1984 75hp mercury outboard help needed.

shetland536

shetland536

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25 Jan 2005
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176
Location
poole,dorset,england
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i have purchased a boat that has not been used for a few years.
i have decided to change the impeller and gearbox oil before starting it up.
i have done the work and tried reinstalling the lower leg.
i seem to have lost my gears!

in forward i should not be able to turn the prop counter clock wise. this is fine.

in neutral the prop should be free but it is the same as if in forward.

in reverse i should be able to turn the prop around 1/3 of a turn each way but again it is as if it is in forward.

i have taken the leg off again and am working with it on the bench now, i can move the lower gear mechanism in and out about 3mm and if i jiggle the prop i can turn the gear mechanism about 4 splines one way or another.

i did not check if it was working in and out of gear before removing the leg so i dont know if it is something i have done or if it was like it already.

one thing that is constant when i turn the prop clockwise is that it "clonks".

i presume i should be able to move it in and out of gear ok on the bench?

i am getting very frustrated now as it is probably something small! i hope!

can anyone give me any advise or can they recommend a mobile boat engine person near me that will not rip me off for coming to take a look.(poole area). i have just changed my car and have no towbar so i am unable to take it to someone.

thanks
 
It appears to be a simple dog clutch that slides on spines on the prop shaft to engage either forward or reverse gear, although it looks as though forward gear may be designed to free wheel.

Id say the prop shaft should be free to turn either way in neutral.
The dog clutch will tend to prevent operation of the gear selection when the engine is not running but rotation of the prop shft a little should allow the gears to engage

May be the diagrams at http://www.boats.net/parts/search/Merc/Mercury/1984/parts.html will help you figure it out.

Maybe the shift shaft is not correctly engaged with the cam (#48 in the propshaft diagram)

If no help is forth coming on this forum I suggest you ask for help on the Mercury board of the iBoats forums http://forums.iboats.com/forumdisplay.php?f=4

BTW you should be able to find an owners manual in the Download Center of the Brunswick Marine Website if you do not have one
http://download.brunswick-marine.com/download/main;jsessionid=105vjo07c1lcd?type=corp
 
Erk. You really need to leave the engine and gearbox shiftshafts untouched, then do the pump work, then reinstall the gearbox, then the splines will line up perfectly

Given where you are, I'd put the gearbox in forward on the bench. Youll feel it go in, as you turn the spline with a socket or something, and you can test you're in forward by rotating the vertical driveshaft with molegrips and rag on the spline and checking the (horizontal) propshaft turns clockwise looking up the exhaust pipe from the rear. Then put the engine end in forward, which is easy to see becuase you can see the full stroke of the shift arm (the small banana shaped crank) into the forward position. Then offer up. The splines where the shift shaft connects to the gearbox are deliberaltely very coarse, 6 splines in total iirc, so as to make sure you cannot mate them incorrectly (becuase you'd notice if you were 1/6th of a turn adrift)

BTW, if engine has not been run, while you have the gearbox off I would take the plugs out and squirt 2 stroke oil in the cylinders, and spin the engine with the plugs out first by hand and then using the starter motor, to lube everything inside

Good luck. Lovely engine
 
Last edited:
shetland536 said:
i have purchased a boat that has not been used for a few years.
i have decided to change the impeller and gearbox oil before starting it up.
i have done the work and tried reinstalling the lower leg.
i seem to have lost my gears!

in forward i should not be able to turn the prop counter clock wise. this is fine.

in neutral the prop should be free but it is the same as if in forward.

in reverse i should be able to turn the prop around 1/3 of a turn each way but again it is as if it is in forward.

i have taken the leg off again and am working with it on the bench now, i can move the lower gear mechanism in and out about 3mm and if i jiggle the prop i can turn the gear mechanism about 4 splines one way or another.

i did not check if it was working in and out of gear before removing the leg so i dont know if it is something i have done or if it was like it already.

one thing that is constant when i turn the prop clockwise is that it "clonks".

i presume i should be able to move it in and out of gear ok on the bench?

i am getting very frustrated now as it is probably something small! i hope!

can anyone give me any advise or can they recommend a mobile boat engine person near me that will not rip me off for coming to take a look.(poole area). i have just changed my car and have no towbar so i am unable to take it to someone.

thanks
Click to expand...


I dont know this engine directly, but 3 mm of travel of the gear selector doesnt seem enough. more like 15 mm on the yamaha I have stripped.

I have had the gear shift get stuck on commission, with limited travel, which is what \I think has happened here. Should definitely selectable on the bench, using hand tools.

While you have the leg off see if you can get a new seal for the in and output shafts, as these are the failure points on most outboard gearboxes.

