Lower unit needle bearings

[Matthew A.]

A quick question for those of you who might know. Regarding, whether any of the needle bearings located in the lower unit have two piece housings. Lower unit is from a single exhaust, 85 hp. 88' Force "B" series short shaft.

 

[Frank Acampora]

Re: Lower unit needle bearings

Inside the gearcase, pressed into the casting is a caged needle bearing that the lower end of the drive shaft rides on. This is a one piece needle bearing and is difficult to remove. The case must be heated and in all probability, the bearing race will be deformed by removal, requiring replacement. It is a standard bearing that can be purchased from any bearing supply house.

The reverse gear hub also rides in a caged needle bearing and against a thrust bearing. It (needle bearing) is one piece and is pressed into the thick aluminum disc called the bearing cage. Thrust bearing rides against the back face of the gear and a (set-in) steel washer in the bearing cage face. I have never had the need to replace either one, but I'll bet they are also standard bearings. The reverse gear, thrust bearing, caged needle bearing, and bearing cage are only sold as an assembly by the manufacturer. Therefore, if all else is good it would pay to see if the bearing is available at a bearing supply house. Do not lose the steel washer! In addition to providing a riding face for the thrust bearing, it also properly locates the reverse gear with respect to the pinion. Replacing it with an improperly sized one will cause gear failure due to mismesh. That's why the factory sells those parts as a complete assembly.

Lastly, there is a caged needle bearing that the prop shaft rides in, inside the spool. It is also a one piece, pressed in bearing, just behind the seal. Again, I'll bet standard. Removal of this bearing will probably require replacement of the prop shaft seal.

 

[Matthew A.]

Re: Lower unit needle bearings

I am way ahead of you Frank. I already have the lower unit completely disassembled. Including removal of the tappered bearing from the forward gear assembly. I am now in search of replacing that particular bearing and it's race. Along with the drive shaft's tappered roller b. also. I figured since I was replacing those bearings I might as well replace them all. Inorder to get a quote from a local bearing supplier to replace all 5 sets of bearings, they wanted to know if the needles bearings had split bearing housings or is they are one piece housings. Although, I have a gut feeling that the needle bearings probably are not in need of replacement. I say that because of the overall condition of the foward gear bearing. The rollers are worn and the bearing races have chatter marks. Just it's overall feel is rough when spinning the bearing against it's inner race by hand. I am fairly certain that the bearing in the lower unit are all ISO bearings. All are manufactured by who else other then Timken.
As far as getting the two prop shaft needle bearings out of their perspective bearing carriers, looks to be a good reason why I am hoping they don't need replacement. Plus, installing them without damaging them is probably just as tricky.
Since I have your attention Frank...any chance you might have an extra gear housing cover in good condition laying around that you might want to part with. The water pump gasket surface that seals around the drive shaft opening is so badly corroded that it allows saltwater to get past the gasket where it sits untouched by rinsing with fresh water and does the shaft seal no good.

 

[Frank Acampora]

Re: Lower unit needle bearings

Nah! Nah!, Nah! Those things are expensive. The ones I have are already spoken for.

I did rebuild the webs in a corroded one with JB but I have not yet tried it to see if the repair will hold. Should though--there's no mechanical stress on it just the compression of the gasket and screws.

Be careful with the forward gear. Use a mike or calipers and measure the distance from the rear face of the gear to the inside bearing race (outside surface--surface furthest forward in the gearcase) BEFORE you remove it from the gear. Be sure the new one has the same dimension to within 1 or 2 thousandths when installed. Some of the gears have a shim behind the bearing; most do not. This dimension locates the forward gear for proper mesh with the pinion.

 

[Matthew A.]

Re: Lower unit needle bearings

Uh...Oh oh...Hmmm, Seloc never mentions taking that measurement before removing the bearing from the gear. My particular gear/bearing combo came with three shims between them. two @ .013" and one @ .011". However, all three were slightly damaged removing the bearing off the gear. Hopefully, I can add or subtract any differences in dimensions between old and new bearing and carry them over to figure out what shims if any will be needed. If not, I guess I'm screwed.
Considering how tight the tolerences are between the bearings I.D. and the the O.D. of the gear, which made seperating the two a bit difficult, I am sure it would be wise for me to install the new bearing by placing it in a tank of heated oil first. Had I not visited the Timken website, in my ignorance, inorder to get the bearing on, I probably would of tried heating it with a propane torch. I wasn't aware that temps higher then 200 degrees F. will alter the hardness and temper of the metal.
Thanks for the tip on using J.B. for the gear housing. For some reason, the idea totally escaped me. ?! lol.
Another thought concerning the gap between gear and bearing. Isn't that gap particular to each lower unit? I ask because new forward bearing/gear sets come with the bearing installed correct?

