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  • Question about lower unit bolt.

    I have an F40LA and had an issue with the long bolt under the trim anode. It's a M8 x 65mm and my service manual states torque to 30 lb ft. This seems high but I tried it. The bolt snapped and I used a multi spline extractor and left hand drill bit to remove. I think the service manual is wrong and it should be 30 nm instead of lb. ft. I used Loctite 572 as per the manual and just torqued it to 20 lb. ft. based on a 30 nm spec? any thoughts since the M10 bolts call for 30lb ft. and this seems like a high torque spec. for an M8 x65mm bolt? Thanks.

  • #2
    Good and snug with NO loctite is fine.

    20 lbs is fine, It's not going anywhere.

    .
    Scott
    1997 Angler 204, Center Console powered by a 2006 Yamaha F150TXR

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    • #3
      Yeah, just do it to "feel". I've never put a torque wrench on things like this. I know that sometimes bolts like this come with loctite (low strength like the 572) on them, but I've never purposefully put it on anode bolts. Granted the chance is slight, but I don't want to chance interrupting the electrical connection.
      2000 Yamaha OX66 250HP SX250TXRY 61AX103847T
      1982 Grady Weekender/Offshore (removed stern drive & modded to be an OB)

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      • #4
        I hardly ever use a TW. 45 years of wrenching and my wrist is calibrated just about right. Head bolts? Sure. Most other stuff, nah. How accurate is your TW? As a **** I was working on a buddy's old Porsche. I was installing the half shafts using the TW he set up for me. SNAP.

        Turns out the wrench was way off. I can't imagine why a lower unit bolt needs to be that closely monitored. Sure, they need to publish something but your commonsenseometer ought to compensate if you don't use one.

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        • #5
          Absolutely, to the above. I like the "commonsenseometer" And, yes, TW's should be calibrated - never assume they are correct when you first buy them.
          2000 Yamaha OX66 250HP SX250TXRY 61AX103847T
          1982 Grady Weekender/Offshore (removed stern drive & modded to be an OB)

          Comment


          • #6
            Studies have been done and show time and time again that an experienced mechanic can come no where close to properly torquing a fastener. More than likely it will be over tightened.

            Use of a calibrated torque wrench on air craft is mandated. So much so that the wrench has to be recertified each year. Fail to use one, or fail to use a calibrated one, and you can lose your job.

            Is this a manly thing? Like not getting vaccinated?

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            • #7
              Originally posted by boscoe99 View Post
              Is this a manly thing? Like not getting vaccinated?
              No, not at all. I think 'yer stretching a little with that generalization

              I do use a torque wrench on critical things - like mentioned above, heads and covers... aluminum wheels... etc. I also calibrate my wrench.

              There's absolutely nothing wrong with someone using a torque wrench on that lower unit bolt - but to do it correctly, in addition to a calibrated wrench (which maybe Byron has), the hole and threads should at least be cleaned. I think the only point was that on bolts like that, you can make life easier by doing it by feel/experience.
              2000 Yamaha OX66 250HP SX250TXRY 61AX103847T
              1982 Grady Weekender/Offshore (removed stern drive & modded to be an OB)

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              • #8
                I was referring to those that say they never have and never will need to use a torque wrench. They can go by "feel".

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                • #9
                  Originally posted by boscoe99 View Post
                  I was referring to those that say they never have and never will need to use a torque wrench. They can go by "feel".
                  Gotcha!
                  2000 Yamaha OX66 250HP SX250TXRY 61AX103847T
                  1982 Grady Weekender/Offshore (removed stern drive & modded to be an OB)

                  Comment


                  • #10
                    It's seldom that important to get it right. If your job or regulation calls for it, sure. If you're sucking down frosty pops while hanging a LU, I'd skip it. Never had a bolt fall out that I put in a little too tight.

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                    • #11
                      Originally posted by DennisG01 View Post

                      I do use a torque wrench on critical things - like mentioned above, heads and covers... aluminum wheels... etc. I also calibrate my wrench.
                      how do your calibrate the wrench?
                      maybe just check to see if it is in spec or do you adjust it somehow?
                      Last edited by 99yam40; 2 weeks ago.

