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Originally Posted by dkveuro
In the interests of chain longevity, it depends on the load the chain sees.
On a 2 valve per cylinder I4 motor, the cam lobe ramp feed back is heavy and loads of 70,000 lbs shock the chain at high rpm's.
On a 2 valve I5 or I6 motor, the ramp load feed back is nearly all cancelled out due to an opening ramp is being opposed by a closing ramp.
This is why the early simplex chain on the 380's was so short lived as it was in effect doing double duty in that it was running two seperate 2 valve I4 cams.
Next time you get a chance....use a wrench to turn an assembled cam in a head on a I4 motor...and then try a I5 or I6 motor.
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Speaking of timing, I was just replacing the chain tensioner & rails on my 220d yesterday and was noticed how the cam would kick back when I turned the motor by hand. I'd never seen it so severe in all the Detroit Iron (50's 60's) v-8's I worked on. So I started watching the cam and saw what was happening. Made me glad the chain was duplex. Post's like those above are invaluable.