John95z28

Ok, I'm aware this question has been asked before. It usually ends up with a conclusion that it doesn't matter which way they face. However I found one expert that made a good point that oil is fed from the back of the engine, so it may be best to face the oil holes toward the back.

I recently replaced my lifters with a set of stock melling ones and followed that logic. While I was doing a warm lifter adjustment I noticed that #3 was squirting about 6 inches at idle, and under throttle shot over the fender. It also took very long to get any oil to #1 and when it finally did it was very little seeping. So today I returned that lifter in case it was defective and swapped the direction of that one lifter. It immediately cleared the issue right up and allowed oil to flow more evenly.
It no longer squirts several inches either.

Previously I had the old ones all facing forwards and I noticed that the front received oil first. This actually makes sense, but I've never heard anyone talk about this specifically.

I cannot be sure if the lifter was actually defective, or if changing the direction forced the oil pressure to flow downstream better.

What do you think happened?

Shangrila

Doesn't matter which way they face.

John95z28

According to my observation it actually did. When they faced forwards the oil filled the front of the engine first. When facing backwards the back of the engine gets filled first. From what I've seen this part has a factual basis. A real running test like this requires the intake manifold be removed a few times unfortunately.

In my new understanding, since the bias is towards the back first on cold start it makes sense that those should face forwards thus allowing the front of the engine to fill/pump up quicker. The fronts may want to be faced backwards thus accepting oil a little better. I'm sure that oil will fill either way eventually, but we are talking about cold start(2-5 minutes).

Shangrila

After pulling the intake manifold off my 1995 z28 with original 25k miles I could see that the factory had them in all different ways. The lifter oil hole position is not mentioned anywhere in any manual. The only thing I can think of that might cause such behavior is that you used assembly lube on your lifters.

John95z28

That was a good thought, but no I did not use assembly lube for that reason. I soaked them in oil for 30 minutes before install. I actually drove it about 400 miles over 2 weeks with the new lifters. I figured I would give it some time in case the factory shipped the lifters with any kind of lubrication or anti-corrosive jelly. When I opened it up yesterday I thought it would have began working properly by now. Since it didn't I replaced it under warranty.

The directional flow probably has little to do with this defective lifter though, except that it made me think more about the change I made.

My observation of cold starts(actually running w/manifold) was: