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Birkin Engine Mount bolt shear problem

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  • Birkin Engine Mount bolt shear problem

    Hi There,
    The left front engine mount bolt has sheared off on my Birkin. (Both left side bolts sheared off a few years ago and I managed to removed the broken bolts and replace them.)
    I am trying to repair it but have a few questions I am hoping the forum can answer.

    Q1. I need to raise the engine to re-align the engine mount bolt holes with the engine bolt holes.
    Can I use a jack and block of wood against the sump and gently jack it up or is the sump too weak to handle it?

    Q2. Once I drill out the sheared bolt can I make a larger hole and re-thread it to use a larger sized bolt or is that un-wise?

    Q3. My Birkin Engine mounts are 'Y' shaped and have two arms that hold the engine and a single arm that attaches to the Birkin frame.
    I notice that the engine has what looks like a couple of extra engine mount holes on each side. Is there an updated Birkin zetec engine mount that spreads the load to more than just two engine mount arms?

    Any advice gratefully received,
    thanks
    Paul
    Paul. Birkin S3 /Dunnel zetec/emerald ECU

  • #2
    A1: Don't be such a sissy. The sump is ample strong to hold the engine up. The wood block is nice but I would consider it optional.

    A2: I would be careful with that. You could helicoil it but there is always a risk of finding the nearest coolant or oil channel.

    A3: There have been different engine mounts over the years. On my car there are vertical cylindrical vibration dampers with vulcanized plates and threaded studs. Works well but the dampers have a limited life. On the left side the bracket is bolted to the block with four M10 bolts and on the right hand side with three M10 bolts.
    I know the newer Birkins have a kind of horizontal rubber bushing damper but they still have only 2 arms and chassis mounting points.

    If you can get the sheared bolts out without mangling the threaded holes, replace them with 12.9 grade socket cap bolts (long enough to go 20mm into the block). Tighten them to let's say 50 ft-lbs with blue thread locker. I never had one shear off.

    Edited to say...A1 is valid for the cast aluminum sumps like Raceline. If you have a "cut and shut" modified stock sump I don't know.
    Last edited by slomove; August 10, 2015, 09:07 PM.

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    • #3
      Hey Gert!
      Many thanks for the tips. Ha! yes, sissy indeed!
      Wow, your left side uses 4 10M bolts! That sounds better. My 'Y' type mount has that horizontal rubber bushing damper (same on both sides) it only uses 2 10M socket cap bolts to attach to the block.
      This is the second time the left side has sheared off in about 4000 miles. Last time I did upgrade to 12.9 grade bolts, That's what sheared off this time!
      Do you think maybe the rubber damper is shot and could be making the bolts shear? Something seems wrong.
      Paul. Birkin S3 /Dunnel zetec/emerald ECU

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      • #4
        I would post the question on the Birkinowners Yahoo group. They would know better.

        For that matter, if you have 12.9 alloy bolts stuck in the block it will be fun to drill out.....maybe a carbide bit.
        Last edited by slomove; August 10, 2015, 09:35 PM.

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        • #5
          Yes, I'm dreading attempting to get that bolt out of the block. I think I need to use a right angle drill chuck too.
          Thanks for the idea of using a carbide bit.
          Paul. Birkin S3 /Dunnel zetec/emerald ECU

          Comment


          • #6
            Find a left hand twist bit, if you can. The drilling force frequently pulls the broken bit out, with one of those.

            Comment


            • #7
              Is the bolt threaded all the way to the head (i.e. no shank)? You may want to consider buying your next bolts with shanks (if you can space them appropriately) as you should try to avoid putting the threaded portions in shear.

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              • #8
                Thanks for the advice!
                I managed to get the sheared bolt out with a Grainger carbide tipped left hand drill bit and a 90 degree drill chuck.
                http://www.grainger.com/product/B-A-...AS01?$smthumb$
                It cut into the 12.9 grade bolt pretty well and the bolt unwound itself with just 1/4" hole drilled in it. Makes me wonder whether maybe it had got loose and maybe that's why it sheared?
                I couldn't find any bolts with shanks of that length locally so used grade 12.9 all threaded bolts but this time used some high temperature thread locker and tightened them as tight as I dared.
                I just got back from a long test drive. Mulholland to Leo Carrillo, PCH, then Latigo Canyon back to Mulholand and home. So far so good!
                many thanks, It's great to be back on the road!
                Paul. Birkin S3 /Dunnel zetec/emerald ECU

