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  1. #1

    blown center cylinder what to do now

    Aloha, Had a bad compression check reading on my Yamaha SUV & pulled the head off. this is what I found. Click image for larger version. 

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    I need to know what to do next...

    I take it the head is no good. So should I buy new or used?

    I know I need to pull the Cylinders off & check for scoring. probably have them all bored out just to be safe.
    buy new pistons to fit the newly bored out cylinders.
    buy new or used head.
    put back together.

    Should I be concerned that there may be any metal parts from the piston in the bottom end of the motor block? What should I do to make sure there is nothing in the bottom end?

    any advice tips or instruction is welcom!
    Thanks in advance!
    mahalo,
    Erik


  2. #2
    Quote Originally Posted by [email protected] View Post
    Aloha, Had a bad compression check reading on my Yamaha SUV & pulled the head off. this is what I found. Click image for larger version. 

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Views:	133 
Size:	118.4 KB 
ID:	321147Click image for larger version. 

Name:	photo.jpg 
Views:	132 
Size:	113.0 KB 
ID:	321146Click image for larger version. 

Name:	photo(2).jpg 
Views:	142 
Size:	125.8 KB 
ID:	321148
    I need to know what to do next...

    I take it the head is no good. So should I buy new or used?

    I know I need to pull the Cylinders off & check for scoring. probably have them all bored out just to be safe.
    buy new pistons to fit the newly bored out cylinders.
    buy new or used head.
    put back together.

    Should I be concerned that there may be any metal parts from the piston in the bottom end of the motor block? What should I do to make sure there is nothing in the bottom end?

    any advice tips or instruction is welcom!
    Thanks in advance!
    mahalo,
    Erik
    The cylinders are nikal celled so they are very hard. Your cylinders may be ok or just require honing. You will not bore the cylinder due to the nika celled treatment. If a cylinder is bad you may either buy a used replacement or send it to millineum technologies for repair. I would tear the entire engine down and inspect. If the crank has over 100 hours on it I would consider replacing it even if you do not find any issues. I would find a used head to put back on it. The dings in the head can have high spots and they will get hot causing detonation causing an early failure on the next motor. Their are some excellant rebuild threads created by Oside Bill (r.i.p) out there that are very informative.

  3. #3
    showmepro1200's Avatar
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    Step you missed - make sure you diagnose and correct the condition(s) that caused the cylinder to go.

  4. #4
    Quote Originally Posted by showmepro1200 View Post
    Step you missed - make sure you diagnose and correct the condition(s) that caused the cylinder to go.
    I am going with the concensus on here that the carbs need to be rebuilt. the ski sat for a year with fuel in it.


    What else should I be looking for as a cause?

    E

  5. #5
    "I would tear the entire engine down and inspect. If the crank has over 100 hours on it I would consider replacing it even if you do not find any issues."


    this engine has 70 hours on it... & I am really feeling a bit overwhelmed to attempt a complete rebuild! I would prefer to just have the Cylinders honed as you suggest, Buy new pistons, rings, gaskets, Head, & put it back together, Have the Carbs rebuilt by the local wave runner mechanic & run it. I am considering a 4 stroke conversion so I am looking to spend as little as possible on a repair, in preparation for the big expenditure of the conversion!!

    Thanks for the info on the rebuild posts.. I Sure do miss having Oside Bill on here... May he rest in peace. He was the nicest guy that would allways be the first to jump on a SUV thread! miss his advice, encouragement, & enthusiasm.

    If I chose to not pull the engine what advice would you give for making sure theres nothing damaging in the bottom of the block??

    Thanks I am open to all advice

  6. #6
    Quote Originally Posted by [email protected] View Post
    "I would tear the entire engine down and inspect. If the crank has over 100 hours on it I would consider replacing it even if you do not find any issues."


    this engine has 70 hours on it... & I am really feeling a bit overwhelmed to attempt a complete rebuild! I would prefer to just have the Cylinders honed as you suggest, Buy new pistons, rings, gaskets, Head, & put it back together, Have the Carbs rebuilt by the local wave runner mechanic & run it. I am considering a 4 stroke conversion so I am looking to spend as little as possible on a repair, in preparation for the big expenditure of the conversion!!

