blueband 20hp gearbox change

[Boatnut]

My mate picked up a 12ft. tinnie with a 20hp blueband wrap around cowl 15" tiller. the whole unit is in tip top condition except somehow mate went boating, first day out, without oil in tha box.:(
He got sold a gearbox from a red band, price was right, bloke said it would bolt up, Mate's happy until he puts it in reverse to back out and moves foreward an hits tha dock:eek:, puts it in foreward and backs out into tha river:confused:

Can tha shifting action be reversed in tha gearbox??

Since the gearbox is the only thing that got changed it would seem that there is a difference in tha box.

Any suggestions????? please?????

[jeff55vDSH]

I could be wrong. But I don't remember any difference between the two lower units you have. My first assumption would be that the shiftshaft is not oriented correctly. I think the service manual advises to install the lower unit onto the towerhousing while both parts are in the neutral shift position. Problem is, the lower unit has a real tendancy to pop into the forward position upon the slightest nudge. This makes it a real pickle to get the shift shaft splines oriented correctly.
Don't be forceful with the shift shaft. The end in the lower unit consists of a cam with detents. The cam will rotate in either direction, unless you go past the high point (reverse) on the cam. Then it will only rotate one direction until you get back around to the detent area (F-N-R) side of the cam. Be gentle.
Disconnect the spark plugs. Do this test: When the lower unit is in forward, you should be able to rotate the prop gently by hand in one direction only with a clicking sound when you do it.
While in reverse, the prop will only rotate maybe 1/8th turn by hand in either direction, with a solid thump stopping movement in either direction.
While in neutral, the prop will spin freely in either direction.

Hope this helps. Cheers.

[F-12]

It does sound like it was installed incorectly. MOST every time I worked on a Merc, it was advised to install while both sections are in the forward position. Since the lower unit has a forward default, it will slide together and work. If you installed the unit with the shifter in neutral, and the lower unit snapped into forward, you will get this condition. Good luck..............

[Boatnut]

Jeff and F-12, thank you for your replies, i fitted tha box and it would seem very likely to me that what you have described is what has happened. I won't get a chance to go and refit tha box until later in the week but at least now i have a good idea of what may be wrong and i'm sure i'll be able to rectify it easily, as for being gentle, i hear ya, thanks again:D:D:cool:

[bobvdinghyracer]

its most likely installed CORRECTLY ! ... i have several of these diff . years and yes i forget which is which but some went 1 way and other years went just the oppsite apparently you have ran into this problem , the box is a bolt up with exception to that problem which creates another problem which is the safety lock / throttle stop you need to either remove it and pay attention when starting / shifting or ya need the stop assy from the other engine !! / or use the guts in the other gearbox / they will interchange if the case is still good also keep the shift CAM with same box / they are just the oppsite internally

[Boatnut]

Hey Bob. I'm a bit surprised to hear your comments only because i have not heard of the different rotating boxes before BUT i appreciate your comments and thank you for them. i won't have a chance to look at it again until the weekend but when i do i will keep in mind what you've said. If it is indeed the problem then the first and best solution will be to return it to where it came from and get the right box, if that can't happen i'll have to look at the throttle stop issue, not really the safe way to do it but it is only a 20 on a tug boat.:D Changing the cam only would be possible but probably not all the internals, the old one was run without oil till it locked up, i will however pull it apart and see if the gearz and cam are salvagable but i have my doubts.:cool:Thanks for the reply