Engine mount support on a '85 Peterborough Monza Runabout-Need Help!

billv45

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Jul 10, 2022
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Pulled the Mercruiser 2.5L engine for a rebuild and decided to check the wood under the engine mount and found mush. Not sure what wood it is, as it was leaching black water back into the bilge it may have been a railroad tie? Pic below, had to handle it very gently not to have it come apart. Wish I had snapped a couple pics before removing it but didn't anticipate a issue with something as simple as this, surprise, surprise.

There was also some plywood under it that had rot, one on the port side all the way to the transom so I removed it and part of the starboard side until I found good wood. I then cut replacement pieces and built up a replacement for the railroad tie of laminated ply.

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I glued up the support and epoxied all three pieces and installed the two pieces of ply. After I fill the gaps and throw a little fiberglass on the seamed piece, I'll be ready to install the beam. It was hard to tell but the one removed didn't appear to be glued down and had a nice piece of fiberglass securing it front to back. Must have been fairly strong as a 900lb. Mercruiser front feet were lagged into it with no help underneath. The beam wasn't seemingly sealed at all, just raw wood.

Now my questions, first, what is that support called? My burning question is how di I install the new support? Do I glue or epoxy the bottom to the replaced ply? Do I use some lesser holding adhesive (in case it ever needs to come out) like PL375 or Premium to fill in any voids and fiberglass it down? I did widen my replacement so I could fiberglass it to the stringers as well. The old one was 2" shy from them and was only glassed in front to back. Do I only lay glass from the top to the floor and sides and let it float?

I've spent hours searching with very limited success and nothing definitive. I'm a newbie to boating but generally can figure things out but this has me stumped.

Thanks
Bill
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
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Jul 23, 2011
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49,574
At the top of the restoration forum are stickies. 4th one down is the DIY for boat restoration.

Links 14, 15, 18, 2, 3, 4, and 4a have all the information you need
 

billv45

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Jul 10, 2022
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At the top of the restoration forum are stickies. 4th one down is the DIY for boat restoration.

Links 14, 15, 18, 2, 3, 4, and 4a have all the information you need
wow, that's a lot of info. Even found couple threads with very similar issue as mine. A lot on material and how to make them but not one on how to install one or how it is attached yet. So what is that support under the engine named? Something to search on
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
49,574
wow, that's a lot of info. Even found couple threads with very similar issue as mine. A lot on material and how to make them but not one on how to install one or how it is attached yet. So what is that support under the engine named? Something to search on
Go thru link 14 in it's entirety. All the info you need is in there
 

Baylinerchuck

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Jul 29, 2016
Messages
2,726
If it was me, I would glass in all the plywood deck first. Then make reinforced, (hairy) peanut butter to glue down the motor mount support. Make sure to create filets. Then encapsulate the entire support with 2 layers of 1708, tying into the hull.
 

billv45

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Jul 10, 2022
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If it was me, I would glass in all the plywood deck first. Then make reinforced, (hairy) peanut butter to glue down the motor mount support. Make sure to create filets. Then encapsulate the entire support with 2 layers of 1708, tying into the hull.
That was my original plan but then started second guessing myself after thinking about the lack of fiberglass under the previous beam. The center stringer directly under it was still sporting it's pristine 1708 wrap with nothing ever being glassed to it. The beam seemed to be held solely by some chop strand over it front to back with the "ends" open (they fell 2" short of side stringers making up the engine box.) I've read the entire link 14 in the sticky notes and a lot of the video's had already Googled up and watched previously. I like the two separate feet in his engine mount support build but mine has this solid beam thing for the Iron Duke like front mount and I didn't think to be directly applicable. (And yes I know my 120 is NOT a Iron Duke but if you think about it, it's a Iron Duke Daddy.)
Thanks for your clarification I was on the right course to begin with.
So, when do I stop throwing money into my hole in the water?
 

Baylinerchuck

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Jul 29, 2016
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Thanks for your clarification I was on the right course to begin with.
So, when do I stop throwing money into my hole in the water?
Ha ha, you never will until you stop using it is the answer. That normally happens when you stop having fun. Then it sits around and either collects dust or rots away before you sell it or give it away. But enjoy the crap out of it while you have it.
 

todhunter

Canoeist
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Sep 15, 2020
Messages
1,311
well .... you could. But the normal progression is Hot Rod, Boat, Plane then Chopper :)
Nice work on the mount BTW.
Oof, I did plane (didn't finish it though), hot rod, boat, and I'll never have a chopper!
 
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