Mating a Yanmar to an OMC Cobra?

[RobWales]

Whilst looking at a project for the rapidly approaching winter, I have come accross a half decent looking boat with a GM V8 gas guzzler running through a Cobra outdrive....

A good friend of mine has a Yanmar 4LHA bobtail which needs a bit of work in the corner of his shed....

Hence with the Yanmar at 240hp rated and the GM original lump pushing circa 260hp out I was wondering if any of you might know if its possible to mate the Yanmar to the Cobra outdrive??....

Have searched but unable to find the answer on the interweb?, Plenty of reference to a Bravo 2 but none on the Cobra!

Prefer a bolt on off the shelf solution, but do have access to extensive machining and fabrication facilities if required.

Thanks in advance,Rob.

 

[aquapower]

Whilst looking at a project for the rapidly approaching winter, I have come accross a half decent looking boat with a GM V8 gas guzzler running through a Cobra outdrive....

A good friend of mine has a Yanmar 4LHA bobtail which needs a bit of work in the corner of his shed....

Hence with the Yanmar at 240hp rated and the GM original lump pushing circa 260hp out I was wondering if any of you might know if its possible to mate the Yanmar to the Cobra outdrive??....

Have searched but unable to find the answer on the interweb?, Plenty of reference to a Bravo 2 but none on the Cobra!

Prefer a bolt on off the shelf solution, but do have access to extensive machining and fabrication facilities if required.

Thanks in advance,Rob.

I would think your biggest problem here will be the drive ratios, also parts for the Cobras are getting hard to find.

 

[RobWales]

Ah ok thanks AP....have experience of Merc and Volvo outdrives but nothing on OMC!

Thought it odd after extensive searching earlier I was unable to find anything.

 

[Spi D]

Cobra was OMC's last attempt before going under. Volvo bought the rights and fixed the worst issues, later marketed as the Volvo SX.

In honesty I'd stay away from anything OMC. Outdated, unsupported, unreliable and def. not to be mated to anything even slightly powerful.

If you like to make a project on a boat with this sterndrive, begin by dumping OMC and get something worth your effort and money.
Avoid ZF, rebrands like BMW, any OMC and others that did not make it over time. Early Volvo and Merc drives need thorough investigation before accepted.

 

[wipe_out]

Your other issue apart from the gear ratios is also the engine torque.. If you look at comparable boats with petrol and diesel engines you will notice the HP numbers on the Diesels are usually much lower because diesels strength is in its ability to produce loads of torque.. So where a petrol version is running 2 x ~225-250hp the diesel version will be at 2 x ~150-170hp.. That's why the outdrives matched to diesel engines are usually specific to that purpose and designed to handle the high torque without being destroyed..

 

[Spi D]

Your other issue apart from the gear ratios is also the engine torque.. If you look at comparable boats with petrol and diesel engines you will notice the HP numbers on the Diesels are usually much lower because diesels strength is in its ability to produce loads of torque.. So where a petrol version is running 2 x ~225-250hp the diesel version will be at 2 x ~150-170hp.. That's why the outdrives matched to diesel engines are usually specific to that purpose and designed to handle the high torque without being destroyed..

ie. the Yanmar will rip out the gears and bearings of the Cobra since it was made for a way lower load - and didn't even cope with that.

 

[RobWales]

Ok thanks guys, exactly why I asked, knowledge is power...
Bravo 2/3 it is then....well that is if my offer on the boat is accepted.

 

[GrahamHR]

Ok thanks guys, exactly why I asked, knowledge is power...
Bravo 2/3 it is then....well that is if my offer on the boat is accepted.

Not necessarily; Mercruiser offer Bravo outdrive units specifically for diesel power, as do Volvo Penta, A Bravo 1/ 2/3 drive designed for petrol engines may be no better than a SX/ DPS drive for petrol engines in terms of handling the diesel torque long term. I vaguely remember some issues with such "petrol" Bravo 3 drives that had Yanmar diesels fitted around 2004/ 5 or thereabouts.

Some OMC Cobra drives were in fact identical to VP drives of the same period, as they were produced under a joint venture agreement So, an OMC transom shield, fitted with a VP diesel outdrive would be no different to a "full" VP diesel set up.

 

[RobWales]

Not necessarily; Mercruiser offer Bravo outdrive units specifically for diesel power, as do Volvo Penta, A Bravo 1/ 2/3 drive designed for petrol engines may be no better than a SX/ DPS drive for petrol engines in terms of handling the diesel torque long term. I vaguely remember some issues with such "petrol" Bravo 3 drives that had Yanmar diesels fitted around 2004/ 5 or thereabouts.

Some OMC Cobra drives were in fact identical to VP drives of the same period, as they were produced under a joint venture agreement So, an OMC transom shield, fitted with a VP diesel outdrive would be no different to a "full" VP diesel set up.

All good info thanks....
You're correct regardingvthe Yanmar and B3 drives of that period by the way, one of my former boats a Bayliner 2858 had a 6hla and B3 combo fitted new circa that period,...touch wood though I had no issues and that motor was pushing out 315hp.

 

[rhino_mac]

My Monterey has a Yanmar 4LHA fitted instead of the usual 350 mag. It's got a Bravo out drive but it has "diesel" on the mercruiser plate so they obviously make appropriate specs.