priming an engine?

[tford]

I've been around for a few engine transplants. All that I've ever seen, they didn't prime it. They just let the lifters pump up and after a few seconds of tapping, they quiet up and all is good. Why will this technique not work for a regal or gn? What are the consequences? Thanks, Tim

 

[RmvBfrFlght]

I've been around for a few engine transplants. All that I've ever seen, they didn't prime it. They just let the lifters pump up and after a few seconds of tapping, they quiet up and all is good. Why will this technique not work for a regal or gn? What are the consequences? Thanks, Tim

On a Buick engine I would never just start it up without priming it first. As for other engines, some you can get away without priming, but are still taking some what of a chance with it.

To help understand here is a comparison between a small block chevy (SBC) and a GN 3.8l engine:

On the SBC the oil pump on on the rear main cap and is submerged in oil. The oil filter is also installed in the vertical position. So one can fill the filter with oil and screw it into place. Then put the remainder of the 5-quarts into the pan. With that the oil pump is also filled with oil.

Fire up the engine and it quickly builds oil pressure and away it goes. Just a note: I AWAYS prime a new SBC before the first fire up. It is just the right way to do it.


Now the 3.8l Buick engine: the oil pump is off the side of the front cover. And the oil filter sits mostly horizontal. This makes it difficult to pre-fill the oil filter before installation. And the pump is dry. Although packing it with petroleum jelly is recommended.

Put oil in the pan and the pump is still dry and so is the filter. Crank to start it and.... you hope that the pump pulls a prime from the pan and fills the filter then goes on to build pressure.

And if it doesn't? The assembly lube is OK for a little while. But the chance of damage is very high. So on these engines it is a requirement to prime the oil system via the cam sensor opening. Even then sometimes they won't pull a prime.


A side note about priming first is that it is a good check that there aren't any leaks. Such as from a missing oil filter seal or a missing plug in an oil gallery. My favorite is when a SBC is assembled with the top rear plug missing (1/8" NPT).

Start the engine with that missing and it's like a oil well was opened up. Glad I was standing far enough away that it was amusing, and not taking an oil shower.

RemoveBeforeFlight

 

[vacuum 6]

Assuming the engine is still on the stand, prime it good and check for leaks. Not sure how to do this but if there's a way to simulate heat cycles...re-torque the heads now.

 

[Devil Car]

I had a friend start a 4.3 Vortec without priming it after replacing the main bearings, and the engine emitted a nice loud squeal for only a couple of seconds as he put it. Needless to say that engine was toast after only 20K more miles. An extra hour of work would have made sure those main bearings hadn't fried that quickly.

Personally, I like knowing that all of the oil bearings have oil on them before starting my engines. Otherwise, you're going to run a high risk of damaging them.

Take the extra time and do it right the first time!