Engine Knocking (sometimes)

[misterkni]

I purchased a used engine for my '91 Ls400, had it installed, no problems.

After a few days it started knocking (loudly) on the drivers side. So I took a chance and drove the car back to the shop.

Got there and guess what? NO KNOCKING. The mechanic said it may be the lifters.

Drove home, Knocking again. Called the mechanic back. He said, if it was something wrong with the engine it would knock all the time.

I don't think it's the lifters because the knocking is too loud. Oil level has remained consistent.

The intensity/loudness of the knocking does not change when you increase the rpm of the motor.

Any ideas?

Thanks.