Help Identifying old Merc Drive
 

I have a 1977 Thunderbird FC-20L with a Chevy 350. I've been told that I have a TR-II drive but also have been told that it is a TRS-II drive. I have never worked on a sterndrive boat before and don't know much about identifying them. I was wondering what people here would say I have and get a for sure answer.
Here are some pictures of the drive.

http://imgur.com/a/6m0ck

Looks like a trs to me

Same here, looks like a TRS. Or possibly a "TR", which is a little longer TRS used on cruisers back in the day.

According to this chart (http://www.bluewatermarinesvc.com/pd...year_index.pdf) the serial number that is off the drive which is 4545516 shows up as a TRS 280. But I thought the TRS 280 was the powerdrive package and that outdrive was different from the powerdrive package or am I mistaken?

Pics look to be at an odd angle to get a good look at the lower (TR/TRS share the same upper gear case) but the TR spun a 20" dia prop. TRS, max of 16" It's probably a TRS with MercTrans

The previous owner had a new prop sitting in the garage and it is a 15 1/4inch prop which makes me think that it is a TRS since the max prop is 16inches.

It is a TRS, measure the prop hub diameter and check it against any other standard merc prop hub at the marina , if it is the same then TRS for sure as the TR had a larger bullet diameter and hub. Also the TR was a 2:1 ratio I think, that prop looks like a 17 or 19 pitch that would be way too small for a 2:1 on an F20 350 combo
Biggus is right on with the mercy tans too

Serial if it is 4645516 falls under II - TR outdrive

On a 1977 Formula Thunderbird with Mercruiser 350

The problem is that the serial number on the drive and on the engine cover are both faded but the engine serial number is barely faded. So I can't tell if the second number is a 5 or a 6. Because if it is a 5 then that would mean it is a TRS but if it is 6 than it would be a TR.

BUP which list of serial numbers are looking at for reference? Because I have found some that say that the serial is a TR and others say it falls under a TRS.

List the serial of what you think is with the 5 and then list it with the 6. I can check both ways and see what pulls up. You can not look into what I look at unless you are dealer. just saying

When I first looked at the serial it looked to be 4545516 but after I kept looking at it and zooming in the number looks like 4645516. The longer I look at it the more I keep seeing different numbers though. If it is any help the engine serial is 4499399.

Hopes this clears everything up.

TR / TRS - years made 1977 - 1993 starting serial #s - 4794900 & up

II - TR - years made 1973 - 1976 starting serial #s - 3377316 - 4794899 ending serial #'s

YOU have a -

II - TR regardless with those 2 serial numbers you posted.

Thanks for the help. Now on to inspecting it and making sure everything is in decent shape.
Is it correct that the TR drive run a 20" prop? Is the new 15" prop I have in a box good for the drive then?

Cant really tell by camera angle. If you have 10 inches between propshagt ctr and bottom of cav playe it is a TR. If only 8 inches it is a TRS.

Yes hard to tell from the angle. What size is the prop shaft nut? 1 7/16 = TR2 (20" props) 1 1/16 = TRS (16" props) but I think I agree with BUP, TR2

Check if the 15" prop even fits on the prop shaft. If it does than it is a TRS. TR has a larger prop shaft and I have never even seen a 15" prop for a TR. If it fits and there is little clearance then it's a TRS.

If you look at the tag it looks like it says 1.50 R for rt hand rotation and 1.50 ratio

I would say TRS but the measurement will tell all.

Which transmission is in the boat ? BW red tag 71 ?

The prop nut is a 1 1/16 nut. Does that mean it's not a tr since the tr is suppose to be the 1 7/16?

Also the transmission is a merctrans serial#09148 model mcm-b if that changes anything.

Trs