78 Merc 85HP not shifting

[dallaschargo]

I am new to boat motor repair, i have a 78 Mercury 85 HP that the motor runs fine but the prop wont spin, any ideas what i should take a look at?<br />Dallas

 

[tashasdaddy]

Re: 78 Merc 85HP not shifting

have you checked to see is the shift cable is still connected? go to 'oldmercs.com' and order a merc. manual for your engine,

 

[Chris1956]

Re: 78 Merc 85HP not shifting

Dallas, That motor has two cables which control the throttle and forward-neutral-reverse gearshift, respectively. Remove the cowling and check the bottom cable moves (in and out)when the throttle arm on the control is moved from all the way forward, to all the way back.

 

[dallaschargo]

Re: 78 Merc 85HP not shifting

I checked the cables, they both seem to be working properly. That leads me to believe there is something inside the motor. What connects the powerhead to the geartrain? I'm gonna get a manual. Thanks for the advice.

 

[studlymandingo]

Re: 78 Merc 85HP not shifting

It could be the shift shaft, the cam or any number of things. If it turns out to be more serious, a broken shaft or stripped splines, don't give up hope. The lower units are not hard to rebuild following the instructions in a GOOD repair manual. The first one you take apart may look intimidating at first, but once you get inside, it's not too bad.<br /><br />Good luck, and keep us posted how your project turns out.

 

[dallaschargo]

Re: 78 Merc 85HP not shifting

I took the bottom end off the motor and inspected the shaft that connects the linkage to the gear train. I found a broked plastic peice not sure what it is called or what it does, i have included a pic, can you guys help?<br /><br /> http://www.public.iastate.edu/~jchargo/merc/merc4.JPG <br /> http://www.public.iastate.edu/~jchargo/merc/merc1.JPG

 

[phatmanmike]

Re: 78 Merc 85HP not shifting

yep, thats the culprit. without that, you aint shifting.<br /><br />on the mercury motors, that shaft turns from side to side telling the gear case what gear to shift into.<br /><br />that peice should be easy to aquire. any merc dealer should stock them as they fit many many years and hp of motors, and they are real cheap.

 

[Chris1956]

Re: 78 Merc 85HP not shifting

Dallas, Without that piece, you will find that the upper shift shaft (connected to the shift cable) is not connecting to the lower shift shaft. The purpose of theat piece of plastic is to force them to mate. When you get the new piece, stick it in the upper part of the motor (actually the motor's midsection) with some grease or tape or something, and then install the LU. Make sure the control handle and the LU are both in neutral or the same gear.

 

[roger3645]

Re: 78 Merc 85HP not shifting

Dallas, but some good news. That driveshaft in the photo looks real good as far as I can tell.