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No oil pressure in rebuilt 170 motor

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  • #16
    I can see your frustration and desperation in your posts. Low oil pressure is one thing...but NO oil pressure is another thing all together! While I am just a bungling backyard tinkerer, I would like to see some comments from our professional mechanics who do these things for a living. I don't know how you are turning the engine to check out the oil pressure, but if you are cranking it up and running it...I don't know how much the engine can run without damage by only being lubricated with the assembly lube?

    On the V8 engines, you can use a dummy shaft and spin the oil pump without cranking on the engine. But I'm not sure about how these six cylinders work without cranking up the engine unless you remove the spark plugs and try to spin it on starter power with no compression? Even then, I'm not sure you will get enough speed (rpm) to build up the oil pressure?
    John Clary
    Greer, SC

    SDC member since 1975

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    • #17
      Same thing happened to me a couple years ago. The problem was that the gasket on the oil pick-up tube was defective so the pump was sucking air. I replaced it, primed the pump and plenty of pressure. There is a key on the shaft that can be left out in which case the pump won't turn. You'll have to remove the pan to see what is going on in there.

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      • #18
        Prime that engine with a pressurized oil tank before starting or you'll wipe out your bearings. I would use a two gallon paint pressure tank filled with oil and connected to the oil gallery and pressurized with your air compressor. Set the regulator for about 20 pounds. Can also be used to check the crankcase for excessive leaks by removing the oil pan and placing a plastic catch pan under the engine. Bearings should drip oil; any big streams of oil will show where the oil is going.

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        • #19
          I hate to say it, However; If the oil pump relief has been left out, and you still don't have any pressure at all-------- I'd suspect anything else they did to that engine.

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          • #20
            Maybe blocked oil pick up tube (gasket), or an air gap in the tube (crack). But back to the gears in the pump, they may rotate without the moon key, but they will stop with the slightest oil pressure if the key is not in place. Its worth checking again.

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            • #21
              I spose if they forgot the relief valve they may have forgotten something else. I had a similiar situation but not on a fresh engine. Very perplexing but eventually discovered the gasket where pickup tube was connected to the block was bad and leaking. Replaced it and primed the pump and good oil pressure. Don't recall enough about 6's but they probably have internal oil plugs that could be 'forgotten' Good luck and hang in there!

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              • #22
                Oh, I forgot; hook up a gage directly to an oil line to be sure gage is not at fault.

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                • #23
                  I DO have a gauge hooked up. Key in keyway on shaft is there. Oil pump drive is connected to camshaft - I watched it turn as I turned the motor from the flywheel. Both gears in the pump come out easily altho, according to the Stude repair manual, a special puller is needed. Also, according to illustrations I have seen, there is supposed to be some type of thrust washer(?) on or behind the drive gear in the pump. Mine is missing. I primed the pump using a suction gun full of oil. When I had the pan off, I made and installed a new pick up tube gasket, tightening bolts down firmly. I also looked over the pick up tube for cracks but it had none. I've taken the spark plugs out, oiled the cylinders, and cranked the starter at twenty second intervals, still no oil pressure. I've worked on dozens of motors in my time but this one has me baffled. All comments really appreciated. Thanks.

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                  • #24
                    Gary, are you certain your gauge is functioning?
                    Joe

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                    • #25
                      New update! After much research I discovered that my oil pump is missing a "horseshoe shaped thrust washer"! Obviously the part isn't supposed to be in there for decoration!! It must have a purpose.
                      I called up Stephen Allen's and ordered one. Will let you all know how it works out. Thanks again for all your suggestions.

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                      • #26
                        Originally posted by CrazyCars View Post
                        New update! After much research I discovered that my oil pump is missing a "horseshoe shaped thrust washer"! Obviously the part isn't supposed to be in there for decoration!! It must have a purpose.
                        I called up Stephen Allen's and ordered one. Will let you all know how it works out. Thanks again for all your suggestions.

                        That's Great news! I have been following this thread with intense interest. I did a in place overhaul on my truck way back in 1975. As ignorant as I am now, I was at least ten times more ignorant than I am now and still have a long way to go. In addition, I also spent years specifying and applying pumps in various applications. Automotive oil pumps are generally one of the most precision made and durable components across the totality of the industry (with some few exceptions). I can't think of any of them with unnecessary parts. Our oil pumps are basic gear pumps. The clearances in the pumps, and the space of gear meshing determines volume of intake and outflow as the pump operates. It could be that missing thrush washer causes one gear to slide out of place and affect the pumping action. This is complete theory on my part because I have not studied the components thoroughly. That's why I was hoping one or more of our professional mechanic members (I'm certainly not one) would speak up with a credible explanation of how you could be having this problem , unless there is some kind of horrible hack job by the machine shop who did your rebuild.

                        Get that oil pump back together properly and let us know. I am very interested in the outcome.

                        John Clary
                        Greer, SC

                        SDC member since 1975

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