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Another cracked head!

Discussion in 'Ocean Yacht' started by praetorian47, Nov 1, 2019.

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  1. praetorian47

    praetorian47 Senior Member

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    My 55SS with 8v92's has cracked both heads on the starboard engine in the last 2 years. Today, I take the boat from my dock to the travel lift for winter haulout and find the port engine coolant bottle full and foaming. The engine was warmed up and never more than idle.

    I'll have to figure which head but thinking of just replacing both over the winter because I have more time and can pull the floor to make it a bit easier.

    Is there anything I should check while I'm doing this that might help explain it?

    The only common thread is that the previous owner replaced the heads. The mechanics around here say he wasn't the mechanic he thought he was so maybe he used poor heads or faulty installation? I don't see how, I've owned the boat for 3 years so I think faults would have shown up before.

    The only other information i have is that the previous owner did an engine flush prior to me buying it and i did fint lots of crap in the overflow bottles that I had to clean out repeatedly for a year.
  2. Capt Ralph

    Capt Ralph Senior Member

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    Injector tubes also come to mind.
    The last tube issue I worked on was just after a flush and new coolant.
  3. praetorian47

    praetorian47 Senior Member

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    Thanks, I'll definitely check that.
  4. PacBlue

    PacBlue Senior Member

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    Could be "gray market" replacement heads, lots of DD 2-cycle parts bandits in business. See if they are Factory/reman parts to start with.
  5. Robertoman

    Robertoman Member

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    Heat exchanger leak? Raw water into the freshwater cooling side will fill up the coolant overflow bottles
  6. boatpoor

    boatpoor Member

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    What did the temperature get up to between the dock and the travel lift? A bottle full and foaming doesn't necessarily mean a cracked head. You may want to do some more troubleshooting before you tear into it.
  7. Beau

    Beau Senior Member

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    From an amateur, is a full bottle even a primary symptom of a cracked head? Why? Usually a crack head lets coolant escape or puts it in the oil, no?

    First things I might look at are my temperature gauge then my thermostats. The volume of water seems to be increasing somehow, either heat or saltwater are the first candidates?
    Last edited: Nov 1, 2019
  8. praetorian47

    praetorian47 Senior Member

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    I’ve cracked both heads on the other engine and this was the symptom. The engines did not overheat, they got to running temp of about 150.

    I will definitely check before I tear it down. The check is pretty easy. Pull the thermostats off and turn it over. Bubbles mean cracked head. My 2 stroke DD expert says foaming is likely cracked head.
  9. Beau

    Beau Senior Member

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    Interesting. I have to learn something about that. Good luck in your analysis, and I hope its something simple and inexpensive.
  10. praetorian47

    praetorian47 Senior Member

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    The cracked heads aren't too expensive, but the outboard one is anything but simple!
  11. Capt Ralph

    Capt Ralph Senior Member

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    If their TAs, I hope the outboard head is on the stb engine at least.
  12. Beau

    Beau Senior Member

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    Is that a negative feature of those motors - cracked heads?
  13. Capt Ralph

    Capt Ralph Senior Member

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    Yep..
    IMO The cast is pretty thin supporting the 4 valve head. Fatigue of the cast fails.
    Valve seat gets overheated and pushes against the head as it burns up.
    Not quite boil over overheating but still, poor coolant action in the head.
    Liner height issues after rebuilds.
    Poor torque down sequence from last head service (or two).
    Over boost and just stretching that last HP from motor (JT, SS and other tunes).
    And, just ship happens.
    92 head failure are more often than 71s.

    As I've always stated, 92s are not forgiving.

    Fine spider cracks are near invisible by eye and mag/flux may not catch it because it's such a fine pattern.
    My guys try to find used NA heads and after cleaning and polishing the head surface, dye and a make shift microscope come into play.

    New heads are advertised usually twice the price (or more) over used when they are available.
    Somewhere in the price, there may be a core charge the selling shop taps on. Cracked heads are not a good core.
  14. praetorian47

    praetorian47 Senior Member

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    My buddy used to run service for Harper Detroit and still has all the old connections, so I get the best parts - even when I don't know what the best is (which is just about always). I think poor torque down and/or poor replacement heads may be the cause.

