1967 merc 650 shaft swap questions

Hello,

I suppose this has been asked here a million times before but here goes. A bit of background. last year I bought two 1967 Mercury 650's. A short shaft, and a long shaft. The long shaft was an "extra" motor the PO had laying around and wanted gone from his yard. I do not know what condition it is in, nor if it even runs or not. I stupidly mounted the short shaft to my boat thinking all would be golden, but upon test running it this weekend, I discovered that I had made a major miscalculation. As my boat goes up on plane, the prop ends up about 1/2 way out o the water, and thus I lose power, traction, whatever you call it, and the engine revs. The shaft on my motor just isn't long enough! So I was wondering how huge of a job it is to swap the short shaft leg parts with the ones from the "junk" motor? Possible??

I cannot modify my boat's transom to put the motor any lower. It is a 1989 Bayliner Capri 1500. It is in pretty good shape yet, I would like to get a couple of good years out of her yet. Thoughts?

Don

Re: 1967 merc 650 shaft swap questions

Got to, http://johnsoldmercurysite.com/phpBB3/
Ask the guys there if any of them have the extension kit. Bolts on to the midsection giving you a long shaft.
Or swap the powerheads.

Re: 1967 merc 650 shaft swap questions

Thanks for the fast reply bcg, but I am left wondering why I would purchase a $200.00+ kit when the other motor already has the parts I am looking for?

Re: 1967 merc 650 shaft swap questions

When I think of an "extra" motor, I think of an engine for cannibalizing. If she will run then just swap engines. If she wont swap power heads.
Its not as easy a just swapping the lower unit, midsections are different.

Re: 1967 merc 650 shaft swap questions

Drive shaft length is the difference.it will take numerous hours to convert to long shaft.jack plate can be installed on the transom to compensate for long shaft

Re: 1967 merc 650 shaft swap questions

OK, so how difficult is it to swap the powerhead out?

Re: 1967 merc 650 shaft swap questions

8 bolts as i remember and a gasket kit.mid cawling has to come off.1 1/2 with 16 tpi flywheel puller will be helpfull

Re: 1967 merc 650 shaft swap questions

dfuehrer said:

OK, so how difficult is it to swap the powerhead out?

Click to expand...

Its not bad, Remove the top cowling, shift and throttle control arms, disconnect the fuel line from the pump or pull the connector. The trim panel below the bottom cowling hides the 8 nuts holding the powerhead to the midsection. A bit of penetrating oil will help with the nuts. The powerhead has been there many years and will be tightly bonded to the gaskets. Dont pry as aluminum like to break, I applied pressure on the water cover with my hands to break the seal. You will need a powerhead to bottom cowl and bottom cowl to midsection gaskets.
Thake a look at the link below my signature, plenty of pics on what this looks like.

Re: 1967 merc 650 shaft swap questions

Thanks bcg! I'l take a look.

Right now I am evaluating my options, trying to deciede if I even want to take on this project. Thought I was water ready. To use a pun here, it kind of takes the wind out of my sails... I may end up selling the boat and motor(s) off, and get out of the game entirely. Stay tuned.

Re: 1967 merc 650 shaft swap questions

I have decieded to go with kazek's suggestion and try a Jack Plate. After seeing just how much some of these units can be, I went with a T-H Marine Hi-Jacker Fixed Jack Plate (JP-4fA-DP). It should be here in a few days. I believe I can mount this upside down, thus lowering the mounting height of my motor. It also give me 4" of extension so the prop should be in smoother water.

After looking at the "extra" motor I have, I went this route. Although it is a long shaft, and 5" longer, it is in rough shape, And I do not know if it even runs. It does seem to have compression, as I can turn the fly wheel by hand with difficulty, and can feel each cylinder as I do. The lower unit turns at the prop shaft, but that is the extent of what I know about it. I would like to sell this motor for parts and/or repair but do not have a clue what I should ask for it. Ideas?

Don

Re: 1967 merc 650 shaft swap questions

Hang on to it for parts......I just paid 180.00 for a distributor cap that cracked and another 75 for points......Hunting Craigslist now for a backup motor.....

Re: 1967 merc 650 shaft swap questions

An update, in case anyone is interested.

I installed a jack plate, to lower my motor the 4"-5" needed to keep it from ventlating. The ant-cavitation plate is pretty much aligned with the bottom of my hull in the back. I discovered that one modification leads to another, and another, and...

I ended up having to adjust my steering so that I could get *some* turning ability out of her. I still need to figure out a way to improve this! Upon lowering and moving the entire motor down and out aprox. 4"-5" I can no longer tilt up my motor without the steering cables/bar hitting the transom. Hmmm...

I also discovered to my dismay that the skeg barely cleared and sometimes would drag the street when trailered! Not good when leaving the garage or driveway. Certainly not good a the ramp when launching! So I modified the bunks on the trailer to be an additional 4" higher. Whew! Never again will I attempt a project like this one!

New problem now. The 65 HP pushes my boat wonderfully, once it deciedes to get up on plane. I know that I still need to adjust my shift and throttle cables a bit, but I do not believe that this is why my out of the hole is so delayed. 10-30 seconds, or not at all! When up on plane the boat's speedo says I am going 30-32 MPH if I can believe that. Seems like it. Is the pitch of my prop wrong for my boat? It is the standard 15 degree pitch that came with it, I suppose. Where would I find a different pitch prop, and what pitch would U need anyway?? The motor is 1 1967 Thunderbolt 650. Not sure how many splines. I notice that many of the online stores don't even carry props for anything older than a 1972. A friend of mine suggests that a lower degree pitch, say a 13 degree woudl improve my hole shot performance. I just don't know enough about it to be certain.

Don

Re: 1967 merc 650 shaft swap questions

Modifications can be frustrating and expensive......I feel your pain.

PropCo is where I have been getting mine from. For your engine they have props from a 10" 10 pitch to a 13" 25 pitch.
There are some basic calculations that will assist you in finding the right prop but nothing will take the place of a good tachometer. With a light boat and an under pitched prop you can over rev the motor.
Mercury Outboard Boat Propellers - propco marine boat propellers

Re: 1967 merc 650 shaft swap questions

Sorry to hear bad news.not sure what to think about skew hitting the road.as for the throttle/shift cables preventing to tilt...I will try to recreate your set up and post back.initial setting on the angle of motor trim would be 2nd hole from bottom.if set incorrectly,boat will push water instead of getting on plane as you describe.operating range of your motor is 4800 to 5300 RPM at WOT.thats how prop pitch is established.different boat,weight,length and pitch will differ.if motor bogs down when getting on plane,then adjust carbs