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Results 1 to 18 of 18
  1. #1

    Default 1968 Mercury Thunderbolt 650 65hp outboard problems (PLEASE HELP!)

    I have recently purchased an older boat with a 1968 mercury 65hp 650 thunderbolt with a mercontrol. I start the motor in neutral just like you would any motor, but the boat/prop move forward. If I move the mercontrol to forward, the prop/boat moves forward, but when moving it into reverse it moves it forward as well at almost the identical speed as in forward (which isn't the motors full speed potential that it should be, only aprox. 10mph). With the motor out of the water I've continuously tried to "play" with the lower unit shift lever and remount the lower unit to see if I could find neutral. No success! When turning the prop, it is not free. I make a hard click in the direction of forward. Same clicking noise happens when the lower unit is detached, with it not allowing me to move the prop in neutral unless forced. I took the impeller of and it appears in good condition. With the impeller off the prop allows me to spin it freely in both forward and reverse. I then slid the lower unit back on without the impeller, and it still stayed the same in forward with the clunking noise and not allowing me into reverse nor neutral. I wouldn't think it would have anything to do with the locking mechanism, but I could be wrong. I may have forgot some details, but I'm pretty sure that's everything I've tried thus far. Please give me advice! Anything is highly appreciated!

    -Brad

  2. #2
    Join Date
    Oct 2011
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    maplevalley WA
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    Default Re: 1968 Mercury Thunderbolt 650 65hp outboard problems (PLEASE HELP!)

    The throttle has to be in the slow position for the shift to work first off with the gearbox off can you shift it into forward and reverse. Allways turn the driveshaft clockwise when shiftin to line up the clutch dog. It can be a biotch to get it right. Pull both shift cables off of the motor and push the throttle on the motor all the way slow and shift it into neutral. Once you have the water pump back together remember only turn the driveshaft clockwise carefully put the lower unit in. It helps to pull the spark plugs so you can rotate the flywheel clockwise to line up the splines. Once you get the lower unit in and it shifts into forward and reverse by hand just turn the prop to line up the clutch dog. If it shifts good by hand the look close at the shift cables the first one to move goes to the shift lever on the motor. make sure the gearcase is in neutral and the control handle is straight up and adjust it to fit the motor. Once again have someone spin the prop as your trying to shift gears hopefully it shifts good. then return the control handle straight up and make sure the throttle lever is all the way slow and adjust the cable to fit. Then check the fast idle lever advances the timing. Then once again have someone spin the prop as you shift it into forward gear and then give it WOT the throttle butterfly should fully open. Just take your time and just remember the engine is running when you shift so you need to spin the prop when shifting with the engine off to line up the clutch dog in the gear.

  3. #3
    Join Date
    Oct 2011
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    maplevalley WA
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    Default Re: 1968 Mercury Thunderbolt 650 65hp outboard problems (PLEASE HELP!)

    http://www.marineengine.com/parts/me...1-thru-2803561
    You have the ratcheting forward gear it is not necessary to spin the prop to shift into forward but it sounded like the first issue you were having was the shift cables were backwards but not for sure. Have you changed the gear oil and was there any metal shavings or water in the old oil?

  4. #4
    Join Date
    Sep 2010
    Location
    ontario
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    Default Re: 1968 Mercury Thunderbolt 650 65hp outboard problems (PLEASE HELP!)

    No need to turn the prop on that motor to go from nuetral to forward.---If going from nuetral to reverse then you need to turn the prop.

  5. #5

    Default Re: 1968 Mercury Thunderbolt 650 65hp outboard problems (PLEASE HELP!)

    Click image for larger version. 

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    Thanks for replying to my message! I'm not extremely good with motors, but am trying and learning throughout this process. I disconected both the shifter and throtle cables. They were in the correct place on the motor, with the shift cable engaging first when moving from neutral to fwd or reverse on the mercontrol. With the cables disconected I removed the lower unit. In the first picture is the lower unit with what I believe is the spline which the shift shaft selects the gears from down in the clutch dog. I've tried "playing" with that, turning in in various position but still can't get reverse. I was able to find a neutral at one point (at least I think), but still no reverse. I would move the little spline on the lower unit and put the lower unit back up in place. My friend would manually move the shifter piece on the track (picture 3) and that's when I was able to find neutral (the prop spun free in both forward and reverse direction). Almost any other time I tried moving that spline to a different position I would just get the "clunking" noise with it only allowing me to spine the prop clockwise in a forward direction. Is reverse suppose to do the same clunking noise in the opposite direction? Am I not doing something correct, or have I just not found the right placement of the little spline piece? I've did some reading about people with bad clutch dogs..Would there be signs if my clutch dog was bad? It's became 24+hrs of frustrating learning for myself..Any advise and/or pointers I highly appreciate. I can post any pictures requested, or even a video if needed. Thanks! -Brad

  6. #6
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    ontario
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    Default Re: 1968 Mercury Thunderbolt 650 65hp outboard problems (PLEASE HELP!)

    When you assemble one of these lower units your best bet is to have the shift cable hooked up at the motor and the control in forward.----Then you put the lower unit in forward.--Then you assemble them.----------After you do this correctly you might say----" that was easy "

  7. #7

    Default Re: 1968 Mercury Thunderbolt 650 65hp outboard problems (PLEASE HELP!)

