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Setting TDC in the M42

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    Setting TDC in the M42

    Hi friends, I'm currently doing the head gasket on my M42. I'm a bit confused about the proper way to set TDC. Everywhere I've searched (and in the Bentley, too), it says to use the flywheel locking pin. That's great, except my engine is on a stand without the flywheel mounted, so I can't use this pin. I know that the woodruff key at the front should be pointed straight up, but I'm not convinced that this visual test will be accurate (without another tool that I don't have). And how do I ensure that the distance between the cam sprockets and the crank sprocket isn't off by a tooth or two when I do this?

    Alternatively, should I take the engine off the stand and mount the flywheel before setting TDC? I'm not sure how this would work either, the Pelican guide doesn't say anything about aligning the flywheel to the crank (only the clutch and pressure plate to the flywheel), and the bolt pattern looks symmetric.

    Not really sure how to proceed, I'm in a bit over my head. I'd appreciate any advice.



    Side note, this engine has almost 270k miles and I still see hone marks on the cylinder walls. No other evidence that it was ever fully rebuilt (though turns out someone swapped an M44 timing case at some point), but I thought that was kinda neat.

    #2
    You can use the arrow on the oil filter housing to the dot/hash on one of the crank trigger wheel teeth for crank agreement. This should get you almost spot on. You can double check this once you have the FW back on, and worst case you'd have to remove cam gears to get everything centered. Also, just aim for close to centered in the cam "windows" until you reference with the locking pin. Cams should point up and towards each other at cyl 1, flats at rear should be square with each other. E marked cam goes on the intake side in case you didn't mark it.

    FW can only go on one way IIRC, pretty sure there is a pin or two that make that happen.

    Not sure if you took the front timing case off or not, but just be sure the chain doesn't bunch, and that you only rotate clockwise during your timing setting.

    It's a little bit fiddly, but really easy enough.

    Comment


      #3
      Originally posted by roguetoaster View Post
      You can use the arrow on the oil filter housing to the dot/hash on one of the crank trigger wheel teeth for crank agreement. This should get you almost spot on. You can double check this once you have the FW back on, and worst case you'd have to remove cam gears to get everything centered. Also, just aim for close to centered in the cam "windows" until you reference with the locking pin. Cams should point up and towards each other at cyl 1, flats at rear should be square with each other. E marked cam goes on the intake side in case you didn't mark it.

      FW can only go on one way IIRC, pretty sure there is a pin or two that make that happen.

      Not sure if you took the front timing case off or not, but just be sure the chain doesn't bunch, and that you only rotate clockwise during your timing setting.

      It's a little bit fiddly, but really easy enough.
      Got it, so the arrow can align with any of the trigger wheel teeth. I guess I can visually set TDC since it's only off by a degree or two probably and then turn the crank to get a tooth aligned. I was able to get the head off without removing the cams, but I noticed that on the square heads at the rear, only the vertical surfaces were machined. Is it close enough to just clamp a bar across the top surfaces, or is that unmachined surface going to be an issue? I was planning on cutting a small block of wood to fit in between the two to keep the vertical edges parallel, but clamping something across the top would be easier.

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        #4
        The arrow on the flywheel aligns with one and only one tooth on the trigger wheel. If you look closely, there is one tooth with a little notch in it, and that is the one.

        Similarly, the cams can be put into rough position by having the lobes for cylinder 1 point up and toward each other, and the precise position can be set by making the flat/square rear ends parallel. I believe that the faces which should be parallel at TDC also have some small holes pecked into them. I used a flat block of metal to lay across the ends and check for parallelism, and a wrench on one of the hexagonal parts in the middle of the cam to adjust it.

        It does not take much timing error to get pistons to hit valves. Get TDC set as best you can with the tensioner piston installed and released (fully extended). Turn the engine through a few full rotations using a socket on the crank bolt and re-check the timing.

        Comment


          #5
          Originally posted by sedrat View Post

          Got it, so the arrow can align with any of the trigger wheel teeth. I guess I can visually set TDC since it's only off by a degree or two probably and then turn the crank to get a tooth aligned. I was able to get the head off without removing the cams, but I noticed that on the square heads at the rear, only the vertical surfaces were machined. Is it close enough to just clamp a bar across the top surfaces, or is that unmachined surface going to be an issue? I was planning on cutting a small block of wood to fit in between the two to keep the vertical edges parallel, but clamping something across the top would be easier.

          Originally posted by roguetoaster View Post
          You can use the arrow on the oil filter housing to the dot/hash on one of the crank trigger wheel teeth for crank agreement
          The cams cannot be reliably locked with wood. Two adjustable wrenches will work, and then you may be able to clamp those together, but it's hard to also check flatness at the same time.

          Generally on the cam flats I'll get one to visually flat, bolt down the cam gear, adjust the other with a flat reference material, then I'll make small adjustments to one or both as needed to hit a flat agreement.

