4.3 to 470 swap

[Mithories3980]

I know this is a little backwards, so that's why I'm having trouble finding just what I need.
In the past i was planning on rebuilding the stringers and deck on my old boat, but recently I came across a structurally sound boat for a great deal, with a bad Mercruiser 4.3 and Alpha 1 outdrive in it (cracked block).

I purchased a Mercruiser 470 to put in my boat. So, if it were possible, I want to put the inside transom plate from my 470 on to the outside transom plate of the 4.3, and use the 470 on the Alpha 1. If that can't work, the outdrive and everything that is on the 470 is fine.
So all i really need to know is if the 470 and 4.3 transom plates have the same bolt patterns. Or, is there anything else i would need to do?

please let me know if this is discussed elsewhere or if you need more information

Thanks!

 

[Bondo]

So all i really need to know is if the 470 and 4.3 transom plates have the same bolt patterns.

Ayuh,..... Welcome Aboard,..... Yes, same pattern,.....

All I can says is,...... Good Luck,.......

 

[achris]

If the 470 is 1982 or prior, no, completely different. If it's later, you will not have the 2 holes in the inner transom plate at the top. You'll have to drill them... You will also have to remove the forward 'O' ring from the drive yoke...

Chris........

 

[Scott Danforth]

You want to take a well designed motor out and replace it with the problem prone 470?

May as well look for an omc pinto motor next.

4.3 motors are plentiful and if properly maintained will last nearly forever

 

[dlogvine]

Why don't you get a chevy 4.3 block which are quite a few on the market and rebuild it using the parts from Mercruiser 4.3? You might have to change the oil pan, intake manifold and gaskets (maybe change the main bearings as well if you want a nice running engine) and you are good to go, can just drop it in.

 

[Mithories3980]

I'm really not looking for opinions on the motor I want to put in the boat here.

The thing is I got a great deal on this motor, its in great shape and I already have it. I live in an area where boat motors are not as easy to just pick up as they may be where you folks live, so I can't just go buy a 4.3 or I already would've.

I understand the 470 wasn't one of Mercs best, and I am well aware of the problems that may arise and what preventative measures I can take. Another thing is that this boat probably won't get run as much as some of your boats, and I sure won't be taking it far from shore (all rivers and lakes no more than a few thousand acres if that). So I'm really not bothered by the motor. Thank you for your input though.

I pretty much just need to know if the inner transom plate on my 470 will fit on to the outer of the 4.3, and if I can use the Alpha One outdrive with the 470. If there's anywhere you know if to help me figure that out or other information I can get for you from my boats, I will do my best.

I would also like to reiterate that I am not just "taking out a good motor". I'm taking out a motor that very unfortunately does me no good the way it is.

 

[achris]

....I pretty much just need to know if the inner transom plate on my 470 will fit on to the outer of the 4.3, and if I can use the Alpha One outdrive with the 470. ....

What year is the 470?
What year is the 4.3?

 

[Mithories3980]

The 470 is 76-79 I believe. Serial #5386685
the title for the boat the 4.3 is in says 89, owner says it is the original motor (I don't have easy access to it right now)

while looking for this info, the gentleman selling me the boat says he has a 4.3 located, rebuilt for $950. Do you guys think that's a good deal if i went that route?

 

[achris]

Any 470 prior to 1982 will NOT fit. The inner transom plate will not bolt up to an Alpha One gimbal housing.. This 'match' is a non starter.

Getting a rebuilt 4.3 is the best way to go.

Chris....

 

[Mithories3980]

Well you'll be happy to know that is the route I went. I'm glad the guy had that found for me, it'll definitely make this much easier.

is there anything I really need to know about putting the 'new' motor back in? I imagine it's pretty straight forward

 

[achris]

Make sure it has marine head gaskets and brass core plugs...

Chris.......

 

[Mithories3980]

I've encountered my first real problem. With the fuel pump.

When I bought the motor, the guy said I would have to use an electric fuel pump since the block is out of a blazer. My local boat mechanic and I didn't think that made sense, and I went about my business planning on just swapping the mechanical pump over.

It appears that the block on the new motor does not have a spot to mount a mechanical fuel pump - which would explain why he said I need an electric pump (which is fine).

So my problem is when I go to install an electric pump (which I found some pretty decent instructional videos for), where is the "Oil pressure galley" on this motor to install the pump safety switch into? Or do I need to worry about that at all?

If it is of importance to the topic, from what I can see on the block castings the "old" motor is an 88 and the new one is an 89. Am I missing something with this fuel pump issue? I really don't have any experience with them.

 

[achris]

GM dropped the mechanical fuel pump around 88/89, yes... No more mechanical pumps.

So, you install an electric pump, which needs to be wired in with 2 'special circuits'. The second because of the first (you see when I explain).

The first is, as you eluded, the oil pressure switch. You need a normally open switch that closes when the oil pressure is up, and you install it where the oil pressure sender (for the gauge) is (under the exhaust manifold, on the port side of the engine block)... Pull the sender out and put a tee piece in, put the sender into one end of the tee piece and the switch in the other.

Now, because of the pressure switch, when you turn the key on, no fuel pump (no pressure to close the switch). So the second 'special circuit'.. You take a feed from the starter motor (should be marked 'I' on the starter motor solenoid) and run a wire from there to the fuel pump. This causes 12v to be fed to the pump while the engine is being cranked, and before oil pressure is up, pumping fuel to the carb as the engine is being cranked.

Chris.......

 

[Mithories3980]

That makes perfect sense with the research I did plus the info you added to it.

Thanks so much Chris!

 

[Mithories3980]

Well it made sense until I went and looked for the pressure sender. All I see there is a brass (looks like it anyway) piece that sticks in to the block...what exactly is it that im looking for? What I found doesn't look like any wires or anything hook to it.

 

[achris]

What you (should) have...



What you need....



Chris............

 

[Mithories3980]

Ok...Im pretty sure I don't have what I should, but thats probably ok. But to make sure that when I get the pressure sender I put it in the right place, it goes in place of this, correct? This is on the left side of the motor, while I am facing the front. Right beside the oil filter, as you can just see to the right in the photo

 

[achris]

That's the water jacket plug. Above and to the aft of that....

 

[Mithories3980]

I think I see the spot - there must be nothing in it.

 

[achris]

I've just noticed something. Those engine mounts. They were the ones used with the first generation V6 engines, without a balance shaft. Not sure what engine was in the boat, but I'd be reluctant to put that engine in.