Driveshaft and Bearing on Force 1251X9B

21BaylinerCC

Seaman Apprentice
Joined
Jun 17, 2015
Messages
48
So as if i did not have enough projects already, i found a pretty good deal on a 1989 125hp force. I decided to buy it for $250 to use as a parts motor/practice tear down motor so that i can understand how my current 1988 125hp (which i run on my boat) works. Now, my though is that i can restore it to have as a back up engine. I have the lower unit off, removed the water pump, and have just removed the gear housing cover. There was a buildup of sand and some corrosion in the driveshaft seal, and i am afraid that some may have gotten in the driveshaft bearing when i removed the gear housing cover. Is there any way to remove the driveshaft bearing without having to remove the entire driveshaft?
 

Frank Acampora

Supreme Mariner
Joined
Jan 19, 2007
Messages
12,004
NO! You must first remove the entire reverse gear and prop shaft assembly. Then you must remove the pinion gear. Now the drive shaft and bearing will pull out of the lower unit. You must have a heavy duty press to remove the bearing but installing a new one is easier. Simply heat the new bearing on top of a 100 watt incandescent bulb for about 15 minutes. Cool the drive shaft in a freezer. Using gloves quickly drop the new bearing over the drive shaft. It should slide right down to its seat. Do not damage or lose any shims. They are no longer available and they are critical to the life of the gears.

Depending upon the production model the 1989 engine may have a different drive shaft and gears. It may have the two piece drive shaft and 1.92 ratio gears while your 1988 should have the one piece drive shaft and 1.76 ratio gears.

The two piece drive shaft lower unit is certainly a better one with larger more beefy gear teeth and a bigger lower drive shaft bearing.
 
Last edited:

21BaylinerCC

Seaman Apprentice
Joined
Jun 17, 2015
Messages
48
Ok thanks! What should i look out for when removing the shaft? the shims, but what specifically. I have the manual, and it says that i will need a special puller to remove the spool propeller shaft/bearing. Is this true? i tried looking for one, but they are discontinued (as far as i know). Also, the manual mentions that i will need a gauge to adjust the shims... Is this correct, or should i be fine since i am going to use the original shims?
 

Frank Acampora

Supreme Mariner
Joined
Jan 19, 2007
Messages
12,004
Bearing tolerances are so very tight that if you replace the tapered bearing you should not need to change the shim pak. If you change the gears then you definitely need to have the gauge and multiple shims so you can correctly shim the pinion for .005 backlash. You are not going to change gears so don't even bother. It would be less expensive and way easier to simply buy a good used lower unit.

To pull the spool you need to remove the anode and the four bolts holding the spool in.. Using the two anode screw holes use some 1/4 X 20 all thread rod (big box store) and a piece of heavy steel or aluminum to fabricate a puller.

Once you pull the spool. tap down on the internal reverse gear bearing carrier. Then remove the two half rings holding it in. You can now pull the reverse gear/ prop shaft assembly. Removing the pinion is a real "witch" with a capital B. You must get in there with the correct sized socket and breaker bar and pack it in so the socket does not slip off the nut. Pad the lower unit case. THEN you must make a tool to turn the drive shaft and remove the nut. After all this you must make a wedge to drive in against the threaded shaft and force the pinion off the locking taper. Not an easy job if you don't have the correct tools and a big vise and I don't recommend it unless there are signs of definite damage.

After removing the cover and seal, clean the bearing with solvent. NOW, depending upon whether the bearing is down loaded or up loaded you press the bearing into the cup or outer race and turn it. If it does not turn silky smooth then it is damaged.

Two piece drive shaft lower units have the gear teeth meshed so that running the engine tends to push the pinion UP so for these lower units pull UP on the shaft while turning it These lower units have a large "nut" holding the outer race down in the lower unit casting. You can try to remove the outer race and examine it for signs of damage or corrosion and, of course, once you have removed the outer race you can see the rollers of the inner race.

Single piece drive shafts usually have the cover pressing down on a "squash" ring to hold the inner bearing down into the outer race. Push down on the shaft while turning.

Hmm---Someday if I get time I will make a video about disassembling a lower unit.
 
