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Old 06-05-2012, 05:59 PM   #21
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We needed to remove our Twin Disc MG90990 transmission for a major service (mind you, you need to remove it for any type of service!!) last Fall. As with yours, the transmission housing included the rear engine mounts. We raised the engine up with a 2"x 6" using a bottle jack (Harbor Freight) and blocking as we went. Biggest challenge was barely having enough engine room height. Necessitated removing the exhaust riser and other parts just to get enough clearance. Once the transmission was separated from the prop. shaft, we pushed the shaft out of the boat - we have a dripless system- to get enough clearance to remove the tranny. Not sure I would plan to do this in the water - pretty sure it would not work on our boat. This is definitely a job for two people. Manhandling the tranny in/out of position was pretty awkward - ours weighs about 200lb. We began the project to deal with a leaking transmission seal. It turned out the clutch plates were fried (no obvious symptoms) and clutch parts had damaged the seal and the bearings. $3.5K later we have a rebuilt, as new, transmission installed.
Also, take the opportunity with the transmission out to replace the rear engine seal. It is pretty easy on our Cummins with the transmission removed. You certainly would not want to do this job twice if/when that starts leaking!! Best of luck with your project.
Chris
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Old 06-05-2012, 06:12 PM   #22
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SD-- whenever you remove and replace any component of the drivetrain-- engine, transmission, shaft, cutless bearing(s)-- the engine-propshaft alignment must be checked and corrected. We're talking fractions of an inch here. IIRC the yard we use and our diesel shop use an allowable misalignment of one ten thousandth of an inch. Anything more than that and they say it must be corrected out by adjusting the motor mounts to bring the alignment back to no more than one ten thousandth of an inch.

The alignment is checked by separating the two halves of the shaft coupler and measuring the gap around the circumference of the coupler with a feeler gauge. The engine mounts are then adjusted to tilt or yaw the engine relative to the shaft until the gap is the same measurement all the way around.

As was said previously, while it is a mechanically simple process, adjusting the engine mouts for proper alignment is something of an art form.

The penalties for running with an out-of-alignment drive train are shaft vibration at best and shaft bending and premature wear on things like cutless bearings at worst.
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Old 06-05-2012, 06:32 PM   #23
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IIRC the yard we use and our diesel shop use an allowable misalignment of one ten thousandth of an inch
I don't think that is the correct figure.
The "rule of thumb" is one thousandthof an inch (.001") per inch of diameter of the coupling. Hence a 4 inch diam coupling would be aligned within .004"maximum.
I was able to get mine to about .002"

One ten thousandth (.0001") would be impossibleto measure with feeler gages.
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Old 06-05-2012, 06:42 PM   #24
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I don't think that is the correct figure.
The "rule of thumb" is one thousandthof an inch (.001") per inch of diameter of the coupling. Hence a 4 inch diam coupling would be aligned within .004"maximum.
I was able to get mine to about .002"

One ten thousandth (.0001") would be impossibleto measure with feeler gages.
I'm sure you are correct. We had a new shaft and bearings put in the boat several years ago so it's been awhile since the topic was discussed. One ten thousandth does seem like an extreme measurement given the components we're talking about here.
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Old 06-05-2012, 08:19 PM   #25
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Yes, I agree with jleonard. We adjusted to 0.004inch on the hard. Now we need to do the same after the boat has been in the water for a couple of weeks. Another job for 2 people. Amazing how many boat jobs need very long arms!!
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Old 06-06-2012, 10:48 AM   #26
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The improvement on stability to this approach I used when placing new mounts under my 3208s was.... I used 4x6s across the engine hatch and long threaded eyes to shackles and chain to the engine.

A little grease on the threads and I raised the engines with one finger and a long box wtench.
This is a great idea I think it will be the one I use to raise the tranny.

Perfect control as I can raise it slowly a thread at a time.
Perfect Thanks.

Sd
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Old 06-06-2012, 11:31 AM   #27
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This is a great idea I think it will be the one I use to raise the tranny.

Perfect control as I can raise it slowly a thread at a time.
Perfect Thanks.

Sd
I wasn't positive it would work as well as it did...2500 pounds hanging and yet up and down with a little side movement was onlt a fingertip in the box wrench...way cool...

I was more worried about the floor after I got setup rather than my rig...

I did get the 18 inch long forged eye bolts (the kind used in building floating docks)...they were rated at over 2000 apiece and they were nice enough I figured I'd find some use for them after the project. Don't forget big washers as they help turn the nuts...
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Old 06-06-2012, 12:15 PM   #28
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Yup,
As I am only lifting about 225# I will use a 4"X4".
I am not sure what model tranny I have so I will check the tag this weekend and then I can buy the part and be ready to go next weekend.
Chrisjs mentioned the rear seal. How much trouble is it to replace that.
I think I do have a leak there.
Anyone replaced the rear seal on a 3208?

Sd
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Old 06-06-2012, 12:16 PM   #29
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You are correct on the use of a Come-Along. I used one and had to keep climbing in and out of the engine room to get the trans properly lined up ( I was working alone)on the re-install part of the job. Could not use the windows as the aluminum frames would have collapsed. I used a "Little Giant" aluminum ladder as an "A" frame and it worked just fine.
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Old 06-06-2012, 01:17 PM   #30
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I used all-thread and a timber as well. Worked great.
I did block the floor from below to take some of the strain.
The one problem I ran into is that the rudder kept the shaft from sliding far enough to alllow the tranny to be removed. I ended up lifting the back of the engine 4" or so to clear the shaft. Of course this required a complete re-alignment after the rebuilt trans. was in place.
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Old 06-06-2012, 01:56 PM   #31
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Max, Perfect that is just how I invisioned it.
Thanks for the picture.

