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  1. #1

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    1996 Polaris SLT 700 mag cylinder problem

    Hey all,
    I'm new here and had a question. I got a new-to-me slt 700 ski last Sept and its been great this far. It was a 1 owner, shop maintained ski before me and I haven't needed to mess with anything, at least I didn't think I did. I had it out last weekend and was cruising at around 3/4 throttle on flat water when it suddenly felt as if I had let my hand off the throttle; no power. I then limped back a 1/4 mile to the boat ramp on one cylinder got it out of the water took it home and did the normal after ride flush and rinse down etc. I then proceeded to do a compression test: PTO: 120 ; Mag: 0. On the mag end, the needle didn't even flinch. I broke into the engine the next day to see what I could find. What I did find is that the reeds are fine, and there are little metal bits in the crankcase of the mag end. I tried to get the head off the cylinder but it seems stuck. (any tricks to this) I have a hunch that this happened from a mixture prob, just from reading, and I won't really know until I can get in there to see whats up. Does anyone have any advice or words of wisdom as I try to figure this out? Also, I know it is probably impossible to tell at this point, but does anyone have any idea of what I may find when I get in there? Thanks for any help; and please excuse my nooby-ness.

    --Justin


  2. #2
    Click avatar for tech links/info, donation request K447's Avatar
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    Welcome to the Hulk!

    You can find the Polaris Factory Service manuals here.

    How long have you had it?
    Was it sitting around for a long time before you bought it?
    Was the gasoline in the tank fresh?
    How many operating hours on the engine?

    I suspect you will find a hole burned through the top of the MAG piston. This is normally caused by a clogged up or incorrectly adjusted carburetor, or an air leak from a leaking seal, or some other problem with the fuel system (leaking fuel hoses or selector valve, weak fuel pump, very low fuel level in the tank, low fuel pressure).

    In addition to the engine repairs, you should plan to disassemble, clean, and rebuild those carbs. Do you have two carbs, or one?

    Since you found metal bits inside the crankcase, you should consider pulling the engine, and opening up the crankcase to properly clean it out.

    This would also allow you to replace the crank shaft seals, and fully inspect the engine internals. If the front crankcase seal was leaking, it would allow excess air into the engine, causing excessive piston temperatures. This is known as lean burn, and it can melt a piston in seconds.

    Before you pull the engine apart, if you are curious, you can perform a leakdown test. This would tell you if any of the engine seals are leaking air. It involves sealing the engine openings, then applying modest air pressure or vacuum. The sealed engine must hold the pressure for several minutes. If it does not, there is an air leak somewhere.

    You might want to do a leakdown test after the engine is repaired, before you put it back into the hull. This would confirm that you have assembled the seals and gaskets correctly.

    The good news is that your twin cylinder Polaris engine is small and not very heavy, so working on it isn't that hard.

    The folks here can guide you in terms of what parts you need, and where to get them. We can also answer questions you have along the way.

    One of the advantages of these 2-stroke engines is the mechanical simplicity - there simply are not a lot of moving parts inside.

    One downside of these high performance (and they are high performance, for their weight and size) 2-stroke engines is that the engine and carburetors must be 100% correct and within specification, or engine life will be short.

    BTW, tell us a little about yourself. Where are you located?
    To update your Green Hulk Profile, click here.

  3. #3
    casey67's Avatar
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    Hey Justin ,Welcome to Green Hulk.
    The red head cover(4 bolts) and the cylinder head (6 bolts) are sealed with an o-ring each to the cylinder. A lite tap or twist should break the seal.
    With 0 compression,I would imagine the piston will be bad.Those little bits of metal usually tear up the head also.It's very important to look inside to know better.

    Post some pictures of the damage,the folks here will be happy to give an opinion or 2.

  4. #4

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    thanks a bunch for the warm welcome;
    A bit about myself:
    I'm a mechanical engineering student at Florida Atlantic University in Boca Raton, Fl and am currently a senior. my other hobby, other than breaking my jet ski, is off roading/driving/working on my 1996 Land Rover Discovery. I'm confident in my mechanic abilities after having to maintain that rover for 5 years, so I think I can handle anything this ski can throw at me. However, I'm new to the jet ski scene; obviously since I didn't realize how easily it is to burn a hole in a piston; or whatever happened.

