Main bearings, oil pressure, etc

[Bmartin]

My fuel pump actuator arm fell off into the block on a road trip, swapped on the side of the road and it promptly did the same thing within 10 miles.  Got it home and dropped the pan and it was not pretty.  Silver soup and a nice silver coating on everything.  Actuator #1 was chewed up by the crank and bounced pieces all around.  Cam lobe is chewed up.  In my inspection, I grabbed the crank bearing caps and I can rock them back and forth. So my question is, how is it that I still read good oil pressure?  It sits at 40 lbs most of the time.  If I bog down the engine to 6-800 RPM, after a full heat cycle, it'll drop into the 18-20 range.  But comes right back up.  I would have thought with that much clearance, I'd have low pressure.  For history, this is a relatively fresh build I had done.  Maybe 5k miles on it.  Curious on opinions.  

[Loren]

My theory has always been, if you look at the oil passages you will see that the cam bearings get more oil than they should.

As the engine ages the cam bearings wear and the pressure drops.

This is not exclusively a Plymouth problem many engines need restricters in the oil lines to the cam bearings.

The fact that your engine was recently rebuilt might mean that the cam bearings are nice and tight. Some Mopars have two sets of holes for oil in the bearings. The guys who know use the small ones.

You might try replacing the bearings cleaning things up and see how it runs. Bearings are fairly cheap.

[Bmartin]

Interesting.  This would seem to mean that oil pressure is not a reliable indicator of main bearing condition, or at least in this case.  As for the bearing swap, its possible.  But it has not run as well since the fuel pump incident.  Still working on a full diagnosis.  Concerned that a valve may have been damaged by the flailing metal.  Need to finish up the leakdown check as a next step.  

[kencombs]

18 hours ago, Bmartin said:

My fuel pump actuator arm fell off into the block on a road trip, swapped on the side of the road and it promptly did the same thing within 10 miles.  Got it home and dropped the pan and it was not pretty.  Silver soup and a nice silver coating on everything.  Actuator #1 was chewed up by the crank and bounced pieces all around.  Cam lobe is chewed up.  In my inspection, I grabbed the crank bearing caps and I can rock them back and forth. So my question is, how is it that I still read good oil pressure?  It sits at 40 lbs most of the time.  If I bog down the engine to 6-800 RPM, after a full heat cycle, it'll drop into the 18-20 range.  But comes right back up.  I would have thought with that much clearance, I'd have low pressure.  For history, this is a relatively fresh build I had done.  Maybe 5k miles on it.  Curious on opinions.  

I am assuming that the red refers to rod caps and that they move freely fore and aft.  If my assumption is correct, that is perfectly normal.  Even new bearings on a good crank should move freely in that direction.  If you are concerned, just remove the cap and bearing wipe the oil off and measure with a plastigage strip.

[Matt Wilson]

11 hours ago, Bmartin said:

Interesting.  This would seem to mean that oil pressure is not a reliable indicator of main bearing condition, or at least in this case.  As for the bearing swap, its possible.  But it has not run as well since the fuel pump incident.  Still working on a full diagnosis.  Concerned that a valve may have been damaged by the flailing metal.  Need to finish up the leakdown check as a next step.  

I agree that a leakdown test is a good idea.

[Bmartin]

22 hours ago, kencombs said:

I am assuming that the red refers to rod caps and that they move freely fore and aft.  If my assumption is correct, that is perfectly normal.  Even new bearings on a good crank should move freely in that direction.  If you are concerned, just remove the cap and bearing wipe the oil off and measure with a plastigage strip.

Correct, I can rock it front to back of the vehicle.  Not as if the bolt holes were wallowed out, left to right of the vehicle.  I only have basic knowledge of engine internals.  I was reading the service manual and saw the process for measuring clearances using a feeler gauge/shim steel.  Plastigauge may be easier.  I'll keep that in mind.  Thanks for the input.  I got the fender off yesterday and pulled the valve covers.  Will work on the leakdown as soon as I get the time.