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No Compression!, Troubleshooting Procedure ?

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  • No Compression!, Troubleshooting Procedure ?

    I've got a '94 Yamaha WaveBlaster 700. I did a BIG No-No and lent it to my fiend a few weeks ago. I get it back, and it won't start (Cranks but wont ignite). I test compression, and get a reading of 20 p.s.i per cylinder. I ask what happened, and he tells me that he turned it on in the parking lot, and the throttle seemed to be stuck, cause the engine revv'd up at full speed for some Unaccounted period of seconds, and it just SHUT OFF on him. I assume he ran it WITHOUT water since it was in a parking lot.

    I have the ski now, it just cranks but won't start. I've got spark, I've got fuel, just NO compression. Service manual says that it can be one of the following:
    1- Head Gasket
    2-Cylinder Head
    3-Oil Seal/crank
    4-Reed Valve
    5-Piston, Cylinder Wall, Piston Ring

    What's the most effective order and procedure of diagnosing, to get to the bottom of it ? Any way that I can tell where the compresson leak is coming from, before I start tearing apart ? I was reading all possible compression postings, and read the "wet test" in which you pour oil into the cylinder and re-check compression, to see if the compression rises. So I'll apply that when I check for the rings. I have NO clue of any methods for the other possible problems. ANY help would be greatly appreciated. Thank you.

    Studio 500
    Last edited by Studio500; 07-29-2006, 04:49 PM. Reason: Typo

  • #2
    Re: No Compression!, Troubleshooting Procedure ?

    Stop 'testing', it's done. Yes if he ran it without water, he got it so overheated that it glowplugged - the spark plugs were so hot it was self igniting and ran away, until it seized. At this point you need a complete rebuild or a new engine. Ours start at $699 for that one. I would be asking him for compensation real fast.
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    • #3
      Re: No Compression!, Troubleshooting Procedure ?

      Thank you for your diagnosis/response. I'm prepared for the worst, and frankly, I don't think the guy's gonna cough up the money (guess that's the end of that friendship)... About the "seizing" part, I don't understand. The engine is cranking, just without compression. If it were seized, wouldn't it NOT crank and NOT turn-over? I'm hoping I'll have to rebuild the top end only, since my budget isn't all that great here. I'll anxiously await a response. Thank you once again.

      p.s. If rebuilding the top end is optional, What's the cost for a top end rebuild ?

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      • #4
        Re: No Compression!, Troubleshooting Procedure ?

        The chances of getting away with just the top-end are slim to none. To verify, you need to completely tear the engine down and hold the crank in your hand for a full inspection. Any non-butter smooth bearings, discoloration, etc. means it's toast.

        Siezures are not permanent. When the engine enters a condition such as your overheat, the pistons expand from the heat beyond the bore, and it siezes. After a little while they cool off and contract back to normal size, and it moves again - but the damage has been done.
        SBT Tech Support is here to help with your problems.
        We try to answer each question quickly and accurately.
        Please do not use Private Messaging for Tech Support, use the forums.

        Comment

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