Just curious -- I see the warning "don't turn the engine backwards" in almost every "how to check your timing chain for stretch" thread. What happens if your Do turn your engine backwards? I saw the warning in time to NOT turn my engine backwards, but what is the harm that is done? Thanks!

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1992 300D 2.5T
1980 Euro 300D (sadly, sold)
1998 Jetta TDI, 132K "Rudy"
1974 Triumph TR6
1999 Saab 9-5 wagon (wife's)