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And this overhead cam system and shim adjustment is exactly the system used on the "50's" Jaguar XK 120's

Only the manufacturer "requires" service because they don't want to pay for warranty reparis that could have been avoided. The dealer only "recommends" service to make money.

But the Jag (wonderful and beautiful as it is) didn't have variable valve timing of the Prius!

(Both are a helluva lot better than my VW's solid pushrod system that requires valve lash adjustment every 3-5000 miles)

Variable valve timing is wonderfull for fuel economy but not necessarily for performance.

Honda's VTEC technology seems to have been invented as a way to provide high performance in a smaller engine.

there are no shims for the lifters in the 2g prius. there are no hydraulic tappets either.

That would imply that they would do a physical valve clearance check just as the maintenance site calls for.
Right?

yes... technically. but it is not done in practice. like, ever. techs don't sell it. my husband has only ever measured valve clearance while doing engine overhauls, and even then it wasn't ever really needed. he only did it because he was in there anyway and he's a bit of a perfectionist on his engine work.

we've run camrys well past 250k without so much as measuring valve clearance. in DH's experience with yota engines (considerable) the cylinders wear before valves go out of adjustment.

Again, the word "inspect" does not really mean open up and measure. An inspection could simply be listening to the engine to determine if further investigation is necessary is probably all that is implied. Like I said, when they check your heart during a routine doctor's appointment, they don't cut you open. They listen to it with a stethoscope. If they hear anything abnormal or you have any additional complaints they may schedule further tests. The same thing should apply here.

Sounds good to me, I guess the OP will know soon.

I don't know, but I have never heard of any internal combustion engine where the cam lobes turn directly on valve stems. If there is anything in between and there are no screw adjustments then it is as Rickey stated, there are "shim" type adjustments in the valve train. (probably in "buckets" riding on the valve stems)
If Dan Man is monitoring, I am sure he has a "PDF" schemetic of the valve train and can clear this up. Sorry I "dumped" my service manuals. At least some of the drawings in Japanese would have clarified this.
(Of course, the next guy in for service can ask a Toyota service manager to explain this.)

There are no shims used in the 2g prius. If there is excessive clearance you replace the lifter assy. with one of the correct size. There are 35 different size lifters to choose from. We do fleet maintenance. I've had them torn down.

So no more adjusting "shims' adhering to the bucket ( Used to be across entire Toyota engines )
Valves: No adjustments via the shims according to Toyota Service, replace the entire lifter.
Lots of work involved, remove timing chain, remove cam shaft. remove lifter assembly.
then measure the _worn lifter, find new lifter thickness. replace with the closest one.
Intake A=B+(C-0.20 mm ( 0.008 in.
Exhaust A=B+(C-0.30 mm ( 0.012 in.

My Certified Master Prius Tech says: with every 5k normal Oil changes the Prius ICE
valves should never need adjustment for at least minimum 150k miles? Sometime the worned
down side of the lifter ( the part that pushes the valves ) gets noisy because of tolerance enhancement but it is just "Noise" disregard noise, engine should run fine.

Probably anyone owning Prius will change for the Gen III before spending money to adjust valve replacing the lifter.

pictures here
http://priuschat.com/forums/prius-techn ... tment.html