Help! Did I blow up my engine?

Discussion in 'Bike Mods, Performance, Maintenance & Repair' started by DrMattyz125, May 19, 2009.

  1. DrMattyz125

    DrMattyz125 Rookie DRN Member

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    As i was cruising along a gravel road at half throttle on 4th gear my bike sputtered and stalled. It still kicks over but there are two head bolts that missing. Actually one was broken off. There is black gunk/grease around the spark plug on top of the head and some antifreeze on the head. Does this sound like a big project? I am an amatuer with the wrenches. Would I be better off taking it in to a pro?
    any help advice would be appreciated.


  2. mathd

    mathd Rookie DRN Member

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    sound like the top end is blown, i would see if it start and have compression.
    if it are broken the best way to know what state it is have to open it and check.

    For the repair, its a 2 stroke top end so its not hard to work with.
    if you arent enough confident in your skill get a service manual, it will give you better understanding of the bike/engine/repair and will make you good with a wrench :)
  3. oldguy

    oldguy Always Broken

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    Despite what mathd (maybe that is the grade he got in math?) advised DO NOT start the bike. You have 2 headbolts missing and if you try and are succesful you will only do more damage. Chances are you didn't have the headbolts torqued properly or the studs were stretched from use.
    You need to do a topend teardown and remove the head, cylinder, and piston to check out what happened. Be carefull to not drop anything down into the bottom through the cylinder. A manual will be your best friend as you do it so get a good manufacturers one instead of a generic clymers type.

    Once you have the head and cylinder (jug) off take some good clear pictures and post them. That is the best way to get real usable advice on how to proceed. At least it is a 2 stroke which makes working on it much easier
  4. DrMattyz125

    DrMattyz125 Rookie DRN Member

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    Thanks for the help. Once it stalled, I initially tried to kick it over, and it had less compression than normal, but after a few kicks I stopped and haven't kicked it over since.
    I got a manual with the bike. NOt sure if it is a good one or not. I will try get the pictures up ASAP.
    Thanks Again,
    Matt YZ 125
  5. mathd

    mathd Rookie DRN Member

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    My bad, yeah am sorry i should been more clear.
    i trough the guy would consider fixing the bold before starting/testing it as its evident the engine cant run or have compression in this state the user also said it stalled and dosent run. after the gasket/bolt fixed he could kick once or twice as he already did kick it over a few time to see if it have enough compression to start ... So if it dont have compression or do not start its blown wich answer hes first question.
    I also said in my first post that the best way to know what state it really is, he have to open and check.
    The engine can not be blown but because of unknown internal engine damage it can blown in the near futur.
    At this point i would consider order a top end kit and make sure the cylinder/crankshaft and bearings/seals are fine and also check for debrits in the crankcase, like coolant etc. but he didnt ask for that only asked if it was blown, and I DID advice at the first post to tear it down and check for damage because it is broken!

    btw, i was really good in math, not good with french.
    mathd is my name, Mathieu D, so thanks for the comment.
    Last edited: May 20, 2009
  6. m4i2k2e2

    m4i2k2e2 Rookie DRN Member

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    i just completely rebuilt my entire 250 2 stroke engine with my my clymer manual and it is not by any means generic. i also have one for my 97 kx125 and my brother has one for his motorcycle and they are all great as i stated above. so, i dont know why you would say they are generic?

    -mike.

    -mike.
  7. oldguy

    oldguy Always Broken

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    Often Clymers will lump together several years and or models where as the manufacturers manual is specific to that bike. A 2 stroke isn't so bad because the basics stay the same so I guess a clymers would work just fine. I stand corrected if they don't come that way anymore it has been many years since I bought a clymers
  8. oldguy

    oldguy Always Broken

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    Mathieu D proper sentance and paragraph structure (as well as some spell check) would have made your point clearer. As you typed it the first thing you told him to do was try to start it then some undecipherable gibberish
    as the second thing to do hence my recomendation not to try starting it before tearing it down.
  9. DrMattyz125

    DrMattyz125 Rookie DRN Member

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    I opened up the head, and there was a little antifreeze on the crank. The piston was a little black on top, but didn't seem to have any major damage to the cylinder. On the other hand I can't imagine antifreeze on the crank would be very good. As an amatuer wrencher, is there maybe a crack in my engine somewhere? I just bought this bike for 850 and don't really want to put too much back into it at this point. After a couple more paycheck probably, but not now. Any guesses to what may be the problem and what it usually costs if I was to do it myself or get it done professionally?

    Matt yz 125
  10. oldguy

    oldguy Always Broken

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    It would be normal when the head studs let loose for coolant to get into the cylinder and make its way to the lower end. You need to figure out why the studs let loose but I would guess as in my original answer they were not torqued correctly or they had just stretched over time.
  11. DrMattyz125

    DrMattyz125 Rookie DRN Member

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    The front left head bolt is stuck inside the threads and it looks like this had happened before to the left rear head bolt that was completely missing. When I was taking the power valve off another bolt broke off in the threads. Would a typical machine shop be the place to bring this type of problem to fix the busted off inside bolts? I imagine I should take down the lower end and clean that up too and remove the small amount of antifreeze on the lower end?
    Matt yz 125
  12. mathd

    mathd Rookie DRN Member

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    i dont like the claymer manual for the same reason as oldguy.
    also nice price for a 97 yz125.
    i paid 1700$ CAD for my 98 yz125 with a 01 frame for parts...

    for the coolant, like oldguy said its kinda normal, its there because of the gasket and loose head bolt that is to be fixed.

