Re: Light knocking noise in the engine.
Posted: Sun Apr 18, 2021 9:49 pm
I would suspect that the damage to the edge of the conrod and the camshaft was caused by the debris from the dropped valve, possibly the broken off valve head getting between the conrod and the camshaft. I take it the dropped valve happened before you bought the car but it appears not to have done too many miles since the the piston and valve was fixed hence the marks on the conrod and camshaft still look fresh.
I too thought the conrods might be handed and this one had been put back together the wrong way round, but my experience of A-Series engines, which are handed, suggests that the conrod would not align correctly on the crank journal if that was so. Also it wouldn't affect the clearance between the edge of the conrod and the camshaft.
As to the 'light knocking noise', I must admit it sounded like a an MGB engine - at least like mine! But the metallic sound my engine makes is down to using spacers between the rockers rather than springs, and once it warms up it gets quieter. So I think you need to look further for the source of the noise. Have you taken the head off and checked the rocker shaft? Dropping a valve is a very violent occurrence with a lot of energy being dissipated in a very short space of time. Check the rocker shaft is ok and hasn't broken. Also check there are shims under pillar 1 and 4 which put a slight bow in the rocker shaft - BMC's solution to customer complaints of noisy tappets I believe.
One other thought - if it has dropped one of the valves are the other 7 just waiting to let go? Perhaps it's time to change them before they wreck another piston.
I too thought the conrods might be handed and this one had been put back together the wrong way round, but my experience of A-Series engines, which are handed, suggests that the conrod would not align correctly on the crank journal if that was so. Also it wouldn't affect the clearance between the edge of the conrod and the camshaft.
As to the 'light knocking noise', I must admit it sounded like a an MGB engine - at least like mine! But the metallic sound my engine makes is down to using spacers between the rockers rather than springs, and once it warms up it gets quieter. So I think you need to look further for the source of the noise. Have you taken the head off and checked the rocker shaft? Dropping a valve is a very violent occurrence with a lot of energy being dissipated in a very short space of time. Check the rocker shaft is ok and hasn't broken. Also check there are shims under pillar 1 and 4 which put a slight bow in the rocker shaft - BMC's solution to customer complaints of noisy tappets I believe.
One other thought - if it has dropped one of the valves are the other 7 just waiting to let go? Perhaps it's time to change them before they wreck another piston.