                Comment


                • #9
                  Originally posted by prabjohns View Post
                  I managed to get the sheared bolt out with a Grainger carbide tipped left hand drill bit and a 90 degree drill chuck.
                  Congratulations. Whew! :)


                  Originally posted by prabjohns View Post
                  It cut into the 12.9 grade bolt pretty well and the bolt unwound itself with just 1/4" hole drilled in it. Makes me wonder whether maybe it had got loose and maybe that's why it sheared?
                  I couldn't find any bolts with shanks of that length locally so used grade 12.9 all threaded bolts but this time used some high temperature thread locker and tightened them as tight as I dared.
                  You might want to consider either drilling the bolts that you have or purchase some already drilled and then install safety wire on them. If loosening up was the cause of your original issue the safety wire would ensure that it doesn't recur.
                  EscondidoRon

                  '62 Lotus Seven
                  '84 Turbo Esprit (x2)
                  '14 Evora
                  '77 Esprit S1 (RIP) :(

                  "A man must keep a little back shop where he can be himself without reserve. In solitude alone can he know true freedom." -Michel De Montaigne 1588

                  Comment


                  • #10
                    Originally posted by prabjohns View Post
                    ...It cut into the 12.9 grade bolt pretty well and the bolt unwound itself with just 1/4" hole drilled in it. Makes me wonder whether maybe it had got loose and maybe that's why it sheared?!
                    Absent corrosion, that's expected. Without the head holding the bolt in tension, the threads should turn pretty much freely. Just like you are threading them together before applying the final torque.

                    Randall

                    Comment


                    • #11
                      Huge thanks to Doug for spending so much time working on my engine mounts with me on Friday.
                      FullSizeRender(4).jpg
                      Removed the left side engine mount due to concern that the locktite I had used would make the bolt difficult to remove if they sheared again.
                      The bolts came out a little too easily. Slomove might be tempted to say that I sissy torqued them....He'd be right!
                      Re-tapped the threads to remove the locktite and clean them upFullSizeRender(2).jpg
                      Doug cut new shanked bolts to lengthFullSizeRender(3).jpg
                      Installed the engine mount and torqued the bolts to 45lb.ft, (well Doug did.)
                      Re installed the exhaust and headers. Lastly, quick check of the right side engine mount bolts and then done.
                      First bolt fine, second bolt...oh dear... Sheared!! I guess it had been taking too much load since the other side sheared off.
                      FullSizeRender(6).jpg
                      After some skillful drilling by Doug, out it came. Phew!
                      FullSizeRender(7).jpg
                      I will be keeping a regular close eye on them now to make sure it doesn't happen again.
                      Last edited by prabjohns; September 1, 2015, 12:56 AM. Reason: spelling
                      Paul. Birkin S3 /Dunnel zetec/emerald ECU

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                      • #12
                        You can't really tell from photo 6 but the bolts broke off a thread or two inside the hole.

                        I am not sure the full size shank will make a difference but perhaps they weren't tight enough. The broken bolts were a plated grade 12.9 Allen head, the replacements are the standard black oxide finish.

                        Did you check them to be sure they are still tight?

                        We also need to thank neighbor Ray for supplying the angle drill and a good hard drill bit, without which the job would have taken much longer.

                        Doug
                        Last edited by Doug Liedblad; August 31, 2015, 11:45 PM.

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                        • #13
                          Wow, I have not looked in detail at how the newer Birkin motor mounts are designed. I guess they overdid it a bit with the "added lightness". I my car they are pretty heavy duty welded sheet metal fabrications with a 5mm plate attached to the block using 3 or 4 bolts. I can imagine that a 2-bolt design tends to flex and fatigue over time with that stiff bushing damper. If that happens again I would consider welding on an additional strut to a 3rd threaded hole in the block (there are ample).

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                          • #14
                            Do you know who's Birkin is the newer one?

                            Paul might consider contacting Birkin and asking if the have the engine mounts that bolt to the block in three or four places.

                            Easier than building your own.

                            Comment


                            • #15
                              I have the old ones. Not sure if they are still available. Tom Carlin or Dick Brink might have them.
                              Unfortunately, the chassis mounting points have changed with the engine mounts as well. But I would guess that is easy to modify.
                              As mentioned earlier, This type of engine mount used the cylindrical dampers with vulcanized end plates. They do have a limited life but are easy to swap when they fail.

                              I can try take pictures how that looks on my engine. Should have done that 2 weeks ago before when I had the exhaust and intake off.

                              Edit: I tried taking the pictures but there is just too much junk in the way...sump guard, oil hoses exhaust and intake.
                              Last edited by slomove; September 1, 2015, 06:48 PM.

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