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Clacking Engine IV - The Autopsy

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    Clacking Engine IV - The Autopsy

    I had a phone call from Peter at LD the other night as I was having difficulties with his site and had emailed him. He had tried responding to my email but it had been returned undelivered, so he had tracked my landline down from an old order.
    He asked what the problem was and he explained the crank sprockets are the sacrificial link and would be the first part to wear and if other parts fail the consequences could be worse. When I went through the previous rebuild, and said I'd fitted new camshafts he said "ahhhh" suspect that is the root of the problem and you have a binding camshaft.

    Now that is service.

    Well, timing gear stripped today and here is what I found.

    The rear crank sprocket for LHS is nearly non-existent, effectively reducing the PCD of the chain run.

    The LH cam sprocket showing signs of wear 1/3 to 1/2 way round. Left hand cam out and Nos.4&5 bearing a little shiny in places, cam journal showing shiny (rubbed) one side only.

    This would suggest to me the LH cam could be, or has been binding slightly at a certain point and Peter could be right.


    The cams were BL NOS 10,000 miles ago so it would make sense. I checked they turned freely before the valves were fitted but not easy now without pulling the head which I REALLY don't want to do again. I'll look at "easing " the bearings and see how the new timing kit fares.

    Jackshaft bearing feels fine, no sideways play at all, just expected normal end float. Turns freely, smooth, not suspecting jackshaft.
    Tensioners both extended, oil holes not blocked, oil oozing ok from the tensioner supply when the jackshaft is turned.

    Front RH cam chain stretched but gears all "as new"

    The clacking? varying the tension of the chain as the cam turns? flapping it about a bit and now this noise is transferring to the jackshaft, possibly by the action of the extended tensioner? I really don't know.

    I won't know if it's gone until it's all back together.

    Question is, do I need to do anything with the camshaft to ease or scrape the bearings further or will they have run in after 10,000 miles and won't be an issue?





    New sprockets have "sharper" teeth compared to the old ones fitted 15 years ago

    IMG_9642.JPG

    Signs of a camshaft bearing rub. Is this still a problem?

    IMG_9651.JPG

    Cam sprocket teeth worn only half way around

    IMG_9647.JPG


    Rear and front crank sprockets removed today
    IMG_9645.JPG

    Jackshaft sprocket old and new

    IMG_9633.JPG


    #2
    Originally posted by Mark S View Post
    .........................

    The cams were BL NOS 10,000 miles ago so it would make sense. I checked they turned freely before the valves were fitted but not easy now without pulling the head which I REALLY don't want to do again. I'll look at "easing " the bearings and see how the new timing kit fares.
    ...........................


    IMG_9633.JPG
    My lump is an RV8 so I'm being a bit cheeky butting in regarding a TV8, I'm assuming you don't want to turn the cams in case the valves hit pistons and get bent. Perhaps if you rotate the crankshaft to 45 degrees BTDC the pistons will be halfway down the bore and it would be safe to turn the camshaft.

    John.
    Your wife is right, size matters. 3.9RV8

    Comment


      #3
      Originally posted by jakesmig View Post

      My lump is an RV8 so I'm being a bit cheeky butting in regarding a TV8, I'm assuming you don't want to turn the cams in case the valves hit pistons and get bent. Perhaps if you rotate the crankshaft to 45 degrees BTDC the pistons will be halfway down the bore and it would be safe to turn the camshaft.

      John.
      I suppose I could rotate the crank 45 degrees and none of the pistons but would be at the top, but would there be enough clearance for all the valves to open? .

      There was no clacking though until the engine has been running for around 30 secs, then gets louder, so would I pick any binding cold? The engine certainly turns fairly freely by hand with the plugs out. I think whilst the valves are in it would be difficult to tell what was binding and what was spring resistance.
      Last edited by Mark S; 12 June 2021, 18:45.

      Comment


        #4
        I had a failure after 6k miles with new chains and sprockets. i had the right hand head rebuilt but caught it before the left head failed. He said in my case the cam was not binding . I did have those tensioners were the oil feed is down. I've been told that none of the sprockets are hardened.

