oil pressure and knocking
 

I'm grasping at straws here since my motor is sounding like it's got major rod knock, but here goes. I finally drove my truck more than a few minutes on thursday. I went a couple miles and it started to rattle pretty good while I was accellerating, but would not rattle at idle. I noticed the oil pressure had dropped, when before it would be at 40lbs at idle, it was maybe 20. I cautiously continued on and at the next light the oil pressure was about 5-10lbs. The rattling was worse. I got where I was going and it seemed to be running the same, but if you hit the gas it would rattle like a diesel.

So here's my question. If the oil pump failed, I'm guessing it wouldn't be so sudden, unless something actually broke vs. normal wear. Just before all this happened I had pulled the oil filter to see if there was any metal in the filter, since the guy at the tuners noticed the rattle. he thought it was rod knock, and it kinda sounded like that to me too. Since I found no metal in the oil or the filter, I just put a new filter on and refilled the oil. That's when I took the trip on thursday.

After really getting a good listen, it almost sounded like the sound was top end, like the valves were loose, or the lifters were clacking. I'm kinda at a loss here, hoping that my 402 isn't toast! I've had a few strange issues with this motor (including a mechanical advance that retarded instead of advance) which I resolved by swapping in a different HEI.

So if the oil pump failed, would I get no sound at idle, rattling sound at accelleration, and at decel? I am shopping for engines, but would try swapping the oil pump if that could possibly be it. I mean at this point, what do I have to lose? :lol: just the money for the pump and the gaskets, right?

Re: oil pressure and knocking
 

Oil pumps don't generally fail. The reduced oil pressure is due to increased bearing clearances. Pull the pan and look. Big pieces don't show up in filters, they show up in oil pans and oil pump screens. While you're there check for any obvious damage to rods and mains. Good luck!
Jeff

Re: oil pressure and knocking
 

I've had them fail but gradually, not all of the sudden. I plan on dropping the pan anyway, just grasping at straws like I said. $60-70 is much easier to stomach than $2000+!!!
It was pretty all of the sudden that the oil pressure dropped, which is weird, but when bearings go, they go out pretty fast.

Re: oil pressure and knocking
 

I replace them, but haven't seen many primary oil pump failures. Two gears submerged in and pumping oil from a screened inlet is a pretty solid system. Usually killed by low oil, plugged pick-up screen or a broken shaft (after seizing from no oil).

Re: oil pressure and knocking
 

If it's not rattling at idle then it's not the pump.
I'd check the timing!
Sounds like detonation.

Re: oil pressure and knocking
 

Well yea, like I said, grasping at straws :lol:

Crate BBC here I come. :chevy:

Re: oil pressure and knocking
 

One last straw I'm going to grasp at... I had an HP4 filter on before, and now I have a PH30. When I drained the oil today, I looked up and the new filter was covered with oil, and the surrounding block area was also... then i looked up the specs on both filters. Seems the gaskets are different, even though the filters are both for a '71 Gen 4 402. They're not THAT different, .10", and the HP4 has the bypass... I'm going to grab an HP4 for the hell of it, and see what happens. I only wound up grabbing the PH30 because they didn't have the HP4 in stock, figured it would work for the time being while I cut open the old filter.

And oddly enough, no metal shavings in the oil that I saw. If the bearings were really that bad there would some shiny stuff in there. :confused:

Re: oil pressure and knocking
 

I was at my neighbors dad's engine shop and they had a motor that came in that someone else had built and failed in less than 1000 miles. After pulling the oil pan we found a shop towel that someone must have left in the oil pan that was sucked up into the oil pump screen and oil pump. Talk about a big woops. Lol

Re: oil pressure and knocking
 

I gave the cousin of a friend of mine a quote on rebuilding his f%rd 390 years ago. It was a stupid low quote since I wanted to help the kid out. He said "I can build it myself for less". I explained to him that he certainly could, would learn a bunch, but make sure you have someone with you that has some experience in case you have a problem. Over the next couple months I heard about how many special tools he needed to borrow and how much longer it was taking him. I encouraged him and told him it will only go back together right one way. He called me when they fired it up. He told me there was no oil pressure and it was making noise. I gave him instructions to make sure he had oil, how to check the gauge and some general tips. He told me they had ran it for about a half hour and never had oil pressure. Ended up being the "extra part" his uncle and him had left over. The oil pump drive shaft. He vomited when I told him his motor was done. I guess just having oil pressure should give you hope! Good luck!

Jeff

Re: oil pressure and knocking
 

no one else has said it yet so I will....get rid of that POS Fram filter and get a good Wix 51061 or NAPA 1061 (made by Wix) filter. I have heard of multiple oil pressure issues from using Fram filters.

Re: oil pressure and knocking
 

Never had an issue before, been using them for years. I'll see if they have the Wix one at Baxter's tomorrow though, never tried one.

Re: oil pressure and knocking
 

Baxters stocks them, but I order them by the dozen or "master pack" from Rock Auto for way less than the local stores.

Re: oil pressure and knocking
 

junk can build up in the pain with time as it cannot drain out right, inside the pan is a nut welded over the hole, and only 2 small holes are drilled into the sides. meaning over the years any hard carbon [ mostly from oil slapshed on back of pistons,only place really where it can stick and slowly cook into hard carbon that wont disolve when it drops ] it collects and never leaves the pan, then slowly gathers into the pickup screen with time.

Re: oil pressure and knocking
 

I can usually hear a rod knock at idle as well as revving. The only other thing I can think of that sounds like a rod knock is a cracked flex plate. That noise can come and go until it completely fails. Since you are losing oil pressure, it does sound like a bearing problem. If you are really down to 10-15 lbs of oil pressure you better stop driving it or you will ruin it when the rod lets go.

Re: oil pressure and knocking
 

Yes, you can hear a rod knock @ idle....you will also hear it @ speed....more when you let it down? If you talk 10-15 oil pressure @ idle, I have seen many "tired" sb chevs live with that....as long as they pull40-50 @3000 plus? A rod will knock @ idle....you don't , as a rule,you don't get get a main bearing knock out of a Chev? A main bearing knock,you will hear on the rev up....A piston knock. you will also hear on the rev up ? After she warms up , that piston knock , will go away...longhorn

Re: oil pressure and knocking
 

Sounds suspiciously like a spun bearing to me. They 'can be' semi quiet at idle and give them a little RPM and the HAMMERING begins. Oil pressure will be all over the place as the two bearing shells climb on top of each other.

PARK IT till you get it apart and see what is going on. If it is a spun bearing or to,,, every rotation is destroying the crank more and more. You can take a salvageable crank and turn it to scrap iron in very short order.

Re: oil pressure and knocking
 

+1 on wix oil filters. They are all I run in any of our vehicles.

Re: oil pressure and knocking
 

http://youtu.be/lczjEyfxkMY

So yea, not an oil problem. Crate engine is a comin' :lol:

Re: oil pressure and knocking
 

What your oil psi like?

I had my Buick 350 do something similar. but it ran fine, parked it, next time started a similar racket, good oil psi on gauge but nothing is getting to the top end.

Re: oil pressure and knocking
 

I had 60-70psi when it was making that racket. It's hard to see because it was dark, but I had the camera on the oil pressure gauge in the beginning of the video.
I'm going to start tearing it down, going to start with the valve covers, see if maybe something like that was going on... but it was doing that racket but not as loud, and had 5-10psi at idle before. So I dunno :josh:

Re: oil pressure and knocking
 

you can pull the plugs, and use a battery charger to spin it over fast and see if oil is pumping to the top or not with out running it.