And this is why we do our maintenance.

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
Thought I'd do a quick video for you guys using my new 'drive lift'... It's been a couple of years since my drive was removed, so I thought this would be a good opportunity to kill two birds with one brick.... How quickly things can go south!

Used the lift to remove the drive. Very easy. Just loaded up the lift with the drive weight, pushed the rear trim cylinder anchor pin through, removed 6 nuts and washer and pull. Drive came straight off. :) Checked the engine alignment... Perfect. More :)

Got a flashlight and had a peer in at the gimbal bearing. That was looking and feeling good too... But, a small pool (about a teaspoon) of drive oil in the aft end of the uni bellows. Hmmm. Front drive seal leaking... Oh well, it is 12 years old, so yeah, that's fair. I had the parts I needed in the 'spares' box, so drained the oil, then removed the top cover and front cover nut, then pulled the yoke and drive gear out. Checked the top bearing outer race in the cover and it's not looking so good. Go to clean the surface and the race spins, in the cover. Ok, this is bad. Pulled the race out and this is what the inside of the cover looks like....

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Here's what's left of one of the pre-load shims under the race. (those 3 were originally the same size :eek:)

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So, a new top cover required (apparently it comes with a new bearing and a shim set :thumb:). As it was getting late and the local shop had already closed I though I'd pull the rest of the driveshaft housing down ready to start assembling when I get the parts. Had a good look at the upper driveshaft lower bearing and it's also not looking too swish... :(

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So, from a single 'let's have a quick peek inside' I found a grenade with the pin pulled...

As much as I'm not happy about this, I'm happier than it exploding 10 miles out to sea on a great day....

I'll update this thread with the repair and the original plan, the video of the drive lift in operation.... :facepalm:

Cheers all...

Chris...........
 
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Scott06

Vice Admiral
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Apr 20, 2014
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5,542
Would be great if you can post a how to rebuild the outdrive , see almost no info on this. I assume with right tools is within the capabilities of most folks here
 

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
Would be great if you can post a how to rebuild the outdrive , see almost no info on this. I assume with right tools is within the capabilities of most folks here

The hardest part is setting up the drive gear bearing rolling torque, which I have a video on (link in my signature).. The rest is simple 'mechano'....

Chris......
 

alldodge

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The hardest part is setting up the drive gear bearing rolling torque, which I have a video on (link in my signature).. The rest is simple 'mechano'....

Chris......

and a few some special tools, right?
 

harringtondav

Commander
Joined
May 26, 2018
Messages
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The hardest part is setting up the drive gear bearing rolling torque,
Chris......

I think checking/adjusting either upper driven gear bearing preload, or FWD gear backlash is worse. If you're lucky enough to hit the upper preload on the first set of top cover shims, pull the lower bearing race, drive the seals home, then the lower bearing race, again. If not, pull the race from the top cover, adjust shims, cross fingers and start over.

Same with the FWD gear backlash. Except setting up and having to remove all the preload apparatus to pull the FWD brg race for a shim tweak seems worse to me.

Of course a pro like you Chris can dial in the shim packs with one try. Generally not the case with me.
 

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
I think checking/adjusting either upper driven gear bearing preload, or FWD gear backlash is worse. If you're lucky enough to hit the upper preload on the first set of top cover shims, pull the lower bearing race, drive the seals home, then the lower bearing race, again. If not, pull the race from the top cover, adjust shims, cross fingers and start over.

Same with the FWD gear backlash. Except setting up and having to remove all the preload apparatus to pull the FWD brg race for a shim tweak seems worse to me.....

Shouldn't need to pull the lower bearing outer race to fit the lower seals in. They fit through the race.

First set up the drive gear bearing preload, then the gear positions (backlash) is 'easy'. Just fit the drive gear and using the tool, measure clearances. It's simple arithmetic to get the right shim from there (and the service manual explains it too)... Then remove the drive gear and fit the driven gear, remembering to fit the top cover and torque the screws to spec (20ft-lb). Check the gear height with the tool, and do a check on the preload at the same time. That will help in setting up for the preload. For example, if the gear is too high (less than 25thou) and the preload is also too high, just remove a shim from the lower bearing. If the preload is right, then add or subtract the same from both lower and upper bearings. If the driven gear is too low, and the preload is too low, you need to add shims to the lower bearing, and less shims (or even none) to the upper. Once you have the lower gear correct, that leaves only the upper driveshaft preload, which can be a bit trickier, and does involve a bit of 'guess work'. But in the process of getting the driven gear right, a lot of work of getting the preload will have been done.... But there's always the questions, how much change does adding/subtracting 5 thou of shim make? Trial and test.

and a few some special tools, right?

Apart from skinny hands.....

Front cover nut spanner
Drive gear shim height tool
Driven gear shim height tool
Old drive shaft with a 1/4" drive socket welded to it (for upper driveshaft preload check)
Dial torque indicator with a very low scale (I have 0-150in-lb. I would prefer a 0-30in-lb unit)
Standard 200ft-lb torque wrench
3/8" 12-point socket (top cover screws)
Very long 25 thou feeler gauge
Slide hammer with attachment to pull bearing races
Factory service manual

That about covers it...

Oh, one more thing... The ability to do simple addition and subtraction (it's a dying skill!) or a calculator. :facepalm:

Chris......
 
