1973 I/o transom replacement

Discussion in 'Restoration Projects & Questions' started by Ian D, Jun 9, 2017.

  1. Ian D

    Ian D Hydrodyner

    Joined:
    Jun 9, 2017
    Messages:
    12
    Boat Model and Year:
    1973 18 I/o
    I'm fairly certain that I took out two layers of 3/4 inch plywood. The transom did measure 2 inches on top and in the keyhole cutout. I only have about 1 5/8 between the engine mount stringers and the fiberglass. It's about 3/8 thick and the inner skin was about 1/8. I could use 3 1/2 inch layers. I was thinking about making the seams in the wood vertical but horizontal seams may work better. Hopefully Menards will take the 3/4 back and for 1/2 plywood. Also the gentleman at express composites recommended I use 1.5 oz mat for everything.
     
  2. tj309

    tj309 Composite Specialist

    Joined:
    Jul 19, 2010
    Messages:
    393
    Location:
    LA (lower Alabama)
    Boat Model and Year:
    1972 18' Hydrodyne
    Ski Team:
    Former Hodag Water shows
    Menards will take the wood back. Vertical seams would be the worst thing you could do. Horizontal seams would be ok if staggered and the lengths of the pieces goes side to side.
     
  3. kevinb

    kevinb Elite Hydrodyner

    Joined:
    Sep 10, 2006
    Messages:
    420
    Location:
    Brookfield, WI
    Boat Model and Year:
    75 HD 18' I/O SOLD & 1985 HD 20' (Boat #2) I/O 350
    Ski Team:
    Portable SL Course Posse
    Hi Ian D and tj:

    I think this was discussed before but for an i/o, 2 inches to a max of 2 1/8 is the correct thickness. This is not an outboard so if you go with a thicker transom, you will not be able to bolt up the outdrive (studs and driveshaft spline will be way too short). Not sure what to say about piecing the transom but when mine was done for the HD 20 i/o, I sandwiched two pieces of 3/4 marine-grade together with a single layer of glass and cut the engine stringers out to let the installer have access (the engine stringers were questionable so had them replaced as well with micro-lam material). Transom and stringers were done by a mercruiser-certified shop, did not want to go it alone and have alignment issues.

    Good luck with your project,

    Kevin-
     
  4. tj309

    tj309 Composite Specialist

    Joined:
    Jul 19, 2010
    Messages:
    393
    Location:
    LA (lower Alabama)
    Boat Model and Year:
    1972 18' Hydrodyne
    Ski Team:
    Former Hodag Water shows
    Good point Kevin. I have very little experience with IO's.
     
  5. Ian D

    Ian D Hydrodyner

    Joined:
    Jun 9, 2017
    Messages:
    12
    Boat Model and Year:
    1973 18 I/o
    I know it was 2 sheets of 3/4. 3 sheets of 1/2 will actually be better due to nominal lumber dimensions. 1/2 inch is only 15/32. It will give me room for the additional glass layers. I understand the mercruiser stuff, iboats forums have a lot of good info. I have an alignment bar. I'm also upgrading from the old mc1 to the alpha 1 transom assuming. The transom measured 2 exactly when I took it off.

    Kevin did you have the floor out and or cap off to put the transom in? Did you remove the back of the floor where it meets the transom? If I can get it in in one piece I would remove the mount stringers.
     
  6. kevinb

    kevinb Elite Hydrodyner

    Joined:
    Sep 10, 2006
    Messages:
    420
    Location:
    Brookfield, WI
    Boat Model and Year:
    75 HD 18' I/O SOLD & 1985 HD 20' (Boat #2) I/O 350
    Ski Team:
    Portable SL Course Posse
    My 20 is in the "Restoration Section" with several pics of the process that it went through. This is a 20 footer so the transom is a little different than an 18 but the same principals are applied. my deck remained in place but the engine was out of the boat. the 20 footer has a bit more room to deal with when approaching this sort of project. Did not have the floor out. The transom was dry fitted, the the lower inch or so was filled with resin and the transom was dropped in and glassed in.
     
  7. Ian D

    Ian D Hydrodyner

    Joined:
    Jun 9, 2017
    Messages:
    12
    Boat Model and Year:
    1973 18 I/o
    Got the transom in today. I'll Put a layer of glass over it then tab it in later this week. Have any other I/o owners moved the plug to the middle?
     

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  8. jim

    jim Hydrodyne 18 Specialist

    Joined:
    Jun 14, 2006
    Messages:
    2,276
    Location:
    FL
    Boat Model and Year:
    77 Dyne 18 I/O converted to Outboard
    Hi Ian,

    The vertical core grain is the later and better construction. I converted my I/O to outboard. I ran it as an I/O for about 7 years. The transom is the original thickness, but backed up with an aluminum plate. It has been an outboard for 20 years with no issues.

    The alignment is a piece of cake with the tool.

    I think your transom will be fine. If it does flex, it will crack the skin and you will know.

    Jim
     
  9. Ian D

    Ian D Hydrodyner

    Joined:
    Jun 9, 2017
    Messages:
    12
    Boat Model and Year:
    1973 18 I/o
    Well the motor went back in today. Aligned with the tool just fine. I found a defect in the bellows so I'll be replacing them next week. I have found quite a few little snags putting a first gen alpha transom assembly where an old mc1 888 was. I think I have it all sorted out though.
     
  10. kevinb

    kevinb Elite Hydrodyner

    Joined:
    Sep 10, 2006
    Messages:
    420
    Location:
    Brookfield, WI
    Boat Model and Year:
    75 HD 18' I/O SOLD & 1985 HD 20' (Boat #2) I/O 350
    Ski Team:
    Portable SL Course Posse
    Ummm... Something about the word defect in association with a boat or airplane always bothers me. Glad you got it sorted out.
     

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