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Engine Overhaul: don't forget to clean out oil returns

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  • Engine: Engine Overhaul: don't forget to clean out oil returns

    To All:

    I am now in the process of reassembling the Studebaker 259 engine from my 1957 Commander Station Wagon. The block and Heads were recently returned from by a local racing shop that did all the machining and cleaning.

    In reviewing the Shop Manual, I found a paragraph that stated that for an engine overhaul, all the oil galleries need to be purged and cleaned completely. The galleries included the oil returns which include the two (2) rear dowel pins that align the head to the block. With my engine on the assembly stand, I probed the first dowel with a piece of stranded wire. I pulled it out only to find carbon, burnt oil and metal chips. The second dowel was just as bad. For the next hour, using various screw drivers, drill bits, wire and suction from a shop vac, I managed to clean both returns. These returns are also described in the chapter defining how the lubrication system is designed and functions.

    I pass this story along to all so that in your engine building efforts, you don't miss this small but critical detail. Had I not found that paragraph, I would have contaminated (metal chips) a newly machined engine and in all probability, damaged new bearings, pistons and cylinders. I called the shop and informed the owner of what I had found. He was grateful for the information and that I didn't chew him a new one.

    Dave W

  • #2
    Yep...good catch Dave.
    These two small holes at the back of the block are the only oil return from top of the cylinder heads. While each pushrod has a drain location of sorts the top of the head/rocker cover would have to be nearly "full" of oil.

    If the heads are apart, it helps to chamfer and polish the drain hole opening to encourage the oil flow. Do both ends so you won't mess up and put the head on the wrong side..!



    • #3
      I couldn't agree with you more, I "rebuilt" my 259 and did not clean the oil passages, I assumed they were clean. After about 12 hours of test running the engine was seizing when hot and would not restart after running for 20 minutes. The rod bearings were completely ruined in that short time. The engine was completely disassembled to find the rod bearings damaged and the oil galleys totally plugged. Fortunately the crankshaft was salvaged with a polish and new rod bearings were installed. The engine now starts up cold and hot with no issues.


      • #4
        Doesn't hurt to add one more time; the soft plugs must be removed from both ends of the rocker shafts and the interior cleaned with a bore brush. There's always an amazing amount of crud inside.

        jack vines


        • #5
          Note to self: make sure to tell my machinist about these passages. Trust your shop, but always verify. Thanks for posting this DW.


          • #6
            To All:
            In cleaning the rocker arms, I found another potential blocked oil passage.

            As described in the shop manual, oil is pumped through the rocker arm tube to the rocker arms. The Rocker arms have an internal oil hole that allows oil to pass to the tappet screw and to the push rod. My engine, as you may have surmised was severely abused; no oil changes and shorted plug wires resulting in a huge amount of carbon to build up in small oil passages.

            While cleaning the bores of the rocker arms I saw the internal passage leading to the tappet screw. I removed the screw to find the oil passage block with carbon. So once again, if you are rebuilding an engine, take the time to pull the tappet screws to be sure the passage is clean. If you have loud tappets even after adjustment, you may have blocked oil passages. Oil flow, It's a good thing!