A standard rebuild using stock components or a modified engine? (ported head, bronze guides or anything else that might affect this area of operation?)
There are numerous reasons why a valve might hit a piston but no point listing them all until I know what the score is.
Surely when you rebuild an engine you turn it over by hand with the spark plugs (or glow plugs) out so there's no compression, and watch the valve action? That way you could see if the timing is badly wrong.
Sorry to be vague, but the guy in my car club isn't perhaps as clewed up as some.
Everything was meant to be standard - just a reconditioned engine, to as new. It started and ran ok for a few minutes then the noise commenced. Which he was told was a valve hitting a piston due to old petrol gumming things up.
The Rover V8 doesn't have any valve to piston clearance issues as stock due to the deep wedge chamber design so contact means a major mechanical failure and a valve that sticks out several mm from where it should be. The most likely cause is insufficient guide clearance causing the valve stem to physically trap. This can be caused by two issues. Valve guides need to be fitted at a fairly precise interference fit to make sure they are tight enough not to move but not so tight as to crush and close up inside. Aftermarket guides tend to come a tad oversize to cope with potentially worn holes in the head and this excess needs to be polished off in a lathe if it is not needed to generate the correct fit which in this engine should be about 1.75 to 2.0 thou max greater than the diameter of the guide bore in the head.
Using a tighter fit than this can cause the guides to crush and close up although reaming them out after fitting should cure this but if not done properly regardless of guide interference fit is the second cause. Stem to guide bore clearance should be about 1 thou min on the inlets and a tad more, 1.25 to 1.5 thou max on the exhausts although I've never seen an engine problem with as little as 1 thou clearance on the exhausts as well.
A full forensic stripdown and measurement would easily find the cause of this unless the reconditioner has already destroyed the original evidence. Get back to me if you need more advice.
He's been had.
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