Sd
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Old 06-06-2012, 09:57 PM   #32
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SD-- whenever you remove and replace any component of the drivetrain-- engine, transmission, shaft, cutless bearing(s)-- the engine-propshaft alignment must be checked and corrected. We're talking fractions of an inch here. IIRC the yard we use and our diesel shop use an allowable misalignment of one ten thousandth of an inch. Anything more than that and they say it must be corrected out by adjusting the motor mounts to bring the alignment back to no more than one ten thousandth of an inch.

The alignment is checked by separating the two halves of the shaft coupler and measuring the gap around the circumference of the coupler with a feeler gauge. The engine mounts are then adjusted to tilt or yaw the engine relative to the shaft until the gap is the same measurement all the way around.

As was said previously, while it is a mechanically simple process, adjusting the engine mouts for proper alignment is something of an art form.

The penalties for running with an out-of-alignment drive train are shaft vibration at best and shaft bending and premature wear on things like cutless bearings at worst.
"and shaft bending and premature wear on things like cutless bearings at worst"

You will Not bend your shaft from an out-of-alignment shaft. Statements like this are why you should take comments from 'backyard mechanics' with a grain of salt ( and shot of rum).
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Old 06-07-2012, 07:54 AM   #33
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Our boat bent its shaft and wore out its cutless bearings fom a bad alignment from the previous owner. Cure was a new shaft and a proper alignment job.

Situation was analyzed and repaired by one of the best yards in the area, not "backyard mechanics.". Since this work was done several years ago there have been no problems since.

Not a good idea to second guess the pros. They will generally prove you wrong, which you are in this case.
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Old 06-07-2012, 12:25 PM   #34
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"and shaft bending and premature wear on things like cutless bearings at worst"

You will Not bend your shaft from an out-of-alignment shaft. Statements like this are why you should take comments from 'backyard mechanics' with a grain of salt ( and shot of rum).
Not sure where you heard that you can't bend a shaft from misalignment....BUT...this seems to be the consensus...

Here's a short list of the problems that can be caused by engine/shaft alignment faults:
  • Rapid cutlass bearing wear.
  • Misaligned strut galls shaft, requiring shaft replacement.
  • Causes stuffing boxes to wear out and leak, not infrequently sinking the boat.
  • Bent or broken shafts
While I agree a bent/broken shaft seems unlikely...it may be possible based on the number of documented writings of "experts" that say it is so.

While I agree that the amount of misalignment would have to be extreme or the vessel have an unusual shaft alignment to begin with...and you may have to be a rock to miss the symptoms before damage occurs....I can't say that it is out of the question..
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Old 06-07-2012, 02:15 PM   #35
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I spent a good portion of a day trying to align the motor myself. On paper, it seems straight forward. Finally gave up and hired a pro and $300 later it was aligned. I do question the tolerances though. Can it really get to 1/1000 of an inch? With rubber engine mounts and any small amount of flexing in the shaft, or the engine torque throughout the RPM range seems that it would be unrealistic.
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Old 06-07-2012, 02:44 PM   #36
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I am hard mounted to the stringers, no rubber motor mounts at all. From what I can see the only adjustments I can make are port and starboard. There may be adjustments for up and down but I am hoping that I can remove the tranny without removing or tampering with the adjustments at all.
If I look at replacing the rear seal I will have to unbolt the mounts.
I think I have to remove the fly wheel to get to the rear seal. I am not sure the tranny housing will have to come off or not as the tranny housing is where the mounts are located.
I will have to stand on my head and try to learn how to drink a beer in that position untill I can get this all figured out.

Sd
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Old 06-07-2012, 07:16 PM   #37
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[*]Bent or broken shafts
As it was explained to us, a potential for bending a shaft can arise if the boat with an out-of-alignment shaft sits for quite awhile without being run. Months was the measurement I recall they used. The uneven loading on the shaft from the misalignment can, over time, put a "set" in the shaft. While it won't be an obvious visible bend this "set" will nevertheless be there and can not only contribute to making it difficult to align properly but will contribute to vibration and the potential damage it can cause to struts, bearings, etc. until the shaft is either straightened or replaced.
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Old 06-08-2012, 07:00 AM   #38
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As it was explained to us, a potential for bending a shaft can arise if the boat with an out-of-alignment shaft sits for quite awhile without being run. Months was the measurement I recall they used. The uneven loading on the shaft from the misalignment can, over time, put a "set" in the shaft. While it won't be an obvious visible bend this "set" will nevertheless be there and can not only contribute to making it difficult to align properly but will contribute to vibration and the potential damage it can cause to struts, bearings, etc. until the shaft is either straightened or replaced.
I agree...I wasn't ruling out the possibility...as you have posted...ANTHING that can happen...just might.

Given the right parameters I can see a shaft taking a set....although I think in many cases the size and length of the shaft are such the engine would have to be so out of line it would be terrible to run by anyone but the complete newbie...on some boats the shafts are so long how they don't bend is beyond me.
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Old 06-08-2012, 07:03 AM   #39
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I spent a good portion of a day trying to align the motor myself. On paper, it seems straight forward. Finally gave up and hired a pro and $300 later it was aligned. I do question the tolerances though. Can it really get to 1/1000 of an inch? With rubber engine mounts and any small amount of flexing in the shaft, or the engine torque throughout the RPM range seems that it would be unrealistic.
That's almost the joke about shaft alignment...there are other issues with some boats when they are running, alignment changes from the at rest situation.
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Old 06-08-2012, 11:40 AM   #40
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That's almost the joke about shaft alignment...there are other issues with some boats when they are running, alignment changes from the at rest situation.
Yes the dynamics do change things. However, you might as well start off statically as close in alignment as you can get.
I was able to get my Mainship to about .0015" near as I could tell.
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