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  1. #11
    Quote Originally Posted by macGruber View Post
    Just revisiting an old post. FAMT, doing a compression test is not always a good answer IMO. Pulling all of the plugs and then manually rolling the motor over with a long screwdriver or other narrow (less than 10mm wide will typically fit all ski models) item will tell you if one of the pistons are not traveling up and or down without hitting the start button and possibly doing even more damage in the event of the motor having a busted rod. The last thing I want to do is find a ski that was killed in a timely manner before it destroyed the head or punched a hole in the block...and then crank it over upwards of 40 times to test compression in each cylinder. That's just asking to do damage to parts that would have been otherwise usable. If the pistons all travel...then I do a compression check...but you do you.
    A "busted" rod?

  2. #12
    Site Admin Green Hulk's Avatar
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    Apr 2005
    Morgan City, LA
    Quote Originally Posted by macGruber View Post
    Easiest way to see if you have a broken rod. Spark plugs out, drop a Phillips head screwdriver down into the hole, manually turn the crank. If the screwdriver moves up and down it's possible that you have good pistons and rods... If one of the Pistons doesn't come up or doesn't come up as far as the others then you probably have a busted rod
    A bad piston will also make your screw driver move up and down. Compression test is the only way to tell.

  3. #13
    Guys, something must not be translating well here. "If the screwdriver moves up and down it's possible that you have good pistons and rods". POSSIBLE is what I'm saying here. And we are talking about a motor where a Yamaha mechanic tells me that a piston is not traveling already...not a seller just saying "it doesn't run".

    "doing a compression test is not always a good answer IMO": I'm suggesting that I'm always going to drop something down in each cylinder and manually turn over a motor when I am diagnosing it off of a basic statement from someone who tells me that one of the pistons is not traveling properly. If it turns out it in-fact doesn't move up or down...I have no need to do a compression test. That will do nothing more than POSSIBLY do more damage to a crank or the bottom of the head. Why do more damage than necessary by doing diagnostics based on available information on a unit? Doesn't make sense to me.

    IF, the screwdriver travels up and down on all 4 next gets a compression test of course. That is not in question here but the order of testing based on someone reporting in with no movement on a piston sure is. Like I said...go ahead and throw a compression test kit on as your first step every time. I'll keep doing this and hopefully we both get away without further damage to our damaged motors I guess. All I know is that I didn't run a compression test straight away on this one and got away with a very basic welding of the are right under #1. Had I rotated the motor over 20-30 times...who knows what the busted rod would have punctured next.

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