Announcement

Collapse
No announcement yet.

Compression Test - Engine Rebuild necessary?

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • #16
    Originally posted by weisen View Post
    OK, did one last test with the now luke-warm Motor, this time not with the rubber-hose of the tester but with the solid tube and the rubber cone pressed in. Results as follows:

    Cyl 1: 190 Psi
    Cyl 2: 174 PSi
    Cyl 3: 190 PSi
    Cyl 4: 177 Psi

    So next step is the leak-down test. Regardless of Motor warm or cold or if I used the hose or the tube Cyl 2 and 4 are the ones that are worst. Have to buy such a tester first....
    what compression tester are you using? should screw into the spark plug hole with oring seal. the tools you are using may be the problem.
    88 M3 Henna
    95 M3 Orange
    97 M3 Techno

    Comment


    • #17
      Hi,

      I used the digital compression tester from BGS https://www.bgstechnic.com/en/catalo...460318/page/19
      I numbers from my first posts were tested with the hose and adapter and screwed it with oring seal in. Screwed it in only by hand and did not use a tool for that. The last numbers were with the solid tube and pressed the cone in. But the numbers give the consistent picture that Cyl 2 and 4 are worse than 1 and 3. That I got in all tests.

      Comment


      • #18
        For your high idle, have you confirmed that the throttle butterflies are fully closed at idle? I thought some of the other owners had misrouted their throttle cables, and with the incorrect, longer distance the cables were holding the butterflies open just a little leading to a high idle.

        Comment


        • #19
          Did you blow out the plug wells before starting? You can't get any grit down there. Make sure you have all plugs out, engine at operating temp (water and oil) then have a helper in the car bump the ignition for 3 cranks, check number - release pressure then have them do 5 cranks and check the number again. If you do this for each cylinder you will have more consistent results, unless of course... there is an actual issue.

          Comment


          • #20
            Originally posted by Chris W View Post
            For your high idle, have you confirmed that the throttle butterflies are fully closed at idle? I thought some of the other owners had misrouted their throttle cables, and with the incorrect, longer distance the cables were holding the butterflies open just a little leading to a high idle.
            Good hint, checked it. They close completely. So I guess a leak is more likely. Idle is also fine on the first 10-15 min driving, then it is too high.

            Comment


            • #21
              Originally posted by proctor750 View Post
              Did you blow out the plug wells before starting? You can't get any grit down there. Make sure you have all plugs out, engine at operating temp (water and oil) then have a helper in the car bump the ignition for 3 cranks, check number - release pressure then have them do 5 cranks and check the number again. If you do this for each cylinder you will have more consistent results, unless of course... there is an actual issue.
              Yes, plug wells blown out. Even when engine warm the deviation of cyl 2 and cyl 4 is concerning me. Therefore the next step is the leakdown test. One thing I would like to ask here as well. Since a few months the car is leaking out a little from the filler cap. I replaced the filler cap with a new gasket, still oil is coming out there. Could this indicate worn piston rings? So maybe also back to topic engine rebuild:

              Car has 146.000km, oil pressure is slightly retarded at startup after sitting a while (see my other post here), it has a too high idle, compression results not perfect, the header is not completely tight, two nuts came already loose (stud still in). So there will be things to do and I tend to do them thoroughly now as I think that it is more economical when you already started with many things. Two years ago there were already many refurbishments, mainly on chassis and brakes, clutch but also rod bearings, waterpump, thermostat and I am still angry with myself that I have not let do the full engine refurbishment then (I mean, gearbox was already out for the clutch, so engine could have been pulled out as well). So the car is in good shape and I would like to keep it. And I am not feeling well driving around with an engine that already indicates some problems, I am concerned that continuing driving will cause more trouble in the end. Want to keep it stock, so normal rebuild to have a solid engine in the end in an original 320is, not that many around there anymore. So I tend to do the big rebuild now to have longer fun with the car. The engine has to be rebuild anyway sooner or later when I keep the car. Big task is to find a workshop that I trust to do the engine rebuild.

              Comment


              • #22
                Small update: Found a trustworthy and experienced workshop to check the engine. Same results as I had, Cyl 2 and 4 way to low in compression and leak-down also failed on these cylinders. I will let them do the rebuilt now. They will do a whole foto documentation, provide complete protocols and keep me in the loop to discuss the progress and repair options.

                Comment


                • #23
                  Hi,

                  update on the rebuilt of the engine (and other stuff like differential and A/C): The reason for the low compression was that the pistons and rings were worn. Rebuilt is possible with oversize pistons, no need to install liners. They make good progress, head and block are refurbished and I hope that it will be finished soon, we are just waiting for the cylinder head screws, they needed to be back-ordered by BMW. That slows everything down currently.

                  One question since there are different opinions. What are your recommendations for breaking-in a rebuilt engine? I still have this break-in procedure sticker on my windscreen but are there other/better ways to break in the engine?

                  Regards

                  Nils

                  Comment


                  • #24
                    HI,
                    Mine was stock rebuild with genuine pistons and standard cams, basically after the initial test drive and then back home to check it was all good I went on a holiday just drove it like a new car for 1000km did not rev it too hard or let it labour on the hills. I figured that is what the original owner would have done and no different than most new car owners do, after 1000km I changed the oil and filter.

                    E30 M3 1987
                    Mini Clubman GT
                    BMW E36 323 Msport
                    Toyota Corona
                    KTM 200EXC
                    Honda CB50 (1979)

                    Comment


                    • #25
                      I dont think there is a right way or a wrong way but if its just a street car then as Dave says above is good. Tuners who build fast engines usually dont even let them idle much and then put the engine through its paces, when I worked at BMW you could always tell which M3/M5 had been driven hard since leaving the forecourt as they were always faster and felt loose. Is that best for longevity, potentially not but I didnt see any failures relating to it.

                      Comment


                      • #26
                        Re-use the head bolts, they are NOT torqued-to-yield (überelastisch angezogen).
                        Have done so on 3 rebuilds, never had a problem.
                        Clean them, oil them lightly with fresh engine oil and you're good.

                        I run them in using the mototuneusa way. Do a search here to find the details of how-to

                        Comment


                        • hardtailer
                          hardtailer commented
                          Editing a comment
                          Re-read your post and saw that the diff is being rebuilt too.
                          If you get a new crown and pinion wheel then (and only then) I'd stick to the instructions on the window sticker in order to gently break those in and end up with a quiet diff.
                          If only bearings and seals were replaced in the diff then go for this method http://www.mototuneusa.com/break_in_secrets.htm

                      • #27
                        Thanks for the replies so far. As I understood from various sources is that high loads (not high-rev) during the break-in is helpful to seat the piston rings correctly.

                        @hardtailer: The diff only needs new bearings and seals. Concerning the head bolts. I prefer to wait some more time and get new ones as the car had a unknown past in Italy. But what we have experienced so far is that some things had been done (partly improvised/unconventional) over there and I am not fully sure if the head was already down once in the past and how the bolts had been torqued down back then. Therefore I feel more comfortable with new ones.

                        Comment


                        • #28
                          Some update and pictures. The rebuild comes to an end, after some issues sourcing parts, Covid related issues and other surprises. But the result so far is making me happy and I am looking forward to have the finished car (still some other work to do on it, when you started once, one thing comes to another). In general, the rebuild was really necessary, the engine was really worn and even the cylinder head was cracked but could be fixed.

                          Comment


                          • #29
                            Some pics from the rebuild

                            Comment


                            • #30
                              Almost done

                              Comment

                              Working...
                              X