has anyone used a sierra 18-2171 mercruiser coupler for an omc cobra outdrive?

[duane.mosley]

i bought a smooth running two piece rear seal motor to repower my 87 cobra drive with a one piece seal. of course the bolt pattern is different. has anyone used this coupler, sierra 18-2171? i have been doing a lot of reading and this seems to be the part i need but would like confirmation that it will work. i do not want to buy another part that doesn't work just to have to deal with returning it and losing on the shipping. i got the smooth running 350 for a great price so i would like to make this work without tearing the motor down and reworking a one piece seal crank into the motor. your assistance is greatly appreciated. and howard, i know to check evinrude.com but none of the diagrams show the coupler that i was able to find. not to mention, the sierra rep that my local supplier deals with, is telling him they don't make a coupler to match specificly for cobra on a two piece seal bolt pattern. i have been doing more research since the last time i posted about this issue.

 

[Bondo]

Re: has anyone used a sierra 18-2171 mercruiser coupler for an omc cobra outdrive?

i bought a smooth running two piece rear seal motor to repower my 87 cobra drive with a one piece seal. of course the bolt pattern is different. has anyone used this coupler, sierra 18-2171? i have been doing a lot of reading and this seems to be the part i need but would like confirmation that it will work. i do not want to buy another part that doesn't work just to have to deal with returning it and losing on the shipping. i got the smooth running 350 for a great price so i would like to make this work without tearing the motor down and reworking a one piece seal crank into the motor. your assistance is greatly appreciated. and howard, i know to check evinrude.com but none of the diagrams show the coupler that i was able to find. not to mention, the sierra rep that my local supplier deals with, is telling him they don't make a coupler to match specificly for cobra on a two piece seal bolt pattern. i have been doing more research since the last time i posted about this issue.

Ayuh,... If I'm not mistaken, the 2 couplers(OMC, vs. Merc) are a different length...

 

[Howard Sterndrive]

Re: has anyone used a sierra 18-2171 mercruiser coupler for an omc cobra outdrive?

seems to only be about $40 more for the proper OMC coupler from an Evinrude dealer over that Sierra unit.

just order from a 1986 4.3/5.0/5.7 setup, or 2.5L/3L 1986-1989 - those were the 2 pc rear main chevy engines OMC put in front of Cobras.
knowing those GM dates of changeover from 2 pc to 1 pc rear main is the trick
put the details together and you'll find 983902 at shop.evinrude parts books.
http://www.boats.net/parts/detail/brp/B-0983902.html
your supplier is right - Sierra doesn't make one. But BRP does.

 

[mad dwarf]

Re: has anyone used a sierra 18-2171 mercruiser coupler for an omc cobra outdrive?

Have you bought a new coupler yet? I had the same issue and was able to redrill the bolt holes, works fine. One other thing you will need is a different flywheel.

 

[duane.mosley]

Re: has anyone used a sierra 18-2171 mercruiser coupler for an omc cobra outdrive?

mad dwarf, no i haven't bought a new coupler. we had considered drilling new holes but it seems like there isn't enough material on the outer perimeter once i make the 3-1/2 bolt pattern. did you drill the holes yourself or have a machine shop do it for you to make sure the coupler and the flywheel were balanced and centered correctly?

 

[mad dwarf]

Re: has anyone used a sierra 18-2171 mercruiser coupler for an omc cobra outdrive?

The guy who I bought the motor from drilled out the holes. He made some calculations and determined it would work. Not sure what his calculations were but pretty much all the bolt holes after being drilled out lined up exactly with the previous ones only closer to the perimeter, except one which was maybe 1/16th of an inch slightly off. One recommendation would be to buy the correct coupler you need, line up the bolt holes to your coupler and mark where the holes need to be drilled, then return the new coupler. I would be willing to bet the distance to the perimeter would be the same as on the new coupler. You will definately need a new flywheel though.