 

[Frank Acampora]

Re: Lower unit needle bearings

If it's any consolation, Clymers doesn't mention it either. You are expected to buy a whole forward gear/bearing assembly. Don't go crazy with hot oil. Just place the inner race of the bearing on top of a 100 watt light bulb for about 15 minutes--gets nice and hot and slips on slicker 'n snot. (Hot enough that you will need gloves). If you want to ensure quick fitting, place the gear in your freezer until ready. The race is what is called a light interference fit on the hub. Its inside diameter will be about .0001 to .0005 (that's one ten thousandth of an inch) smaller than the hub outside diameter. That is why it is so difficult to get off

I suspect that the shims are to standardize the assembled bearing/gear combo--Because If you really look into it, the only adjustment on the pinion is depth of engagement. Thus, the tolerance on the placement of forward and reverse gears must be standardized and the tolerance of the machining of the gearcase must be controlled very carefully. Remember: This is mass production. They are not going to check each bearing/gear for fit into each gearcase. Everything must be standarized so the worker or machine picks-up one gear and stuffs it into one gearcase. Period! Remarkable piece of work! That's one reason why new lower units are so expensive: They are a lot more complex than they look. I have successfully re-used the shims on the forward gear of a two piece lower unit that needed a new forward bearing. But to date I have not needed to do it to a one piece lower.

Bearings are routinely held to .0000 tolerances so you probably will be ok if you re-use the existing shim pak. However, if they are slightly bent or damaged, remove any burrs and press the whole assembly together with a "C" clamp while hot to fully seat them. Prepare beforehand: You must work quickly before everything stabilizes to the same temperature--only a matter of seconds.

 

[Matthew A.]

Re: Lower unit needle bearings

Thank you again for the help Frank. I can't begin to express how much I appreciate it.
Considering the amount of in and out play the prop shaft had prior to my dissassembling the lower unit, I am uncertain whether or not this play could have developed from wear of the forward gear bearing alone. I am guessing, but I would have to say the in and out play approached .050" to .060". Side to side play at the threaded end of the prop shaft about the same.

Regarding drive shaft play, is there a trick to figuring out proper drive shaft shimming other then having to buy the special tool listed for making such measurements? The tool consists of one half of the middle needle bearing carrier and some sort of plug that fits snug into center with an area for slipping in a feeler gauge between the plug and the bottom of the drive shaft.
Also, another question. This one regarding the radial bearing. Is the radial bearing only used while the gear box is in reverse gear?

 

[Frank Acampora]

Re: Lower unit needle bearings

Because these are bevel gears: Anytime the engine is running, the pinion will want to push apart the driven gears. And, anytime the engine is running, because of the curve of the teeth, the pinion will want to pull down into the case further. Thus: there is always a thrust load on both the forward bearing and the rear thrust bearing, and there is always a lateral load on the bearings also. The greater the load on the prop, (that is: the more horsepower you are using) the greater these forces will be.

If you are real good, you can use indicator dye on the drive face of the pinion teeth and adjust shims to match the wear pattern on the driven gear teeth. The tool is not an absolute necessity but it sure makes lfe easier.

Again, if you are real good, while the gears are out of the case, mesh them by hand. You will note that at various depths of engagement they are noisy and rough. At one point they will be smooth and noiseless. This is the sweet spot you are looking to hit inside the case by shimming the pinion. If you carefully note and mark this sweet spot, you can closely approximate it inside the case without using the tool. An old Chrysler and Force mechanic told me that the lower units are set up "loose" and he never used the tool. For myself, I do not use the tool. Rebuildng for others, I would use the tool so I could say for certain that the gears are set to factory specs. That way, if anything happens, It could not be attributed to shoddy workmanship.

 

[Matthew A.]

Re: Lower unit needle bearings

Concerning the amount of side to side play that the prop shaft has when I slide the rear bearing carrier w/needle bearing onto the shaft there is some axial play of the needle bearing while on the shaft. There is also a bit of axial play of the forward gear when the forward gear is slid onto the prop shaft. I attribute the play of the forward gear to the tolerance of the copper sleeve bearing and that of the prop shaft. The copper sleeve bearing does show a bit of wear. I am wondering does this axial play in the prop shaft reveal that either or both needle bearing and/or copper sleeve bearing need replacement?
Or, will the side to side play of the prop shaft be somewhat limited once the in and out play of the prop shaft has been correctly shimmed to within the .010" tolerance recommended for end to end play of the prop shaft? That is... assuming that once the forward roller bearing and/or along with the forward gear thrust washer begins to wear, the resulting end to end play allows room for axial play to develope?

 

[Frank Acampora]

Re: Lower unit needle bearings

The forward gear bushing should have no wear. The only time it actually turns on the shaft is when the engine is in neutral or reverse, so loads on it are relatively small (that's why they use a cheaper sintered bronze bushing instead of a needle bearing). In forward, the dog clutch, shaft, and forward gear turn as an assembly. Same for the forward gear shim (the hardened washer that sits inside the dogs). This should never show signs of wear.