    Thanks for the info on the rebuild posts.. I Sure do miss having Oside Bill on here... May he rest in peace. He was the nicest guy that would allways be the first to jump on a SUV thread! miss his advice, encouragement, & enthusiasm.

    If I chose to not pull the engine what advice would you give for making sure theres nothing damaging in the bottom of the block??

    Thanks I am open to all advice
    I know that it is scary to do a total rebuild, but I would at least inspect the crank. You will have to pull the motor (or it would be easier at least) to replace the pistons anyways. To inspect the crank, you would have to remove the stator cover (no big deal), flywheel (use flywheel puller), PTO coupling, and split the cases. The crank will be staring you in the face. The bearings have alignment dowels and it is easy to see how to position them. The crank seals are easy to replace. I had to split the cases on mine to replace the crank seals. In order to replace them, you had to raise the crank out of the block. I personally would inspect the crank bearings and try to wash them out and re-lube the bearings to insure no metal is in there. I know it sounds scary but what I would fear more is paying for all the parts 2 times due to some metal in the case. I don't know much else you can do without splitting the case. The biggest deal with splitting the cases is to perform the pressure test after you reseal the case to insure no leakage. I bought my kit from Lowell Horning but there are ways to make a pressure test kit. It is just a gamble to not inspect the crank imo. Also, be sure to get the carbs checked out to find the root cause of the failure as someone mentioned earlier. Good luck Erik.

  7. #7
    So If I pull the motor out, & split the case how what am I looking for to inspect the crank. Do you need to pull the Connecting rods off the crank? Then would'nt I be doing a complete rebuild with all new Bearings? Connecting rod, Crank, Oil Seal... can you recommend a rebuild kit?

    thanks

  8. #8
    Duke's Avatar
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    The 65U motor has cast iron sleeves and most likely damaged the center cylinder. Looking at the piston I would suspect a crank going bad possibly from oil injection failure, impossible to know without splitting cases and inspecting.

    By the time you remove pipe, cylinder and carb rack there isn't much left and might as well pull block out. Crank is pressed together with bearings and rods all as one assembly. Just separate cases and crank will come out. Will be a colossal waste of time to do anything without inspection and cleaning of crank assembly.

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  10. #9
    "The 65U motor has cast iron sleeves and most likely damaged the center cylinder. Looking at the piston I would suspect a crank going bad possibly from oil injection failure"

    This 65U is from a SUV. I am getting mixed replies on wheather it has the cast iron sleaves or not. Also it was converted to premix so no oil injection problem possible..

    Will be a colossal waste of time to do anything without inspection and cleaning of crank assembly.

    OK OK So I am leaning towards at least pulling the block & having a look at the crank & cleaning it. What & How do you recommend cleaning the crank? what am I looking for in a bad crank?

    Thanks in advance
    Erik

  11. #10
    Quote Originally Posted by [email protected] View Post
    "The 65U motor has cast iron sleeves and most likely damaged the center cylinder. Looking at the piston I would suspect a crank going bad possibly from oil injection failure"

    This 65U is from a SUV. I am getting mixed replies on wheather it has the cast iron sleaves or not. Also it was converted to premix so no oil injection problem possible..

    Will be a colossal waste of time to do anything without inspection and cleaning of crank assembly.

    OK OK So I am leaning towards at least pulling the block & having a look at the crank & cleaning it. What & How do you recommend cleaning the crank? what am I looking for in a bad crank?

    Thanks in advance
    Erik
    The crank, rods, bearings will be removed as an assembly. The front bearing is the only one that will slide off the front of the crank. It will only go onto the crank one way for the dowels to properly line up. Just take pictures as you are removing items. BTW, take the PTO coupling off the crank before you remove the flywheel. Sometimes they "stick". Personally I would wash/rinse the bearings out with Diesel fuel since Diesel fuel does have lubricity but others may have a better idea. After I thouroughly rinsed the bearings I would re-lube with 2 stroke motor oil when I was ready to re-install. You should rinse the cases out thoroughly also. It would just be a shame to lose a good crank over a little metal. Good luck Erick.

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