Mercruiser 3.0 installed instead of Mercruiser 4740?

[Blueghost924]

Hi, As a couple of folks know, I'm still trying to get my 1982 Mercruiser 470 running. A guy is selling a Mercruiser 3.0 1996 that runs just fine for a decent price. My boat is a 21 foot Renken cuddy cabin designed for the Mercruiser 470. Thoughts about trying to put the 3.0 in my boat? My thoughts about the challenges are: 1. Having to modify the engine mounts and/or the 3.0 not fitting well. 2. The transom being set up for an MC-I drive. My s terndrive is a 1.84 gear ratio. 3. Significant loss of power dropping down to a 3.0 135HP motor. Thoughts? Maybe just keep working on getting my 470 running?

 

[achris]

Keep working on the 470...

 

[JimS123]

The 470 was a problem since day one. If a 3.0 could be made to fit I'd go with it. Just prop it right and you'll be fine. You'll be slower, so if that matters then you have a decision to make.

 

[achris]

The 470 was a problem since day one. If a 3.0 could be made to fit I'd go with it. Just prop it right and you'll be fine. You'll be slower, so if that matters then you have a decision to make.

At lot slower. Yes, the 470 had issues, but all engines do... Once those issues unique to the 470 are dealt with (and there are fixes for all of them) it's as good as any engine...

 

[aerobat]

At lot slower.

i would not bet on it. the 165hp on the merc 470 are crankshaft where the 3.0 delivers 135hp on the prop. there has be done conversions with these two engines and people reported the 3.0 fully equals the 470 in power or even sligtly outperforms it, at least when there is the talk of a modern vortec 3.0.

of course - if it makes sense in regards to the work for the conversion vs repairing the 470 is another story.

 

[JimS123]

At lot slower. Yes, the 470 had issues, but all engines do... Once those issues unique to the 470 are dealt with (and there are fixes for all of them) it's as good as any engine...

That's true. But a cast iron block 3.0 can be run for years and years without an issue, and you don't keep having to address "fixes" all the time.

 

[stonyloam]

Keep working on the 470...

I'm with Chris... Again

 

[achris]

That's true. But a cast iron block 3.0 can be run for years and years without an issue, and you don't keep having to address "fixes" all the time.

That cast iron engine runs salt water through the block, and WILL eventually rust, and it needs winterising every year. And mess it up, just a little and you're looking for a new block. The 470 is close cooled, and winterising is a matter of removing the drain plug on the back of the heat exchanger, job done! And the fixes are not 'all the time', they are once offs. Fix it properly the first time and have a very good engine. Powerful, economical, reliable.

And I

I would not bet on it. the 165hp on the merc 470 are crankshaft where the 3.0 delivers 135hp on the prop. there has be done conversions with these two engines and people reported the 3.0 fully equals the 470 in power or even sligtly outperforms it, at least when there is the talk of a modern vortec 3.0.

I'm sorry, a 3 litre is 140Hp at the crank, a 470 is 3.7litre 170hp at the crank. And you're trying to tell me the 3 litre will out-perfom the 470??? I don't think so!

Chris.....

 

[Blueghost924]

Interesting discussion about the 3.0 - I was too late on the 3.0 and the guy sold it. Maybe it's for the better so I can concentrate on my 470.

I didn't know the 3.0s were cooled by the raw water (salt water for me). This is a disadvantage in my opinion since I'm by the ocean.

 

[JimS123]

That cast iron engine runs salt water through the block, and WILL eventually rust, and it needs winterising every year. And mess it up, just a little and you're looking for a new block. The 470 is close cooled, and winterising is a matter of removing the drain plug on the back of the heat exchanger, job done! And the fixes are not 'all the time', they are once offs. Fix it properly the first time and have a very good engine. Powerful, economical, reliable.

And I

I'm sorry, a 3 litre is 140Hp at the crank, a 470 is 3.7litre 170hp at the crank. And you're trying to tell me the 3 litre will out-perfom the 470??? I don't think so!

Chris.....

The 3.0 was introduced in the 1960's, and I believe its the longest running I/O of all times. Still in production.

The 470 was short lived - it was discontinued because of problems in the real world.

Nuff said!

 

[stonyloam]

OK there are 3 real world problems with the 470:

If you overheat the engine it is likely you will blow a head gasket because of the mating of an aluminum block with a iron head. This is mostly the result of preventive maintenance issues. Both the 3" and 4" heat exchangers are adequate to cool the engine (4' better obviously) IF the outdrive water pump is maintained properly, meaning changing the impeller after no more than 2 years service, and watching the engine temperature like a hawk.

The cam driven engine waterpump will develop a leak and Spedi Sleeves and new seals will need to be instilled. PITA job, but fairly straight forward.

The water cooled voltage regulator can fail. easily replaced but the parts are so expensive that most just install an alternator (kits readily available).

That's about it. with proper maintenance should be ideal for salt water use.

 

[Blueghost924]

Understand the lessons particular about the 470. I measured compression of all 4 cylinders following the Tech Service Bulletin steps (except my engine was cold naturally), and I'm getting at least 115 for each cylinder. To me, that's hopeful. I'd like to get it started up, get some use from it, and perform the alternator upgrade.

 

[stonyloam]

Actually the alternator is not really an "upgrade", the rotor/stator with the water cooled regulator works just fine. The alternator is a much less expensive repair of a failed regulator. If yours is charging in the 14 volt range keep it till it fails then go for the alternator.