401 oil pressure drop

[acofficer]

I have read all the posts but haven't found one with the exact same symptoms as me. I would love some input from the experts here on the board.

The history of the engine is somewhat unknown. I bought a 1976 J10 from a guy. He said it had been rebuilt with a mild cam. I ran a compression test on it and got 120 psi on all cylinders here at about 6000 ft above sea level.

I just finished swapping it into my Jeep. It is running a little warm.... about 210 under load. I am going to flush it with BG cleaner.

My big problem is that at startup I get about 30 psi oil pressure. As the engine warms the oil pressure drops to about 0-5 psi. I am going to pull the filter and get a napa gold. I will check the bypass valve then also and try to check my clearances. Does this sound like a oil pump issue or a cam bearing issue?

Also, if my clearances are bad, I may try and grab a timing chain cover off a cpl of 86 and 87 360's my friend has in his garage. Will these covers interchange?

Any thoughts on what you think is going on and what I should check. Thanks!!

[jeepsr4ever]

I would start with the cheapest. New set of gears and a midplate to cover the damage on the top of the oil filter adaptor/bottom of the pump. Sounds like the T cover is out of tolerance.

[tufcj]

Like MC says, cheapest and easiest first. I've seen that the spring on the pressure relief valve weakens with age.

A new pump gear set usually comes with a new plunger and spring, and a mid-plate from here at Bulltear. Make sure the relief plunger is installed point forward. If that doesn't solve the problem, then replace the timing cover. Yes, all V-8 covers interchange.

Look at your oil filter adapter. Older ones have a 90* bend going into the filter, newer are 45*, the newer ones flow better. A 76 should have the 45*, but it could have been changed.

Bob
tufcj

[acofficer]

Ok, I ordered the HP pump kit and the midplate. I will try that first. If no luck I will then change the timing cover. I am praying it is not cam bearings.

[acofficer]

I have not had a chance to check the tolerance between the side of the gear and the timing cover yet, but I am wondering if anyone has ever tried a speedy sleeve inserted into it. Here is a link to the chart of sleeves:
http://www.skf.com/files/344136.pdf

What are the dimensions supposed to be?

[acofficer]

oops, didn't realize till I got in there that the cavity is not round. Sleeve won't work.

[acofficer]

Just FYI new gear set and midplate did nothing. I changed to a mechanical gauge though and the actual readings are 18 psi at hot idle and bumps up to about 40 psi as rpms go up. I think I am going to leave it as is now.

[dagazio]

I am looking at a simular situation. However, I believe my 401 is not rebuilt and has 95000 miles on it. I have a 1974 Cherokee and it looks like the motor was never pulled. However, the rear main seal had let loose and when I pulled the bearing cap to replace it, the bearing was pretty well worn. The gauge on the dash, it starts out around 40 psi and drops near zero when hot and idling. I'm using 10w-40.

I'm not interested in rebuilding the motor at this time. I would like to get a few more mile out of it before I go though the trouble. What worries me is from experience, zero oil pressure spins bearings.

[acofficer]

I just ordered a new timing cover. Hopefully that will bring my oil pressure back up.

[tarior]

I strongly doubt a new timing cover will do it. You'll likely need to tear it down and put some cam, main and rod bearings in it. That's been my experience.

[dagazio]

I thought I'd update my situation. I decided to bypass the dash meter after reviewing my setup. The wire from the sensor was cracked, making intermittent connection and I measure the resistance of the sensor which looked to be off quite a bit. It was reading 80 ohms across it when the engine was off and the wire disconnected, where I believe it should be 240 ohms. With that said, I shouldn't read low psi ever, but the open wire could cause it.

Therefore I decided to install a mechanical gauge, just to see what that said. After it warned up, it looked to have about 7 psi, in gear. It's low, but I think my motor won't spin a bearing. The pressure jumps right up with the rpm. I'm running Autozone 20W50 and a Fram filter. After reading a post elsewhere, I decided I'll probably change to an AC Delco filter and try another brand of oil, Castrol. I decided the filter might make a difference because the Fram is 18 micron vs the Delco at 25 micron and should offer less resistance, which will mean less pressure drop through the filter. I'm not sure about the oil, but I'll do one at a time to see the difference.


I also would like to do the first mod mentioned here:
http://www.planethoustonamx.com/main/AMC_V8_oil_system_mod_1.JPG

I'll try to remember to post my results. Good, bad or ugly.

[acofficer]

So the timing cover did nothing. Motor pulled and new bearings going in.

[tufcj]

Be sure to check/change the cam bearings. I've seen probably 50% of the high mileage engines I've rebuilt with the coating flaking off the factory cam bearings. It has a bigger effect than rod/main bearings, since the AMC oil path oils the cam first. You might try Bulltear's bearings with the reduced size oil hole. I'm running a set of those in my AMX 390 with good results.

Bob
tufcj

[tarior]

X2. Absolutely change the cam bearings.

[Blown7]

BTW for what it's worth I had a old 304 years ago that ran 0-5lbs pressure at idle on a mechanical gauge years ago that ran for years.Never did blow that engine just retired it.

[dagazio]

Okay, I got my Delco filter and installed it. I'm not driving the car, so I can't tell how it's running under load at speed. I did get it good and hot. I really couldn't see a difference. It might have been 1 psi higher in gear, hot. I would say there was nearly no difference between the Fram and Delco filters in my engine. I'm not going to try a different brand (Castrol) of oil until it needs a change.