        Comment


          #5
          I suppose you've checked you have 120 lb ft on the crankshaft pulley ? On engines I've seen woodruff keyway wear when loose (50-80 lb ft), only torque has been put on the crankshaft bolt. It allows the pulley to vibrate back and forth making an "orrible" clacking noise and cutting a slot into the pulley woodruff keyway sideways with the woodruff key (I've seen a 6mm slot).

          Micky
          Last edited by Motorsport Micky; 13 June 2021, 13:47.

          Comment


            #6
            Originally posted by Motorsport Micky View Post
            I suppose you've checked you have 120 lb ft on the crankshaft pulley ? On engines I've seen woodruff keyway wear when loose (50-80 lb ft), only torque has been put on the crankshaft bolt. It allows the pulley to vibrate back and forth making an "orrible" clacking noise and cutting a slot into the woodruff keyway sideways with the woodruff key (I've seen a 6mm slot).

            Micky
            Pulley bolt was torqued, sprocket a good tight fit on the key, aligned to the jackshaft sprocket and wouldn't have been able to rattle about.
            Curved chain guide and tensioner shoe not too bad but a bit more worn than the front chain. It would suggest the rear chain has done more work, but it is pumping the water and oil in addition to turning the cam.

            The noise was also slightly worse when the old oil pump with 60psi spring was fitted, which could point to the noise originating from the action of the extended tensioner?

            Has anyone enlarged the hole in the Rolon tensioner body? Or are the inlet/spray holes sized to regulate the pressure in the tensioner?

            I'm at work today but will DTI the cam to check it is straight.

            Comment


              #7
              Originally posted by Mark S View Post
              I had a phone call from Peter at LD the other night as I was having difficulties with his site and had emailed him. He had tried responding to my email but it had been returned undelivered, so he had tracked my landline down from an old order.
              He asked what the problem was and he explained the crank sprockets are the sacrificial link and would be the first part to wear and if other parts fail the consequences could be worse. When I went through the previous rebuild, and said I'd fitted new camshafts he said "ahhhh" suspect that is the root of the problem and you have a binding camshaft.

              Now that is service.

              Well, timing gear stripped today and here is what I found.

              The rear crank sprocket for LHS is nearly non-existent, effectively reducing the PCD of the chain run.

              The LH cam sprocket showing signs of wear 1/3 to 1/2 way round. Left hand cam out and Nos.4&5 bearing a little shiny in places, cam journal showing shiny (rubbed) one side only.

              This would suggest to me the LH cam could be, or has been binding slightly at a certain point and Peter could be right.


              The cams were BL NOS 10,000 miles ago so it would make sense. I checked they turned freely before the valves were fitted but not easy now without pulling the head which I REALLY don't want to do again. I'll look at "easing " the bearings and see how the new timing kit fares.

              Jackshaft bearing feels fine, no sideways play at all, just expected normal end float. Turns freely, smooth, not suspecting jackshaft.
              Tensioners both extended, oil holes not blocked, oil oozing ok from the tensioner supply when the jackshaft is turned.

              Front RH cam chain stretched but gears all "as new"

              The clacking? varying the tension of the chain as the cam turns? flapping it about a bit and now this noise is transferring to the jackshaft, possibly by the action of the extended tensioner? I really don't know.

              I won't know if it's gone until it's all back together.

              Question is, do I need to do anything with the camshaft to ease or scrape the bearings further or will they have run in after 10,000 miles and won't be an issue?





              New sprockets have "sharper" teeth compared to the old ones fitted 15 years ago

              IMG_9642.JPG

              Signs of a camshaft bearing rub. Is this still a problem?

              IMG_9651.JPG

              Cam sprocket teeth worn only half way around

              IMG_9647.JPG


              Rear and front crank sprockets removed today
              IMG_9645.JPG

              Jackshaft sprocket old and new

              IMG_9633.JPG
              To me the whole tooth design seems wrong on the new sprocket, the lands, pitch ,radii ,etc and being soft ? makes them wear rapidly , we are getting more and more of this, there must be someone that can make sprockets that last a similar mileage/time as the triumph ones or we all all domed to changing chains etc at 10,000 miles or less
              "The UK,s 2nd Most Easterly Stag" Quad Exhaust- ZF 4 Speed BOX

