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Cam Timing Off After Timing Belt Replacement?

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    Cam Timing Off After Timing Belt Replacement?

    I just finished replacing the timing belt, tensioner, and reset valve clearances. I was careful to double check that both the crank damper wheel and cam sprocket were aligned with their respective block and head markings. The engine starts but doesn't run well and will stall when put into gear. I put a vacuum gauge on the manifold port and the engine is only pulling 15" vacuum which suggests possible bad valve timing. Does this make sense given poor running symptoms?

    I am assuming that to correct this I need to drain down and remove the radiator and hoses again in order to completely disassemble the up and lower covers.
    JB
    Massachusetts
    '85 323i Baur

    #2
    vacuum leak somewhere?

    Comment


      #3
      I think your heading may answer your question. Did you spin the engine 2x by hand and then tighten the tensioner ?

      Are you sure the valves are not too tight ?
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        #4
        Originally posted by jeffnhiscars View Post
        I think your heading may answer your question. Did you spin the engine 2x by hand and then tighten the tensioner ?
        what is the point of that? If marks aligned, tensioner is tightened and it's as good as it gets. Spinning it with the tensioner loose can compress the tensioner spring delaying the cam with the belt slack and risking P to V contact.

        Comment


          #5
          Originally posted by jb02 View Post
          engine is only pulling 15" vacuum
          The m20 does not pull a lot o vacuum in my experience. I came from the domestic car market before working on classic BMW's primarily. They really don't pull the typical 20" as most guides suggest (even stock cams have a lot of overlap compared to pushrod motors). I wouldn't use vacuum as a diagnostic on a BMW motor, in most cases anyways (~230ー vs ~250 stock cams - hence m20's not needing a PVC valve, or EGR to pass emissions). You can line up the crank using the reluctor wheel, and pull off the upper timing cover with just a few bolts and visually check timing (small mirror makes the job easier).


          Originally posted by zaq123 View Post
          what is the point of that? If marks aligned, tensioner is tightened and it's as good as it gets. Spinning it with the tensioner loose can compress the tensioner spring delaying the cam with the belt slack and risking P to V contact.

          It's actually easy to have the belt off one tooth (cam retarded) due to the belt design and oil pump drive. Cam timing can be off several teeth, car will still run and not have V to P contact - EDIT: on a stock cam/pistons design.



          To remedy this, I actually start by bolting the tensioner in the full "loose belt" position (spring completely compressed). Then back the crank up one tooth, wrap the belt starting at the crank, then cam, then pull the tension towards the tensioner and rotate the crank as I slip the belt on the tensioner. Then leave the tensioner spring fully compressed, rotate the engine two full times to be sure the marks repeat. Then loosen the tensioner bolt, let the spring do then tensioning, then re-tighten the tensioner bolt.
          Last edited by ForcedFirebird; 07-08-2019, 07:53 PM.
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            #6
            Originally posted by zaq123 View Post
            what is the point of that? If marks aligned, tensioner is tightened and it's as good as it gets. Spinning it with the tensioner loose can compress the tensioner spring delaying the cam with the belt slack and risking P to V contact.
            As you wind the engine over slowly the resistance of valvetrain ensures there's always tension so no harm is done by doing it loose. The purpose of doing it tensioner loose is it ensures the tension side is under some tension when the tensioner is locked off. If you had a bit of slack on the tension side and locked of the tensioner as soon as the crank rotates you'd get some slack.
            89 E30 325is Lachs Silber - currently M20B31, M20B33 in the works, stroked to the hilt...

            new build thread http://www.r3vlimited.com/board/showthread.php?t=317505

            Comment


              #7
              Originally posted by digger View Post
              As you wind the engine over slowly the resistance of valvetrain ensures there's always tension so no harm is done by doing it loose. The purpose of doing it tensioner loose is it ensures the tension side is under some tension when the tensioner is locked off. If you had a bit of slack on the tension side and locked of the tensioner as soon as the crank rotates you'd get some slack.
              Isn't that what that spring is doing, picking up any belt slack? I just trying to imagine how the tensioner will be steel loose with the spring applying all that pressure on the belt.

              Comment


                #8
                Originally posted by ForcedFirebird View Post

                To remedy this, I actually start by bolting the tensioner in the full "loose belt" position (spring completely compressed). Then back the crank up one tooth, wrap the belt starting at the crank, then cam, then pull the tension towards the tensioner and rotate the crank as I slip the belt on the tensioner. Then leave the tensioner spring fully compressed, rotate the engine two full times to be sure the marks repeat. Then loosen the tensioner bolt, let the spring do then tensioning, then re-tighten the tensioner bolt.
                I do something similar as well, install the belt with marks aligned, spring fully compressed and its bolt locked; Release the spring and lock it, recheck marks; Rotate a couple of time a check them marks again; Put the dial gauge on the valve, gear on the crank and find the exact cam timing.

