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Detroit 8v71 Alignment

Discussion in 'Engines' started by Cthulhu, Mar 26, 2009.

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  1. Cthulhu, Mar 26, 2009
    #1
    Cthulhu

    Cthulhu New Member

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    Recently, we hauled out and were required by the USCG to change the cutlass bearings. While disassembling our shafts, the coupling between the transmission and intermediate shafts was revealed to be out of alignment. Mainly, my engine needs to get shifted 0.675" inboard so that I don't damage my coupling, my split bearings, and my cutlass bearings.
    The Detroit Diesel that I have is through-bolted to four raised flanges that sit on the engine beds. Was told by the yard mechanic that all I need to do is loosen the mounting bolts, use the "lifting bolts" that are part of the mount assembly, and shimmy the thing around a bit.
    Today, a young mechanic accustomed to "Tiaras" said that it was a three day affair.

    Anyone have any ideas?
  2. K1W1, Mar 26, 2009
    #2
    K1W1

    K1W1 Senior Member

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    Hi,

    It would be a help if you could post some pictures of your mounts.

    I have to also ask what exactly what the USCG has to do with your Cutlass Bearings?
  3. Cthulhu, Mar 26, 2009
    #3
    Cthulhu

    Cthulhu New Member

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    K1W1-

    Will try to get some photos taken and post them later tonight.

    As for the second query, as an inspected passenger vessel, subchapter T, the United States Coast Guard has the final say on just about every last thing on my boat. Ironically, had the inspector not required new bearings, I very well may not have been aware of the dangerous nature of this mis-alignment.

    From the records that I have, there is no evidence that the cutlass bearings were replaced in 2007 at our last haul, which would mean that they were last replaced in 2004.

    At our second most recent haul (2007), it was suggested that we replace the intermediate shafts and the muff couplings at either end. It would be wonderful to know that this problem would go away if we replaced these shafts, but it would mean coming out of the water again.
  4. Cthulhu, Mar 26, 2009
    #4
    Cthulhu

    Cthulhu New Member

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    Here are some visual aids of what I have to work with. Obviously I can adjust the engines up and down, but the rotational alignment is what has me stymied.

    Attached Files:

  5. K1W1, Mar 26, 2009
    #5
    K1W1

    K1W1 Senior Member

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    Hi,

    Thanks for the reply, I wasn't aware that the USCG had anything to do with Mechanical Things, I thought that side of things was left to the ABS.

    I was doing a mental calc after your first post 0.675" is about 11/16" if my Imperial System memory doesn't fail me. I am surprised that you could get the coupling bolts in with this amount of deflection.

    How has this mis alignment actually been determined to such an exact degree?

    Are there any rubber type mounts involved in the engine/gearbox mount arrangement?

    EDIT: I do not see any way that you can get the required amount of movement you say you need with those mounts without some type of elongation of some holes.
  6. Cthulhu, Mar 26, 2009
    #6
    Cthulhu

    Cthulhu New Member

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    K1W1 my decimal equivalent math is a bit off. The mechanic who did the work told me it was 5/8" off, which is more like 0.625".

    Along with the line of thinking that re-aligning the engines is rather difficult, if not impossible, I have to suspect that the problem lies abaft my engine. So far as I know, it has not been moved since it was put in. Have been aboard for eight years, and we've only ever had shaft work done.
    The floor timbers and a plank under the aft strut were replaced in 2007 due to some rot caused by galzanic corrosion of fasteners. I can only guess that this is where my mis-alignment begins.
    The fact that the old cutlass bearings were secured with chockfast when they were last replaced has made every thing else that much more difficult. Perhaps I could adjust the alignment by moving my split bearing? The only problem there is if I do indeed replace the intermediate shaft, which was suggested in 2007, will I need to put it back to the original position?

    May need to haul out in a year's time, rather than the two year period specified by the USCG/Code of Federal Regulations

    As for what the Coast Guard says, if they don't like my carpeting, they can take away my COI. In fact, if they don't like me personally, they could just as easily tear up the piece of paper that helps this old boat support herself.
  7. K1W1, Mar 26, 2009
    #7
    K1W1

    K1W1 Senior Member

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    Hi,

    Setting Cutlass Bearings in Chockfast is not an unheard of procedure.

    From what I can remember from my days on a machine 1/8" = 0.125", 5 x 0.125" = 0.625" + 0.062.5"(1/16") = 0.687.5" so as 5/8" + 1/16" =11/16". This is 0.012" more than the 0.675" you first posted- close enough for Government work.

    How much room do you have between your Gearbox Output Flange and your Prop Shaft Input Flange?
    Is there room to put a jackshaft with two Universals in there?

    Where is the Thrust Bearing in your Shaft arrangement?

    EDIT: Before someone chips me on my maths I worked out that the closest size is 43/64" using the old fashioned pen and paper.

    You just have to love the Metric System, everything is in whole numbers- no fractions.
  8. Marmot, Mar 27, 2009
    #8
    Marmot

    Marmot Senior Member

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    The pictures don't really show it too well but is the sequence reduction gear/intermediate shaft with bearing/shaft coupling?

    If so then how is the alignment between the intermediate shaft and the prop shaft? Is all the misalignment in the intermediate to gearbox? Is the misalignment duplicated in the gearbox to intermediate shaft?

    You really have to start at the prop shaft coupling and work forward, but If there was an issue with the strut mounting previously, you should loosen the strut and see if it is the source of the misalignment. I had a boat recently (40m glass production boat) that was delivered with a misalignment in the struts that required cutting them and removing 1.5 inches and rewelding to obtain correct alignment so anything is possible at that end.

    If this is a wood boat on the hard is it blocked properly?
  9. Ken Bracewell, Mar 27, 2009
    #9
    Ken Bracewell

    Ken Bracewell Senior Member

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    Having lots of experience with large wooden boats, this would be my suspicion. It may also be an old problem whereby the alignment was previously done on the hard with the boat improperly blocked.
    Wood is flexible. Rotten wood is even more so (no offense cthulhu).
  10. Pascal, Mar 27, 2009
    #10
    Pascal

    Pascal Senior Member

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    even with glass hulls, you want to do the alignment in water, NEVER on the hard.
  11. Fishtigua, Mar 27, 2009
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    Fishtigua

    Fishtigua Senior Member

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    Why not fit a small flexi intermediate shaft.

    I saw some from a Dutch company website the other day but cannot remember the name, Euroflex or something. As Kenny said, wooden hulls and engine beds do shift, these flexi shafts could accommodate such a difference as 5/8ths.

    Fish
  12. Bamboo, Mar 28, 2009
    #12
    Bamboo

    Bamboo Senior Member

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    How did anyone arrive at this .65" figure? Is this for the front of the engine or the back? If it's for the back that sure seems strange how the shaft coupling is considered to be that far out- how do the bolts even fit in?

    While I worked at Viking we had perhaps 100 boats that needed new struts- which of course required a full alignment. ALL of them were done on the hard and then allowed to settle in the water before the final. You cannot install a strut with the boat in the water. Not trying to making a argument here. When I set engines/installed shafts and struts for Liberty Yachts new builds we did it on the hard. Never had a issue later, and checking later revealed a dead on alignment.