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  1. #1
    Resident electronics hacker UnityRacing's Avatar
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    Lets talk MSX140 and SBT

    Just bought a used MSX140 long block with a scored cylinder and bad piston. Ok no problem the price was right, and I can use the crank and cases anyway.

    Got the engine in, and saw an SBT sticker on the MAG cylinder. Uh oh. Closer inspection revealed that all 3 cylinders were not plated - typical SBT procedures, replace with Iron sleeve. My guess at this point is the entire engine was SBT rebuilt.

    So that leaves me wondering about the crankshaft. Per SBT's website, their cranks are rebuilt, and welded. Does this mean the crank should hold up better, and not lose index?
    Do they normally get rid of the locating ring on the bearing?

    Now I have this crank that is probably SBT rebuilt, and while I have not split the cases, it seems to be in good condition, no odd noises, spins smoothly, etc. and I also have the OEM crank that had a rod grenade from the other engine. My original plan was to sell off the parts not needed from the engine I just picked up and use some of that cash to get the rodless OEM crank reworked. For about $550 I can have the crank rebuilt with new rods, welded and trued.

    What would YOU do?

    While I'm at it, what are the pros/cons of running iron cylinders on the MSX? Looks like the ports are the same as the OEM plated ones I have, and the iron ones are 85mm also.


  2. #2
    ripcuda's Avatar
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    I would think it should be fine. They warranty their engines for a year or more and they know a thing or two about engine rebuilding.

    I've sleeved a few Webers to fix bad Nikasil, similar but not quite the same as a ported 2-stroke sleeve you have. It gets you back to proper cylinder diameter, plus can be overbored if ever needed in the future.

    The other possible alternative is well worn but usable MSX 140 Nikasil plated cylinders... that even with new piston rings... don't get you back to new spec compression. Unless you want to send off your cylinders and have them replated back to new spec for $260+ each (my quote from Millennium).


    If I were you, I'd split the cases and inspect the crank, bearings and replace the seals. I'd confirm if the crank has the middle retaining ring. SBT sells a specific MSX 140 crank, so I think it should. And I'd true up the sleeved cylinders and use them. You can use standard Polaris 1200 oversized pistons and rings now with the steel sleeves.

    Cheers!

  3. #3
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by ripcuda View Post
    I would think it should be fine.

    ... not quite the same as a ported 2-stroke sleeve

    ... I'd true up the sleeved cylinders and use them. You can use standard Polaris 1200 oversized pistons and rings now with the steel sleeves...
    I have forgotten all the differences between MSX 140 and overbored red engine configuration.

    SBT had some issues with the early days of MSX 140 sleeved engine rebuilding. Going from memory, at first they were using the same iron sleeves as the red engine 1165cc cylinders but the porting did not match up.

    I do not know how well the current MSX 140 sleeves align compare to the stock cylinder porting.

    I think the MSX 140 piston dome is a different shape than the red engine piston, so a difference there. I do not recall if the piston differences resulted in a compression difference.

    Nikasil cylinder has less piston ring sliding friction than iron sleeves and nikasil conducts heat better than iron.

  4. #4
    Resident electronics hacker UnityRacing's Avatar
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    I'm mostly interested in the crank, and how their quality is. I had originally planned to sell this crank as a good used crank and offset the cost of having one rebuilt.
    I guess my question now becomes, assuming this crank is "good" IE: bearings, no wear, etc - would an SBT crank be worthwhile to use on a full ski rebuild, or should I still go after a 'fresh' crank?

    Cylinders I was mostly asking about so I could sell them. I have one or two good plated cylinders (one has a broken head bolt stuck in it) from the failed engine, and 3 unknown cylinders in the ski I'm picking up. More than likely these are OEM plated cylinders also. I plan to run the best 3 I have, and sell the rest, including the iron sleeve ones.

  5. #5
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    I think there is a compression difference between the 2 different pistons. I wonder if those sbt sleeved cylinders are ok to put a custom sleeve in? If they can be used as a core to put a different sleeve in i may be interested in buying them.

  6. #6
    Resident electronics hacker UnityRacing's Avatar
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    I'm not even worried about pistons. I'll just go with the SPI ones. Yes though from what I have read the domes are different between OEM MSX and 85mm pistons for the other 1200's (non MSX). The SPI ones are made for the Nik plated cylinders that are also found in the snowmobiles so should be a direct replacement for the OEM MSX ones.

    If it's a sleeve you are looking to do, then yes they can have sleeves put in. SBT does it, that's how they get the iron ones in. In fact you can even buy the sleeves for $70ish.

    I do have the 3rd cylinder also, but the sleeve in that one is scored pretty bad. The cylinder body itself is in excellent shape though.

  7. #7
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    I wouldnt do SBT sleeves. Im more looking for back up cores to use.

  8. #8
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    Quote Originally Posted by FlMike View Post
    Sleeving nikasil cylinders is not a problem.
    Depends on what you use for a sleeve and how well its done.

  9. #9
    Rasta Mon Condoms We Be Jammin!!!!! TxVirageTx's Avatar
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    maybe run the sbt crank and those cases with the nickasil jugs your gonna get (reniked) and fresh pistons.i'd be real leary of the sleeved msx jugs,do they have the triple exhaust ports in them?if not they'd be good for some kind of bastard mega porting combo only

  10. #10
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    Quote Originally Posted by TxPro1200 View Post
    maybe run the sbt crank and those cases with the nickasil jugs your gonna get (reniked) and fresh pistons.i'd be real leary of the sleeved msx jugs,do they have the triple exhaust ports in them?if not they'd be good for some kind of bastard mega porting combo only

    http://www.shopsbt.com/polaris-jetsk...2003-2004.html

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