Mercury OB info needed

[budds]

I just received a mercury 20 hp thunderbolt short shaft engine. I am unable to find the serial # since the plate has been removed. I removed the cover and the only # I found was 5765900 with a large M under it. The cover has blue stripes with: Mercury, 20, & thunderbolt writtings on it. The cover is a metal band that goes around the block that clamps together in the front with a snap on plate to hide the clamps. I was told that it might be a 1982 to 1986. I am looking to find out the year and model number to locate a prop nut and to have for future reference.<br /><br />Thanks in advance

 

[Chinewalker]

Re: Mercury OB info needed

Hi Buds,<br /> Your motor is a 1980 model - the last year of production for the old 22-cubic inch twin. They're a solid design and were built in various configurations for 20+ years.<br /> For a prop nut, you should be able to find one at your local hardware store (in stainless) as a nylock type nut...<br />- Scott

 

[budds]

Re: Mercury OB info needed

Thanks for the info. Do you know if the wrong prop nut used along with washers could cause the motor to cavitate or ventilate. Worked great last year but over the winter my buddy put on a new inpeller and used ordiany washers and nut to hold the prop on. Now this year I bought it and took it out for the first time last week and now after I get to half throtle the engine rev's high and lose all power.

 

[Solittle]

Re: Mercury OB info needed

I kinda suspect that the prop nut is not the problem. Ask your buddy to take it back and get it fixed or return your money. Looks like he sold you a problem.

 

[andrewkafp]

Re: Mercury OB info needed

The prop is splined and the nut does nothing more than hold it on. Make sure you use a NEW tab washer (Locking washer) each time it's removed and bend it over the flat section of the nut.<br />Or the prop will vanish... one day <br />Have a look in my pictures here.<br /> http://www.myfishingpictures.com <br />Search by username unicorn, and you will see many Merc pics (I'm a bit obsessed) The 1980-1 has two tone blue stripes and silver text. In 1982 the text went to white.<br />This is my 1980 -50<br /> http://www.myfishingpictures.com/watermark.php?file=527/1413merc50b-med.jpg

 

[budds]

Re: Mercury OB info needed

I took the nut off last night and looks like the<br />front thrust hub might not have been fully seated <br />properly. He then used a lock washer with a non nylon nut. Could this be a problem if the nut got<br />loose and the front thrust hub became loose. I also need to check the lower transom oil, not sure the last time he changed it or if it is low. When I had it out last it worked great, then shut it off to drift downstream then when I went to go back upstream is when it started acking up. I guess I can't complain the engine was basicly free.

 

[Solittle]

Re: Mercury OB info needed

Can't beat that price!!