    I just replaced the outboard stbd head in August! That job sucked. This one will be better. We have all winter, and I can just move the couches and pull the floor up giving me much easier access.
  15. Capt Ralph

    Capt Ralph Senior Member

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    I hope so, If your TA, all the after-cooler hoses and hard connects are on that side. Including the after-cooler heat exchanger.
    Hope your in a shed during the winter.
  16. boatpoor

    boatpoor Member

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    Have you found any broken head bolts when the other heads cracked? Did you check the block deck and head with a straight edge to make sure neither were warped? Seems like you're having more than your share of head problems! I've cracked a few 671 heads but it was always due to overheating. I've never had a 92 head crack, are they cracking between the valves every time?
  17. Capt Ralph

    Capt Ralph Senior Member

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    You must have really fried the 71s.
  18. boatpoor

    boatpoor Member

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    An old Detroit mechanic used to say "if a a Detroit is running at 180 degrees and you light a cigarette too close to it, you may as well order a head ". Other than that they're great engines. I run several of them and can't complain about the dependability.
  19. praetorian47

    praetorian47 Senior Member

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    It's been between valves both times so far, yes.
    My plan, after validating which head it is just to be sure, is to replace both over the winter. I'll keep the undamaged one as a spare - if there is an undamaged one.
    Head bolts are all good, and have been torqued properly after I've replaced them - I can't speak to the work prior but nothing stood out. We pulled the heat exchanger off the other engine and had it looked at - all good.

    I think after the PO did that flushing, there's a ton of crap floating around and wonder if occasionally the crap just blocks things. I need to clear it out but not sure the absolute best method. I'm looking for one I can do over the winter inside the (heated) building the boat is in. I don't have water, so will have to bring buckets in with me (which I can and will do). Any advice here would be really appreciated. After the first head replacement, we emptied the overflow bottle and cleaned it out at elast 6-8 times after each run and there was crap in it. We did both. I'm seeing more crap now in the port (cracked) engine.

    As to overheating, I don't think I'm overheating but I'll add this bit of information in hopes it means something to somebody smarter than me...
    On my starboard engine, we installed a murphy gauge to one of the thermostat ports, and the regulat thermostat that displays on the bridge to the other. They read differently, almost 20 degrees off. I've switched them around and the difference is always about the same. I'm assuming the murphy is accurate and the 30 year old wiring to the bridge might be suspect for the others. I'm going to rewire those this winter also. I'm also considering setting up a N2K gateway and throwing a few different temp sensors to it so I can monitor different areas better and have alarms so I can be notified if necessary. I like the idea of the N2k solution, but not the cost.
    The engines run, according to the bridge displays, around 185-190 when on plane. the port engine always runs a bit cooler (>5 degrees cooler).
    Would multiple temp senders be beneficial, or just more distraction?
    I don't think it's ever gone over 200. It has creeped up a few times past 190, and I simply back off the throttle and it cools down right away and I'm up and running a moment later. This is what makes my amateur mind think there may be some blockage floating around in there and backing off lets it move, unblocks it.

    I'd been using Powercool Plus but now am using Powercool (non-plus). It's lighter coloured pink instead of darker orange. Nobody can say there's a difference or which is better. I just figured I'd pass this info along. Hopefully something stands out to somebody.

    I love this boat. I love these engines. I spend a day or two each week during the winter waxing, varnishing, doing repairs, updates/upgrades. I know it's old, and Ocean isn't the best name out there, but unless I really win the lottery, I haven't seen a boat I'd rather have. I cracked the head the second day of my summer vacation, just kept to hull speed but stayed out for 5 weeks, traveling each day (and returning the overflow to the engine each morning before leaving). I'd just like to know why this is happening!
  20. Beau

    Beau Senior Member

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    I need some teaching. Why would a cracked head fill the over flow bottle? Why, depending upon where the crack is, does the water not wind up in the oil? The thought of running for 5 weeks with a cracked head would frighten me.

    To me, I wouldn't want "stuff" in the fresh water side of my cooling system. I'd drain and flush that until its clean?

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