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Old 25-08-2010, 22:05   #1
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Alignment

I have a 50 HP, Perkins diesel engine, model 4-108 in my 27 foot boat.
I just noticed an engine mounting bracket broken. It looks like the engine has been operating on 3 mounting brackets for a while. The bracket bolts to the engine and to the suds in the hull.
there does NOT seem to be any major vibration or anything unusual about the alignment with only 3 brackets.
I am replacing the bracket but it will throw off the alignment of the shaft through the stuffing box.
How could this have happend and any recommendations?
I would welcome any comments
Saga
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Old 25-08-2010, 22:42   #2
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Proper engine alignment is very important for the drive assembly. The PO of our boat had an engine mount bracket come loose and caused the damage below. (And yes I know it looks gross but I promise it's clean now) After reattaching the bracket and replacing the four mounts, output shaft and coupler all is good.

Engine alignment is supposed to be within 0.001 of an inch per inch of couple diameter (4" coupler would be 0.004')

It is not that hard of process. Really just time consuming. There are lots of books/articles written on the subject.
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Old 25-08-2010, 22:53   #3
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Just a couple of other things I should have added........

An poor alignment could have caused a vibration. This could have caused the bracket to break. Could be a bad mount. The engine may not have been putting an even amount of weight on the four mounts, this would have caused extra stress on that particular bracket. It could be any number of things. It is good that you caught it before any more damage was done. Make sure that you inspect all the other Brackets and their mounts.
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Old 29-08-2010, 19:43   #4
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I never put my engine back on its mounts yet, I am still getting some engine repairs.
I'm not sure how to inspect the mounts. All 4 seem to be in the same condition.
Jeff
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Old 29-08-2010, 19:52   #5
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Quote:
Proper engine alignment is very important for the drive assembly.
You want this aligned by a pro. The specs usually about .007 - .009 of an inch but someone that knows can get it to .003. The whole idea is to get the drive train all lined up so it just sings. The rattle and banging you get from an "adequate job" sounds even better when done tighter. I blew a mount that was not properly done by the PO and it broke the coupling and a second mount, then ate out the stuffing in the stuffing box. It didn't trash the cutlass bearing. It's didn't eat all the stuff at a desired moment either. Tending to it sooner would be the way to go. Mounts don't last forever or even all that long. Replace the mounts and set the coupling and alignment as well as possible. Get help if you don't know how.
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Old 29-08-2010, 20:09   #6
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I have a book, "This Old Boat" by Don Casey that outlines how to align an engine. You can read it and then decide whether or not you want to tackle the project yourself. I didn't find it hard but did find it tedious after installing my engine.
kind regards,
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Old 29-08-2010, 20:19   #7
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If you are suspicious of the engine mounts - Replace them. They are not expensive and you can get into a world of trouble if they fail on you. Remember, the propeller does not push your boat, it pushes the shaft that pushes the transmission that pushes the engine itself that then pushes the Engine Mounts and finally pushes the boat.
- - One check is to mount a gauge at the prop shaft flange and set it to an edge of the flange. Then put the boat in forward and watch as the whole engine moves forward in the engine mounts as the boat starts to move forward. Then stop and put the boat into reverse and see how far the engine moves aft as the boat starts to move. There should be very little movement of the engine forward and aft. Such movement is caused by the rubber inside the engine mounts wearing away.
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Old 29-08-2010, 21:26   #8
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If you can find them, by a set of "go-no go" feeler gauges.

They look just like regular ones but are graduated.

in other words.....say you have an .008 gap.

if you select the .007-.009....it will go in so far but no further.

saves time.
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Old 29-08-2010, 21:41   #9
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Chief I need to do the mounts on my Yanmar. I have the correct installation manual for the the engine. Is that a good enough reference to do a good job? Will I need metric feeler guages for a Yanmar? I also have a zero drip stern bearing (not sure of the make). Are there additional considerations in that case?

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Old 30-08-2010, 07:05   #10
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Originally Posted by IdoraKeeper View Post
. . . I also have a zero drip stern bearing (not sure of the make). Are there additional considerations in that case?
Todd
Remember, if the boat is out of the water, you need to do the process twice. First while in the jackstands to get as good as you can and then again later once the boat has been in the water for awhile. Putting the boat back in the water will change to curvature of the boat a little bit from when it was being supported on the jack stands. This can change the shaft/engine alignment depending upon how flexible your hull is.
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Old 30-08-2010, 07:29   #11
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I am not going to haul out till March. Looking at what Del Marrey has done in his most recent post has given me alot to read and think about. Fortunately I have time.
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