spun coupler 3.7 mercruiser

[mm82831]

I have a 81 mercruiser 485 outdrive and a mostly 85 mercruiser 170, but it does have some parts from a 81 485 3.7. First question - please confirm I must pull the engine to replace the coupler (no easier way). Next, it looks like the coupler for a 81 is the one in the boat - the parts diagram for the 85 shows a different looking coupler. Will either coupler (the one for the 81 or the 85) work? For the 81 looking coupler, I see a 'gm' 18-2171 and a 'ford' 18-2173 listed. I cannot tell, but I think the bolt patterns are different - please confirm I need the 'ford' one? thanks for the help.

 

[Bondo]

Re: spun coupler 3.7 mercruiser

Ayuh,..... You'll need to Pull the engine to change the Coupler,....<br />It's bolted to the end of the Crankshaft.........<br /><br />The 81 is a Pre Alpha,... It uses a coupler bolted the the crankshaft,.. Ford pattern.......<br /><br />The 85 is an Alpha,.... It's coupler bolts to the Flywheel,..........<br />No,.. They're Not Interchangeable...........

 

[cslaufer]

Re: spun coupler 3.7 mercruiser

I have a coupler in perfect condition splines are perfect, no wear. If you are interested, I can send pics, email me theboss@techemail.com<br />Cameron

 

[mm82831]

Re: spun coupler 3.7 mercruiser

Thanks Bondo for the info. I have a 81 485 pre-alpha outdrive and a 85 170 3.7 engine (with the coupler bolted to the flywheel). Is there difference in the shaft length of a pre-alpha vs an alpha outdrive? I am wondering because the remains of the coupler were in the splines at the very end of the outdrive shaft - maybe the shaft did not go into the coupler far enough - about how far should the outdrive shaft spline go into the coupler? Thanks.

 

[Bondo]

Re: spun coupler 3.7 mercruiser

Is there difference in the shaft length of a pre-alpha vs an alpha outdrive?

Ayuh,............ About an Inch............<br /><br />The In-line motors used a 8+" inputshaft with the older drives,....<br />The Alpha uses a 9+" shaft......<br /><br />I'd say you've found the Cause of your problems.........

 

[mm82831]

Re: spun coupler 3.7 mercruiser

Thanks Bondo, you are a big help. I was wondering what caused the failure. Is the dia of the universal joint the same pre-alpha vs alpha - so i could just find a 9+" alpha input shaft, remove my existing input shaft at the universal, and install the 9+" shaft? Looks like a new coupler is pretty expensive - do you know any place I can check for a used one?

 

[Bondo]

Re: spun coupler 3.7 mercruiser

Ayuh,....... Input shafts are the Same,.. Except for the length............<br /><br />ebay is Always a Good Place to Look........<br /><br />NAPA's part# 18-2173 lists for $256.54... jobber $163.19.... Which should be the part You need......

 

[mm82831]

Re: spun coupler 3.7 mercruiser

i have removed the engine and you are correct, the coupler was for the 83-89 engine and the input yoke shaft was 8" (and too short) - the yoke was only in the coupler about half way (stripped half way thru). my yoke input shaft is fine. from what i can tell, it looks like the earlier coupler for the pre-83 engine is higher and may compensate for the shorter yoke shaft. i cannot tell if the mounting holes for the pre 83 coupler are the same as the 83-89 coupler, and if there are other possible problems. the earlier coupler is is more available right now, and if i could use this, i would not have to also replace the yoke shaft with the longer shaft. please indicate if the earlier coupler can be used with my existing yoke. thanks for the help.

 

[Bondo]

Re: spun coupler 3.7 mercruiser

Now I'm Guessing here Mike,........<br /><br />I Don't Know if the Difference of an Inch is made up by the Coupler or the Transom Assembley,......<br />If your Flywheel Cover is from the Alpha(9"s between the motor mount bolts),....<br />I Also Don't Know if the crank mounted Coupler will Clear the cover......<br /><br />I Do know that a crankshaft mounted coupler Will bolt on to your motor,.....

 

[mm82831]

Re: spun coupler 3.7 mercruiser

I think you identified an issue that the old style coupler may not fit thru the flywheel cover opening - I will check closely for this. Thanks again for the input. Mike