more than ~0. > > I don't think this is negligible. And detailed engine friction studies > have verified the reduced friction using mechanical lash systems. Don't forget that you also have more reciprocating mass therefore the valve springs would need to be heavier for the same RPM capability. nate
From: Leftie on 24 Jul 2008 17:16
Steve wrote: > Leftie wrote: > >> >> There are two problems with hydraulic lifters: they are more >> expensive to build and, more to the point for us, they tend to fail long >> before the rest of the engine. Who wants to have to spend $1k on new >> lifters on a car with 150k miles on it? > > > They FAIL before the rest of the engine? Hardly. Ask any mechanic how > many hydraulic lifters or lash adjusters he's had to replace because the > lifter or adjuster ITSELF was a root cause of a problem in the last 10 > years and I'll bet you can count the average answer on 1 hand, and if > you probe further you'll find that those were typically in badly > neglected sludged-up engines. My engines were not "badly neglected". The motorcycle was given full synthetic oil. The two Mazda engines may have had poorly designed oil passages, but I've also heard from other people abut lifters failing. Think of all the "stuck lifter" stories out there, and you may realize that it isn't just bad maintainance causing it to happen. |