Drain the oil from the leg, it should smell like final drive oil, ie hypoid, and not be white or paste due to water contamination.(sorry if you knew this all ready as I dont wish to instruct you in egg sucking etc)
 
dont worry about teaching me to suck eggs..any input is great i have only done 2 impellers so far, one on my 20hp yamaha and this one .
the controls were in forward when i took the leg off.
i have only tried turning the spline with my fingers, i have not tried with a socket or mole grips, i will try that later..gently.
 
ok, i had it on the bench with molegrips around the main drive shaft and a socket on the gear spline, i had a little trouble making out reverse so found the neutral position and have reinstalled it back onto the boat--with the controls in neutral.
gone through all the gears and it seems fine.
i have replaced the gearbox oil.
i have sprayed some 2 stroke oil into the plug holes and turned the outboard over without the plugs in to lube stuff up.
all ready to connect up to my fresh tank of fuel and see if it will start after being stood for so long...excited and worried.
oh the suspense has been killing me......
omg!!there is no fuel line connector at the tank end!!!
now i have to wait until tomorrow morning to pick one up.
oh the frustration...
 
shetland536 said:
ok, i had it on the bench with molegrips around the main drive shaft and a socket on the gear spline, i had a little trouble making out reverse so found the neutral position and have reinstalled it back onto the boat--with the controls in neutral.
gone through all the gears and it seems fine.
i have replaced the gearbox oil.
i have sprayed some 2 stroke oil into the plug holes and turned the outboard over without the plugs in to lube stuff up.
all ready to connect up to my fresh tank of fuel and see if it will start after being stood for so long...excited and worried.
oh the suspense has been killing me......
omg!!there is no fuel line connector at the tank end!!!
now i have to wait until tomorrow morning to pick one up.
oh the frustration...
Click to expand...

Much anticipation here too. Let us know how it goes!

You could have dried up gummy old fuel in the carbs, but if you're lucky it'll be ok and just fire up. With these motors, if they don't fire, it's gotta be fuel or spark - there is nothing else!
 
might be worth removing carb bowls to clean out & get the fuel through.

personally I would prepare a double oil strength petrol mix in an oil can, & squirt a bit through the carb butterfly.. A to aid a start, and b to oil the crank quickly, after all it last ran many years ago. It is not unusual for the reed valves to stick. not certain this modle has reed valves, but they are common on out boards.

A spin over with the plugs removed and connected and grounded will check not only the spark, distribute the oil added to the cyl, and give an oportunity to check crankcase compression.

Have fun
 
david_bagshaw said:
It is not unusual for the reed valves to stick. not certain this modle has reed valves, but they are common on out boards.
Click to expand...
Yes it has reed valves. On this partcular model they happen to be helpfully very resistant to sticking. And there are (iirc) several separate reeds in each valve unit so the chances of them all sticking, or even a significant number of them sticking, is very small fortunately
 
jfm said:
With these motors, if they don't fire, it's gotta be fuel or spark - there is nothing else!
Click to expand...

There can also be water.
Lots and lots of water.
The term "porous block" is a term I understand all too well in the context of outboard engines.
 
wee

SHES A RUNNER

FANTASTIC

fuel line connected and 5 mins of coaxing and off she went quiet and smooth.

BUT... no wee yet!
i have run her up 3 times now leaving a couple of minutes between each one and only running for no more than 5 seconds each time. very nervous!

i have no wee coming out at all. i have slid some plastic garden trimmer line up the wee hole untill it stops but no joy.

after each fire up i can hear gurgling coming from somewhere so something must be trying.(apart from me!) i am taking the gurgling as a good sign.

now. how long do i give it to come through? will it get to a certain temperature before it comes through.

i know the possible results i will get if i leave it too long. should i leave it for 10-15 seconds? it seams like a lifetime when you are watching and wishing it through.

nearly there!
 
Only a small percentage of the water comes out of the wee hole. It could just be that it's blocked.
Water should come out pretty much immediately.

I'd run it for 60 secs, then see how hot the block gets - any more than "lukewarm" isn't good.
 
Are you using muffs for the water or is it in a tub?
If you use muffs you should see the water spraying out from the prop hub.
Did you get the water feed pipe back in properly at top and bottom when you re-assembled?
 
Lakesailor said:
Are you using muffs for the water or is it in a tub?
If you use muffs you should see the water spraying out from the prop hub.
Did you get the water feed pipe back in properly at top and bottom when you re-assembled?
Click to expand...

And if its in a tub be sure the water is deep enough to cover the water pump
 
i am using muffs, the double sided feed type. water shooting out all over the place.
when i next have a go i have got a barrel i can fill so i`ll try that.
i dont know about 60 seconds! wouldnt that wreck the impellor if its not pumping?
 
shetland536 said:
i am using muffs, the double sided feed type. water shooting out all over the place.
when i next have a go i have got a barrel i can fill so i`ll try that.
i dont know about 60 seconds! wouldnt that wreck the impellor if its not pumping?
Click to expand...

If totally dry, but you used some glycerine based impellor lube when it when it, yes?
 
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