Merc 90 no drive to prop.

[smithy900]

Hi all, I’m new to outboard motors, I have just acquired a mercury 90, I have ordered a manual for the engine but the problem is it has no drive to the prop, the motor runs fine ( did not run it for long incase I damaged something more) I bought the outboard knowing this, I am a motor cycle mechanic.
From your experience and at a guess, what things could be causing the lack of drive to the prop, I am not going to strip it down until I have the manual. I did not pay a lot for it and it came with a boat!
Any information would be well appreciated.
Paul (in the not so sunny uk)

 

[Boatin Bob]

Re: Merc 90 no drive to prop.

When you ran it did any water come out the peehole, was it in the water or did you attach muffs to it? Could be anything from a broken shaft or gear. Does the prop not engage at all or does it just slip? What year is it?

 

[smithy900]

Re: Merc 90 no drive to prop.

When you ran it did any water come out the peehole, was it in the water or did you attach muffs to it? Could be anything from a broken shaft or gear. Does the prop not engage at all or does it just slip? What year is it?

Hi Baotin bob
ran it with the muffs only for about 20 seconds,
the prop does not engage.
I don't know the year as yet, it is 6cylinder.
Do you know of any problems with the drive on this motor? Just fishing round at the moment.
thanx

 

[Motor Boater Bill]

Re: Merc 90 no drive to prop.

With the motor off, you should be able to work the shifter and see if the linkage is working properly. You should be able to follow the linkage visually for this purpose, up to the point where it connects to the vertical shaft that runs down to the lower unit. Turn the prop by hand as you shift it (the manuals say the motor has to be running to shift, and on some motors the shift rod can be damaged by trying to shift without the LU parts in motion. However, you can accomplish the same thing for diagnositic purposes by just turning the prop while shifting. This lets the shift dog engage). Usually forward will engage without the prop turning but not reverse. Most motors, not running, in forward gear, the prop will turn one way with a ratcheting sound, and not turn the other way. In neutral will turn both ways. In reverse, will not turn either way (there will be a little slop, then it stops.

How long has it been since the motor was run? Have you drained the LU oil? Capture it and inspect for water and metal.

 

[tashasdaddy]

Re: Merc 90 no drive to prop.

bill gave you very good points, you can use you foot to turn the prop while shifting at the engine. post serial # of the steering pipe below the front of the engine.

 

[smithy900]

Re: Merc 90 no drive to prop.

With the motor off, you should be able to work the shifter and see if the linkage is working properly. You should be able to follow the linkage visually for this purpose, up to the point where it connects to the vertical shaft that runs down to the lower unit. Turn the prop by hand as you shift it (the manuals say the motor has to be running to shift, and on some motors the shift rod can be damaged by trying to shift without the LU parts in motion. However, you can accomplish the same thing for diagnositic purposes by just turning the prop while shifting. This lets the shift dog engage). Usually forward will engage without the prop turning but not reverse. Most motors, not running, in forward gear, the prop will turn one way with a ratcheting sound, and not turn the other way. In neutral will turn both ways. In reverse, will not turn either way (there will be a little slop, then it stops.

How long has it been since the motor was run? Have you drained the LU oil? Capture it and inspect for water and metal.

Thank you, I will try this tommorow, i notice that tha prop will not turn clockwise (looking from the back) but turnes the other way with that ratcheting sound you talk about, by the way i have found out that it is a 1979 motor(inline 6)

 

[smithy900]

Re: Merc 90 no drive to prop.

Hi all again,
I have just taken off my gearbox( I can’t strip it down yet it seems like I need a special tool to get the gears out of the end, looking to make one)
The splines on the drive shaft are in good condition and as far as I can tell the crank shaft splines seem ok as well.
How much resistance should there be on the selector shaft to change the gears?
I can turn it about half a turn by hand, there is no change in the gears at this point, I then have to use a pliers ( being careful not to damage the selector splines) about a quarter of a turn gets what seems to be neutral and then another quarter turn what seems to be reverse, is this normal? During changing gears I am turning the driveshaft
Oh by the way the gearbox had water in it, is it a lost case??????:%.

 

[tashasdaddy]

Re: Merc 90 no drive to prop.

the neutral and reverse are correct., wish you had check for spun prop before pulling lower unit. well while it off replace the seals. you may have nothing wrong, other than seals. because a spun prop can act like no drive in forward. the inner and outter hubs are bound buy a bib rubber bushing when it becomes damage the inner turns and the outer does not or not as fast. this could be why the previous owner said that.

 

[smithy900]

Re: Merc 90 no drive to prop.

[quote time1153255694= usertashasdaddy= uid67942= fid29= tid= rid7= the neutral and reverse are correct., wish you had check for spun prop before pulling lower unit. well while it off replace the seals. you may have nothing wrong, other than seals. because a spun prop can act like no drive in forward. the inner and outter hubs are bound buy a bib rubber bushing when it becomes damage the inner turns and the outer does not or not as fast. this could be why the previous owner said that.[/quote]

thank you very much

 

[Motor Boater Bill]

Re: Merc 90 no drive to prop.

I agree, don't write off your LU based on the water in it. Two options:

1. Pressure test it with air, put it in a bucket and see where it bubbles, and replace seals as needed. May or may not require teardown. Then see how it does with a good prop.

2. Tear it down, inspect the innerds, repair as needed and reseal.

I'd lean toward #1 if slipping is the only issue and the LU feels good when you turn it by hand, shifts properly, etc. Resistance on the shift shaft is normal. If slipping was the only symptom, and the LU feels good, your problem is likely the prop, not the LU. Your LU won't slip--or not without making obvious ugly grinding sounds!

 

[smithy900]

Re: Merc 90 no drive to prop.

I agree, don't write off your LU based on the water in it. Two options:

1. Pressure test it with air, put it in a bucket and see where it bubbles, and replace seals as needed. May or may not require teardown. Then see how it does with a good prop.

2. Tear it down, inspect the innerds, repair as needed and reseal.

I'd lean toward #1 if slipping is the only issue and the LU feels good when you turn it by hand, shifts properly, etc. Resistance on the shift shaft is normal. If slipping was the only symptom, and the LU feels good, your problem is likely the prop, not the LU. Your LU won't slip--or not without making obvious ugly grinding sounds!

Thank you Bill, how much end float on the prop shaft would you expect?