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  • F300 belt issues

    Two year old F300 with 278 hours and run easily and properly maintained

    During a recent removal of the cowling notice bits of rubber missing from the top of the belt. After speaking with a few dealers one is replacing the belt under warranty. Yamaha said was probably a bad belt.

    Should I be concerned that something is causing this like a bad pulley or something ?

    Has anyone seen or heard of this before ?
    Attached Files

  • #2
    here again, I cant open the pic.
    I can tell you if the belt is being shaved off.
    the crank thrust bearing is failing.
    just a fact jack.

    dem dar belts simply DO NOT wear unless sumpin happens.

    have that dealership do a check on crankshaft end play.

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    • #3
      I have the exact same problem. Twin F300 Mfg Feb 2012 and port side has some belt dust upon inspection and the starboard side has small chunks about 1/4 inch missing along the top edge of the belt - maybe a dozen of them. There is < 700 hrs on the engines I believe. Not under warranty. Mechanic too a screwdriver and pried up on the flywheel and it moved maybe 1/16 or 1/32 of an inch just eyeballed it because he didn't have the tool to measure or the specifications on what the travel should be as he had a laptop issue and the shop manual wasn't available. Both motors seemed to have the same amount of play when prying yo the flywheels. I really don't want to fix one of them not to mention two... We are wondering if cleaning the belt dust off both engine interiors and replacing the belt on the one with chunks missing and keep a close eye on it is the right decision. I've had the boat three months, not happy about having this problem on an engine(s) that I was assured would run for thousands of hours without issue with normal use. I can't afford a catastrophic failure of one of my engines, I'm already broke just from buying them!!

      Any chance its not a thrust bearing issue? Was this a problem seen with F300s with the MFG date Feb 2012?

      Thanks
      Last edited by hog guts; 10-02-2016, 11:23 PM.

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      • #4

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        • #5
          Have your mechanic call Yamaha.

          Actually, he should have already made the call.

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          • #6
            He said he called the other day and was told - "we have not heard of any issues with the F300 timing belts adn there was no service bulletins regarding the issue...." He did say he was going to call and talk to somebody else because he was not convinced the first person he spoke to was forthcoming...

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            • #7
              your motor is already toast.
              you have suffered the dreaded thrust bearing failure.

              I don't have the SM in front of me but typical thrust movement(flywheel up and down) is about .003-.007".

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              • #8
                Originally posted by hog guts View Post
                He said he called the other day and was told - "we have not heard of any issues with the F300 timing belts adn there was no service bulletins regarding the issue...." He did say he was going to call and talk to somebody else because he was not convinced the first person he spoke to was forthcoming...
                If someone calls Yamaha (the USA division we presume) and asks if there have been any problems with the belt then a correct answer might be 'there have been no issues with the drive belts'. A correct but disingenuous answer. It helps to know how to ask the correct question.

                The problem is with the thrust bearings. Not with the belt. It is well known issue. Bearing(s) fail, crank shaft has excessive movement which in turn damages the belt.

                If your motor was made in Feb 2012 then it does not have the latest thrust bearings. Your motor has 6CB-11426-01-00 and a 6CB-11427-00-00 bearings. The latest bearings are 6CB-11426-03-00 and 6CB-11427-03-00.

                As far as I know the service manual does not provide a specification for vertical movement of the crank shaft. It is a bit of a judgmental call when using a tool to pry the crank shaft upwards. But certainly noticeable movement, combined with the belts being damaged, would indicate a bearing failure. Maybe have the oil filter opened up, or the variable cam drive mechanism filters checked for the presence of excessive metal debris in the oil system.

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                • #9
                  Originally posted by rodbolt17 View Post
                  your motor is already toast.
                  you have suffered the dreaded thrust bearing failure.

                  I don't have the SM in front of me but typical thrust movement(flywheel up and down) is about .003-.007".
                  Thanks for your input and I appreciate your time (everyone's). It hasn't been officially checked but I am guessing the thrust movement will be approx 0.050" based on what I saw. Can you elaborate on what you mean exactly when you say "your motor is already toast". I understand there may be a problem, but you are suggesting what... the whole motor is worthless - throw it away and buy a new one? Or something less dramatic, like, replace the thrust bearing, replace timing belt, clean filters etc... I am trying to grasp the extent of my problem and the cost to fix it. And remember, I have the same approx movement on both engines, but the belt is only getting shredded on the top of one of them. The other does have some wear dust and I suspect given some time might end up in the same shape. I'll provide the exact scientific measurement once its been acquired just for completeness. I'll also continue to update here whats going on. I sure would like to hear from some other folks who had this issue to see ultimately how they resolved their dilemma.

                  I may have a heart attack before this is over so I'll keep checking in so you know I'm ok....

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                  • #10
                    first verify actual crank thrust movement.
                    if excessive have the filter cut open, you will most likely see it is full of metal.

                    now will come the fun part.
                    this will requires a TOTAL teardown of the engine AND oil sump.
                    may require disassembly of the cam sprockets.
                    then it is on to removing the crank and pistons for inspection.

                    there is not but so much metal you can feed bearings until they puke.

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                    • #11
                      Originally posted by rodbolt17 View Post
                      first verify actual crank thrust movement.
                      if excessive have the filter cut open, you will most likely see it is full of metal.

                      now will come the fun part.
                      this will requires a TOTAL teardown of the engine AND oil sump.
                      may require disassembly of the cam sprockets.
                      then it is on to removing the crank and pistons for inspection.

                      there is not but so much metal you can feed bearings until they puke.
                      Old thread, but . . . So will an oil analysis give an indication of a thrust bearing problem? My F300s were made in 10/13, and I "think" they have the old thrust bearings. Thanks.

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                      • #12
                        Originally posted by 28Regulator View Post

                        Old thread, but . . . So will an oil analysis give an indication of a thrust bearing problem? My F300s were made in 10/13, and I "think" they have the old thrust bearings. Thanks.
                        I think when they fail, they fail. It was stated on this thread earlier that the filter could be cut open to look for metal fragments. The end play of crankshaft can be measured externally. Too much and you likely have an issue. Wouldn’t bother paying for oil analysis.

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                        • #13
                          Anybody have an idea when (model year) the thrust bearing issue most likely was resolved on the F300?

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                          • #14
                            Originally posted by pstephens46 View Post
                            Anybody have an idea when (model year) the thrust bearing issue most likely was resolved on the F300?
                            well, Boscoe has told us:

                            Originally posted by boscoe99 View Post
                            The latest bearings are 6CB-11426-03-00 and 6CB-11427-03-00.
                            plugging one or the other of those numbers into boats.net
                            shows us that they were first introduced in January 2013 -
                            and continue to be used through the January 2018 listing...

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                            • #15
                              Originally posted by pstephens46 View Post
                              Anybody have an idea when (model year) the thrust bearing issue most likely was resolved on the F300?
                              According to the parts manuals, F300s made in 2014 and later seem to have the new thrust bearings. Edit: I hope that fairdeal's comment above is right about 1/13 though! I get a little confused about model year vs. when made on boats.net and simyamaha.

                              Unfortunately, mine were made in 10/13. I've got the same scalloping and a slight tear on one of the belts - similar to the OP above (belt on other engine looks fine). Just replaced it around 1100 hours, and purring like a kitten for now. I've also got numerous oil analyses for the past several years (due to fuel dilution issues) which indicate no abnormal wear metals, so I'm going to assume no thrust bearing issue for the time being.
                              Last edited by 28Regulator; 1 week ago.

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