Crankshaft/Rod Bearing Question

[dlrides]

A friend of mine recently bought a '51 Plymouth, and the engine was rebuilt approximately 5k ago. The car runs perfect ! The problem is when you drive it for an extended time in hot weather is starts to lose more oil pressure than it should. At max RPM when hot, 20 PSI is all the pressure there is, and at 2k RPM barely 10 PSI. Installed a new oil pump, exact same results. I recently drove it on a hot day, and I noticed when I barely loaded the engine, like up a hill, I heard a faint knocking in the bottom. He couldn't hear it, but I could, so it is faint, and disappears when the engine RPM's increase.

 

70 PSI oil pressure when cold. Compression is excellent 103-105 all cylinders. Pulled a valve cover, all looks perfect. Pulled the pan, to check rod bearings, problem found. Two rod bearings have .0031, and .0032, should be .0015 max. VERY slight grooves on these two rod journals. Mains seem perfect.

 

Looks as if when the engine was rebuilt they skipped having the crank turned, and just replaced the bearings.

 

Questions :

 

) Is it feasible to pull crank, have rod journals turned, polish only mains. Install proper sized rod bearings, and install new mains the same as they are now ?

 

) Can the crank be pulled without pulling engine ?

 

 

The engine seems too perfect to go through the expense of a total rebuild. Any other options/opinions greatly appreciated.

 

 

Thanks,

 

Don C

Edited July 20, 2014 by dlrides

[TodFitch]

 If they were that sloppy about the crank it leads me to wonder about other areas that might have been skimped on. Specifically, I wonder about the condition of the cam bearings. . . It is my understanding that worn cam bearings can be a source of low oil pressure too.

[Dodgeb4ya]

If it were mine I'd take the engine out and carefully check everything over just because of whats happening with the oil pressure.

The crank needs to be carefully miked- mains and rods. It probably needs to be machined. Very critical tolerances are required for long bearing life and good oil pressure.

I wonder abount crank end play, rod side play, cam bearings, were the rods hung and aligned, was the block professionally cleaned-oil galleys  ect, ect. You don't want to have to do it again!

Bob