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M42 Head Gasket and Timing Question

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    M42 Head Gasket and Timing Question

    I am in the process of putting the M42 from my '91 318i convertible back together. It was about time for a timing refresh when the head gasket went and demanded attention.
    I have refreshed, refurbished and resealed countless things along the way, now I am about to put the cylinder head back on the block. I have been reading obsessively and taking lots of pictures; I plan to add my observations and lessons learned here once it is complete.

    One question for the forum experts, since I have found conflicting information: Do I need to add sealant (RTV) to the channel the rubber gasket fits into on the top of the timing case? (#10 in the RealOEM picture below)
    Thank you in advance for any advice or guidance.

    Click image for larger version

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    I wouldn't do the gasket (#10) itself along the channel unless there is significant porosity or damage in the metal mating surface. You can put just a dab to keep the gasket in place if you think it will be an issue for you, but generally that gasket stays put easily when the head is reinstalled.

    Of course you'll likely want some at the butt joints where the front timing case rubber gasket interfaces, but that can happen when you install the front timing cover.


      Thanks Rogue - I hope to get back in the garage this weekend. I will leave the rubber gasket without and add it only at the butt joints.


        not sure if you are the same from the FB post, but from factory some sealant is required where #10 meets the head but only at the junction. Adding it to the entire junction is not necessary.
        Alex 88 m5 | 91 318is | 19 Subaru Ascent
        BMW Tool Rentals & Fender Roller


          You 100% need some oil-proof RTV in the butt-joint between the rubber profile gaskets. Also, you need to trim the paper timing cover gaskets so that they do not overhang into the area where the rubber profile gaskets are or you will have an oil leak. It is OK if you trim them a little "too high" since RTV will fill the gap between the cover & head / timing case. This is one reason why that gasket joint is so notorious for oil leaks. Don't be shy with the RTV in the butt joints, you want it to fill in all the little gaps and stuff there.

          Personally, I like to clean the various gasket surfaces with brake cleaner (or 99% rubbing alcohol) and then apply a thin bead of RTV into the groove that the profile gasket sits in, as well as a THIN layer on top where the upper cover mates.

          More crucial than that is proper installation of the upper timing case cover. You will note that the bolt holes around the outside are ovaled. Basically, you need to compress it down onto the profile gasket so that the top of it sits flush with the head. I usually do this using the valve cover. If you remove the VC gasket and get the right combo of 6mm bolts and stacked washers, you can use it as a clamp to push the cover into place. So get the upper timing cover & gaskets into place after doing what you want with RTV, tighten the 6 outer cover bolts (the ones around the tstat can be partially threaded too) JUST enough so that there is no gap between the head/gasket/cover (but not "finger tight"), then clamp it down with the valve cover. Once it is pressed down, you can install the bolts around the thermostat housing, and then do the 6 outer bolts, in that order.

          Give the RTV 24 hours to cure before running the engine.
          Last edited by bmwman91; 10-28-2020, 10:10 AM.


            ^ This. OP Id recommend some Motoseal. Ive used it on several engine builds over the years. It is grey in color. By no means the cheapest but it is very good quality sealer. It can be had at most auto hardware stores.

            Turbo M42 Build Thread :Here
            I like the tuna here.
            Originally posted by lambo
            Buttchug. The official poster child of r3v.