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  1. #1
    2MSX140's's Avatar
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    MSX 140 questions

    Hey everybody, always used this site for problems in the past and always got great answers so I decided to join. Anyway, within the past month me and my brother picked up two 2003 MSX 140 projects. I've always loved the looks of these things! The weird thing is that on both of them the front (gas tank side) of the motors have failed. On my brothers the rod to crank bearing is completely gone resulting in the piston getting chewed up bad as well and on mine it looks like the piston seized and bent my rod at about a 70 degree angle. My question is if this is happening to anyone else? I know I have many things to go over before running once I rebuild the engines. I'm suspecting maybe bad oil lines or maybe the other guy just plain ran out of oil? The machines only have 116 and 150 hours on them. I've got two new cranks on the way and then I'll put new top ends on them so I want these new motors to actually last! I have 1 more question also, I've read you cannot tow these machines as they fill the motor up with water? Is this true? Can I put a valve on one of the hoses where water comes in? Thanks in advance!


  2. #2
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    Most cranks fail due to rust. Either from water ingestion or improper storage.

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

    The MSX 140 engines have an extra oil line that directly feeds the front crank shaft bearing, plus three oil lines to each cylinder air intake.

    Make sure the correct oil is in the oil tank. If you dont trust it, drain the oil tank and replace with known good quality 2-stroke oil. Also change the oil filter.

    The MSX 140 cylinders are Nikasil coated, not iron sleeves. If the cylinders are worn or damaged they will need to be re-plated. I just rebuilt my own MSX 140 engine last summer.

    Regarding towing, most watercraft of any brand have the same requirement, often outlined right in the owners manual. The cooling system includes a water injection spray that cools the exhaust gas flow. When being towed the cooling system can pressurize if the tow speed is too fast. That allows water to accumulate inside the exhaust system. Tow it far enough and fast enough and the water will back flow into the engine itself, which is bad.

    I carry a hose pinch clamp in my storage bucket. If a tow is needed, the cooling feed hose from the waterpump can be clamped off before beginning the tow. On most Polaris models this is straightforward. I recently installed a water shut-off valve in a Virage i, which makes it more convenient to do than using the clamp. Granted one does not anticipate needing to be towed often, but knowing it is ready to use and cannot be lost makes the valve a nice alternative to the clamp.

    The MSX 140 makes this difficult, as the water feed hose is buried down low on the right side of the jet pump, underneath the black foam holding the battery in place. In addition, there is a tee in the water feed just a few inches in from the rear hull feed nipple.

    See this post for more info;
    Preparation for in-water towing of disabled MSX 140

  4. #4
    Click avatar for tech links/info, donation request K447's Avatar
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    Oh yes, do read up on the common maintenance items for these machines.

    In particular, the protective sleeving of the fuel hoses against the fuel injector brackets, the rebuilding of the through-hull bearing assembly, and the fuel pressure regulator inside the fuel tank.

    I presume these are 2003 models, so they are now ten years old. Even if well cared for, now is the time to go through the machines from end to end and make sure everything is as it should be.

  5. #5
    2MSX140's's Avatar
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    Great information! I did notice that extra oil line. And BryanP I think you are exactly right, the people before us did not do much maintenance at all it seems like. I have heard a lot of people talk bad about these Polaris engines but as long as you take care of them they are great reliable machines! K447, we plan on boring both machines out, where do I send my cylinders to get them re-plated? Also my brothers came with a brand new bored out cylinder and piston the guy ordered from SBT, I measured piston to cylinder clearance and its 13thousanths clearance, isn't that a little big? I've always been told Polaris likes to be around 5 thousandths? I could be wrong though...

  6. #6
    Click avatar for tech links/info, donation request K447's Avatar
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    Nikasil cylinders are not 'bored out'. They are re-plated to original factory specifications, not oversize.

    Boring oversize is something that happens with iron sleeved cylinders, which is not what the stock Polaris engine has. If you do it properly you will have original cylinder size and can use stock size MSX 140 pistons and rings.

    SBT has a product where they convert the MSX 140 cylinder to iron sleeve. I am not a fan of this as it eliminates the benefits of the Nikasil coating (better heat transfer, reduced cylinder wear). The MSX 140 cylinder also has a different port configuration than the standard Polaris red 1200 engine, so if the sleeves do not match the MSX porting then the engine will not run quite the same.

    The red Polaris engine is 1165cc while the MSX 140 engine is 1192cc. The pistons are different too.

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    2MSX140's's Avatar
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    Hmmm, well I have a problem then. All of my cylinders are 1 over, so that means I more than likely have SBT cylinders? Can I send them in to get the Nikasil sleeve put back in them?

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    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by 2MSX140's View Post
    Hmmm, well I have a problem then. All of my cylinders are 1 over, so that means I more than likely have SBT cylinders?

    Can I send them in to get the Nikasil sleeve put back in them?
    Sounds like the entire engine is an SBT rebuild. Is there an SBT sticker with a serial number on the front of the MAG cylinder?

    Once sleeved, there is no going back. You either replace the cylinders with unmodified Nikasil cylinders, or live with the SBT method.

    Before you bore those sleeved cylinders any larger, you need to source the replacement pistons. Start by asking SBT if they can supply the next oversize up from what you have now.

    Typically a machine shop will want to have the new pistons in hand for measuring before they actually bore the cylinder sleeve to match.

  9. #9
    2MSX140's's Avatar
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    You are right, the crank was also SBT and I did see the SBT sticker. I guess ill have to stick with these cylinders. As long as I run good oil and don't run the absolute piss out of it do you think it will stay together for me? I have a local machine shop that has done all of my boring for other machines and have never had a problem so ill probably have him do it. So I need the next size SBT pistons? I cant go with another brand such as wiseco? Thanks for all the info, I have really learned a lot!

  10. #10
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by 2MSX140's View Post
    You are right, the crank was also SBT and I did see the SBT sticker. I guess ill have to stick with these cylinders.

    As long as I run good oil and don't run the absolute piss out of it do you think it will stay together for me?

    I have a local machine shop that has done all of my boring for other machines and have never had a problem so ill probably have him do it.

    So I need the next size SBT pistons? I cant go with another brand such as wiseco?

    Thanks for all the info, I have really learned a lot!
    You are rebuilding the entire engine, correct?

    Rebuilt crankshaft and new bearings, bored cylinders, new pistons, new rings, new seals, new gaskets. If done properly, it certainly should 'hold together'!

    As you now know, by sleeving the cylinders SBT has created a non-standard MSX 140 engine. The pistons you will need to fit the re-bored cylinders will not be 'MSX 140' pistons, simply because a stock MSX 140 only has one size of cylinder and therefore only one piston size.

    Since the entire engine is being rebuilt, consider the cost of replacing it with another complete SBT engine vs. rebuilding the crankshaft and sourcing the other needed parts separately. SBT calls the MSX 140 version of their product '1200DIv2'.

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