Hiya guys. I am a new member here and I am hoping you all could help me out alittle. I have a '69 390 that I recently had rebuilt. I have done all the oiling passage tricks to it already. I have a set of comp cams roller rockers and shafts. I only have about 2600 miles on the engine. Now to the problem. My oil pressure had been a nice steady 60 psi cold and 40 hot. The other day I pulled off the highway on my way home from work and I got stopped at a red light. I glanced over at my pressure gauge and my pressure had dropped to about 10 psi at idle 20-30 at speed. Now, I have had an issue in the past where the end plugs on the rocker shafts had fallen out. So, I pulled the valve covers and checked them, hoping that was the case again. Nope. Both end plugs were in both place on both sides. This morning I pulled the pan and checked the pump out. I found that the pump did not have correct tolerances, and some funky wear marks on the impeller, so I swapped it out for a new one. same problem. All of a sudden I have a low oil pressure problem. I would suspect galley plugs but they are tapped and threaded in, not to mention that if one had fallen out of the rear of the block I would see a hellacious external leak and not have any pressure at all. I pulled the distributor to see if the front galley plug may have come out internally, nope it is still in place. I pulled the filter adapter off to see if maybe the gasket had blown out and I was getting blow-by between the out and in holes. That is also not the case. I do have a remote filter and cooler set up on it with Stainless steel braided hoses. At this point I am stumped. I would appreciate any opinions you guys have as to what could cause this. I can't see it being the bearing tolerances due to the fact this is a fresh motor. I am not getting any unusual engine noises. Oh yeah I even tried 2 other gauges just to see if I had a faulty one.

 

mabie the pickup tube is leaking

 

I thought of that as well, I checked the tube out as thoroughly as I could when I had the pump off. I didn't see any cracks or anything. I would think that something that is causing a 40 lbs. drop in pressure would be rather apparent, especially in a pick-up tube.

 

you said the old oil pump looked in very poor condition, with wear marks on the impeler. Perhaps pieces of the old impeler are pluging an oil passage, or holding the pressure relief valve open a bit.

 

Did the relief spring in your oil pump give up ? I would try a differant pump and see what happens. I recommend the melling M57HV. DF

 

I did swap the pump out for a new one. The relief valve on the old one was not stuck and moved freely. I even cut the oil filter apart and checked it for chunks of metal. It didn't have anything that was obvious in it. It had a small amount of metalic dust in it but that is pretty normal for an engine that is still breaking in. I was thinking about a passage being blocked by something but that would not cause a partial drop in pressure, at least I would think it would cause me to have zero pressure. Not to mention the fact that it would have to be a pretty good sized chunk in order to do that. The old pump didnt have any large chunks missing or anything like that but it did have some substantial wear marks on it. I am going to pull the valve covers off right now and run the engine to see what kind of flow I am getting to the top of the engine.
*sigh*

 

Here is an update. I removed the driver side rocker cover and ran the motor. With the cover off I can hear the lifters on #5 tapping a bit. I am getting oil flow to the shafts but it is not as strong of a flow as it should be. Now, I am concerned because I know the lifters get oil before the shafts do. Looks like i am going to have to pull it out and tear it apart. *sigh*

 

 

[font size="1" color="#FF0000"]LAST EDITED ON 23-Oct-01 AT 08:01 PM (EST)[/font][p]Do you trust the gauge ?

OOPs I see you tried some other gauges.

What about the cam bearings ?
Where did ya put the hole ?


In OZ and seeking 427block /428crank

 

Well, the cam bearings must have been installed correctly as the engine had great oil pressure for 2600 miles. I suppose it is possible one has spun but honestly that is pretty unlikely. I am going to pull the pan back off and take a look at some of the main bearings. I have a feeling that I am going to have to pull the engine and tear it apart again. I just really really don't want to have to do that. I can't afford another rebuild right now.

 

don't pull the engine yet. Take off the oil pan and start looking at the bearings. I think most oiling problems happen at the rear. I'd check the 4,8 throw and the #5 main first just to see if they look good. I think they are the last ones to get oil.

I don't know if you can tell lifter condition based on measuring lift or not, but you might try measuring the max lift on the ticking lifter and compare that to another one. I've seen where you can get a cheap 1" dial indicator and set it on a stand to check valve lift with only removing the valve cover.

the point is that you might have a lifter that didn't break in right and it might be fairly easy to check. I think you can get the lifter out with a special tool without removing the intake and that'll allow you to examine the cam and bottom of the lifter.

Just trying to help.

 

I'm not going to pull it just yet. On friday I am going to drop the pan again and pull some of the caps to see what, if any at all, the damage is. If need be, and if that is all I need I will replace the main and rod bearings. Hopefully I won't have to have the crank machined, but if I do I will. Fortunately all this can be done in vehicle. I highly doubt there would be any damage to the cam bearings and I should be able to tell from looking at it from the bottom.
I do appreciate the help =)

 

can you pressurise the oil system while the sump is off ?

U may be able to see where the problem is
Was the air bleed behind the dist mentioned/considered



In OZ and seeking 427block /428crank

 

I will try to pressurize it when I drop the pan on Friday. As for the plug behind the dist... it is in place.