Last edited:

21BaylinerCC

Seaman Apprentice
Joined
Jun 17, 2015
Messages
48
This seems like i could do some damage disassembling all of this... I would like to replace the o rings along the prop shaft bearings. seeing as how the front o-ring looks suspect. Do i really need to remove remove the pinion gear? I am thinking of maybe just removing the spool propeller shaft bearing so that i can replace the seals. Judging by the schematics, it looks as though i need to take the pinion off if i do end up taking the driveshaft bearing off as well. Am i correct?
 

tommarvin

Ensign
Joined
Nov 22, 2015
Messages
999
Frank is a pro and has massive experience, this a very hard and risky thing to attempt, more damage than good.. Your not sure how much if any sand you may have dropped in gear case.

I would turn it over and drain out all the gear oil, if there is a way to flush it out, or suction out gear oil, blow it out, I would do that first, then add 100% marine gear lube, tested with 10% water contamination,and fill it up, and call it good.

Most boat's don't get used much per year, I would be shocked if you ever had a problem with this LU., I'm new, get more input on this approach.
 

Frank Acampora

Supreme Mariner
Joined
Jan 19, 2007
Messages
12,004
If I understand you correctly you now want to replace the O Rings on the spool. The other seal on the prop shaft is a regular garter spring seal. All three can be replaced without removing the propeller shaft OR the shaft needle bearing. You only need to pull the spool.

The outer O ring (larger one) doesn't do much. It seals the water intake from low pressure behind the propeller. It needs to be in very bad condition before it will affect water pick-up. It usually can be re-lubricated and re-used. The inner O Ring, however, is important. It seals the water out of the gearcase as do the four small O Rings under the spool bolt heads. Replace them as a matter of maintenance. Do not take the chance of re-using the old ones.

You initially said you wanted to inspect and replace the drive shaft bearing. To replace this there is no choice: You MUST remove the pinion. To inspect it only, you may be able to do so without removing the pinion IF it is a two piece drive shaft. If it is a single piece drive shaft you can do nothing without removing the pinion and drive shaft.

The one piece drive shaft has a lower needle bearing that will stay in place after you remove the shaft. If you need to replace it you must drive it down, out of the gearcase. This will very likely destroy it so don't do it unless absolutely necessary.

The two piece drive shaft has a much more massive loose roller bearing. the rollers MAY fall out into the case when you withdraw the shaft or they may decide to stay in place, held by the oil. The outer shell, however, is again pressed into the gearcase and must be carefully driven out.
 
Last edited:

21BaylinerCC

Seaman Apprentice
Joined
Jun 17, 2015
Messages
48
Yes. After the helpful info you have provided, i decided not to tackle the job as i think it is more of a risk than reward. I will try to flip the lower unit over to see if any sand falls out. Otherwise i will try to blow some compressed air in the bearing. I plan on doing a pressure test after i reassemble to make sure that there are not any leaks.
I tried to remove the spool on the propeller shaft using a harmonic balance puller and the threaded rods, but the spool did not budge at all. I bought a lower unit seal kit, so i will replace what i can while i have the LU off.
Thank you Frank and tommarvin for the advice!
 

Frank Acampora

Supreme Mariner
Joined
Jan 19, 2007
Messages
12,004
Since the outer O ring is in water and the lower unit is cast aluminum. it does tend to get a bit of corrosion. Many of these spools are very tight and need a soaking in penetrating oil and some heat to finally move. You may damage the ring itself and if you need to use a lot of heat the prop shaft seal may also be damaged.

When you do re-install the spool coat the groove and O ring with anti-seize to facilitate removal the next time. If by chance you do strip the 1/4 X 20 bolt holes you can re-tap to 5/16 X 18. 5/16 X 18 Allen head bolts will fit in the recess of the anode. Prior to stripping the bolt holes you can also drill through and tap all the way through to 1/4 X 20. There will be many more threads engaged and the likelihood of stripping is reduced. Once the anode is in place the holes will effectively be sealed anyway.. To reinstall the spool use a long piece of 5/16 threaded rod as a guide. Thread it into one of the holes in the bearing carrier and slide the spool down over it. It is very difficult to turn the spool as it enters the case so guiding it is way simpler.
 
Top