Hey all!

It's been a while since I've been on here.  Sidetracked, work, life gets in the way, etc., lol  Anyway, finally got the '56 up and running but shortly after break in, the engine started knocking after it would warm up.  On cold start, I get about 45lbs of oil pressure and all seems well.  Quiet, smooth and runs well.  As it reaches operating temps, the oil light will start to flicker at idle then stay on as it gets fully warm.  After, say, 1500 rpm's the oil light will go out but will immediately come back on after I let off the gas.  Oil pressure when the light is on is 0.  I have a separate oil gauge and temp gauge installed, temps never go over 180 so it isn't running hot.

The engine is a rebuilt 292.  It was built back in '05 and broken in then but never driven.  Everything seemed fine with the break in at the time.  Fast foward to now and the car is on the road and now the oil pressure problem.  Last night I pulled the pan and the first four main caps.  Engine has about 30 minutes break in time and maybe 50 miles on it.  Bearings look scuffed but there are no marks on the crank, cylinder walls still have a nice cross hatch.  I'm hoping I can get away with just putting new mains in.  Looking for suggestions/advice.

Thanks!

Rodger

Can't seem to post a pic of the bearings.  Says "can't find instance of the editor"??

I did get it to upload as a profile pic.  Makes it hard to see thought! 

Here we go. 

Looking at the wear pattern of the bearings in the picture, it appears to be too much clearance.  I’ll suggest a micrometer check of the journals and bearings and verify what the actual clearance values are.  There’s a chance that the bearings are simply the wrong undersize for the crankshaft journals.

Lorena, Texas (South of Waco)

Thanks Ted, I was kind of suspecting the same thing.  The receipts for the engine work show the crank was polished not cut and the bearings were standard sized.  Looks like some measuring is in order.

Rodger

Hmmmm...  Consider using Plastigage (red 0.002-0.006) to do a quick check on the main bearing clearances before pulling EVERYTHING apart to use the micrometer... 


NoShortcuts
a.k.a. Charlie Brown
near Syracuse, New York

From what you've said, when the oil is cold you've got some pressure, Rodger.  When the engine is up to operating temperature and the oil viscosity changes, the pressure is lost.No argument that clearances someplace are likely the issue.  Consider checking the clearances in your oil pump, too, even if it is 'NEW'... and check the oil pressure relief valve mechanism.
Let us know what you find as you work through this.   

NoShortcuts
a.k.a. Charlie Brown
near Syracuse, New York

if you are checking clearance in the car,install cardboard in2 mains along side  one to be checked snug them up and check others (you need the crank sucked upto get a acurate clearance)

Hmmmm...  GooD point!I've only used Plastigage for checking engine bearings when an engine has been bottom-side up, i.e. with the oil pan up.Thanks for correcting my suggestion. 


NoShortcuts
a.k.a. Charlie Brown
near Syracuse, New York

Thanks for the suggestions.  Using the red plastiguage I had a clearance of .0035 with new bearings.  We rolled the new bearings in primed the engine and everything looked good.  Initial startup with 20w-50 gave right at 60 psi but pressure started to drop as the temp came up.  Put maybe 10 miles on the car and by the time we got back had around 5 psi at idle and an audible knock from the crank just like before.  

Is that too much clearance?  Should I have went with the .001 or .002 oversized bearing?  Anything else that can cause a drop in pressure like the cam bearings or something?  Maybe I can talk Mr. Mummert into selling me one of his engines!

Thanks again,

Rodger