Newby here

[Ron Goodman]

Hello everyone, I'm new to the forum, just picked up an 1980 Thompson fisherman , I have a lot of questions and I can't find much on the Internet. I know it has 470 on the valve cover and it's a mercruser , I'm not sure what out drive it has . Any info would be helpful

 

[CrazyFinn]

Post a few more times with your questions, then you should be able to post pictures. Then you will probably start getting more replies. People respond better to pics here, but you need a few posts before you?re allowed to post pics.

 

[Ron Goodman]

OK sounds good , the boat is 21' . I'll post pics as soon as I meet required # of posts

 

[Ron Goodman]

I'm not sure if the outdrive is alpha one or other

 

[Skipper Sean]

No Title

Don?t know if this will help you

 

[Skipper Sean]

No Title

I have a 1984 Alpha 1 and the serial number was under the port side upper decal I had to pull it off to get the number. If your drive has a round eye on the upper part of the gear case it is a pre alpha.

 

[Ron Goodman]

Good morning Sean , thanks for the info , I'll post some pics as soon as I can , the ones I have are to large, I'll have to resize, happy thanksgiving

 

[Bayou Dave]

Look here for drive identification:

http://forums.iboats.com/forum/engi...miscellaneous-mercruiser-information?t=329915

 

[Skipper Sean]

Thanks DRS4164 there is some great info from that link.

 

[CrazyFinn]

If there is a round "lifting eye/loop" on the top of the drive (as mentioned earlier), and the sides of the upper part of the drive are ribbed, it's a MR series drive (commonly referred to as a "pre-alpha", although Mercury never called them that).

The next drive after that was the Alpha 1, Gen 1. The parts between the MR and the Alpha1/Gen1 are interchangeable - to the point that if a previous owner swapped parts, it could be a combination of the two. My smaller boat came with a Alpha 1 transom/gimbal assembly, but with a MR series drive attached to it.

 

[Skipper Sean]

Ron Goodman so your boat has a 470 in it. You will get a bunch of mixed feelings on that engine here on the forum. Guys either live them or hate them. But if you are vigilant with the 470 and just properly maintain it it is a good little motor. Plus you can winterize it right on the launch in about 3 minutes the last time you take it out for the year. The biggest thing you have to watch out for is over heating issues. So you may want to switch to the bigger heat exchanger used on the later models for the closed cooling system Change your raw water pump impeller in the outdrive every year and you should be fine. The next issue would be the stator it isn?t the most reliable charging system on the water, I would recommend doing an alternator conversion. Lucky my 470 was converted to an alternator system by the PO before I purchased it.

 

[Ron Goodman]

OK it does have the eye hole on top so it must be mc, I'm looking at another boat that has a 3.0 with alfa 1 , it's just for parts and from what I'm reading I can swap the outdrives,

 

[Ron Goodman]

Is that true about using an alfa 1

 

[2boatsinMI]

Gear ratios for the 470 and the 3 liter are different.

 

[Skipper Sean]

The ratio on mine is 1.98:1 it?s a 470 with alpha 1 (1984 model)

 

[chevymaher]

The ratio on mine is 1.98:1 it’s a 470 with alpha 1 (1984 model)

My 3 liter is listed as a 1.94 to 1 in 1987, So it isn't far off.

 

[Ron Goodman]

How dependable ate the mc's??

 

[Ron Goodman]

And can the ratio be changed

 

[chevymaher]

They can be changed but it is like doing a rear end in a car. Not for a novice.

Deal is the lower ratios go for cheap compared to the Higher gear units. More demand. Just hunt and find a upper unit with the gear you want is the simplest.

In my neck of the woods mercruiser drives are all people want. Fairly tough and best selection of repair parts.

 

[Ron Goodman]

OK thanks for the info , I'll look into it