    For the coolant in the crank, i really dont know if it have to be removed or not and how.
    I guess if it have alot of coolant you really gotta have to get it out, probably without to take down the lower end(there probably a little trick around for that)?
    Or if there is just a bit of coolant maby the engine will burn it?
    other people should answer this..

    For the screw, there is some removal tool for that, but a machine shop could do this better and for cheap i think.

    some picture could help the guy giving better answer.
    Last edited: May 21, 2009
  13. DrMattyz125

    DrMattyz125 Rookie DRN Member

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    I will try get some pics posted tonight for you guys of the head bolts, and engine where the coolant is. Last night was the first time I had taken down my bike and took me forever!
  14. rmc_olderthandirt

    rmc_olderthandirt Subscriber

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    How long have you owned this bike?

    What surprises me the most is the number of missing or broken bolts that you are dealing with.

    If you were missing two adjacent head bolts then I am not be at all surprised if the head gasket failed. At best that would simply stop the engine from running properly and it could easily have led to head or cylinder damage.

    Once the bike stopped running a blown head gasket would also allow coolant to leak into the cylinder and bottom end. That is generally no big deal. When you are rebuilding the top end I would recommend flipping the bike upside down so that the water can drain out of the bottom end.

    Repairing the broken/missing studs and bolts is something you can do yourself but if you are not comfortable doing it a machine shop should be able to do for you. I wouldn't be surprised if the missing head bolt has stripped threads and needs a heli-coil. The broken bolt related to the power valve might be extracted without damaging the case threads but it might need to be drilled out and a heli-coil installed there as well.

    As I said above, I am concerned that you have had several break or come loose. This suggests to me that something is very wrong. It is possible that a previous owner applied way too much torque to the bolts which can damage them. It may be wise to replace all the studs to ensure that the problem doesn't recur.

    Rod
  15. jsantapau

    jsantapau Rookie DRN Member

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    you could take a turkey baster and a small hose or anything like a fork oil level tool too suck most of the water up , blow it out with an air compressor, just don't blow down the oil valley holes that feed the mains, dribble some oil down there to flush it out.

    I have left water,coolant in the bottom end before but be forewarned that where ever water is there won't be any oil.

    " I just bought this bike for 850 and don't really want to put too much back into it at this point. After a couple more paycheck probably, but not now. "

    you will save money in the long run to make sure everything is ok now. You have it apart, you are talking about sending the parts to machine shop for thread repair, make sure that the crankshaft,connecting rod are still within service limits and the piston and cylinder bore are good would be a real shame to spend a 100$ or so at the machine shop to fix a bolt hole just to toss a rod or shatter a piston trashing everything else.


    my advice would be before you spend any money, take the most accurate assesment of what the bike needs that you can, call for pricing, see what everything will cost, figure out what the bike is worth to you and then go from there,

    You don't want to get trapped into a money pit,and you don't want to create yourself problems later by not addressing concerns now. You may want to learn how to properly care for a bike on this thing before you buy something new or anything in between. That decision is a compromise that you will have to figure out for yourself
  16. whenfoxforks-ruled

    whenfoxforks-ruled Old MX Racer

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    You should have the top of the cylinder and head checked for warpage. You could fix the threads yourself, but getting a stud crooked is scrap time. I would replace all the studs, and hopefully they will not need inserts to repair stripped holes. Do you have a torque wrench?
  17. Brian&Brian

    Brian&Brian Rookie DRN Member

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    I would get a clymer. My 08 Kx 100 manual tellys you nothing. Me and my dad got a motor im a box (03 RM 100 for 175$ and it only needed a topend and a frame with no paint missing) and he had to do it on all memory. Old manuals were good because the gave you a compleat tear down of your motor. Now factorys are cheap and want you to take your bike to them.
  18. DrMattyz125

    DrMattyz125 Rookie DRN Member

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    I took some pics of the bolts (lack thereof) on my phone to download, but the forum said the file is too big to upload. Anyway, I talked to a professional today and he told me that since I had already taken the bike apart this far to take the engine completely out and he will see what he can do or have someone else give a second opinion if they can fix it. It appears like this had happened before since the left rear cylinder base stud bolt has a half inch or so tube added above the normal base where the stud bolt rises where it has maybe been replaced or tapped. I bought the bike this spring and the guy seemed pretty honest about everything except didnt tell me about this. I've only put 5-7 hours on it and it's finally getting nice in Northern MN to ride on half way dry trails. Hopefully I will be able to replace the stud bolt. The professional seemed leary, but hopefully it will be replaceable.

    Matt yz 125

    Here I am enjoying my new toy when it was running like a champ!
    http://www.youtube.com/watch?v=LIYIxggFH_g&NR=1
  19. whenfoxforks-ruled

    whenfoxforks-ruled Old MX Racer

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    That tube sticking up around the stud could be a dowel pin for aligning the head, should be 2? If the guy working on it does not know this, I would find someone else.
  20. mathd

    mathd Rookie DRN Member

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    hell yeah if the guy dont know that it have dowel pin :O. this remember me why i never let anyone else thant myself work on my bike.

    my 98 have 2 dowel pin for aligment, the other pin is at the left front cylinder base stud bolt on mine.
    Maby i should post my yz125 98 factory service manual .pdf if it can help? its not the 97 but shouldnt be much different from 97 to 98?

    also nice vid :)
    Last edited: May 22, 2009



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