First trailer test - knocking sound
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First trailer test - knocking sound

  1. #1
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    Default First trailer test - knocking sound

    I got the boat wet and running for the first time today. After getting it fired up it has a distinct "knock" when you rev it up or it revs down. It is louder than a rod knock, this sounds like a diesel idling (slowly). I took off the PTO cover and it seemed like it was coming from that area. U joints maybe? Is there anything in the pump that could make that noise? I was thinking maybe a sloppy fit between the PTO spline and the shaft spline maybe? Is there a spec for spline backlash?

    Also I went to set the pressure on the cooling water bypass/relief valve, but the mechanical gage I have on the engine never moved off 0 psi? There was definitely water running, the hoses were getting hot. I am running logs/snails and didnt see the pressure gage move at all.

    Thoughts on those items?
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    AKA OhOneWS6 Last Mohican's Avatar
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    My Pontiac with logs has no pressure at the motor as well. From what I understand that is the norm for log exhaust. The restriction at the logs is greater than the restriction of the motor. The only place there would be any noticeable pressure is before the logs. (assuming you have the water plumbed from the pump to the logs first)

    Can you take the drive shaft out to run the motor without turning the pump? That will help you determine if the knock is the pump or the motor.
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    Senior Member 1975sleekcraft's Avatar
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    Quote Originally Posted by Last Mohican View Post

    Can you take the drive shaft out to run the motor without turning the pump? That will help you determine if the knock is the pump or the motor.
    x2
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    Yeah I was planning on pulling the shaft - unfortunately it is a 3 point mount so its more of a PITA... I was hoping someone would have a good idea what a bad spline would sound like.

    I have a spare PTO as well as a complete spare pump so I was hoping to isolate the problem rather than swap everything to save myself some work. Maybe I have enough room to slide the PTO back a little and try that.

    I guess as far as the water pressure, I will re-locate the gage to the inlet side by the valve and set it there. Based on what I saw so far it cant be much pressure.
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    If the sound was from the pump I think you'd know it, that's a good distance from the engine. U joints can definitely have a knock, did you try a bit of grease to see if it quiets them a bit?

    You might try regulating water flow based on engine temp, not pressure.
    '86 Eliminator Sport 20, Chevy 454, Berkeley 12JG w/jetovator
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    It turned out to be the u-joints. I was able to feel quite a bit of play in there, so at least one of them is shot. They have a grease fitting but it is in the corner of the joint where no regular grease gun is going to be able to fit. My other PTO has grease fittings on the ends in the center of the cap, so easy access. I will have to look around at the parts store for that kind of u-joint for my spare.
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    Senior Member 1975sleekcraft's Avatar
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    i would fire it up without the driveline in still, too make sure!!!!!
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    Senior Member wolfie's Avatar
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    Quote Originally Posted by slim pickens View Post
    Yeah I was planning on pulling the shaft - unfortunately it is a 3 point mount so its more of a PITA... I was hoping someone would have a good idea what a bad spline would sound like.

    I have a spare PTO as well as a complete spare pump so I was hoping to isolate the problem rather than swap everything to save myself some work. Maybe I have enough room to slide the PTO back a little and try that.

    I guess as far as the water pressure, I will re-locate the gage to the inlet side by the valve and set it there. Based on what I saw so far it cant be much pressure.
    So how did you get the bellhousing and driveline off with the 3 point mount? Just curious because I'm facing a similar situation.
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    Living in a cage of fear thatguy's Avatar
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    In cases like this, an engine stethoscope like doctors wear is a great item to have.

    In a pinch, a length of wooden broom handle against one ear works wonders, just DO NOT put the end near ANY moving parts!!
    Tommy
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    Tommy please remove all Jimsplace quotes from your sig and don't put more back. He doesn't like it and it is against the rules. Thank you.
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    Senior Member GRoper's Avatar
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    Quote Originally Posted by thatguy View Post
    In cases like this, an engine stethoscope like doctors wear is a great item to have.

    In a pinch, a length of wooden broom handle against one ear works wonders, just DO NOT put the end near ANY moving parts!!
    handle end of a long screw driver to your temple and metal end to trouble area works pretty gd as well.
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    Senior Member Delemorte's Avatar
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    Quote Originally Posted by wolfie View Post
    So how did you get the bellhousing and driveline off with the 3 point mount? Just curious because I'm facing a similar situation.

    Its actually really simple.... Pull the motor.. No other way with out a blow torch and some prybars .. Oh and a big ass hammer...




    JK.. just pull the motor or i guess you could pull the jet out the back.. No other way
    Quote Originally Posted by jetboatperformance View Post
    the ensueing fire would likely be extinguished by the sinking however
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  14. #12
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    Quote Originally Posted by wolfie View Post
    So how did you get the bellhousing and driveline off with the 3 point mount? Just curious because I'm facing a similar situation.
    The first time around (long story) I had to basically pull the motor, but I didnt pull it completely. I had enough slack in all the hoses/electrical/fuel lines that I just loosened the exhaust clamps, took out the engine mounts, and was able to slide things around enough to raise the engine about 12". It was a serious fight to get it out of there. Then i took off the rear bellhousing mount and cut a big U in the bottom to allow it to drop over the driveshaft. So now when I put the engine in/out, I attach the driveshaft as normal, slide the coupler onto the jet spline, and leave it about an inch or 2 from the pump. Then throw on the bellhousing and bolt it on, then slide the engine back and bolt it the rest of the way on. It was easier for me to do this with the left and right side engine mounts (the automotive style) unattached until it is in the final position. Hope this makes sense.

    This whole deal was aggrivating enough to make me decide that I will definietly go to rail mounts if I ever stray from olds power. The only thing stopping me now is I dont want to spend money on olds parts when I might switch to BBC/BBF later anyway.
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