2001 Yamaha OX66 250hp - Rattling noise

GettinHammeredGettinHammered Posts: 53 Deckhand
I bought my first boat a few months ago, a restored 1981 25ft Sea Vee with a bracketed 2001 Yamaha OX66 250hp. 650 hours on the motor to date. Got most of the minor issues fixed up, new VHF, bilge pump, fuel gauges, etc. Had my mechanic come out, did a 100 hour service the motor, and everything is checking out with no issues, compression 115 on all cylinders. However, while running the boat in the water there is a "rattling" sound around the 3200-3500 rpm range, and just that rpm range give or take 100 rpms. The boat runs strong, doesn't loose any power or bog down. My mechanic went through the motor looking for any loose bolts, possible adjustments, etc. Can't seem to find the problem. Any thoughts or suggestions?

Also, I was wondering if anyone had a spec sheets on this motor? LX250TXRZ. Searched the internet, can't seem to find any specification info on this motor.

Could this be a timing issue? If so, what degree if timing is normal for these engines? How can the timing be adjusted or how would of it been thrown off if it can't be adjusted? I read that on some of the other Yamaha motors the timing was not adjustable...

Thanks in advance for your help!

Replies

  • CaptTaterCaptTater Posts: 20,096 AG
    What do you mean by "went through"? Did he look for a lose piston? If you put a pencil in each spark plug hole and rotate the flywheel back and forth each piston should move immediately. If one does not it needs to be torn down. Fix it before it breaks and gets more expensive. A compression check might show it also.


    Another common place is a bushing below the block where the drive shaft goes down.. If that's the case don't worry about it.
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  • GettinHammeredGettinHammered Posts: 53 Deckhand
    CaptTater wrote: »
    What do you mean by "went through"? Did he look for a lose piston? If you put a pencil in each spark plug hole and rotate the flywheel back and forth each piston should move immediately. If one does not it needs to be torn down. Fix it before it breaks and gets more expensive. A compression check might show it also.


    Another common place is a bushing below the block where the drive shaft goes down.. If that's the case don't worry about it.

    The mechanic looked over everything he could think of except for breaking down the motor and rebuilding it. Compression checked out fine (did that before I bought the boat), timing and cylinder #1 checking TDC was on point. Is the bushing below the block where the drive shaft go down something that is fairly easily accessible or do you have a tear down the motor to get to it?
  • Fish HaidFish Haid Posts: 8,050 Admiral
    Would you describe it as a buzzing noise perhaps?

    Mine did that and it drove me nuts for over a year. Turned out to be the bezel just under the lower cowl pan was loose.
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  • Fish HaidFish Haid Posts: 8,050 Admiral
    Have someone put there hand on it while running and see if it stops. Be careful not to fall out and get chopped-up.
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