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    Jackshaft Problem

    The engine in my Stag was rebuilt by a well known professional garage 4years ago and 9500 miles, It recently started dripping oil from what I thought was the oil pump seal. I removed the pump and replaced the seal, and was made aware at this time that the oil pressure I had was too high, being some 70 psi when cold. I acquired a correctly rated oil pressure pump spring from Robsport and reassembled it. After fitting the pressure was a more reasonable 50 psi, but unfortunately the oil leak was still apparent. Not much, but it dripped straight onto the hot exhaust. Eventually, after running the engine upto temperature a few times on the ramp, I traced the oil lead to the cam cover gasket. When I restarted the car it was like there was a flat battery, and the engine tried to turn over, but would not. I checked the battery, and all was ok, so I tried again and it turned, a bit reluctant, but then properly, but it would not fire. After some investigation I found that the distributor was not rotating. Having now removed it, I can see the jackshaft gear is stationary.

    This leaves two questions:

    1. Is there some way that I caused the oil pump / distributor drive to seize up when I replaced the pump?
    2. Is the jackshaft itself likely to be fractured, or can the drive gearing rotate without turning the shaft somehow.

    Any thoughts gratefully received.

    Nigel


    Last edited by Nigel W; 25 May 2021, 22:27.

    #2
    Nigel.
    Did you put oil in the pump and check to see that it would rotate before fitting it? It is not unheard of for them to be "Solid" from bad assembly when new. If you didn't, it needs to be removed and checked.
    I think it is highly unlikely that the jackshaft has broken, but the dowel pin taking the drive from the timing chain sprocket to the shaft could have sheared from the strain caused by a seized pump.
    Mike.

    Comment


      #3
      Sounds to be possibly deep. After distributor drive is checked as per mike’s post, next is water pump. Then front cover.
      There are 2 secrets to staying on top :- 1. Don't give everything away.
      2.

      Comment


        #4
        The oil pump outer rotor has a chamfer on one end of its outer diameter, which needs to face into the pump. If this is fitted the wrong way round it could make the pump tight to turn.

        Nigel

        Comment


          #5
          Thank you all for your comments, very useful. When I removed the distributor, the drive to the oil pump came with it, and required quite a lot of force to remove it. This would tend to indicate to me the the oil pump may have cause the problem, and on the basis its the thing I worked on, that's the most likely cause. I will remove it over the next few days along with the timing chain cover and see what the situation is. I will post my feed back as soon as I can.

          Thanks again

          Nigel

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            #6
            Soon be running again jackshaft screw & dowel sheared. No other serious damage uncovered.
            distributor requires checking over.
            hope you’re ok with that nigel?
            There are 2 secrets to staying on top :- 1. Don't give everything away.
            2.

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              #7
              Thanks very much for your help Julian. The photos show the damage. IMG_4256.jpeg IMG_4259.jpeg

              Comment


                #8
                Distributor had a broken plastic thrust washer.
                Thanks to Mr. Spain for that part.
                There are 2 secrets to staying on top :- 1. Don't give everything away.
                2.

                Comment


                  #9
                  Broken & how it should be!
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                  This gallery has 1 photos.
                  Last edited by jbuckl; 3 June 2021, 23:10.
                  There are 2 secrets to staying on top :- 1. Don't give everything away.
                  2.

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                    #10
                    There was also extra load at the water pump found. Cause yet to be determined.
                    There are 2 secrets to staying on top :- 1. Don't give everything away.
                    2.

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                      #11
                      I noticed on the picture of the timing chains that the outside tensioner head is very close to the body.
                      With the rolon tensioner this can cover the oil spray hole and cause excess timing gear wear until it slacks off enough to uncover the spay hole.

                      If they are the early type with the oil hole in the middle of the rubber this isn't an issue. Made this mistake myself some years ago the first time I used the rolon tensioner.
                      Neil
                      Neil
                      TV8, efi, fast road cams and home built manifolds. 246bhp 220lbft torque

                      Comment


                        #12
                        Neil

                        When we took the front cover off, both chains were very tight on one side. I think it was because of the load from the failed jackshaft. However, you point is very helpful and we will monitor carefully on reassembly.

                        Nigel

                        Comment


                          #13
                          There have been a few items noticed that weren’t correct / or as expected, head misalignment, chainguide distortion, crank pulley & keyway poor fitment, to name a few.
                          There are 2 secrets to staying on top :- 1. Don't give everything away.
                          2.

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                            #14
                            Originally posted by flying farmer View Post
                            I noticed on the picture of the timing chains that the outside tensioner head is very close to the body.
                            With the rolon tensioner this can cover the oil spray hole and cause excess timing gear wear until it slacks off enough to uncover the spay hole.

                            If they are the early type with the oil hole in the middle of the rubber this isn't an issue. Made this mistake myself some years ago the first time I used the rolon tensioner.
                            Neil
                            True… the fitment spacers were used on reassembly & the start point is slightly further out now ~ 3mm from fully back / 3mm out Rolon piston hole tensioners were reused.
                            There are 2 secrets to staying on top :- 1. Don't give everything away.
                            2.

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