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harringtondav

Commander
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Shouldn't need to pull the lower bearing outer race to fit the lower seals in. They fit through the race.

That would be my bad. 22+ yrs ago I reverse engineered the tools from Manual #14. It showed the seal driver registering/setting from the bottom of the race bore. Double sided driver, one end for the deep seal, the other end for the top seal. If I ever spring for that mini lathe I'll whip up a driver that sets off the top face above the race bore.

As far as getting the shims right, apparently I can't hit my a*s with both hands. Add? No, subtract, ...dyslexia.
 

achris

More fish than mountain goat
Joined
May 19, 2004
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...As far as getting the shims right, apparently I can't hit my a*s with both hands. Add? No, subtract, ...dyslexia.

The new world.... :facepalm:

I grew up in a time before calculators. Still get bemused looks from 'checkout chicks' when I put half a dozen items on the counter alongside the correct money.... :D

Chris.....
 

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
Update:

Got a new lower bearing from a local bearing shop. Pick that up tomorrow. But.... phoned every dealer within 50 miles. No top cover assemblies in stock. Also nil stock in Melbourne (Merc's head office and warehouse)... approximately 2 weeks ex-USA...

Common comment was "only ever replaced a couple"... I think, by the time the problem with the cover manifests, the whole drive needs replacing! :eek:

So, that's it folks. See you in 2 weeks. :(

Chris........
 

Lou C

Supreme Mariner
Joined
Nov 10, 2002
Messages
11,802
A great example of why regular maintenance saves money, time and aggravation! While many do not do it, in a salt water region like mine I always pull the drive at the end of every season, to check all those things. The Cobra has been really great, it has survived 15+ years of being moored in the salt, with regular maintenance. Since I've had it, the first year (2002) I had some seals and trim lines replaced and new gimble bearing and bellows. After that, one more bellows in 2016, still have same gimble bearing, no leaks even with the old bellows. Nothing else has been replaced, trim rams, trim pump, upper and lower gears and all bearings, are the same.
I will say that having that drive jack I posted up a few days back makes it so much easier, that I don't dread doing this job like before.
 

harringtondav

Commander
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May 26, 2018
Messages
2,438
Update:

Got a new lower bearing from a local bearing shop. Pick that up tomorrow.

Chris........

Yessir. Every bearing in the Alpha 2 (except for the 31-42647A1 FWD gear drive pinion bearing) is a std. Timken or Torrington bearing. If you're w/in reach of Amazon's std shipping, you can find them for less than Motion Industries cost.

31-42647A1 is Torrington K AG 50936. Sierra 18-1117 is the Torrington and comes up here at iBoats under the OEM p/n.
 

achris

More fish than mountain goat
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May 19, 2004
Messages
27,468
I have a full list of all the Timken bearing numbers for the bearings in these drives. :D I also size the seals when I get the opportunity...
 

TyeeMan

Master Chief Petty Officer
Joined
Feb 27, 2006
Messages
849
Unless I missed something, what was the cause of the shims and the outer race being worn, 12 years of use?
Also, what do you think took out what? Did the shims wear causing damage to the outer race and top cap or was it the other way around?

Last question, was the drive louder or was it making some extra gear noises or something?

Just want to make sure I'm on top of things with my boat as it's new to me two years ago. So far everything sounds just fine.
 

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
I didn't hear anything from the drive. The first clue I had that something was wrong was a very small quantities of oil in the bellows..

The shims were damaged because of the race spinning.. Why the bearing race spun in the housing? No idea....
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
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My experience has been a fine line between proper bearing race to bore interference and a spinning race may only be about 0.001" (0.025mm)

the bore could have been machined on a really cold day in the shop, and when mated to the drive and run in the warm Aussie sun....expand... change the tolerance and lose its grip on the race.

we run into expansion issues here at work. large aluminum weldments machined in winter wont pin together with parts machined in summer as they were machined at different temperatures
 

harringtondav

Commander
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May 26, 2018
Messages
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Bearing "creep" is a vexing phenom for drive train engineers. It can happen with both bore and shaft press fits. We saw it in tractor transmissions. Our housings are gray cast iron, which tends to 'heal' itself before fretting wear happens...most of the time. Maybe the alum. bore in that cap finally gave up. I included a nice short read on creep below.

Confession time: I rebuild my Alpha 2 last winter from extra bearings I had. That same race didn't give up much of a fight when I pulled it from the cover. I was able to push the new race 60% of the way home with my fingers. So I applied green Locktite to the race and pressed it home. Also I discovered the 45-55796-1 upper drive shaft is a pressed together assy. After I removed the cone I noticed the bearing pilot was loose, partially rotating. I pushed it out and saw evidence it had been turning. More green Locktite. This winter I'll remove that assy and replace the cover and shaft.

The top bearing set doesn't see much end/axial loading. But the side/radial loads are significant from the separating forces between the two spiral bevel gears. Bearing creep is over my head, but this could be why that race wants to spin. In my #14 manual Merc states they installed a smaller OD, thinner wall race on s/n>OF680000. Maybe not a good move.

https://www.ntnglobal.com/en/products/review/pdf/NTN_TR81_en_100_103p.pdf
 
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