1995 Jeep wrangler piston slap

Hello. I just purchased about 2 months ago this jeep wrangler. It didn't make any noises when i purchased it. I noticed about a month ago that it started making a pinging/knocking noise.

I took it to a friend, local mechanic, and he said the pistons were bad, i.e. piston slap. He wants me to put in a new engine. Can piston slap be repaired without taking out the engine?

Also, there is oil getting into the air filter, but my oil pressure is good and it deesn't seem to be getting any lower on the dipstick. I used 10w40 oil.

Thanks.

These are two classic problems that occur frequently with the 4 liter 6 cyl engine.

First of all, the oil.
Here is a detailed article on the problem and how to fix it.
http://jeep.off-road.com/jeep/article/articleDetail.jsp?id=257985

Piston slap is very common with these engines as they accumulate some mileage. However, they will run often hundreds of thousands of additional miles with a piston slap. So a bit of slapping noise is to be expected, but usually does not warrant any repair.

These engines usually last a very, very long time, often while making a few odd noises. So don't be alarmed. It is not worth fixing anything on the engine until the engine fails completely..... and it's likely that event is far, far down the road.

However, it's reasonable to remove the accessory belt and run the engine for a very short time and see if the knock disappears. Sometimes a knock is caused by a faulty accessory, like an alternator.
Also, if this is an automatic, check the flexplate for loose converter bolts or a crack, both of which can cause a knock noise.