Incidentally, that's why the reverse gear has so much clearance from the prop shaft and rides in its own bearings--this radically reduces the drag in forward since the reverse gear is turning in the opposite direction and just as fast as the prop shaft. Remember: Both gears are engaged with the pinion and turn at the same speed in opposite directions at all times.

If you have a lot of end play ( more than .010 in and out) on the prop shaft, of course, the front tapered roller will not be seated and there will be more axial play than expected. Compound that with a worn bushing and the play increases. And don't forget, the forward bearing is a tapered bearing. Wear on it will show up as excessive end play AND radial play.

I would expect very little play at the rear needle bearing itself since the shaft and bearing are sized for close running fit. However, there is enough clearance so that the shaft can rock a little in the bearing. Since the rear of the shaft is about as far away from the bearing as the front bearing is, it will show the slop in the front assembly even if the rear bearing is good.

If the bearing itself shows signs of wear, since the prop shaft is the inner running surface, I would also expect it to show signs of wear. It can be repaired, but the cost is more than buying a used one so replacement is the only option. If the prop shaft is not worn with a definite groove where the needles run, it is not worn period. This is not the kind of thing that is a maybe or a possible. It will either be worn or not, and you will not need tools to measure it.

 

[Matthew A.]

Re: Lower unit needle bearings

The only signs of wear on the prop shaft, other then the rear seal surface, are those of chatter marks where the prop shaft spins on the rear needle bearing. However, the surface of the prop shaft, other then showing chatter marks, is smooth.
Concerning the in and out play of the prop shaft and the factory recommended tolerance of .010", Seloc shows how to go about making this measurement, but not how one would make adjustments to it if it is out of tolerance. Would this adjustment be made via shimming the tapperend roller bearing and the forward gear? Or, via different thickness's of the forward gear thrust washer?

 

[Frank Acampora]

Re: Lower unit needle bearings

You don't re-shim the gear. That changes its relation to the pinion. you start with the .054 thrust (washer) shim inside the dogs and increase thickness to get the proper end play. They are sold in various thicknesses up to (I think) .07 something. You only use one shim --not multiples. If you need more thickness than what is available as a single shim, then something else is wrong and you need to investigate.

The old Chrysler two piece lower unit had both forward and reverse gears thrust shimmed. The Force only has the forward gear thrust shimmed. However, it is possible to insert a thrust washer into the reverse gear. This is not factory though and I would only do it if there was no other alternative.

For example: I broke a prop shaft and the break was at the splines on the drive dog clutch. so, it was able to continue running. However, the rear flange on the shaft (which bears on the reverse gear in reverse operation) was thrust hard against the rear gear and wore the surface. to salvage the gear, I refinished the thrust surface but now needed a spacer to correct excessive end play.

 

[Matthew A.]

Re: Lower unit needle bearings

I suspect that the shims are to standardize the assembled bearing/gear combo--Because If you really look into it, the only adjustment on the pinion is depth of engagement. Thus, the tolerance on the placement of forward and reverse gears must be standardized and the tolerance of the machining of the gearcase must be controlled very carefully. Remember: This is mass production. They are not going to check each bearing/gear for fit into each gearcase. Everything must be standarized so the worker or machine picks-up one gear and stuffs it into one gearcase. Period! Remarkable piece of work! That's one reason why new lower units are so expensive: They are a lot more complex than they look. I have successfully re-used the shims on the forward gear of a two piece lower unit that needed a new forward bearing. But to date I have not needed to do it to a one piece lower.

Just to make certain I am not misunderstanding shimming of the forward gear and bearing, the shims that are between the gear hub and the roller bearings inner race, the new bearing will need to have the same shimming as far as combined thickness's. Since the lower units and their inner parts have to be relatively standardized to fit correctly, does this mean that most forward gear/bearing combo's come with the same thickness's of shim washers. Or, is the shimming between the bearing and the gear when it's OEM determined by series of production runs?

Although, I haven't yet removed the race for the forward gears rollers bearing, Seloc states that there may or may not be shims located behind it.

 

[Frank Acampora]

Re: Lower unit needle bearings

Yes! There must be some standarization. otherwise It would become too expensive and time consuming to mass produce the lower units--in fact, they would probably not be able to be mass produced at all without standardizing some tolerances.

However: And don't quote me on this because it's been a long time since I saw it--- The intertech manual shows a chart for later Force engines. In these later engines the gearcase will have a letter, and the prop shaft will have a letter (or something) SO: if the gearcase is blah, and the prop shaft is blah-blah, then according to the chart you use blah-blah-blah gears. As I say, though, I don't remember the exact particulars.

 

[Matthew A.]

Re: Lower unit needle bearings

Yes...Seloc also gives a shimming chart.

One more time just to make certain you are aware...Your time and help is very much greatly appreciated. Thank you Frank