Mercruiser to Volvo Conversion

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thesaintlyone

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I have recently been offered a complete package of Volvo 431's and Stern Drives with Duo Props in fact everything I require from the donor boat from a friend who no longer needs them as he is converting his boat to a static AirB&B. My 1992 Sundancer 290 originally came fitted with twin mercruisers and bravo outdrive all since removed.

Going from Twin Mercruiser to the Twin Volvos what are the differences and solutions etc ?

1) Engine Mounts
2) Current Transom Hole Size
3) Anything Else
 
What we think is a straight forward job, is certainly a lot bigger and more expensive.
We are coming to the end if going the other way!
1) Mounts will be different. So not only new engine beds will be required, the old ones may need cutting out as leaving them in interfere with replacement engines.
2) more than likely round pegs and square holes spring to mind. I doubt you would get away with adapting what you have, particularly if the new outdrives need smaller holes. I'd planned for the transom to be fully filled and new holes cut.
3) This section will be alot bigger than you think. Most likely, you'll be lucky to salvage much that interfaces the engines as you'll find they are completely different set up. This will go from calorifiers, to steering, throttles, your electrics etc etc. Plus, you'll be tempted to get all the 'best do now' jobs done when your boats in bits and the engines out... Bilge pumps, fuel system etc

Don't underestimate the job, it's probably double the effort and cost you think it is. We know!
But it's rewarding and a great project to keep you out the pub and busy.
Just make sure the engines you are putting in are A1. It's not a job you would do twice!
Good luck ,,?
 
thesaintlyone said:
I have recently been offered a complete package of Volvo 431's and Stern Drives with Duo Props in fact everything I require from the donor boat from a friend who no longer needs them as he is converting his boat to a static AirB&B. My 1992 Sundancer 290 originally came fitted with twin mercruisers and bravo outdrive all since removed.

Going from Twin Mercruiser to the Twin Volvos what are the differences and solutions etc ��

1) Engine Mounts
2) Current Transom Hole Size
3) Anything Else
Click to expand...

Depends what drives the Mercs are , Alpha 1?

If the mercs are V6 it’s the same block , give more info.
 
Hard to tell as everything was removed before I got the boat but I presume it was the standard twin engine set up for the year.
 
LBRodders said:
What we think is a straight forward job, is certainly a lot bigger and more expensive.
We are coming to the end if going the other way!
1) Mounts will be different. So not only new engine beds will be required, the old ones may need cutting out as leaving them in interfere with replacement engines.
2) more than likely round pegs and square holes spring to mind. I doubt you would get away with adapting what you have, particularly if the new outdrives need smaller holes. I'd planned for the transom to be fully filled and new holes cut.
3) This section will be alot bigger than you think. Most likely, you'll be lucky to salvage much that interfaces the engines as you'll find they are completely different set up. This will go from calorifiers, to steering, throttles, your electrics etc etc. Plus, you'll be tempted to get all the 'best do now' jobs done when your boats in bits and the engines out... Bilge pumps, fuel system etc

Don't underestimate the job, it's probably double the effort and cost you think it is. We know!
But it's rewarding and a great project to keep you out the pub and busy.
Just make sure the engines you are putting in are A1. It's not a job you would do twice!
Good luck ,,��
Click to expand...

Volvo outdrives have bigger transom cut outs than Mercs.
So the transom is usable.
A big job but with the proper diagrams not so bad.
My V8 to straight 6 diesel conversion was bigger as I had to make the engine bay longer.
And replace the transom as it was rotten.
 
Depends what volvo drives they are,some use the same drilling pattern and hole cut out as mercruiser so if the engines taken out were v6 then it could be a fairly simple bolt back in job
 
If they are both V6s then engine mounts will be the same.
The mercs with the Alpha would have the water pump in the outdrive. The VPs are engine driven. Not an issue if you are going to bravo (presumably these are coming separate again ? Not a VP obviously).
Other difference is that the merc and alpha would have had exhaust flappers in the cow horns. The VP doesn’t. They rely on a flap on outdrive.
But perhaps one of the biggest issues (if I have picked you up right) is mating the 4.3s to a bravo ? Is it a bravo 3 with twin props ? If so the props will be way over pitched for your engines. These usually only came mated and propped to at least a small block V8 5.7 and upwards. Props for these are an arm and a leg.
If a bravo single prop. Not so bad. You’ll still need to get the props suited. Again unlikely the provided props will be suitable.
Other than that. The 431 VP is an identical engine to the merc 4.3 with many of the parts being similar, same or interchangeable.
Only caveat would be the variation between later vortec and fuel injected models.
 
Ok so just read again. Most of what I said will be relevant but just noticed you said it had bravos and you changing to DPs.
If she had bravos originally it wouldn’t have been 4.3’s at a guess. Not impossible but unlikely.
The VP431’s are getting on a bit and will no doubt be from the early early 90’s. Mated to VP 290DPs usually.
Again it will all be about the props.
If you had bravos before. Most cases they were mated to V8s. If you are dropping in power perhaps you’ll notice a difference in perfomcace most likely too.
 
QBhoy said:
Ok so just read again. Most of what I said will be relevant but just noticed you said it had bravos and you changing to DPs.
If she had bravos originally it wouldn’t have been 4.3’s at a guess. Not impossible but unlikely.
The VP431’s are getting on a bit and will no doubt be from the early early 90’s. Mated to VP 290DPs usually.
Again it will all be about the props.
If you had bravos before. Most cases they were mated to V8s. If you are dropping in power perhaps you’ll notice a difference in perfomcace most likely too.
Click to expand...

Think you need to read again! OP says previous owners says "4.3v6s and alpha drives removed "
Any volvo drive will fit as they either use the same transom cut out or larger. The install should be a straightforward bolt in job as front mounts are likely the same too
 
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