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Thread: trust your instincts

  1. #1
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    trust your instincts

    So, having an M52 with an occasional cold start misfire I changed the spark plugs and found one odd looking one. https://www.bimmerforums.com/forum/s...k-plug-reading
    This turned out to be from the cylinder using coolant which finally manifested itself with an overheat and then a hydro-locked cylinder, #4.

    The gasket showed no sign of fire ring failure, nor were there any obvious witness marks on the block or head. I was worried about the head needing resurfacing. Sure enough there was a .007" belly in the middle, adjacent to #4. My "Ah-ha" moment prevented me from investigating further, remember the gasket looked fine.

    Off to the machinist who skimmed .005"(so much for my "straight" edge)to make it flat again. After re-assembling I turned the head over and there is a crack extending from a coolant passage to an exhaust valve in #4. Why didn't I trust my intuition that said the gasket hadn't blown and there should be another problem?
    Feel free to let me have it.

    The bigger bummer is the machinist also missed it and now that .005" has been removed there is little room for another required resurfacing after a repair.
    Before and after, looking at me the whole time.
    cyl head TV leds 001.jpg Attachment 645919
    My haste may have cost me the head.
    Attached Images Attached Images
    Last edited by ross1; 02-18-2019 at 06:48 PM.

    If you can leave two black stripes from the exit of one corner to the braking zone of the next, you have enough horsepower. - Mark Donohue

  2. #2
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    oh man - that sucks.....ugh....
    '95 325iS - auto to manual swap done!

  3. #3
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    A better "after" shot and the gasket;


    head crack M52 003.jpg head crack M52 004.jpg head crack M52 005.jpg head crack M52 006.jpg
    Man, am I a $&$^% dumb ass!

    If you can leave two black stripes from the exit of one corner to the braking zone of the next, you have enough horsepower. - Mark Donohue

  4. #4
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    Not at all, my friend. But your machine shop needs to do a better job of pressure testing. That said, we use an excellent machine shop, I did a race instructor's S50B30 (USA) engine rebuild, send the head off to the machine shop, for pressure testing and machining. They missed it too. He bought a new head after we found it still leaking coolant into the exhaust. Have a look at ECS Tuning. Be aware that their fully assembled heads are Chinese, but they work, even when thrashed exceptionally hard...and they are very inexpensive.

    Chris Powell
    Racer and Instructor since, well. decades, ok?
    Master Auto Tech, owner of German Motors of Aberdeen
    BMWCCA 274412
    German Motors is hiring ! https://www.bimmerforums.com/forum/s...1#post30831471

  5. #5
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    It wasn't pressure tested, I didn't suspect it had any problem aside being a little bowed. I brought it in and said "take the minimum to make it flat".
    If this starts getting expensive the car will meet a different end.

    If you can leave two black stripes from the exit of one corner to the braking zone of the next, you have enough horsepower. - Mark Donohue

  6. #6
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    heli-arc

    I would think a welded up crack could be resurfaced without any additional milling?, my big six was cracked through a cam journal, welding fixed it up fine.

  7. #7
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    It's my understanding that "checking for cracks" was standard when sending a head to the shop. Apparently not.

    Sorry for your troubles.
    ASE and BMW Master Certified Technician

  8. #8
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    Autohead sells the Chinese replacement heads as well. Cheap for a complete head less cam trays and cams. But I would be inclined to buy a good used head or a refurbished used head.

  9. #9
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    Quote Originally Posted by White94RX View Post
    It's my understanding that "checking for cracks" was standard when sending a head to the shop. Apparently not.

    Sorry for your troubles.
    Well, I evaluated the head myself (lesson learned) and didn't ask for anything other than resurfacing. I missed this crack which is obvious in photos but apparently wasn't when facing it. I spent a good hour cleaning the surface so I could check it for flatness.
    I am disappointed the shop didn't spot it either but can't be upset.
    I had it welded today but the crack either deepened into the bowl after cooling or the welder didn't dig deep enough. He's now talking about opening the area up more for better access and re-building the metal again.
    After that pressure test, press in the new valve seat and pressure test again. If all good then resurface and reshape the port. The first welding didn't warp the head so resurface cut should be minimal.
    Welder and machinist will confer Thursday.
    In for a penny in for a pound.

    If you can leave two black stripes from the exit of one corner to the braking zone of the next, you have enough horsepower. - Mark Donohue

  10. #10
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    Quote Originally Posted by pbonsalb View Post
    Autohead sells the Chinese replacement heads as well. Cheap for a complete head less cam trays and cams. But I would be inclined to buy a good used head or a refurbished used head.
    Thanks but it's a 22 year old, 150k E39 with tired shocks so doesn't really merit that sort of cash investment. It is the devil I know, which combined with "free" labor is why I am bothering at all. Had this been a simple resurface and button 'er up my parts cost was only a few hundred $ including a bunch of the hoses and crap you are silly not to change out while having access.

    As it currently stands I expect repair cost will be similar to that of a used head plus freshening, any more and I'll consider another tack. Engine was otherwise quite healthy and judging by the cleanliness of the interior, cam condition, etc. it has had a good life. Once repaired it'll get some new shocks and I'll amortize the cost over more miles.

    - - - Updated - - -

    Quote Originally Posted by 325bob View Post
    I would think a welded up crack could be resurfaced without any additional milling?, my big six was cracked through a cam journal, welding fixed it up fine.
    I expect if jigged perfectly yes, only remove the built up weld. I have .006" to play with.

    If you can leave two black stripes from the exit of one corner to the braking zone of the next, you have enough horsepower. - Mark Donohue

  11. #11
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    head finishing

    Quote Originally Posted by ross1 View Post
    Thanks but it's a 22 year old, 150k E39 with tired shocks so doesn't really merit that sort of cash investment. It is the devil I know, which combined with "free" labor is why I am bothering at all. Had this been a simple resurface and button 'er up my parts cost was only a few hundred $ including a bunch of the hoses and crap you are silly not to change out while having access.

    As it currently stands I expect repair cost will be similar to that of a used head plus freshening, any more and I'll consider another tack. Engine was otherwise quite healthy and judging by the cleanliness of the interior, cam condition, etc. it has had a good life. Once repaired it'll get some new shocks and I'll amortize the cost over more miles.

    - - - Updated - - -


    I expect if jigged perfectly yes, only remove the built up weld. I have .006" to play with.
    I had great success with a belt sander on head finishing.

  12. #12
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    Quote Originally Posted by 325bob View Post
    I had great success with a belt sander on head finishing.
    Gee, I have a nice 4" Porter Cable and some 60 grit belts. Who needs those fancy machinists?

    If you can leave two black stripes from the exit of one corner to the braking zone of the next, you have enough horsepower. - Mark Donohue

  13. #13
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    Ho Lee Chit. This thread went south in a hurry.

    While you're at it, maybe throw some beach sand on the pistons, and crank the starter for a while to refinish the cylinder walls?

    Chris Powell
    Racer and Instructor since, well. decades, ok?
    Master Auto Tech, owner of German Motors of Aberdeen
    BMWCCA 274412
    German Motors is hiring ! https://www.bimmerforums.com/forum/s...1#post30831471

  14. #14
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    So, head is beyond any economic repair. Two welders, three attempts.
    searching for a complete M52, hopefully near Chicago
    Surplus HG repair parts FS here; https://www.bimmerforums.com/forum/s...t-repair-parts
    Last edited by ross1; 03-28-2019 at 07:14 AM.

    If you can leave two black stripes from the exit of one corner to the braking zone of the next, you have enough horsepower. - Mark Donohue

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