              Comment


                #8
                Originally posted by MandM View Post

                To me the whole tooth design seems wrong on the new sprocket, the lands, pitch ,radii ,etc and being soft ? makes them wear rapidly , we are getting more and more of this, there must be someone that can make sprockets that last a similar mileage/time as the triumph ones or we all all domed to changing chains etc at 10,000 miles or less
                Is this another case of "don't replace unless absolutely necessary"? When I did the cylinder heads on my Stag in 2014 I fitted new chains (JWIS), guides and tensioners (from LD Parts), but re-used all the sprockets as they looked unworn. No idea how many miles they had done. Since then I have done 24,000 miles and when I recently checked the tensioners and lower sprockets with an endoscope there was still no signs of wear and the tensioners have barely moved.
                Dave
                1974 Mk2, ZF Auto, 3.45 Diff, Datsun Driveshafts. Stag owner/maintainer since 1989.

                Comment


                  #9
                  The clacking noise I have always thought is the long straight section of chain "flapping" against the guide. It seems to do it irrespective of wear. It may reduce just after the tensioner clicks out another stop, so that the chain is under maximum tension at all times.

                  Your excess wear is caused by excess chain load. That could be camshaft, jackshaft or over-tight chain. You need to make sure that there is a small amount of movement in the tensioner when first assembled to allow lubrication to work (expose the lube hole in the side of the plunger) and for thermal expansion of the head etc. Assuming that is not it, 60 psi for oil pressure is too high IMHO. Should be around 40-50 psi max for long life of jackshaft gears, chains etc. But that may reduce life to 30K miles perhaps. So does sound like the camshaft becoming stiffer. Perhaps warping head plus slightly un-true camshaft?? Perhaps sticky valves, but I have never heard of either before, so real long-shots!

                  Comment


                    #10
                    Originally posted by MikeParker View Post
                    The clacking noise I have always thought is the long straight section of chain "flapping" against the guide. It seems to do it irrespective of wear. It may reduce just after the tensioner clicks out another stop, so that the chain is under maximum tension at all times.

                    Your excess wear is caused by excess chain load. That could be camshaft, jackshaft or over-tight chain. You need to make sure that there is a small amount of movement in the tensioner when first assembled to allow lubrication to work (expose the lube hole in the side of the plunger) and for thermal expansion of the head etc. Assuming that is not it, 60 psi for oil pressure is too high IMHO. Should be around 40-50 psi max for long life of jackshaft gears, chains etc. But that may reduce life to 30K miles perhaps. So does sound like the camshaft becoming stiffer. Perhaps warping head plus slightly un-true camshaft?? Perhaps sticky valves, but I have never heard of either before, so real long-shots!
                    Thanks Mike.

                    Oil pressure has been 50psi since re-build. Only had 60psi for approx 15 mins running after oil pump swap and not whilst on the road.
                    Head and cam bore straightness was checked and ok when rebuilt and the engine has never overheated since. Chain guides set up with the plastic insert and 1mm feeler. Tensioner spray hole could not have been covered.

                    I've spoken to a mechanical engineer at work today who also builds motorcycle engines and he says if it was purely chain load, he wouldn't have expected the sprockets to have be worn evenly in the root but on one side and since the jackshaft sprocket has worn like it has, worse than the cam sprocket, he suggests the chain has been too tight and the issue is more likely to be with the tensioner. Whether or not this has happened due to loading, causing the tensioner to pop to the next stop early, resulting in the chain running too tight, who can say but it would seem feasible. He didn't seem too think the slight rub on the cam bearing surfaces was too much to worry about after 10k.

                    He didn't think much to the shape of the teeth on the sprockets though. I may yet dig out the "original" crank sprockets and fit those.

                    Comment


                      #11
                      Mark,
                      Looking again at your worn sprockets there are a couple of major differences to mine. Firstly with me it was only the crankshaft sprockets that were worn. Not the jackshaft or camshaft sprockets. Also as your engineer colleague rightly pointed out, mine were worn on one side and not symmetrically at the root. So over-tight chain seems to be the correct diagnosis. Best thing is to change tensioners and chains (and sprockets) and hope that is it. To be sure to check with an endoscope or remove the cover after 7K miles or so and see if there is any wear.

                      I am trying to see if I can get get some hardened sprockets made and will report back with my findings in due course. This is a major problem for all of us. I certainly don't wont to strip down my engine every 10K miles, or even 60K miles for that matter.

                      Mike

                      Comment

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