          Comment


            #6
            I see the mark on the trigger wheel tooth now, thanks for clearing that up. Wasn't able to get the head back on today, but I think I have a good idea of what to do now to avoid the pistons hitting the valves. Really appreciate the help guys!

            Comment


              #7
              Back from the dead, I'm still out here working on this M42. Ran into a small issue and I'm not sure if I have the wrong parts or if my crank is somehow misaligned. I was installing a Valeo 52161203 Flywheel kit but it seems like the flywheel doesn't properly align with my crank...

              https://imgur.com/DLWZSn6
              Check out the big hole (in yellow) and the flywheel lock (in blue) on the block. There's about 90 degrees between them.

              https://imgur.com/U8voAJh
              On the flywheel side, the big hole (in yellow) and the flywheel lock slot (in blue) are basically in line with each other. This wouldn't be an issue normally, but I also did the head gasket, and I need the flywheel locked in place to double check that the timing is right.

              https://imgur.com/iddCihC
              At the front of the block, the tick on the trigger wheel is aligned with the mark on the oil filter housing, so I'm pretty sure my crank is aligned at TDC. So the big hole on the back side is in the proper place.

              Has anyone used the Valeo flywheel and had this issue? Any idea how to correct it, or at least figure out the proper timing?


              Side note, I'm replacing the flywheel because my old one has heat marks on it. I thought about bolting the old one up to check the timing using that, but that one doesn't have the slot at all.

              Edit: I checked and cylinder 1 is definitely higher than cylinder 2, so that's good at least. I'm not sure how to measure the height difference, but I could potentially use this to find tdc on the crank if someone knows what this should be. I do have an M44 timing case, could that potentially cause misalignment?
              Last edited by sedrat; 03-06-2021, 09:52 PM.

              Comment


                #8
                You do not necessarily need the flywheel lock to set the crank to TDC. The last few times, I did it through the spark plug bore using a wooden dowel and pen...if you know the stroke (IIRC 81mm), you can set it pretty accurately. The ideal would be to have 12in / 300mm calipers so that you could just use the depth gauge. Anyway, it is not perfect and you'd at least get within a couple of degrees that way, and the engines ran fine. It just took a few passes of checking and re-checking since the piston movement is really small at the extremes.

                The M44 timing case should not affect anything.

                Just make sure to make a clear mark between the crank damper and timing covers or something so that you can easily get it back to TDC when setting the cams. You will want to get it all aligned, then turn the engine a few times by hand (CW crank rotation ONLY, never CCW) and then re-check that the cams are still at TDC with the crank. The tensioner piston should also be fully released and pushing on the guide rail. If you want to be REALLY sure, you can check the cams' alignment again after a short drive if it starts and runs well.

                Comment


                  #9
                  Originally posted by bmwman91 View Post
                  You do not necessarily need the flywheel lock to set the crank to TDC. The last few times, I did it through the spark plug bore using a wooden dowel and pen...if you know the stroke (IIRC 81mm), you can set it pretty accurately. The ideal would be to have 12in / 300mm calipers so that you could just use the depth gauge. Anyway, it is not perfect and you'd at least get within a couple of degrees that way, and the engines ran fine. It just took a few passes of checking and re-checking since the piston movement is really small at the extremes.

                  The M44 timing case should not affect anything.

                  Just make sure to make a clear mark between the crank damper and timing covers or something so that you can easily get it back to TDC when setting the cams. You will want to get it all aligned, then turn the engine a few times by hand (CW crank rotation ONLY, never CCW) and then re-check that the cams are still at TDC with the crank. The tensioner piston should also be fully released and pushing on the guide rail. If you want to be REALLY sure, you can check the cams' alignment again after a short drive if it starts and runs well.
                  Thanks again for being super helpful man. I'm not quite sure what you mean here ("clear mark between the crank damper and timing covers or something") though, would that just be the nick on the trigger wheel and the arrow on the oil filter housing?

                  I ended up buying the cam lock tool, so I was thinking I'd line up the cams at TDC. Then, I'd measure the stroke between cylinders 1 and 2, rotating cw if necessary to align the crank at tdc. Then, I'd torque down the cam gear bolts and double check the stroke again. Hopefully everything should be aligned after that.

                  Comment


                    #10
                    Pretty sure he means that you should set crank TDC via the hash/filter arrow, and then make an auxiliary mark with something like a red paint pen elsewhere so it's easier to see if the crank moved.

                    Comment


                      #11
                      Sorry if I was not clear, as rogue said, I meant to make your own mark on the timing case with a red sharpie or something like that. The arrow on the oil filter housing is sort of far away, especially if you are trying to line up the notch while the engine is in the car (looking down at a sharp angle makes it a major hassle).

                      Comment


                        #12
                        Thanks for the dowel trick. Tried it a few times and the stroke was within .5 mm from just using the mark on the oil filter housing (with the cams locked) each time so I'm going to call it good.

                        Comment

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