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  1. #1
    Chief Petty Officer dvan1901's Avatar
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    Default What are the sure signs of a cracked block?

    With all the talk of cracked blocks (possibly cracked) I began to wonder, what are the tell tale signs of a cracked block? From what I have read, water in the oil is not a definative sign as you can have a cracked manifold, or a bad water pump gasket, bad head, or a bad head gasket. So, what are some sure signs? Water and/or oil in the bilge area? Bad compression? Loss of power? How can you tell for sure without pulling the engine out?

  2. #2
    Fleet Admiral Gary H NC's Avatar
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    Default Re: What are the sure signs of a cracked block?

    Some engines will run fine with a crack in the block so you can't always go by that.Water in the bilge is a good possibilty.A close look at the block under where the heads meet for water seeping.Or have a pressure test done on it..that is the most effective way to find a crack.
    If your oil looks good,its running fine and no water in the bilge i would think you are ok..
    Did you forget to drain something over the winter?


    1981 ChrisCraft 210 Scorpion K,175 Johnson SeaHorse

  3. #3
    Chief Petty Officer dvan1901's Avatar
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    Default Re: What are the sure signs of a cracked block?

    Well, my oil doesn't look good (had posted this in another thread), but I also have good, even compression across all cylinders, with no water in them. I was more wondering if my manifolds are cracked; and those are coming off this week.

  4. #4
    Supreme Mariner bruceb58's Avatar
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    Default Re: What are the sure signs of a cracked block?

    I would pressure test the block no matter what the manifolds look like.
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  5. #5
    Chief Petty Officer dvan1901's Avatar
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    Default Re: What are the sure signs of a cracked block?

    Well, the mechanic I am working with called me and gave me the bad news; 4" horizontal crack. Now I need to get a new one :/

    He thinks we can re-use all the parts and just get a block (this, again, is a Yamaha 4.3L v6 205HP). Some have posted that this is a 4.3L GM block. It has a mechanical water pump too. I believe, but am not 100% sure, that it is the 12 bolt manifold type.

  6. #6
    Fleet Admiral Gary H NC's Avatar
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    Default Re: What are the sure signs of a cracked block?

    Yep,4.3 GM...Yamaha never actually produced any 4.3 that i have heard of..
    I would go with a new long block...Bolt your intake and other external parts on it and drop it in...


    1981 ChrisCraft 210 Scorpion K,175 Johnson SeaHorse

  7. #7
    Senior Chief Petty Officer RandyJ's Avatar
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    Default Re: What are the sure signs of a cracked block?

    I hate the news for ya. Been in the same shoes myself. Where on the block was the crack? I had one with cracked manifolds and a split down the side of the block...but it ran great...until I stopped the engine and tried to start again. The lake water would back up in the manifolds and fill the cylinder thru open exhaust valves. We were out late at night and the bilge was filling with water but it was running great! I put in a cheap block and was still out near $2000 in parts alone. By the time I got everything ironed out I was out of pocket near $3000.

  8. #8
    Fleet Admiral Gary H NC's Avatar
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    Default Re: What are the sure signs of a cracked block?

    Thats usually what happens when you try to save a few bucks. For 3000 you could of had a whole new complete engine with a few bucks left over..


    1981 ChrisCraft 210 Scorpion K,175 Johnson SeaHorse

  9. #9
    Chief Petty Officer dvan1901's Avatar
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    Default Re: What are the sure signs of a cracked block?

    Let me ask you then, since I'm not the one doing the work (don't have the equipment to pull an engine, nor the experience at this point); in your experience, would it be cheaper to buy a whole new engine and drop it in? Maybe I can make a deal with the mechanic that he can part out the engine and cut me a break...? I was thinking of this: http://www.michiganmotorz.com/GM+Mar...replacement%29

    If you have other/better resources, I'm all ears. Thanks for all the help thus far!

  10. #10
    Moderator Bondo's Avatar
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    Default Re: What are the sure signs of a cracked block?

    The Problem with that motor in your link will be Trying to marry it to your Yamaha Driveline..........

    IF everything on your Yamaha is Good,.. Except the Long Block,.......
    Then a GM Goodwrench truck motor would be a Better Way to Go...... You might be able to find the proper Vintage block that way,.... Donno....

    The MM motor is a much Newer vintage,+ I don't know just How that'll effect the marrage between the Yamaha to engine connection........

    I've Never even lain Eyes on a Yamaha in My Life,.... So I'm No Authority on them....
    But,.. I Kinda know My way around a Chevy.....
    Any Grease is Better,..... Than No Grease at All.......

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