JAKE

A slow and painful death.

Over the past several weeks I began to notice lower than normal oil pressure, in gear, idling.

Normally I'd been running 20/22 psi at normal temps (oil around 200/220) while sitting at a traffic light, etc. Then a few weeks ago I noticed the psi drop to 18 once in while, but I didn't attach much significance to it.

Last week it hit 16, so at that point I began to be concerned. So I decided to practice what I preach and do some diagnostics.

I first changed the oil and filter (the "old" oil had only been in for two months of so), just to be on the safe side. Then drive the car for a couple of days while keep a hawk-eye on the oil pressure gauge.

Sure enough, it began to do it again, dropping to 16 occasionally. ( I plan to cut open the "old" filter today to see what's what.)

My next step was to pull the distributor to check the gear. Good as gold. BTW GM melonized distributor gear FLAT works; over 5,000 miles on it and virtually no wear.

While I had the distributor out, I decided to install a manual gauge to verify what my dash gauge was telling me. I removed the sender and the fuel pump switch; plugged the switch opening and screwed in the manual gauge.

Put it all back together and fired it up, and set the timing. I set the engine to run at 2000 RPM, all the while I kept a close watch on the manual pressure gauge. Pressure looked normal but I let the engine run 20 minutes to make sure the oil was good and hot. Only when I dropped the RPM to idle speed - 800 - did the pressure begin to drop down below the previous 20 psi normal pressure.

Right back to the 16/18 readings.

So I started doing some research and found a comment by Melling, the oil pump folks. They said that high pressure oil pumps eventually cause wear to the pump bearing surface. Now that threw me at first because I couldn't recall ever seeing a "bearing" in any Chevy oil pump.

Thinking on it though, I believe what they're referring to is the opening (hole) where the gear/oil pump drive shaft slides through pump body and the hole in the other gear that slides down on the fixed shaft in the pump housing.

Melling has introduced a new HV pump that extends support into the pump cover to prevent that wear problem. Three different screened pickups are offered, depending on pan depth 7", 7-1/2" and 8"; mine's 7". So it looks like I'll be headed to the pump store and half a day on my back AGAIN.

I'll sneak a peek at the mains while under there, since I'll have the pan off anyway. I don't think I'll find any main bearing damage though because 16/18 psi at idle is more than enough pressure. It's good to check though.

This saga never ends, does it?

Jake

bogus

I wouldn't even check'm. I would not risk disturbing them.

16psi is enough to protect the mains at idle.

JAKE

You could be right. I'll know more when I cut open the oil filter.

Thanks for that.

Jake

MikeC4

JAKE - learned something here today....Thanks

vader86

Its good to check the mains, but you probably wont be able to see anything without disturbing them.

Be sure to get a Melling pump, M55A is good.

JAKE

I ordered the Melling pump, 10555, which is the new version with reinforcement going all the way into the cover, not stopping at the pump body as the regular-type pumps do.

I also ordered the correct pickup for my pan, 12557, which is a bolt on pickup, so no tack-welding is needed.

Both are in Summit's catalog and on their website in case you'd like to read up on them.

BTW, I just finished cutting open the oil filter and, no sign of bearing material. Didn't hit silver and, better yet, didn't hit gold. So far so good.

I've got an empty 400 block so I plan to use it to double check the pickup to pan clearance once I get the pan off and cleaned up. That'll be a lot easier than trying to check the clearance laying on my back under the car.

Jake

Corvette Kid

It's been my experience that far too many oil pumps are condemned for oil pressure problems. Not to say that yours indeed may not be at fault, but whether or not it is, don't go in there without checking all of the bearings too. Even though your filter check showed no excessive metal or impending failures, it could just be normal wear. You didn't mention how old the bearings were, I don't believe. Also of course, you'll see if there's any debris in the pick-up. And check your bypass valve and any galleries you come in contact with very carefully. In short, don't overlook anything. I've been doing this stuff professionally for over 30 years and still constantly run into things I haven't seen before and was not looking for or expecting. The devil is in the details, as they say. The longer I do it, the less I seem to know for sure it seems at times. Good luck and keep us up to date!

JAKE

You've got me thinking.

As many of you probably know, I use to build 1/4 mile 8 second engines for several teams in the Chicago area, but the vast majority of my engine building has been with Big Blocks, not SBs.. One of the standard requirements was to run a cross-drilled crank. Even guys who were 'bucks-down' and had to opt for a cast crank always had them cross-drilled.

Now I'm wondering if the main reason for GM coming out with the Priority Main oiling system for the SB was because of that family's tendency to eat main bearings.

There has to be a major reason for GM to cough up all the re-tooling costs to modify the block castings.

I continually read stuff like "The SB Chevy's oiling system is as good as it gets, leave it alone", then I turn the page and see that the "buzz-words" are now 'Priority Main oiling system'.

Does anyone have any feed-back on that? Are SBs noted for short main bearing life?

Jake