Taking a '91 150hp lower unit apart - help!

[HawaiianHooker]

So the bearing from the driveshaft has gone out again (last time it cost me $800) and this time I want to try and fix it myself. This causes the oils seal under the water pump to leak. I have caught it quickly, drained the oils and flushed it out so the damage should be minimal.

I do have quite a bit of experience rebuilding motorcycle transmissions so hoping that experience will help out.

I'm looking for any tips, special tools to take it apart or recommendations on where I can buy them. Any words of wisdom, used tools you may want to sell or any help would be greatly appreciated...

---HawaiianHooker

 

[Frank Acampora]

Re: Taking a '91 150hp lower unit apart - help!

Is it a Mercury midleg and lower unit? Or is it the Mercury redesigned Force lower unit. If it is Force, is it dual exhaust or single exhaust.

Each is slightly different in specifics, but if you have wrenched a bit on cycles, then you are familiar around hand tools. You will need a spanner of some sort which you could probably make yourself and you will need a torque wrench. You will also need to fabricate a puller from some all-thread rod. Whatever you do, do NOT lose or damage any shims. Some of them are no longer available and it is a real pain to try to make your own.

Basically, you need to remove the water pump and lower plate. Then you need to remove the pinion and shaft and press off the bearing. So, this means almost complete disassembly of the lower unit. Depending on design the bearing and outer race will be oriented differently, and shims will also be placed differently. Pinion nut needs to be torqued back on. Even though it is not a difficult job, buy a manual.

MERCURY wants about a couple of hundred for a bearing and shaft assembly--they do not offer the bearing by itself. The bearing itself is standard and will cost you about 50 bucks for the cup and cone at a bearing supply store. Sometimes the outer race does not have a number BUT there are only about three standard ones so when you go to the local bearing supply house they will be able to compare and give you the correct one.

 

[HawaiianHooker]

Re: Taking a '91 150hp lower unit apart - help!

Thanks for the great info Frank...

I'm quite sure this was manufactured by Force and it is the Dual exhaust. It also uses the 2 piece driveshaft.

---Mike

Is it a Mercury midleg and lower unit? Or is it the Mercury redesigned Force lower unit. If it is Force, is it dual exhaust or single exhaust.

Each is slightly different in specifics, but if you have wrenched a bit on cycles, then you are familiar around hand tools. You will need a spanner of some sort which you could probably make yourself and you will need a torque wrench. You will also need to fabricate a puller from some all-thread rod. Whatever you do, do NOT lose or damage any shims. Some of them are no longer available and it is a real pain to try to make your own.

Basically, you need to remove the water pump and lower plate. Then you need to remove the pinion and shaft and press off the bearing. So, this means almost complete disassembly of the lower unit. Depending on design the bearing and outer race will be oriented differently, and shims will also be placed differently. Pinion nut needs to be torqued back on. Even though it is not a difficult job, buy a manual.

MERCURY wants about a couple of hundred for a bearing and shaft assembly--they do not offer the bearing by itself. The bearing itself is standard and will cost you about 50 bucks for the cup and cone at a bearing supply store. Sometimes the outer race does not have a number BUT there are only about three standard ones so when you go to the local bearing supply house they will be able to compare and give you the correct one.

 

[Frank Acampora]

Re: Taking a '91 150hp lower unit apart - help!

Force dual exhaust is relatively easy to disassemble even without a manual. It will almost be self evident. BUT THE SHIMS ARE DEFINITELY NOT AVAILABLE.--I tried to get 'em myself. I don't remember the year of my dual exhaust unit but they should be similar. Most likely Mercury manufactured gears inside and the pinion tends to ride up under load. So, there is a screw gland on top of the upper bearing, the cup goes wide opening down and the shims are below the cup. The gland or ring presses the cone against the shims and locates the cone which is pressed on the shaft. This also adjusts the pinion depth of engagement with the driven gears. Be certain you maintain the proper backlash or the gears will self destruct.

After having bought one, disassembled and reassembled it, I can say that I really don't care for the design. The actual reason I bought it though, was to work on a dual exhaust lower unit. Had not done one before then---always looking to learn something new. So in that respect it was worth the 75 bucks I spent for it.

You can put the new cone on the shaft by heating it over a 100 watt bulb and cooling the shaft in a freezer. The bearing gets hot enough to slip fit on the shaft yet not hot enough to damage itself. You will need to handle it with gloves.

BTW: Mercury wants almost 300 for the 20 inch upper drive shaft and close to 400 for the 25 inch version (new). So, be careful with that too. Don't know what they command used.

Be religious in maintaining oil level as high as you can get it inside the case. The fill and vent holes are above the upper bearing BUT if you do not fill properly or if you allow oil level to get below the upper bearing: there is no groove cut into the shaft to drive or splash oil up into the bearing like on some other brand name engines. If you let the oil get low, the upper bearing will starve and spall.

Are you in Hawaii as your name implies? As an example I bought my bearing at Callahan Bearings here in Philadelphia and the set cost 47 bucks and change, so look in the yellow pages under bearings or even try on line and use the numbers on the cone.