Another "interchangeability" question

[Fishermark]

Well, I have a new project I am working on. I am working on an 18' Sportcraft bowrider. It is a 1989 boat I believe. It came with a 3 liter Mercruiser and an alpha outdrive.

I also have a complete setup from an old boat - a Mercruiser 165 (straight six) with a pre-alpha outdrive. Complete power package - engine, transom assembly, outdrive, etc. (I'm not sure of the year - I THINK it is a 1978, the number stamped on the block by the distributor is F12159SD. The cast number on the side of the block by the starter area is L148. Am I interpreting that correctly as:
L - December
14 - day of the month
8 - year - 1978

There is also a large casting number as follows:
473483
GM
78

Here's what I want to do. I want to replace the 3 liter in the Sportcraft with the 165 straight six. I know the rear mount area is different. So here's my question: Can I use the old inner transom shield with the newer outer transom from the alpha? In other words, keep the outer transom on the Sportcraft and simply replace the inner transom shield with the one that matches the 165? Any reason that will not work?

 

[Fishermark]

Re: Another "interchangeability" question

Here's some pics:

Here is the complete package I obtained:

When I say complete, I MEAN it! The guy I got it from actually cut it out of the boat it was in. You can still see part of the transom:

Here is the stamped number by the distributor:

Here is the casting number:

 

[havasuboatman]

Re: Another "interchangeability" question

If I understand you correctly... You want to attach a pre-alpha drive to an alpha transom assy?
No.
But you should be able to mount the old style transom assy into the hole where the Alpha assy is.
I replaced the older style driveline, like the one you have pictured, with a Merc 454 and a bravo drive and transom assy. The bolt holes that were in the boat lined up, I just had to add a couple that weren't there, and I may have opened up the width of the hole by a little. Maybe 1/8".

 

[Fishermark]

Re: Another "interchangeability" question

If I understand you correctly... You want to attach a pre-alpha drive to an alpha transom assy?

No, I want to attach an old style inner transom plate to a newer style Alpha transom assembly. From the inner plate and inside will be the older 165 straight six. On the outside will be the newer alpha transom assembly.

I know the outdrive will work (I am familiar with the different length of driveshaft). I am just not sure if the two transom assemblies will match up with no hitches.

 

[havasuboatman]

Re: Another "interchangeability" question

Now I get you. (Hit me in the head hard enough and I will understand!)
Yes, they should line up just fine. Look in Dons "adults only" section. He's got the Merc. Service manuels in there that you can look at and compare. Pay particular attention to the tiller arm and the trim lines.

 

[Bondo]

Re: Another "interchangeability" question

No, I want to attach an old style inner transom plate to a newer style Alpha transom assembly. From the inner plate and inside will be the older 165 straight six. On the outside will be the newer alpha transom assembly.

Ayuh,... I agree they Should bolt up,... But,......

Sometime along that time,.. The 2 uppermost thru-studs were moved up or down about 3/4".... Don't remember which way,'n it really don't matter...
And,...
I'm not sure the downpipe bolt pattern is the same or not,... It's has changed over the years...

There's also the 1" difference in driveshaft Lengths..... I'm not sure where it went...
The GM I-motors used the shorter shafts...

 

[havasuboatman]

Re: Another "interchangeability" question

Ayuh,... I agree they Should bolt up,... But,......

Sometime along that time,.. The 2 uppermost thru-studs were moved up or down about 3/4".... Don't remember which way,'n it really don't matter...
And,...
I'm not sure the downpipe bolt pattern is the same or not,... It's has changed over the years...

There's also the 1" difference in driveshaft Lengths..... I'm not sure where it went...
The GM I-motors used the shorter shafts...

The dowpipe shouldn't be a problem... Use the one that's in the boat now, for the alpha transom assy.

The driveshaft, you'll swap.

The bolt's...Oops, But like he said, that's no biggie.

The Improtant thing to remember here is that you're using things together that weren't designed with each other in mind. So be prepared for some adjustments.
One really important thing to check is driveshaft alignment, more specificly, the ability to achieve it

 

[Fishermark]

Re: Another "interchangeability" question

Since I have the complete package from both boats, do you guys think it would be easier to do as I suggested - keep the inner transom assembly from the old package.... or is it possible to put the bellhousing (and hub?) from the 3 liter on the 165? That way I could keep the newer inner transom plate and transom assemble together as a unit. Would that work and create fewer problems?

 

[Bondo]

Re: Another "interchangeability" question

Ayuh,... That'll work Too,... Except you still have the Downpipe problem...

 

[Fishermark]

Re: Another "interchangeability" question

Thanks for the info and stay tuned! More to come as I get farther along. I'll post what I discover works and what doesn't.