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5.7L Mercruiser Engine with Volvo Penta SX Cobra Outdrive

M

Mike_M

New member
Hi, new to the forum and appreciate the help in advance! So, here's my question,

I have a 1997 Larson 226sei for about 6 years now. Since I bought it, it has had a 5.7L Volvo Penta V8 (which I believe is a 1987 block), with a Volvo Penta SX Cobra outdrive. At the end of last summer, the Volvo engine took a dump. I pulled the engine and had been waiting for another engine to pop up for sale. I ended up seeing a good price for a 5.7L Mercruiser (which I believe is a 1977 block). Based on the fact these are both GM blocks, I figured any problems I ran into I could unbolt accessories from the old Volvo, and swap on to the new Merc. That had generally been the case until I got to the drive coupler. When trying to place the Volvo coupler onto the Merc crankshaft, I unfortunately found out the stud pattern was different and they were not compatible. They both have 6 studs, but the spacing is off between the two. This leads me to my first question. Does anyone make a drive coupler that will mount on the Mercruiser crankshaft that is compatible with my SX Cobra outdrive?

From there, as I felt stuck, out of curiously I tried to slide the drive shaft off of the Merc onto my Volvo SX outdrive, and it slid on perfect. I was under the impression that that should not fit? So, I got excited and thought I got lucky and could re-install the Merc drive couple back on to the new Merc engine and would be good to go. However, I took some quick measurements and realized the Merc drive coupler sits 1.5"-ish closer to the engine than the Volvo's coupler did. As the drive spline off the outdrive in only about 2.5", I would almost have no engagement. This leads me to another question, 1.) Does anyone make "spacers" than I could put in-between the flywheel and the drive coupler to set the back face of the coupler 1.5" to regain my engagement? Or is there any other similar slick way to make that Merc coupler work with the different depths?

I feel like I can't be the first one that has tried to get a Volvo outdrive going with a Merc engine but I've struggled to find anything on it.

Thanks!
 
You will have to find out if a volvo penta coupler meant fir a pre 1985 sbc will work with a SX drive. Your new engine has a two piece rear main seal vs newer one piece… cranks are different. Problem is the SX was never mated to a two piece seal engine , nit sure if an omc cobra coupler will work …


might call a place like michigan motors to see if they can steer u straight.
 
Are you sure about that measurement? From my recollection the coupler for a Mercruiser and a Cobra are about the same length. If it were me, I'd try a test fit with everything in place, then take it apart and check the grease marks to see how far into the coupler it is going.
 
Yeah, the MC drive coupler slides right on to the outdrives spline shaft. But the coupler itself is actually about 1.25" "shorter" than the volvo coupler. I whipped up a quick 1.25" spacer in CAD that I'm going to see if a machine shop can make for me. That would set the MC coupler at the exact spacing away from the back of the block that the volvo sat at. Then put the volvo bell housing on the MC and that should get me what I need. Unless I'm overlooking something.
 
The black coupler is the Mercruiser coupler I’m trying to use, the one on the right is the original Volvo. That’s the gap I’m trying to make up.
 
The black coupler is the Mercruiser coupler I’m trying to use, the one on the right is the original Volvo. That’s the gap I’m
Dieter said:
You will have to find out if a volvo penta coupler meant fir a pre 1985 sbc will work with a SX drive. Your new engine has a two piece rear main seal vs newer one piece… cranks are different. Problem is the SX was never mated to a two piece seal engine , nit sure if an omc cobra coupler will work …


might call a place like michigan motors to see if they can steer u straight.
Click to expand...
Well I'm actually trying to use a MC drive coupler with SX drive. The MC coupler slides right on, and feels identical to the Volvo Coupler. The only difference is that 1.25" height difference between them (the MC coupler I'm trying to use being shorter). If I get this spacer machined and installed, do you see any issues with that?

Couplers.jpg
 
Mike_M said:
The black coupler is the Mercruiser coupler I’m trying to use, the one on the right is the original Volvo. That’s the gap I’m

Well I'm actually trying to use a MC drive coupler with SX drive. The MC coupler slides right on, and feels identical to the Volvo Coupler. The only difference is that 1.25" height difference between them (the MC coupler I'm trying to use being shorter). If I get this spacer machined and installed, do you see any issues with that?

View attachment 30410
Click to expand...
So, I drew up this spacer in CAD, and going to try and get it made to put in between the fly wheel and driver coupler in the gap you can see in the photo.

Machined Coupler 2.png

Machined Coupler 2.png

Coupler Location.png
 
Understood that you are trying to use the mc coupler. Would think yes the spacer plus longer studs would work. only suggested a omc coupler since there may be something off the shelf.

if you can machine the spacer dont see why it wouldnt work, its not rocket surgery
 
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