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convert omc cobra to mercruiser 4.2

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ohpoppy

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does anyone know if I place a complete mercruiser drivetrain into a omc boat if the steering and throttle cables will work (Cobra operate Mercruiser). I might could remove the steering wheel and cable as well as the throttle controls from the donor boat but cable lengths may be a problem.. the donor boat is 3' longer.

since both engines have carbs, I suspect wiring can't be too complicated or maybe there is some form of computer in one or the other.. is there?

donor boat is a 91.. receiver is a 92
 
Do the research is the hole in the transom gonna work for the mercruiser transom shield? Are you gonna need to change the supports for the engine mounts? Its easy enough to measure shift/throttle cables but the steering may be a different animal is it power steering?
 
I have done the research regarding the hole and the mounts.. I am doing the research now on the smaller concerns. yes.. it is power steering
 
It wouldnt be that difficult to swap the harness from the 4.2 over you will need to remove some side panels to get to the cable clamps/ties just put a loop up under the dash. At the same time pull a couple of accessory wires from the battery and add a fuse block if it is not already wired for cabin power directly from the battery. That makes it nice for adding accys separate from the ignition system.
 
does anyone know if I place a complete mercruiser drivetrain into a omc boat if the steering and throttle cables will work (Cobra operate Mercruiser).
Click to expand...

Ayuh,..... Steerin' cable will be just fine,....

Throttle might be the same connections,...

Shift cable, I believe is different,....

Transom key-hole is 'bout the same,....

'n there's No 4.2l motors,... 4.3l Chevy, or 4.5l Mercruiser's own,...
 
ohpoppy said:
does anyone know if I place a complete mercruiser drivetrain into a omc boat if the steering and throttle cables will work (Cobra operate Mercruiser). I might could remove the steering wheel and cable as well as the throttle controls from the donor boat but cable lengths may be a problem.. the donor boat is 3' longer.

since both engines have carbs, I suspect wiring can't be too complicated or maybe there is some form of computer in one or the other.. is there?

donor boat is a 91.. receiver is a 92
Click to expand...

FYI:

Yes, the transom cut-out will accept the Merc A drive Gimbal housing. If I recall, you may need to relocate several mounting holes.

The Cobra system may being using Morse 33C style cables. If so, you can buy 33C cable adapters that will allow them to work with the Mercruiser.

There is a kit that adapts the Merc Alpha dog clutch drive to the OMC transom unit, allowing you to leave the OMC transom unit in place.
The Shift Interrupt system (aka ESA) must remain.

There is also a kit that adapts the Volvo Penta cone clutch SX drive to the OMC transom unit, allowing you to leave the OMC transom unit in place.
The shift interrupt system is no longer needed with the cone clutch!

In many cases, the Power Assist steering system is unnecessary if the trim fin/torque tab is adjusted correctly.



 
yes.. it is chevy 4.3.
can everything be transferred from the transom of the donor boat to the receiver boat so no other adapters will be required at the drive?
I heard the shifter unit will need to be the mercruiser but I'm glad steering cable will work.
as far as motor mounts.. if the engine is properly anchored down and there is a approx straight line to the transom hole.. will the driveshaft compensate for it being a little bit off. in other words, how critical is the placement of the motor mounts and how versatile is the driveshaft to compensate. the receiver boat had a smallblock ford V8. 302
 
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ohpoppy said:
yes.. it is chevy 4.3.
can everything be transferred from the transom of the donor boat to the receiver boat so no other adapters will be required at the drive?
Yes!

I heard the shifter unit will need to be the mercruiser
OMC uses their ESA (electronic shift assist) that incorporates an ignition system "interrupt" as well as an "over-stroke" switch, whereas Merc uses their SI (shift interrupt) that interrupts the ignition only.
Since both the Cobra and Merc A drive use Dog Clutch gear engagement, both systems basically accomplish the same thing in order to go from gear back to return to Neutral.


as far as motor mounts.. if the engine is properly anchored down and there is a approx straight line to the transom hole.. will the driveshaft compensate for it being a little bit off. in other words, how critical is the placement of the motor mounts and how versatile is the driveshaft to compensate. the receiver boat had a smallblock ford V8. 302
With either the OMC Cobra or the Merc, the inner transom plate provides the rear engine mounts.
This leaves only the side engine mounts that may require height adjustment in order to align the drive coupler splines to the upper unit's shaft splines.
Click to expand...
 
the raising or lowering to obtain desired height.. is it just a matter of being able to insert the splined shaft or is it critical that it be done exactly.. is there an alignment tool that people use
 
ohpoppy said:
the raising or lowering to obtain desired height.. is it just a matter of being able to insert the splined shaft or is it critical that it be done exactly.. is there an alignment tool that people use?
Click to expand...

OK.... the center of the rear engine mounts and the center of the oscilating gimbal bearing DO NOT share the same axis. If they did, there would be very little need for alignment because the universal shaft (double bearing crosses) would accomodate.

While the upper gear unit universal drive shaft does accommodate a range of articulation, becaise of the non-shared axis, the coupler and shaft must remain parallel to each other.

Yes...... there is a special tool for this alignment.
 

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