low oil pressure

[kidd79]

Guys. What are all the causes of low to no oil pressure in a AMC 258 i6 / 4.2l , besides the obvious no oil, bad oil pump and sending unit that you have run across? I had a rocker arm slide over and the lifter and push rod came out of the head for instance. I'm trying to gather as much info as I can, cuz I have a AMC 258 i6 / 4.2l right now in a 81cj5 that's not making hardly any pressure with a full oil pan. It's got a brand new mechanical gauge, and you can see the oil barely moving up the clear tube while it's running..I just bought the jeep and have no histor on this motor. Looking for a good place to start troubleshooting since I'm out in the gulf of Mexico and won't be home for another 2 weeks.
Thanks.

 

[Muddoc]

Could be blocked oil passages, or in the case of my '79 CJ5 's AMC 258 i6 / 4.2l , I had bad rings in 1 cylinder that ended up pressurizing the crankcase and drove down my oil pressure. I replaced the pump, gauge, and sending units, with no change. The pressure was great enough to blow out the dipstick, the PCV valve, and valve cover gasket. I ended up running a hose from a "T" fitting off the PCV valve to a collection bottle next to the battery until the rings finally failed. Never understood why it was so. I just went ahead and replaced the long block with new.

 

[kidd79]

Dang. That doesn't sound good at all!! Lol. I'm not having any issues with the rings or oil blowing out of the dipstick...Well not yet anyways. But that's some great info to have for in the future. How would I check the oil passages? I didn't really get a chance to open the motor up after I got the jeep. I quickly rigged up an external fuel tank(32oz Gatorade bottle) and hose run to the fuel pump, reset the timing back to stock, cuz it was way off(the plug wires were all over the place in no particular order) and the rotor button was not even close to number 1@tdc, threw in a known good oil pressure gauge, and water temp gauge. Fired that puppy up, ran smooth as silk, but barely any oil coming up the line, not even connected to the gauge.. I'll know more once I get home to tinker with it.

 

[CJim7]

Bearings...

 

[Petescj]

Bearings...

I hope my oil pump is shot but...

 

[kidd79]

Bearings...

Oh I hope not. Lol

 

[johnnyreb]

Bearings...

my thought too

 

[kidd79]

Update.
I didn't get a chance to work on the jeep while I was home last time. I got all my other projects done though..so I should have enough time while I'm at home next time to give it my undivided attention. I'll keep you guys updated as I diagnose what's wrong. But I did crank the jeep, and sadly it didn't fix itself :-\

 

[Torxhead]

A high detergent thicker oil like a Shell Rotella 15w-40 could help with the loose bearings and clean blocked passages. There also could be a problem with the oil pressure sending unit since you said that you just replaced the gauge.

 

[johnnyreb]

I have flushed motors with half a quart of kerosene and ran it till it warmed up. I presume it's a manual gauge, Torx. Certainly would run a higher weight oil.

 

[Torxhead]

There could still be an issue with the stock electric oil pressure gauge or sender. An inexpensive mechanical gauge would be a good way to check it.

 

[harleydragon]

if the gauge is working properly,the biggest cause for low oil pressure is worn bearings,especially bottom end bearings..thicker oil such as 15-40 rotella or delo or even a straight 30 weight if you are in a warm climate should boost it a little.If you need more than that,drain a quart of oil out and replace it with lucas oil stabilizer.

 

[kidd79]

Update.
I finally got a chance to tear of into the motor. I found two bent push rods on the number 5&6 cylinders. One intake, and one exhaust. Also found the#5 lifter laying on its side looking down through the head push rod hole. I'm thinking this is the cause of my lack of oil pressure. Lol. It's strange cuz this happened on the motor that I have in my yj. The yj was built by a shop and the cj which is what I'm working on now was from a completely different individual. Weird!

 

[gert]

thats not to good, i think that something caused the push rods to bend and then when the engine was revved the lifter pooped out of the bore and without a lifter in the bore you have no oil pressure i hope you do nt have anymore internal damage

 

[harleydragon]

are you over reving the engines or gearing them down hard?? could be coincidence but sounds like the only thing that the 2 engines have in common is that you are driving them

 

[kidd79]

thats not to good, i think that something caused the push rods to bend and then when the engine was revved the lifter pooped out of the bore and without a lifter in the bore you have no oil pressure i hope you do nt have anymore internal damage

The previous owner of the cj that I bought for parts said that he had recently swapped out the cam. This is the engine that I'm putting into my CJ7 . The only time it was cranked up was after we set the timing on it and fired it up to check the motor out. It ran, but was rough and this was when I found no oil pressure. So it has never been officially driven by me yet. Lol I'm thinking the previous owner didn't set the rocker arms properly. I hope I don't have anymore internal damage either.

 

[kidd79]

are you over reving the engines or gearing them down hard?? could be coincidence but sounds like the only thing that the 2 engines have in common is that you are driving them

In both cases between the yj motor, and the cj was initial cranking and checking over the motor. The yj motor was rebuilt by an engine shop, the cj motor was bought from a stranger off of craigslist. Since having the yj going for about a year now, it's still running strong. I try not to be terribly hard on my equipment and under 4000 rpm. Lol

 

[gert]

the cj motor was bought from a stranger off of craigslist. .

uh oh another craigslist killer lol ya keping the engines under 4000rpm is a good thing

 

[kidd79]

uh oh another craigslist killer lol ya keping the engines under 4000rpm is a good thing

Yep. Craigslist killer got me. Lol. I did manage to fish the lifter up from inside the block and drop it back where it goes. And for testing purposes put two used push rods back in, tighten up the rocker arms, and spun the oil pump with a priming tool made out of an old distributor. Got roughly 64psi of pressure with my drill motor. Got that problem solved. Next issue is my intake valve will not budge. I tried rotating the motor over with a ratchet and all the valves moved except the#5 intake, and started flexing the push rod. I stopped and backed the motor off, removed the rocker arms and It's sitting about 1/4" lower than the exhaust valve with the rocker arms off. I don't have a valve spring compressor tool to see if I can move it. Any handy tricks out there to see if I can compress the valve?

 

[Hedgehog]

Bite the bullet, pull that head off and have it rebuilt or rebuild it yourself.