Motor Transom Fitting

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castman27

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Apr 23, 2011
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Hi

I have a 1963 seahorse 40hp Johnson , my question is this if i measure my transom it is 19 inch from top to bottom and i did measure the shaft on my motor it is 18.5 will it make a difference for my motor performance since i read that you have at least 1/2 to 3/4 inch above the bottom of the boat. cause before i put the new transom on i want to make sure that if i need to adjust something it is now cause if i cut it to low not good cause you cannot add , they say it is always better to cut some off than add some on. Is this right???
 
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Chris1956

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Re: Motor Transom Fitting

Are you measuring the motor from the transom clamp to the top of the antiventilation plate? Most of those motors would measure about 15", unless they have the 5" extension between the gearcase and the midsection.
 
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castman27

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Re: Motor Transom Fitting

i am measuring from transom clamp to the cav plate right after the antiventilation plate
 
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Chris1956

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Re: Motor Transom Fitting

I do not know what you refer to as the cav plate. The correct measurement is from the part of the transom clamp that would sit on the transom, to the top of the horizontal plate at the top of the gearcase.
 
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sschefer

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Re: Motor Transom Fitting

Is there another boat around you can go measure. With the confusion about how to measure, it might be your safest bet. 15" is standard shaft motor. A long shaft is 20 and a Xtra long is 25. Those are references to transom heights and not actual shaft lengths so I think this is where the confusion is.
 
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castman27

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Re: Motor Transom Fitting

The Cavitation plate i mean , but just found out it is the antiventilation plate, i just want to make sure i got the right height before i do any cuting,transom it is 19 and motor it is 18.5
 
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Chris1956

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Re: Motor Transom Fitting

A lot of those old big twin motors had the 5" extension installed between the gearcase and the midsection. That would make it a 20" motor (longshaft). The extensions are quite noticable. Do you have one? If so, the transom is likely the correct height for the motor.
 
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castman27

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Re: Motor Transom Fitting

Ok i measure the motor and it is a longshaft , so i did my transom took all the measure and did my cutting i wont be to low but if i need to cut some off i am ok. So just to tell you i did glue my 2 piece of transom togetherr and tonight will be able to glass it before installing it tomorrow night before the rain get here on friday.

My question is this when i glue the transom to the fiberglass wall behind the motor how long it as to be set before the rain can hit it, i am working outside cause dont have room in the garage right now to work inside.
 
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Chris1956

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Re: Motor Transom Fitting

Polyester resin sets up very quickly, but is still temp dependent. Epoxy set up slower. Overnight ought to cause either of them to cure. If in doubt, mix the poly resin with a bit more hardener. Epoxy has fast and slow hardener, as well.
 
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castman27

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Re: Motor Transom Fitting

Ok yesterday i did the first coat of resin on the transom both side with some fiberglass film at the bottom of the transom. I will try to put it to the boat tonight but more likely it should be on thursday night .Do i need to drill some holes in the transom and bolt it to the splash wall where the motor will be told it securely???, also i will try to post some pics of where i am at.
 
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Chris1956

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Re: Motor Transom Fitting

Look at the bottom of the transom bracket on that motor. You should see some 1/2 round cutouts where the transom bolts and some washers can fit. These transom bolts wearn't always standard in the days when the motor was new, but I think it a good idea.
 
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castman27

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Re: Motor Transom Fitting

ok thanks i will cehck tonight and see if any holes , if not mistaken i did not see any if there is holes what size of bolt i need and also i cannot install the motor right after i glue the transom to the fiberglass skin at the back????

Ok i just check and there is no hole in the motor bracket so i can bolt the motor in place, do i need to put resin onto the boat shell and also the transom himself?? or just one of the other would be fine.
 
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castman27

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Re: Motor Transom Fitting

ok Well yesterday i have install my new transom on my boat now the question is before i removed the brackets etc... i have to wait what 48hrs or 24hrs is ok , cause i know the temperature went down last night here in Ottawa hope it did not do anything to the resin that i put on to have it stick to the fiberglass skin in the back of the boat??? I will post pics later on the day to show what i have done so far as for the tramson etc..
 
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castman27

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Re: Motor Transom Fitting

ok here is another question for my trnasom, i am going to put a alluminium plate on top of my transom to protect the wood from being ruin by the motor bracket, what i was wondering is that can i put some 3m sealer on the plate before screwing it to the transom???
 
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Chris1956

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Re: Motor Transom Fitting

Sure that sounds like a good idea. Drill the holes for the screws and put some silicone in them as well.
 
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castman27

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Re: Motor Transom Fitting

ok Thanks Buddy, will have pics of it pretty soon.
 
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