What would be the effect of valve not properly lapped on engine operations?

If a valve is not properly lapped, it may not create a tight seal with the seat, leading to compression loss, reduced engine efficiency, and potential misfires. This can cause increased exhaust emissions and may result in engine overheating due to improper cooling. Over time, the poor seal can also lead to accelerated wear on engine components and potential damage to the valve and seat surfaces. Overall, improper lapping can significantly impair engine performance and longevity.