Engine tear down reveals scored piston - 2005 M50
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  1. #1
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    Engine tear down reveals scored piston - 2005 M50

    Hi guys. This is my first post. I live in Minnesota and have ridden bikes on and off for 40+ years. So to get back into the sport cheaply, I just recently bought my 2005 M50 as a fixer-upper for $900. Cosmetically, it's very nice. It has 30,000 miles and a very noticeable loose cam chain rattle, which sounded like it was coming from the rear cylinder? After reading this forum, it sounds like a few folks have had cam chain issues? Anyway, I tore down the top end and was surprised to see scoring on the front piston? It's the classic 4 corner scoring, which is either the bike is running too lean or the previous owner did minimal warm up before riding. The rear piston looks just fine. In inspecting the bike, it appears the baffles were removed. But there is no Power Commander/Fuel Mgmt component on the bike, which seems to me indicates it's running too lean? But the top of the piston has plenty of carbon buildup (rich?). The air cleaner is stock, as is the rest of the bike. Anyone experience a similar situation after removing their baffles? Or run their bike on a dyno after removing their baffles to monitor the fuel/air ratio? I notice Power Commander has a map for stock bikes, but nothing for debaffled bikes. Thoughts? I plan on replacing the cam chains, tensioners, pistons, rings, etc. But not sure if adding a Power Commander on a basically stock bike is overkill?

    Bob J
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  3. #2
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    I think the bigger question here is: What do the cylinder walls look like ?
    I'm not sure that I would call that scoring but maybe just scuffing.
    And what about running lean would cause that......unless the piston was getting REALLY hot ?? which there is really no evidence of.

    Any evidence of a broken ring ?

    The general consensus is that a power commander is not "needed" just with a debaffle.......but of course even bone stock owners swear that the addition of one feels like it gives you an extra 100 HP.
    Don't believe everything that you think.

  4. #3
    Found second gear by accident
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    You should not need a fuel manager for a bike that only has pipes or airbox modded, only if both are modded. I've heard some say that even with both modded, a modern bike's ECU is smart enough to adjust for that. I know that my m50 ran fine with v&h pipes and kury pro hypercharger and no fi manager. I bought a gman bully for the m50 but never got around to installing it and recently traded the bike in for a Valkyrie.

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  6. #4
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    Easy; here are a couple of pics of the front cylinder. No broken rings. Nothing unusual in the oil. It ran well before I tore it down. I'm just trying to find out if this is common wear. The 4 corner scuffing is usually a sign of other problems and I'm just looking to eliminate a possible lean condition scenario..
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  7. #5
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    I don't think you have to worry about a lean fuel condition.
    Where did you learn that was a common cause of cylinder scoring ?

    I think it is more likely that the front is just the result of "manufacturing tolerances" where the sleeve is on the low side and the piston on the high side.....or the piston pin is loose.
    Don't believe everything that you think.

  8. #6
    M-J Lifetime Achievement Award
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    Depending on how deep any marks are I would suggest the bore can be honed smooth and also the piston may be able to be buffed. The marks look more like scuffing than scoring...maybe caused by revving a cold engine as you say. I would be concerned that the front cylinder is the only one affected and, as ER says, check the wrist pin clearance.
    Smoke me a kipper I'll be home in time for breakfast

  9. #7
    Can Ride And Chew Gum
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    Did you read your plugs? They will tell you if you are rich, lean or as baby bear said just right.
    If you can't dazzle 'em with brilliance,Baffle 'em with Bulls!!t!

    Roadburner Street Pro's on my M http://www.youtube.com/watch?v=Hf0IYPcoiVc

  10. #8
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    AloRaptor; the plugs are on the dark side, almost soot-ey. Not the nice brown you'd hope for. And as you can see on the top of the piston, there is definitely some carbon buildup.
    Last edited by rpjense; 08-16-2016 at 07:37 PM.

  11. #9
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    Quote Originally Posted by Easy Rider View Post
    I don't think you have to worry about a lean fuel condition.
    Where did you learn that was a common cause of cylinder scoring ?

    I think it is more likely that the front is just the result of "manufacturing tolerances" where the sleeve is on the low side and the piston on the high side.....or the piston pin is loose.

    I've read it before (4 corner seizure/scoring/scuffing). I did a quick google check too;

    Four corner seizureSymptom - The piston has vertical seizure marks atfour equally spaced points around the circumference.Cause - A four corner seizure is caused when thepiston expands faster than the cylinder and theclearance between the piston and cylinder isreduced.Reason - The main reasons for this problem are tooquick warm-up, too lean carb jetting (main jet), or aspark plug with too high a heat setting being used.

