There
are quite a few posts out there on the 'net from people that have, (or want to), install higher-lift camshafts in Vortec engines and have experienced issues with valve spring bind or interference with the pushrod holes, or valve springs or retainers hitting the valve stem seals or guides at full lift. Some have also put Vortec heads on older blocks, (or vice-versa?), and have had issues with the valve clearance to the bore in the block. A lot of them have come to the conclusion as a result, that the Vortec is indeed an "interference engine". But that isn't what the term "interference engine" refers to.
Interference engine means that in stock condition, operating under the conditions it's designed to operate in, the valves will hit the pistons if the camshaft gets out of time. Several internet posters have claimed that Vortecs are indeed interference engines because
their engine bent its valves when their clutch let go on the starting line and their tachometer needle ventured into territory it doesn't belong in. If that's the definition everyone agrees to go with, we'll have to expand the list of interference engines by quite a bit.
Here's a link to a Vortec "beehive" valve spring kit. A few guys that have installed these have posted that they cured the "interference engine" issue, (that they don't really have as far as I know), with their Vortecs.
Valve Spring Upgrade - Beehive Valvesprings for the Vortec V8 - Car Craft Magazine
The jury is still out as far as I'm concerned. Until I measure one myself or see it in a shop manual, I don't think the Vortecs belong on the interference engine list. Not too far off-topic, I got one of the "shop tips" emails at work from Foley Engines a while back, and it said 2.3 and 2.5 Fords are interference engines, and they aren't. They went on to say that the Deutz diesels with timing belts are too....they did get that one right.
Why would anyone move the crank or cam with the timing set removed?
It's done all the time to get things lined back up if a chain jumps or a belt breaks. A person needs to be careful and know what they're doing though....