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From: C. E. White on 23 Jul 2008 16:26 "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 23 Jul 2008 16:32 >> >> 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 23 Jul 2008 16:39 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 23 Jul 2008 20:43 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 23 Jul 2008 21:28
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. |