From: C. E. White on

"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


From: Steve on

>>
>> Toyotas have been using aluminum heads for as long as I can remember. My
>> first Corolla, a '74, had an iron block and aluminum heads, which worked
>> well for them, but was a fatal combination for certain Chevy (VEGA)
>> models...
>
> Actually Vegas had aluminum blocks and cast iron heads! One of the
> stangest combinations ever.


Similar combination to the '62 Chrysler 225 slant-6 (aluminum block
version). Cost and manufacturing considerations necessitated the use of
a common iron head on both the die-cast aluminum block and the
simultaneously-produced iron block version of the 225. The aluminum 225,
unlike the first iteration of the Vega engine, did have cylinder liners.
Both were, as you noted, open-deck designs with free-standing cylinder
bores.

Later, the notorious Cadillac HT-4100 4.1L v8 of the 80s used cast iron
heads on an aluminum block also. The failure of the 4100 really doesn't
say anything bad about iron heads on aluminum blocks, per se. The
slant-6 had relatively little trouble, although people who build them
today for restoration (and occasional racing- the bare block can be
hauled around one-handed!) note that it doesn't have a lot of margin for
high cylinder pressures and doesn't take well to much boost or any
detonation. But the stock ones held up just fine, and there are a
surprising number out there still running around (sometimes with the
owner completely unaware that its an aluminum engine). But conceptually,
it really is a little backwards to build a light aluminum block and then
penalize it with a pig of an iron head. If you need iron, it makes more
sense to use it in the BLOCK where the extra strength is most needed,
and that's why there are so many iron block/aluminum head engines still
in production. And looking back to the first poster quoted above, I
can't think of ANY iron block/aluminum head engine that proved to be a
"fatal combination." I know a lot of people believed it was going to be
awful when they first started appearing in the 70s, but in practice it
worked just fine with the correct choice of head gasket material to
allow for the differential expansion. Heck, my wife's iron
block/aluminum head Chrysler 3.5 has 260,000 miles and has never had the
heads off (or anything deeper in than the intake plenum gasket, for that
matter).


My memory of the Vega's problems pretty much agrees with yours- the main
flaw was the lack of rigidity of the block itself, allowing the
cylinders to "go egg shaped" with the slightest overheating (or even
normal spirited/agressive driving), resulting in huge oil consumption
and of course power loss.
From: Steve on
Built_Well wrote:
> Ray O wrote:
>> Some older Toyota engines (and current domestic engines) have
>> a single overhead cam, or SOHC.
> ========
>
> Single overhead cam (SOHC)!!!! Well, I guess that's better
> than using pushrods and rollers.

Dumb statement.

V-configuration pushrod engines can be significantly more compact than
OHC designs because the cam is tucked between the banks rather than
having a cam hanging out over the bank making the "V" both taller and
wider. Plus the cam timing wanders less because the chain is shorter.
And when there are other engine architecture considerations that make it
unnecessary to wind them tighter than 6000 RPM, overhead cams don't have
any advantage. That's why so many pushrod engines, ranging from
pedestrian GM v8s and v6 to the Corvette ZO-6 and Chrysler SRT-8 Hemis
are still being designed and built.



From: Steve on
C. E. White 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.
>


Probably a cost-of-production decision, IMO. rocker tip mounted
hydraulic lash adjusters are so tiny they don't add any appreciable mass
to the valvetrain, are almost impossible to "pump up" (I did a quick
calculation a while back that indicates it would require over 700 PSI of
oil pressure to "pump up" a lifter against valve spring pressure), and
keep the valve timing events right on spec over the life of the engine.

Don't forget, Toyota is learning from GM too. Learning how to live on
the laurels of the past and cut corners in the present. And how to
introduce a gas-guzzling pig of a truck just in the nick of time for
$4/gallon gas, leading to idling a shift at the new plant that builds it
in about 1 year of operation. That's gotta hurt. And that doesn't even
count the front suspension and brake recalls.... :-(

From: Dyno on
Steve wrote:
> C. E. White 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.
>>
>
>
> Probably a cost-of-production decision, IMO. rocker tip mounted
> hydraulic lash adjusters are so tiny they don't add any appreciable mass
> to the valvetrain, are almost impossible to "pump up" (I did a quick
> calculation a while back that indicates it would require over 700 PSI of
> oil pressure to "pump up" a lifter against valve spring pressure), and
> keep the valve timing events right on spec over the life of the engine.
>
> Don't forget, Toyota is learning from GM too. Learning how to live on
> the laurels of the past and cut corners in the present. And how to
> introduce a gas-guzzling pig of a truck just in the nick of time for
> $4/gallon gas, leading to idling a shift at the new plant that builds it
> in about 1 year of operation. That's gotta hurt. And that doesn't even
> count the front suspension and brake recalls.... :-(
>
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).

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.
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