                Comment


                  #9
                  Originally posted by zaq123 View Post
                  Isn't that what that spring is doing, picking up any belt slack? I just trying to imagine how the tensioner will be steel loose with the spring applying all that pressure on the belt.
                  Only on the slack side. On a frictionless system it does both sides. there's enough friction in the crank and cam that means you can get some trapped on the other side.
                  You also need to rotate to 100% confirm you got the right tooth.
                  89 E30 325is Lachs Silber - currently M20B31, M20B33 in the works, stroked to the hilt...

                  new build thread http://www.r3vlimited.com/board/showthread.php?t=317505

                  Comment


                    #10
                    Originally posted by zaq123 View Post
                    what is the point of that? If marks aligned, tensioner is tightened and it's as good as it gets. Spinning it with the tensioner loose can compress the tensioner spring delaying the cam with the belt slack and risking P to V contact.
                    When first wrapped around the gears the belt is typically tighter on one side than the other which can effect valve timing so Its SOP to rotate the engine and then tighten the tensioner. I'm surprised you questioned this.
                    Deck Lid and soft top Shocks on hand

                    Seat shocks on hand for immediate shipment
                    https://www.r3vlimited.com/board/sho...86#post4944786
                    Alice the Time Capsule
                    http://www.r3vlimited.com/board/showthread.php?t=360504
                    87 Zinno Cabrio barn find 98k and still smells like a barn. Build thread http://www.r3vlimited.com/board/show...20#post3455220

                    Comment


                      #11
                      Cam Timing Off After Timing Belt Replacement?

                      Originally posted by jeffnhiscars View Post
                      When first wrapped around the gears the belt is typically tighter on one side than the other which can effect valve timing so Its SOP to rotate the engine and then tighten the tensioner. I'm surprised you questioned this.


                      I知 not really questioning this...IMO if the belt is installed correctly, the tensioner spring will take all the needed slack from the get go. Belt teeth are going into sprockets and stay there. Rotate the engine a few times, that unbolt and rebolt the tensioner bolt to equalize the belt. Basically the same concept but different approach. I知 concern with P to V contact when cranking the engine with loose tensioner. The resistance of the aggressive cam can compress that tensioner spring IMO.
                      As it is, belt already has a normal stretch that nets 2 degrees





                      Sent from my iPhone using Tapatalkb
                      Last edited by zaq123; 07-09-2019, 09:41 AM.

                      Comment


                        #12
                        Cam Timing Off After Timing Belt Replacement?

                        Sorry. Double post

                        Comment


                          #13
                          Originally posted by zaq123 View Post
                          I知 not really questioning this...IMO if the belt is installed correctly, the tensioner spring will take all the needed slack from the get go. Belt teeth are going into sprockets and stay there. Rotate the engine a few times, that unbolt and rebolt the tensioner bolt to equalize the belt. Basically the same concept but different approach. I知 concern with P to V contact when cranking the engine with loose tensioner. The resistance of the aggressive cam can compress that tensioner spring IMO.
                          As it is, belt already has a normal stretch that nets 2 degrees


                          Sent from my iPhone using Tapatalkb
                          It's fine if you unbolt after rotating a couple times and relighted but If you do it that way you need to tighten the tensioner loosen it then tighten it again. Why not tighten it once only....

                          You don't crank the engine with tensioner loose you hand rotate it. If you rotate the crank the correct way the belt is skways under tension so the only p to v issue is if you put on wrong tooth and then it doesn't matter what you do.
                          89 E30 325is Lachs Silber - currently M20B31, M20B33 in the works, stroked to the hilt...

                          new build thread http://www.r3vlimited.com/board/showthread.php?t=317505

                          Comment


                            #14
                            Originally posted by digger View Post
                            It's fine if you unbolt after rotating a couple times and relighted but If you do it that way you need to tighten the tensioner loosen it then tighten it again. Why not tighten it once only....



                            You don't crank the engine with tensioner loose you hand rotate it. If you rotate the crank the correct way the belt is skways under tension so the only p to v issue is if you put on wrong tooth and then it doesn't matter what you do.


                            I agree that the belt is always under tension but with loose tensioner, it痴 just the tensioner spring agains all that cam resistance. I知 sure that the spring will hold since that痴 how you guys are doing it....probably just paranoia on my part..haha


                            Sent from my iPhone using Tapatalk

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                              #15
                              The belt has teeth you don't even really need much tension to rotate it slowly provided its sitting on the gears correctly it'll stay in phase. Just don't go backwards
                              89 E30 325is Lachs Silber - currently M20B31, M20B33 in the works, stroked to the hilt...

                              new build thread http://www.r3vlimited.com/board/showthread.php?t=317505

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