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Help please - mercury 75hp outboard

A

arekid

New member
Hi

I have a Mercury 1985 (Brown band) 75 HP outboard. It's a 2 stroke but with 4 cylinders.

The engine was starting and idling fine, but when put into gear would cut out. General consensus is this is fuel/carburettor related, any thoughts on that point welcomed.

Now, however, it won't turn over. I put a spanner on the flywheel nut and it turns counter clockwise ok (i.e. when looking down on the flywheel), but will only return to it's starting point when turned clockwise, i.e. back to the point I started and then is stuck.

I can't start the engine at the moment as a result, it simply sticks at that point.

Any thoughts/advice welcome.

NB: I've tried taking out the spark plugs, still doesn't turn. I've put WD40 into each cyliner (whilst plugs are out) and still doesn't turn?

Thanks

Arekid
 
There must be more to this story.-------But remove drain plug and check gear oil.-----Then remove lower unit to see if motor will turn.
 
flyingscott said:
What he said pull the lower unit off.
Click to expand...
Thanks Peeps.

I've only recently changed the gear oil (as you know it's not bloody cheap), so relunctly will remove the bottom section and check the engine turns without it. if so, as you inimate it's likely a gearing problem I guess?

Not sure what I'll do once it's off (I'm no mechanic that's for sure), but will have a play.

Cheers.
 
No need to drain the gear oil to work on ( remove ) the lower unit.----What did gear oil look like when you drained it ?----How much oil did you put back in the lower unit ?-----Mixing gas and oil at a 50:1 ratio ?
 
racerone said:
No need to drain the gear oil to work on ( remove ) the lower unit.----What did gear oil look like when you drained it ?----How much oil did you put back in the lower unit ?-----Mixing gas and oil at a 50:1 ratio ?
Click to expand...

Thansk Racerone

Great points you raise. I didn't notice much (very little) water in the old oil and only a few shards of metal on the magnet (which I suppose is to be expected on a motor of this age). I followed online instructions and topped up, tried my best not to get any air in the system, to the fullest using Quick Silver oil.

I've only just bought the boat the it came with ready mixed (the guy who sold it to me was dealing from the square I think) at the appropriate ratio I was informed. but won't use again now anyway so will ensure it is next fill up. On that note, would it not completely sieze up if wrong oil was used, rather than simply not turning past a point in the Clockwise direction? It doesn't seem to be seized, more of a bounce when you reach the stop point and I continue to turn the crackshaft.

Any other thoughts welcome. For instance, once I've taken off the bottom, what am I looking for?

Thanks again.
 
I am no mechanic and will defer to the ones above; you could do a few checks to give you a warm fuzzy:
Only use non-ethanol gas;
Having the shop manual is priceless - tells how to adjust the idle screws on the carbs, take apart carbs, and shows electrical specs;
Maybe make sure the shifter and trans are in neutral when you turn the flywheel - in neutral, you should be able to turn the prop in either direction with no resistance; or disconnect the shifter cable at the motor to shift it manually to the 3 positions of forward, neutral, reverse.
My '92 Merc 40 4cyl 2stroke when running turns clockwise when looking down on the flywheel;
Take a compression test on all the cylinders once you get it to turn and note;
If you have a VOM meter, take Ohm readings on the stator leads, trigger leads, coils (maybe not your problem now, but good for future);
To drop the lower unit, my Merc I/O had to be in forward - don't know if that is true for outboards, maybe the techs can say.
 
Did you fill the lower unit from the top or bottom? When a lower unit goes out you can usually turn the flywheel about a 1/4-1/2 turn either way. When the motor locks up it usually does not turn at all. So take the lower unit off and see if the motor frees up. 80w-90 marine lube is usually not that expensive.
 
What flyingscott said; first thing I learned about maintaining a lower unit - buy gear lube pump from automotive or marine store and pump/fill from bottom drain plug till lube comes out of upper vent plug; I always use Merc gear lube.
 
racerone said:
Describe----" shards of metal " -----That you found on the magnet.
Click to expand...

They were only small, more splinters than shards and not many of them. It's similar to what you sometimes see, i.e. metal filings, in engines. didn't look too serious, but could be wrong of course.

Do you know a good place to find a manual you refer to?

Thanks again!
 
Thansk RickM46 and flyingscott

Yes filled with a pump from lower fill hole until it came out the top. then left it open at the top for a few hours just in case air was in so it could find its way out.
 
Thanks RickM46

Funnily enough done most of that. New Stator has been fitted and the compression was showing good on all pistons. When I first got it two pistons weren't firing, now all 4 do so whahey I thought. Started up fine, run on the driveway (water via muffs), then put in the water and when placed into gear the engine cuts out. Then, during the starting process engine locked up (perhaps because I was trying to start too much). got home, put into gear and moved the prop around side to side and hey presto, started again.

This happened twice, now locked up and not moving past a point on the gears in clockwise direction (even when in neutral). Turns the opposite way fine (suggesting to me it's not pistons being seized up). I'll take off the bottom and see if it turns and if I can then get it going again.
 
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