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                      • #12
                        Hey guys. Thanks for the responses. It is greatly appreciated.

                        I use two digital Snap On ATECH torque wrenches(one that ranges 5-100 lb. ft. and the micro torque 1-20 lb. ft. model).

                        They have the angle feature that I have no need for with this motor. My Yamaha 240 jet boat is a different story. I do clean the male and female threads. I use a nylon bore brush sized to 10mm and 8mm for the female threads. The bolts are sprayed down with brake cleaner and scrubbed with a wire brush. Then they are blown down with air to dry. I then use a Thread Wizard tool and run them through via impact wrench (just spins against a wire wheel with pre-set holes to 10mm and 8mm).

                        Then I spray brake cleaner on the nylon bore brushes and run them through the female threads. Then compressed air is blown at an angle (45 degrees) into the mating threads to dry. I use a 10mm and 8mm Yamaha factory bolt that I cut flutes into and then run them through the female threads to confirm the threads are clean and dry. Then Loctite 572 via a circular bead after the 3rd thread and hand tighten in. I then snug them with 1/4" ratchet. Then I torque with my ATECH wrenches to 1/2 torque in the first stage and full spec. via the second stage (I use a star pattern for the M10 bolts). I have the RTD48 thread chaser set but just use the cut factory bolts....they work better for some reason. My torque wrenches are calibrated every 5000 cycles (they have a built in counter).

                        This is why I was surprised when that bolt snapped. The service manual is not correct and the motor is a 2019 model. The manual is specific for my motor and purchased through Yamaha. Older versions called for 13 lb. ft. for the long bolt under the trim anode. This generation calls for 30 lb. ft.?? Maybe I had a defective/stretched bolt?? Not following the manual anymore and just tightening snug. Thanks.
                        Last edited by byron.akhavi@gmail.com; 2 weeks ago.

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                        • #13
                          So, yes, you are obviously doing a proper torque procedure!

                          What type of engineer are you, Byron? Doing all those gyrations for a simple bolt, you must do some type of engineering work for a living?
                          2000 Yamaha OX66 250HP SX250TXRY 61AX103847T
                          1982 Grady Weekender/Offshore (removed stern drive & modded to be an OB)

                          Comment


                          • #14
                            Originally posted by 99yam40 View Post

                            how do your calibrate the wrench?
                            maybe just check to see if it is in spec or do you adjust it somehow?
                            My torque wrench is a 1/2" - which makes things a little easier since we're talking big numbers and a few pounds one way or the other has no real impact on boat/car stuff. I bought that one primarily for wheel studs on aluminum wheels. But, yes, I can calibrate it - there is an adjusting screw in the handle. I'm a pretty simple guy so I do a simple process using a handheld scale - it's one of those things that you use to weigh your luggage ( verified it is accurate using weights). I have to go back and review the procedure each time I do this, but essentially I put the square drive in the vise, attach the scale 12" away and set the wrench to the middle of the scale. Then I adjust the wrench till things match up - then I do the same thing near both the uppper range and lower range.

                            Now, luckily, I work at a place where there are some "real" mechanics with Snap-On stuff that get them professionally calibrated on a regular basis. I've checked my process by comparing to theirs and I'm pretty darn close.

                            If need to do smaller, more accurate torquing... I just borrow there 3/8" or 1/4" wrench...

                            FYI, for anyone kinda "new" to using a torque wrench... never store it "torqued down"... always bring it back to zero.
                            2000 Yamaha OX66 250HP SX250TXRY 61AX103847T
                            1982 Grady Weekender/Offshore (removed stern drive & modded to be an OB)

                            Comment


                            • #15
                              interesting.
                              I have 3
                              2 are beam type 1/2" and I never saw a way to adjust those
                              1 is a click type 3/8" that only goes up to 200inch/lbs I just looked at it and I do not see where it can b adjusted. But the paper work says it can be sent off and adjusted/calabraded

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