    I think I am just really dumb with this, and will need someone to walk me through it. I put the shifter cable back in place on the motor, and tried moving the spline in different positions as well as the controls from fwd to neutral before remounting the lower unit and all I keep coming up with is the forward clunking when spining the prop clockwise. Before I remount the lower unit, the shaft moves freely in both directions, however the prop only in the clunking clockwise rotation. This happens regardless of where I set the little spline in place at. In order to actually turn the spline so it's able to move freely, I have to slightly turn the prop clockwise and if I turn to too much the spline locks in place. At this point I'm really not sure what I'm doing wrong or why I can't figure this out. I have attached a youtube video of what's going on..not sure if it's normal or if something else is wrong..

  8. #8
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    ontario
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    Default Re: 1968 Mercury Thunderbolt 650 65hp outboard problems (PLEASE HELP!)

    In forward gear it will click / ratchet when you turn the prop clockwise.-----Turn the driveshaft to verify the gear you are in !

  9. #9

    Default Re: 1968 Mercury Thunderbolt 650 65hp outboard problems (PLEASE HELP!)

    I figured out that I wasn't probably turning the spline far enough..I finally found neutral, the spline actually clicked into place where I then was able to spin the drive shaft without the prop moving, and the prop actually spins free. I remounted the lower unit and the controls seem to be working properly for forward and neutral, but when attempting reverse the prop "locks up" on me, not allowing spin in reverse on the prop without a compression sound...?

  10. #10
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    Default Re: 1968 Mercury Thunderbolt 650 65hp outboard problems (PLEASE HELP!)

    Reverse is different !!----When in reverse you can not turn the prop shaft either way------It locks up both directions.-Just the way it is.

  11. #11

    Default Re: 1968 Mercury Thunderbolt 650 65hp outboard problems (PLEASE HELP!)

    Thanks so much for you time and patience with me!! So appreciated!!

  12. #12

    Default Re: 1968 Mercury Thunderbolt 650 65hp outboard problems (PLEASE HELP!)

    I have since had the boat out and all of my gears have been working just fine (fwd, neutral, rev.). I have always suspected there has been water getting into my lower unit, so I frequently have been changing the gear oil. The last time I was out I had just put fresh oil in and when I went to put it in reverse, it sounded like grinding. I instantly stopped with reverse and put it in neutral and then advanced into forward with no problems. I drove the boat for a little bit and when I got home I checked the oil and it was the worst it has ever been. Usually it may only be a little cloudy, but this time it was almost a pure white. Not sure if seals are bad or what? I am concerned also because I've seen oil come out of both of the holes shown in the picture I attached...Not sure what either hole really is for, nor am sure if that top whole is really suppose to be there?? Click image for larger version. 

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  13. #13

    Default Re: 1968 Mercury Thunderbolt 650 65hp outboard problems (PLEASE HELP!)

    I also just removed the lower unit and notice some black "coal" like particles around the exhaust tube seal.

  14. #14
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    ontario
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    Default Re: 1968 Mercury Thunderbolt 650 65hp outboard problems (PLEASE HELP!)

    Those wee holes are casting cavity drains. Prevent castings from cracking in cold weather.--------Have seen those holes plugged with sand and also with RTV by owners.--They must be kept clear.---------If water is getting in the lower unit you can / must install a seal kit.------Pressure testing is common practise to find lower unit leaks.

  15. #15
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    Default Re: 1968 Mercury Thunderbolt 650 65hp outboard problems (PLEASE HELP!)

    Your gonna want to pull the gearbox completely apart and inspect the splines on the lower shift shaft and the splines on the cam down in the gearbox. You will need a good manual that explains everything good as far as checking the gearlash once you get it back together. Be careful taking it apart as there may be some thin shims you need to put back in and are easy to damage. Lay everything out on the bench in the order you take it apart. Take your time and carefully look at everything real close, bearings, shafts, gears. Hopefully there was no permanent damage to the gears as everything in one of those oklder gearboxes can be quite expensive. What concerns me most for a complete disassembly is the shift shaft should be tight. It has a three step cam that should snap in all three gears. Forward has the least tension then neutral the reverse. The cam is pushing on the spring loaded pin that slides the clutch dog back and fourth. How much end play is there on the propshaft? when you push and pull it should be within spec very little but some. The biggest challenge can be just takeing it apart without breaking something. If you cannot pull the prop you may consider just finding a good used/rebuilt lower unit.

  16. #16
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    Default Re: 1968 Mercury Thunderbolt 650 65hp outboard problems (PLEASE HELP!)

    Ok now I see what you were doing when you are ratcheting the prop you are also takeing pressure off of the cam that is why the shift shaft is spinning free. Try takeing a pair of vice grips and grab the shift shaft and turn it it will take a little force to shift into neutral. The while spinning the prop in neutral turn the shift shaft in the same direction and it should pop into reverse. Look close at the condition of the splines on the lower shift shaft and the upper splines. It is usually the upper shift shaft splines that get stripped over time, the female end give that a close look?

  17. #17
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    Oct 2011
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    Default Re: 1968 Mercury Thunderbolt 650 65hp outboard problems (PLEASE HELP!)


  18. #18
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    Oct 2011
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    Default Re: 1968 Mercury Thunderbolt 650 65hp outboard problems (PLEASE HELP!)

    http://www.ebay.com/itm/mercury-lowe...98702c&vxp=mtr
    this is what the shift cam looks like it take a bit of pressure to push the follower pin to move the clutch dog.

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