  12. #10
    Found second gear by accident
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    Quote Originally Posted by rpjense View Post
    AloRaptor; the plugs are on the dark side, almost soot-ey. Not the nice brown you'd hope for. And as you can see on the top of the piston, there is definitely some carbon buildup.
    Doesn't that indicate a rich condition, rather than a lean one?

  13. #11
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    Quote Originally Posted by Aussie Steve View Post
    Depending on how deep any marks are I would suggest the bore can be honed smooth and also the piston may be able to be buffed. The marks look more like scuffing than scoring...maybe caused by revving a cold engine as you say. I would be concerned that the front cylinder is the only one affected and, as ER says, check the wrist pin clearance.
    Aussie; along with new cam chains, I was planning on boring and new pistons. With the amount of work it takes to yank the engine out, I don't want to do it again. Interesting what you guys said about the wrist pins. You don't see those go out on other bikes very often? But that's what I like about forums. You guys know this engine inside and out. It's good to know the common failure points on these engines..

    I also noticed the oil pump chain was really loose? Is that to be expected? Or should it just have minimal freeplay?

    I made similar repairs to a VN750 Vulcan last year. Chain tensioners, chains, etc. Though I don't remember Kaw parts being as expensive as Suzuki? Nearly $200 for the 2 cam chains? Suzuki should be selling at cost as a goodwill gesture..

  14. #12
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    Quote Originally Posted by turboyoshi View Post
    Doesn't that indicate a rich condition, rather than a lean one?
    Kinda; on carbureted bikes you have idle, mid range and high speed. 3 different jets. One can be lean, one can be rich. The plug reading is dependent on what part of range you were in at the time of plug reading. Fuel Injection (FI) is a different beast entirely. You'd think the overall readings would be more linear. I did notice 2 brass colored (standard) screws on the Fuel Injection? Normally aren't these capped? Makes me wonder if someone was playing with a mixture screw or something? Then again, I wouldn't think FI would have mixture screws..

  15. #13
    M-J Lifetime Achievement Award
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    The reason for the wrist pin suggestion is that the wear is on the font cylinder only. I wonder if the front cylinder was running super rich and the excess fuel was washing the oil off the bore and piston?

    Either way if you are doing a rebore and fitting new pistons its a problem that can be sorted. I saw a YouTube of a clutch replacement on an M50 and the oil drive chain on his was fairly sloppy too. As for fuel injection this is done via fuel maps which control the amount of time the injectors spray via sensors sending info to the ECU.

    One that often causes problems is the IATS...inlet air temp sensor....Suzuki put the Hayabusa ones right above the engine which can cause incorrect data in hot climates making the ECU lean off the fuel.
    Smoke me a kipper I'll be home in time for breakfast

  16. #14
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    Quote Originally Posted by rpjense View Post
    The main reasons for this problem are tooquick warm-up, too lean carb jetting (main jet), or aspark plug with too high a heat setting being used.
    If you found it on the Internet it HAS TO BE TRUE......right ?? Where exactly did that quote come from ?

    What is a "too quick warm up" ?

    And a plug with too high a heat range makes ONLY the core of the plug too hot. It has virtually no impact on cylinder temperatures.
    But it is a very common misunderstanding about what a plug heat range does.

    I can't argue with the lean thing......IF there is any evidence of it running lean......which in your case there isn't.
    Don't believe everything that you think.

  17. #15
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    Quote Originally Posted by Aussie Steve View Post
    The reason for the wrist pin suggestion is that the wear is on the font cylinder only. I wonder if the front cylinder was running super rich and the excess fuel was washing the oil off the bore and piston?

    Either way if you are doing a rebore and fitting new pistons its a problem that can be sorted. I saw a YouTube of a clutch replacement on an M50 and the oil drive chain on his was fairly sloppy too. As for fuel injection this is done via fuel maps which control the amount of time the injectors spray via sensors sending info to the ECU.

    One that often causes problems is the IATS...inlet air temp sensor....Suzuki put the Hayabusa ones right above the engine which can cause incorrect data in hot climates making the ECU lean off the fuel.
    Steve; good info. I live in Minnesota, which is a cold weather state (notice my avatar). So I don't think IATS is the issue. Since this fixer-upper is now going to cost a lot more than initially planned, I think I might pick up a Power Commander. Cheap insurance. Especially if I decide to add a pipe next spring.


 
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