Bad lower unit ???

[Coork Johnson]

I suspect that my lower unit is bad, I was running wide open with a Mercury 150 HP when motor froze up tight. I was able to get lower unit into neutral and motor fired up.<br />Whaen I put motor back in gear it locked up again. Now I can not get unit back into nuetral to fire it up again. A friend said that a piston may be stuck and that is causing the problem, another stated that linkage may be out of adjustment. Any ideas or sugestions ? I am a novice in this area and would like to have suggestions prior to being "fresh meat" at a dealer.

 

[Dhadley]

Re: Bad lower unit ???

Just drop the lower unit and see if the motor turns over. Or simply drain the oil and see if it's got metal chips in it. Most likely it is the gearcase if the motor ran in neutral and locked up when shifted into gear and now won't shift even with the motor shut off.

 

[ODDD1]

Re: Bad lower unit ???

Well,hadley's got a handle on it.....remember the only thing in the gearcase that doesnt turn ALL the time is the prposhaft. Whenever the motor is turnin over the gears are too. Drop the gearcase an pull the lanyard switch [tether] an see if motor cranks over if it does you narrowed it down to a gearcase prob, but before you spend any money at the dealer a COMPETENT mech is gonna do a compression test for you just to make sure...sucks spendin $ on a gearcase when the powerhead is in the dumper... I simpathize with your comment about "fresh meat" but some people that work on marine motors pride themselves on treating people the way they themselves would like to be treated....your poor earlier experiences are unfortunately pretty common. good luck gettin back on the water odd1

 

[JMF]

Re: Bad lower unit ???

Your problem is in the lower unit. To check, unbolt the lower unit, 7 bolts will unbolt it. (If it's an inline, six cylinders in a row) Lower unit will pull straight down, and then you should be able to start the motor for a very short period. If motor starts, after removing lower unit, the problem is in your lower unit. (DO NOT RUN MOTOR MORE THAN 30 SECONDS!)<br />If motor will not turn over, you have a powerhead problem.<br />I hope I can help you. If you have further questions email me. I may have the parts you need to fix.<br /><br />Jeff

 

[Coork Johnson]

Re: Bad lower unit ???

JMF it is the lower unit, V 6 model. E-mail me a tj46077@sprintmail.com

 

[Coork Johnson]

Re: Bad lower unit ???

I have found a lower unit from a older Merc 150 HP. The owner says that it will work on any 150 HP motor from 1976- 1985. Another source states that units from 1983-1985 only will work. This is for a V-6 150 HP 1984 Merc Black Max, S\N 6409624, lower unit that I found S/N 5108754 part # 1579-6606. Will the lower unit from 5108754 work in motor S/N 6409624 ? <br /><br />------------------

 

[ODDD1]

Re: Bad lower unit ???

Yes, the gearcase will fit......if they both are the same shaft length. [20 or 25 inches] If the case yer buyin is old enuf it might be more difficult to shift.[non E-Z shift] I dont remember when they changed from one to the other.....

 

[Coork Johnson]

Re: Bad lower unit ???

Finally picked up a lower unit today. Any special procedures I need to perform other then having motor in forward gear and greasing drive shaft splines ? Do I need to use sealant between lower unit and drive shaft housing ? One friend say to use silicone between the units another said not to use it. Another said to seal unit with silicone on exhaust divider plate ( whatever that is ). I am a production factory machinist and have decent skills but without direction I am lost. The local bookstore is out of manuals for my model year and the striper season opens Tuesday and I gotta go.

 

[ODDD1]

Re: Bad lower unit ???

Ya, johnson, special things to do fer gearcase install.....the exhausst divider plate yer buddy is talkin about is right behind the water pump/driveshaft. ia a aluminum colored piece that seals exhaust gasses away from water pump.....put a 1/8" bead of silicone along the top edge of it...this aint critical... lot of moyors running around without it....the big deal on case install is the little splined shift shaft when lookin down at it rotates clockwise for FWD gear an CCW for reverse...[only about an eighth turn either way from neutral to either gear. Get both case an boat in FWD and slide case up an in ...first water tube has to go in....then while pushin up rotate propshaft to turn driveshaft an line up splines on driveshaft....keep holdin it up..line up shift shaft, you might have to turn the shaft slightly with a needle nose to line up splines.. when right case should slide up to within 1/8" NO MORE! if you have a big gap DONT try to winch it on with the nuts...you'll buy another case! You might have to try more than once...i've done thosands over the last 20 years and i still miss once in a while. good luck

 

[ODDD1]

Re: Bad lower unit ???

Ya, johnson, special things to do fer gearcase install.....the exhausst divider plate yer buddy is talkin about is right behind the water pump/driveshaft. ia a aluminum colored piece that seals exhaust gasses away from water pump.....put a 1/8" bead of silicone along the top edge of it...this aint critical... lot of moyors running around without it....the big deal on case install is the little splined shift shaft when lookin down at it rotates clockwise for FWD gear an CCW for reverse...[only about an eighth turn either way from neutral to either gear. Get both case an boat in FWD and slide case up an in ...first water tube has to go in....then while pushin up rotate propshaft to turn driveshaft an line up splines on driveshaft....keep holdin it up..line up shift shaft, you might have to turn the shaft slightly with a needle nose to line up splines.. when right case should slide up to within 1/8" NO MORE! if you have a big gap DONT try to winch it on with the nuts...you'll buy another case! You might have to try more than once...i've done thosands over the last 20 years and i still miss once in a while. before you put all the hardware on check an see if you got F-N-R good luck

 

[Coork Johnson]

Re: Bad lower unit ???

Thanks,ODD1 for all of the help. Installed unit today and went out on the Tar river. Unit worked perfectly, only problem was extremely fine metal shaving sticking to fill screw, is this to be expected on old lower unit, or did I purchase a time bomb ? Unit was only $ 300.00 so I did not make a huge investment. I paln to go out on the Roanoke River on Saturday for the Striped Bass Run.

 

[savage]

Re: Bad lower unit ???

"Fine shavings" are normal. The lower plug is magnetised for this very reason, To collect small amounts of steel. The steel is kept out of the gears,bearings and seals,then removed from the unit whenever a gear lube change is done. I would run it awhile longer, then change lube again and this time check it for water contamination. If all is well,I would say you made a good purchase.