Checking for bent valves after suspected over-rev

After compression testing the new car’s engine we found one cylinder giving a healthy 180psi compression whilst the other three were around 90psi. Not so good! The bottom end was relatively new so we turned our attention to the head and suspected the valves were bent. This was more than a hunch the car had a problem getting into 3rd gear which Michael and the previous owner had had trouble with. This will inevitably lead to over-revving on upshifts if not very careful.
If you over-rev (buzz) the engine the springs will not be able to close the valves quick enough for them to be out the way of the piston which results in impact between the two. It may only slightly bend the valves but that’s enough to lose compression. Moreoever the contents of the combustion chamber will end up back in your inlet and exhaust manifolds at the wrong time harming the pulsed flow.
Without vacuum testing equipment, Michael had to get innovative with his testing of the valves.

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