1973 Thompson Tri Hull OMC Rebuild.

[evilbob01]

Hi Everybody, I've been lurking here at the forums for a while but I finally registered. I'm an IT guy not so much of a Mechanic, and this is my first boat.

I know what you may think/say about a rotten 1973 Thompson with an OMC Stringer. I know what I am about to do and Understand it's not exactly a great project, especially for a beginner. I have plenty of time, a little budget, and lots of OMC parts laying around so I'm going to rebuild it.

I'm very open to Suggestions and Criticisms. Any advice is welcome.

A picture is worth 1k words. I don't like to type so be warned my posts may load slow.

Lets get Started.
Before Picture with the 1st mate on board.

The plastic side vent covers broke off during the 1st season Smashed them into the dock a few times replaced them with stainless steel cut to fit with a jigsaw.

Now the easy stuff is done.
Time to take off the Outdrive. I have a spare complete outdrive assembly, It's worth noting that OMC outdrives can be slightly different. 1973 and older are about an inch and a half longer (taller) in the Gear case area. 1974 and above are shorter. They both will bolt on to the intermediate assembly and both work. I like the shorter one as it helps the boat to plane faster (IMHO)

The Brackets that hold the outdrive on One on each side. Also there was a metal strap that tethers the outdrive to the intermediate assembly if the brackets should fail:

Here is the intermediate Assembly where the Outdrive attaches. Sorry Haven't figured out how to rotate the image may be sideways a bit.

I'm missing a few pictures I'll add them in when I find them. I tool off the engine doghouse (screwed to the deck) Then I pealed up the carpet. Beneath the carpet was inch thick plywood secured with screws to the OEM deck beneath. I removed the screws and pulled out all the rotting pieces of plywood someone slapped down to cover the mess that was the original deck.

-to be continued

 

[evilbob01]

Re: 1973 Thompson Tri Hull OMC Rebuild.

Behold in all it's OEM glory 40 old Rotten wood and Saturated Flotation foam.

The Motor Mounts pulled Loose from the Stringers. The engine needs to be removed so I can assess the extent of the rot in the stringers and transom. I decided to separate the engine from the Intermediate assembly / bell housing. I had a mechanic friend over to help with this part it makes it much easier with two people and an engine crane.

First step was to take pictures of all the electrical connections and make notes of where they go. Hopefully they will be simple to attach later.
I don't know what this thingy is but it had lots of wires so it gets it's picture taken.

After disconnecting all the electrical connections, and the electric fuel pump and related hoses. I took out the bolts and put them in separate labeled containers so I know where they are supposed to go. Nest chains are attached to the engine hoist points and secured with bolts. The engine is lifted out of the boat with the crane. Take note there were two alignment pins on the bell housing that needed some persuasion to let the engine go. A flat blade screwdriver and a bit of force was all I needed. Make sure you remove all the bolts if it won't separate.

I did have to raise the trailer tung to tip the back of the boat down in order for the oil pan to clear the fiberglass edge of the boat.

With the engine now out Have a look at the transom. It looks to have some rot. Is it worth replacing? I don't know for sure. Was thinking about cutting out the rotten parts then attaching an aluminum plate and glueing in place, then securing it to the non rotten wood with screws. Being a stringer mount there isn't much force on the transom anyways. any suggestions?
The transom Rot near the bottom:

On to more teardown while I weigh my options for Transom replacement.
Inspecting the stringer where the engine mounts. I cut away a small section so I could look at the wood beneath the front motor mount.

It's all wet but fairly solid. I think It would be ok to replace the mount screws with a larger size but I'm already this far I might as well replace the wood right? Again any suggestions? Note the wood is encased in fiberglass but is not attached to the hull there is an air gap on the bottom. I know because I can stick my finger in the hole the mount ripped out of and feel it.

-To be continued

 

[evilbob01]

Re: 1973 Thompson Tri Hull OMC Rebuild.

-Continue

Again I must decide what to do. At this point I am uncertain of how much of the wood is rotten to the point it needs to be replaced. I'm thinking of having someone come out and inspect the structure and tell me how bad it is. Before I pay for an inspection I am going to remove as much flotation foam as I can.

The small shovel works great at removing the foam.

I managed to get two garbage bags of foam removed and ready for the trash.

I know it's gotta get worse before it gets better.

Hope this is interesting to some people. I'll have more pictures as the project goes on, and Hopefully some good pics of the inside of the OMC outdrive. I need to replace the water pump seals before it goes back on.

This is the end of day one. I have about 8 hours of work in and my friend has about 6 hours of work in. I think it's off to a good start.

 

[greenbush future]

Re: 1973 Thompson Tri Hull OMC Rebuild.

Hey I'm an IT guy too, but that sure doesn't stop me from my passion of boating and tinkering with water toys. Your project will be a fun one, and you appear to have your eye's wide open about the pit falls of investing in older but nice looking boats. Have fun with your boat, keep us posted, we like pictures in between the 0001010100010011100's.

 

[Woodonglass]

Re: 1973 Thompson Tri Hull OMC Rebuild.

Welcome To iBoats!
Where are you located. Just as and FYI the OMC's are very outdated and not a very desirable powerplant for your boat. Parts are becoming more and more difficult to locate and finding someone to work on them is difficult too! Just wanted you to be aware. Base on your pics I'd say you're in for a Full restoration of the Stringers, Motormounts, bulkheads and Transom. Lots of help here on the forum so you're for sure in the right place.

 

[evilbob01]

Re: 1973 Thompson Tri Hull OMC Rebuild.

Thanks for the warm welcome and encouragement.

I'm Located in tropical Cleveland Ohio!

OMC - Yep... It's Old, It's un-desirable, and it could preform better. Those are the main reasons I have it. :joyous:
I am a noob and will defer to your expertise of course. But Finding someone to work on it is easy as long as that person is me.
you are right finding an actual service center or professional is basically impossible.

As for Parts OMC has been out of business for a while now and the outdrive design is ~40 years old. I have had surprisingly good luck finding parts. Iboat.com has some, Also Evinrude is still in Business and they have an online parts catalog for OMC outdrives.
I also have a spare Engine, intermediate assembly, lower outdrive assembly. The Bubble gear in the upper unit is what worries me. I don't have an extra one.

Replacing the Transom makes a Mercruiser conversion much more doable. I'll need to do more research on what a conversion requires. I really like the GM inline 4 cylinder engine as it's great on gas. Can I keep the engine and just swap on a Mercruiser outdrive and intermediate assembly?

Thanks for looking at the pics. I know I need the Stringers, Motor mounts need replacing but I was questionable on the bulkheads and Transom I'll add those to the list. I might as well fix them while I am at it.