Mark 55 won’t shift after impeller change

[John Gleason]

Hi,

New to the forum, boar ownership, and antique outboards.

I have a Mark 55 that I’m getting ready for it’s first season in a while.  The water pump impeller has been changed (took to the shop last fall because I couldn’t get the cover off), but since I put it back together the motor won’t shift gears…it seems to always be in forward (was working before the new impeller).  I took the lower unit off again and tried following the manual.  The only thing I noticed is the shift shaft cover being oriented differently than the manual.  Any advice on what I might be doing wrong?

 

Any tricks to get the lower unit back on?  It was a pain to install last time.

[Sam M.]

I am not knowledgeable about Mercury outboards, but the following should hopefully apply anyway:

When putting the lower unit back in, be sure the gearbox is in the same gear as the gear shift lever BEFORE the gearbox even approaches the rest of the motor.  Trying to do gear shifting so all the linkages line up while holding a lower unit is not easy.

Start by getting a flashlight, looking up into what used to be the darkness, and figuring out where the to aim the driveshaft.  Then lift the lower unit up with the shaft aimed in that direction.  Also, do all of this with the motor securely locked in it’s tilted up position.  Next, line up the water tubes, push the lower unit in a little more so the tubes go together, and then keep an eye on them as they will likely be interested in falling out of place.  Finally, push the lower unit in as far in as it will go, then discover there is still a gap, and it won’t go further (unless you are particularly lucky, or the motor likes you, and it will all go into place without further fuss).  What you do about this gap, is have the person you smartly asked to help you (before you started lining things up) slowly pull on the recoil starter until the splines from the powerhead line up with the splines of the lower unit’s driveshaft in a somewhat startling manner, as the lower unit you are lightly pressuring upward will race into place.  Next, it’s time to hope that the bolts that hold the lower unit on aren’t out of arm’s reach, and if they are, it’s time to hope your helper hasn’t given up on you and gone out of hearing range.

 

You say you’re new to old outboards, so here are a few more tips, not exactly related to what you’re asking for, but that I hope you’ll find helpful anyway:

When running the motor in a barrel (or even on a boat), be sure the water level is higher up than the impeller before starting the motor.  This will help prevent the water pump impeller from wearing out prematurely.

At the start of the boating season, it’s a good idea to replace (or at least check on) the gearbox oil.

While I don’t know the fuel mix ratio for this Mercury, it will quite likely require a lot more oil in the fuel for proper lubrication than newer two-stroke outboards.  The correct mix ratio is definitely something to check before running it.  The correct ratio might be 16/1 but that is only a guess, and TC-W3 rated oil is the kind to get.

Hope this helps!

2 users thanked author for this post.

John Gleason, seakaye12

[dave-bernard]

Call me  914 310 7086 Dave

2 users thanked author for this post.

John Gleason, Tubs

[John Gleason]

Hi all,

Thanks for the help; I have the lower unit installed.  During install, I put the shifter all the way in forward, set the unit in Neutral then rotated counter-clockwise (maybe 30°) to put it back in Forward so shoulders are parallel to the bolts…then installed.  Still, it doesn’t seem to shift.  What confuses me is Neutral is at one end of rotation on the shift shaft but in the middle of the gear selector… How does it go into Neutral if the shifter is all the way forward (neutral is in middle of shifter but at far end shaft rotation…how does it get to N)?  On the lower unit, is Reverse counter-clockwise at the end of rotation on the shift shaft?  Is it possible to shift into Reverse uninstalled?

Thanks,

JG

[opposedtwin]

There’s a cam inside at the front of the gearcase that must be in the correct position. It’s attached to the end of the shift shaft.  It should be noted in your manual as well. The shift shaft lock on top needs to be on the shaft in the correct position to ensure that cam is in the correct position.

Forget the gearshift lever at the box in the boat. Disconnect the cables and get it right in the motor first, THEN hook it up to the shift controls. Maybe a po put the shift blocks back into the controls backwards? You never know.

The cam is #2 in this diagram.

Honestly, I would call Dave B if you haven’t already. The guy is a guru, svengali, yoda or what have you. He’s been there and done that and remembers ALL the details.

[jeff-register]

Not to put anyone down butI have known Dave Bernard for atleast 20 years & he ALWAYS knew the proceedure when it came to Mercury motors. He knows the Mark series backwards & forwards He knows more than the manuals he has built so many of them plus a very nice guy. He helped me with many motors!

[John Gleason]

I appreciate the replies.  I did give Dave a call last week and got some advice…wasn’t able to get it resolved.  Thought the pictures on my last post might help explain my question of how the mechanism works (probably would help to process what he shared with me) than trying to explain over the phone.  New to the forum, but seems like it would be good to get as much of this knowledge documented online as possible.

The advice of decoupling the shift cable is a good suggestion and will try that in the next few days when I get a chance to work on it again.  Would appreciate explanation of where reverse is and how it is engaged on the shift shaft…it’s just not computing for me.  I found neutral and forward…just don’t get where to find reverse.  Thanks again!

 

[dave-bernard]

call me again

[Pondrocket]

John,

when installing lower unit to mid do not have boat side controls hooked up to engine.

• lower unit in proper working order
• set LU shift shaft in forward or Neutral with pliers
• install lower cam on shift shaft at roughly 45 degree angle per book do not disturb shift shaft position
• grease up and install upper reverse locking cam in mid section
• Install lower unit to mid section
• driveshaft 1st into powerhead spin flywheel to engage
• next is shift shaft this is tricky at times need to align upper shift shaft with lower in correct position might need a screwdriver or flat tool to center up then once engaged keep going up.
• last but not least install copper tube to water outlet
• then keep going don’t go all the way up need to thread on 2 bolts then the 3rd 5/16” allen set screw at rear of housing
• once all is installed shift in forward & neutral on engine lever to make sure all is working properly
• this installation can be done by 1 person that understands installation, its best for a 2 person operation to help out.

 

Toughest part is getting shift shaft set up and aligned properly. Hope this helps

 

Travis

 

 

Travis
AOMCI VP Communications
AOMCI Webmaster
webmaster@aomci.org

[John Gleason]

Thanks for the all the advice – I got it figured out today!  I was misunderstanding where F and R are to set the cam on the gear select shaft.  Once I rotated fully counter-clockwise I was able to position the cam and re-install.  Should be ready for sea trials tomorrow.

 

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