    A bit about the ski:

    Its a 1996 SLT 700 that my girlfriend Sarah and myself bought together last september. We had it out several times a week last year until the beginning of Dec. Threw a can of fuel stabalizer in it and it sat until last weekend when I broke it. Before we owned it, one family had owned it and they took it to the same shop for all its maintenance. I've been doing foggings and flushings after every run since I've owned it. I did notice that in some of the recipts that the previous owner gave me that they took it in for smoking too much; I have a feeling that the shop may have leaned it out too much leading to this problem? I don't know. Right now the ski is sitting across the state in Fort Myers at my folks house. The next chance I get I'm going to head that way to start getting this thing back up an running; I'm kind of looking forward to the rebuild. It has two carbs and is oil injected.

    I'm sure I'll be in here with my questions when I get up to my elbows in oil. I'll get some pics posted as soon as I open her up. Thanks again--
    --Justin

  5. #5
    Click avatar for tech links/info, donation request K447's Avatar
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    Since you rode it quite a lot between Sept and Dec, the carb settings may have been OK, or right on the edge.

    That fact that it failed right after it had been sitting for over a month, leads me to think the MAG carb may simply have gotten a little gummed up. This can happen, even with stabilizer, but especially if the engine was not run after the stabilizer was poured in, to circulate the stabilizer through the carbs. A month isn't that long, but we don't know how clean, or gummy, the carbs were when you got it.

    Be sure to clamp off the oil hose from the oil tank, and you will find there isn't too much oily mess involved, since the crankcase does not hold liquid oil (normally).

    Once you have looked through the Service manual, and pulled the jet pump off, getting the engine out isn't too much work. The first time always takes longer, but once you know how it goes together, the engine can often be pulled in under an hour.

    You can start by removing that MAG head, and show us what you find.

    How quickly do you want to get back on the water?

    Do you want to rebuild those carbs yourself, or have it done for you?

  6. #6

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    well, I want to get it back on the water as soon as possible because I don't want it to become one of those projects that just gets pushed around but never done. I'll probably try rebuilding the carbs on my own since I think I'll barely have money for the parts. I saw a top end rebuild kit on some site that was selling for $250; came with piston, rings, and the pin that connects the connecting rod to the piston. Is that price whats to be expected? Also, since the piston didn't seize, would honing of the cylinder walls be necessary? I'm trying to do the job as inexpensively as possible. Anyways I'll stop asking questions until I actually have some evidence and see what the condition is of the cylinder walls and everything else inside is.

    --Justin

  7. #7
    john zigler's Avatar
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    i can get you a complete "top end kit" for 190.00 + s&h.

    this would be both pistons, rings, pins, bearings, c-clips, and top end gasket set.

    it is hard to say, without seeing your cyl in person if you need a bore or not. IMO i would strongly recomend boring it. if your piston has a hole in it, your cyl got very hot, and probably is not "true". a bore would make sure the cyl is straight, and true, and you will then have proper piston clearances as well.

    i understand trying to save money, but typically if you take short cuts in enging building, it will cost you more in the long run.

    give me an email, or call my shop, if i can help out.

    thank you.

  8. #8

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    I definitely understand your point. I don't want to cut corners. I want to do it right the first time but without throwing money at it that I don't need to. I will give you a call when I get inside the engine and see what I've got. Thanks a bunch for everyone's help.

    --Justin

  9. #9

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    UPDATE:

    Alright, I have a confirmed hole in the mag piston. Was able to get my dad to look inside the spark plug hole of the ski, however, the red water jacket part would not come off, it just rotates a bit. (took off cooling manifold bit and four bolts). The pto piston appears to be fine. I had a couple questions now:

    1. should I mess with the pto piston at all or just replace the mag piston
    2. Should I hone the mag cylinder before replacing piston and rings; if so, should I also hone the pto cylinder?
    3. What seals should I replace when I'm in there?
    4. Also, I haven't noticed any fuel leaks inside the hull; can you look at the fuel intake lines to the carbs for bubbles to see if they are leaking air into the lines?

    Thanks a bunch for all your help. I really appreciate it.

    --Justin

  10. #10
    Rasta Mon Condoms We Be Jammin!!!!! TxVirageTx's Avatar
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    what to do

    replace all the fuel line and redo the carbs,the lines dissolve and deposit a green gunk that clogs the internal carb screens.it leans out and bang.to bore or hone??have to see how the jug looks when it comes off.

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