Lower half of the engine is now at the machine shop. They were unfazed by my various concerns and from a visual inspection think it is a good candidate for a light hone & crank polish with standard size rings/bearings. They'll know more once they take their own measurements, but they estimate a ball hone would remove just 0.0005" from the cylinder and still leave me inside the factory service limit.
I'd kind of prefer to bore it since I don't see a hone/re-ring lasting another 250,000 miles, but this machine shop can't bore these cylinders because this block's main bearings are right below the cylinder which doesn't allow enough room for this machine shop's tools.
Their boring machine needs to punch all the way down through the bore, but on the 3MZ the main bearings overlap the cylinders and don't allow this. A different machine shop could do it, but the handful that are well-rated are backed up weeks to months (my first choice wouldn't even accept any new jobs). But I suppose if I was going to attempt a near Toyota-quality rebuild, I'd really want to find/build a torque plate so the cylinders could be stressed into their assembled shape when the machine shop did the actual boring. Perfection is the enemy of good?
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Originally Posted by cRiPpLe_rOoStEr
All other hardware being equal, it's quite intriguing how the 'Yota Atkinson-cycle hybrid engines achieved a greater static compression ratio.
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Unlike most of Toyota's other hybrids, 3MZ-FE in the highlander & RX400h was never converted to run an Atkinson cycle which I think it kind of a bummer (for fuel efficiency anyway). According to automotive press in 2005/2006, the 3MZ hybrid was mainly developed for the Lexus RX400 where power & refinement trumped fuel economy. It was just carried down to the Toyota Highlander to spread development costs out over more units.
The Highlander Hybrid would get the Atkinson cycle in 2011 when it switched to the 2GR-FXE engine. The 2010 & 2011 had the same chassis, but the Atkinson cycle 3.5L hybrid in the 2011 is rated at 28/28 mpg (city/hwy) vs 27/25 mpg for the 2010 3.3L hybrid (and 17/23 for the 3.5L non hybrid).
Those EPA ratings and retroactive estimates based on current methodology - the highlander was rated at 33/28mpg in 2006 (just like the 2006 prius was rated at over 50mpg)