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  1. #1
    auto culto's Avatar
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    strange rattle ? Newbie help

    Hi folks, first post so here goes. I have just picked up a really cheap polaris slx (think its a 780 ? but not sure). This had been stood for many years. Anyway as its my first ski I found this site and with all the posts here have managed to get it running. It starts on the button and runs sweet now having rebuilt the carbs and replaced all fuel lines. Boy was it dirty in there. The whole thing has cleaned up realy well now. Anyway not being able to run it for very long and having no easy access to water to drop it onto for testing I have hit a bit of a brick wall. Now when its running there is a metalic rattle (sounds like a loose pulley on a car). Its definately not a nasty engine noise but I can not for the life of me trace it in the small running time window. I am not convinced it coming from the engine it feels more propulsion end. So am I hunting a normal running sound or not.I am a motor engineer by trade so have a fair idea but these things are strange compared to cars and outboards.


  2. #2
    ripcuda's Avatar
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    Welcome to Green Hulk!

    Glad to hear you did your homework researching and fixing up your ski right. That's the key.

    The noise you describe sounds like the normal Polaris rattle. This is most noticeable out of the water and barely noticeable when idling around in the water.
    This "rattle" is normal... my SLT 750 does it. And I recall my old 780 did too.

    Once you get a chance to put your ski in the water and enjoy the fruits of your labor... you'll forget all about it.

    Cheers!

  3. #3
    Click avatar for tech links/info, donation request K447's Avatar
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    Welcome

    Did you work through the recommended maintenance stuff outlined in my signature links?

    In particular, did you remove the jet pump and grease the drive shaft splines?

    The normal Polaris 'jet pump rattle' can often be made less noisy by greasing the driveline splines.

    There are several other things to check/maintain while the jet pump is out.

  4. #4
    auto culto's Avatar
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    Thanks for the reply's guys. I have not looked at the jet pump yet as I wanted to make sure it was a good runner first. water filters have been remove and inspected, all hoses have be blown out (small amount of sand) and I have fitted a flush tap on the manifold. Looks a little stange compared to everyone elses though lol. Found that a standard brass outside tap is the same thread so I fitted that and a hose lock fitting so all i need to do is conect the hose and turn the water on when its running. Have not worked out if its a modular pump or the other type yet. Do you think its worth while just droping it on the cannal for a load test before doing any more work ? I would not be allowed to race it around but I can nose it upto the slip wall and put some load on the engine for 15 mins or so. I presume (like an outboard) that it would cavitate if i used to much throttle ? And can I work out the year of manufactor from the vin number ? Am I correct in saying its a 780 ? (has the numbers 78 on the heads and on the manifold.

  5. #5
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    You really should remove the jet pump and check the condition of the bearings and seals in it. A failure there will not be a cheap fix. The jet pump can be re done with new bearings and seals for around 50 bucks.

  6. #6
    auto culto's Avatar
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    ok will do that job first then cheers.

  7. #7
    Click avatar for tech links/info, donation request K447's Avatar
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    Last two digits of the HIN plate are the model year.

    Not understanding what you hope to determine by running it under partial throttle against a wall. These machines were designed to run at speed over the water. Heavy load without forward motion creates a non-standard condition. The jet pump load on the engine is different, the engine RPM will different, and the engine may run lean or rich compared to normal. You may also induce detonation.

    The best way is to make sure the jet pump is good, and the other maintenance items have been addressed. Then find a boat or buddy watercraft to tag along and go test riding.

    If the engine is delivering the correct power then the max sustained RPM at speed on open water will be within the expected range for that engine and model. That confirms the expected power is there.

  8. #8
    auto culto's Avatar
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    Just a thought laying in bed last night. As I need / would feel alot happier if I could run this engine upto operating temp before using it. Looking at the pump layout I assume its safe to run for any period of time with the pump removed. Is this correct ? If so what rpm differential is there in and out the water ? as i feel its ticking over to slow at the moment. As I live 210 miles from the coast and have no facilitys there for fixing I need to try and make sure everything is spot on. I do have a own a rib that can be used as a cover boat so thats no issue. I also want to test the auto lube (running pre-mix at the moment) over a given fuel quantity to see if I can use it again as the previous owner allways mixed his own. Its been run very heavy on the oil and there is alot in the exhuast box (took some serious de greaser to remove the bulk)

  9. #9
    Click avatar for tech links/info, donation request K447's Avatar
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    With the driveshaft removed (which means the jet pump is also disconnected) you can indeed run the engine for longer periods.

    The reverse flush water connection on the top of the engine is not ideal for extended engine runs. The cooling flow is backwards (obviously) and the water flow through each cylinder can be uneven.

    A better method is to disconnect the main cooling water feed hose from the jet pump base. This connection is down low on the right side of the jet pump inside the hull, just right of the pump inlet tunnel when viewing from the rear, looking down into the hull. Hose size is 3/4".

    Disconnect the large hose from the jet pump feed nipple (which is one end of the water cooling tube that connects to the side of the jet pump exit nozzle), then install a garden hose barb fitting adapter so your garden hose will feed water in exactly the same flow direction as normal cooling water flow from the jet pump.

    Note that you do not need extreme water pressure and water flow rates from the garden hose to cool the engine. The engine will not have a working load so the heat generation is modest.

    Does this engine have a thermostat installed? Have you inspected the thermostat?

  10. #10
    auto culto's Avatar
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    Figured that bottom hose was the main intake. Thermostat has been tested and it opens ok (near boiling) but didnt know what temp it should open at. When I got the ski there was no battery or battery cover. I take it it should be a gel battery and does the original battery perfectly fit the tray. Does the battery have its own strap or just one that goes over the elec box and battery ? My motor factors list 1 battery for all polaris (gel) but its a fair bit thinner than the tray. Will be pulling the pump down tommorow. Just had a good clean up today and soaked the bolts ready for the next phase lol. Must admit I am really enjoying this small prodject. I have done many boats and engines now but I am finding that these are a very well thought out piece of kit. I always thought all jet ski's were cheap and naff due to the amount of non runners I,ve seen on slipways but there is as much tech in them as a basic boat but on a smaller scale. Its just the lack of maintenance that kills them, same as boats

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