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Change engine but keep sterndrive

R

Roger_70

New member
Hello everyone

My old 431A connected to a 280 sterndrive is in need for major repair but the sterndrive was overhauled a couple of years back so it is in excellent condition. In my hunt for solution to my engine issues I bumped in to a brand new 4.3L MPI engine to a reasonable price but it comes without the sterndrive.

The question is, is it possible to fit this new engine with my old 280 sterndrive?

If yes, what modifications to the shield do I need? I guess the bell housing needs to be taken from the old 431 and the exhaust needs to be modified somehow. Has anyone ever done this?

Thankyou in advance for any guidance!
 
Roger_70 said:
My old 431A connected to a 280 sterndrive is in need for major repair but the sterndrive was overhauled a couple of years back so it is in excellent condition. In my hunt for solution to my engine issues I bumped in to a brand new 4.3L MPI engine to a reasonable price but it comes without the sterndrive.

1.... The question is, is it possible to fit this new engine with my old 280 sterndrive?

2.... If yes, what modifications to the shield do I need?

3..... I guess the bell housing needs to be taken from the old 431 and the exhaust needs to be modified somehow.

4.... Has anyone ever done this?
Click to expand...

1.... Yes, it certainly is.
However, the final drive ratio will change to either 1.61:1 or 1.89:1..... depending on the hull size and engine output.
The flywheel will need to the 153 tooth.... not the 168 tooth.
If this is a pre- 1987 engine (2 pc rear main seal crankshaft flange), these are easy to find.
If this is a post- 1986 (one pc rear main seal crankshaft flange), then the flywheel will be from a Camero car application.

2.... You'll need to find a double exhaust relief transom shield..... typically found on the very late 70s to mid 80s GM V-8 engines for the 280, 285 or 275 drives.
You'll also need the double exhaust relief Y-pipe.

3..... Your diesel may have the Borg Warner Flywheel Cover (aka bell housing in the auto world) using the B/W -slash- Volvo Penta PDS adapter housing.
If so, you can use a GM V-8 Borg Warner flywheel cover to get you to the PDS adapter housing.

If not..... then you'll need the red colored 1 pc GM V-8 flywheel cover.

You'll also need a Borg Warner drive coupler for this particular flywheel bolt pattern.

4.... Not from a diesel to gas.... but many similar.
That's one of the beauties of the AQ series Volvo Penta stern drives...... interchangeability.


I have several 1.61:1 lower units if interested.
I may also have a 1.89:1.... I'd have to look.
I also have the exhaust Y-pipe that you'd need.

A good condition double exhaust relief transom shield may be a bit difficult to find ..... these are very desireable, and this bumps the cost up some.





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Hi

Wow - I am impressed with this forum - very quick response.

Let me correct one misunderstanding though. The 431A is a 4.3l gasoline engine, not a diesel. I believe the model is from 1989.

So with that said, the drive ratio is probably ok, since I am changing an old V6 gasoline to a new model V6 4.3l gasoline with fuel injection. But what about the other parts?
As far as I understand the following components need to be verified:
-Bell housing
-Exhaust relief Y pipe
-Flywheel
-The splines on the drive shaft, both from the crankshaft to the bell housing and from the bell housing to the stern drive so that they fit

Anything else? I would hope that I could take the bell housing from the old VP431A and attach that to the new engine and that would take care of the drivetrain but I also read somewhere that there are two different types of flywheels and different amount of teeth on them. If those have to change on the new engine, wouldn't I have to change the starter then as well?

Thankyou for your patience - I would really like to understand the complexity (and extra cost) if I take on this challenge!

Best regards
 
Roger...

Roger_70 said:
Let me correct one misunderstanding though. The 431A is a 4.3l gasoline engine, not a diesel. I believe the model is from 1989.
My bad.
I'm typically very familiar with these AQ series engines/drives......, but I apparently mis-read that.


So with that said, the drive ratio is probably ok, since I am changing an old V6 gasoline to a new model V6 4.3l gasoline with fuel injection.
Yes.... the final drive ratio can remain the same.

But what about the other parts?
As far as I understand the following components need to be verified:
-Bell housing
The "Flywheel Cover" will remain the same.

-Exhaust relief Y pipe
You can re-use this part. Exhaust components (manifolds and elbows) will also be the same.

-Flywheel
If the previous engine is a 1989, no issues with the later 4.3L that I'm aware of.

-The splines on the drive shaft, both from the crankshaft to the bell housing and from the bell housing to the stern drive so that they fit
I'm not following your terminology.

The rear engine flywheel cover (bell housing in the auto world) is the same between the '89 and later 4.3L.
The shaft that connects the B/W drive coupler to the transmission female yoke is a "PDS" (primary drive shaft) and will require no change.

Anything else? I would hope that I could take the bell housing from the old VP431A and attach that to the new engine and that would take care of the drivetrain
As said... no change required for the "Flywheel Cover"!

but I also read somewhere that there are two different types of flywheels and different amount of teeth on them.
Correct... we'll see the 153 tooth used more commonly until we leave the AQ series..... but since you're swapping a post 1987 engine only for a later engine..... it should fit.

If those have to change on the new engine, wouldn't I have to change the starter then as well?
NO....
The 153 tooth ring gear requires the starter motor with the straight accross bolt pattern.

The 168 tooth ring gear requires the starter motor with the staggered bolt pattern.

Look closely at the flywheel ring gear. If questionable, replace it now as to avoid engine removal later on.
These are inexpensive, and easy to replace. DO NOT let anyone heat it red hot.

Thankyou for your patience - I would really like to understand the complexity (and extra cost) if I take on this challenge!
It really won't be much of a challege.

Best regards
Click to expand...

Roger, this is a Marine 4.3L MPI engine...... not automotive.... correct?


.
 
Hi

Yes, I believe the model is nowadays called V6-225 and it is a marine engine

One more thing about the Y-exhaust. If I look at the pictures of the new engine the just look different and I am still wondering if the Y pipe needs to be swapped:
View attachment 9753 vs. View attachment 9754

Is it a image issue but isn't the connection between the exhaust to the y-pipe different? It seems to be higher up on the new engine (compare to the valve cover) and it also seems to be more leveled on the new one and it is bent more downwards on the old engine.

So I do have some doubts about the Y-pipe....Maybe it would be possible to fit the y pipe from the sx drive to the AQ drive?

What do you think?
 
Roger... your images are not working for me.


I've needed more info on the new engine... but I see now that you mention SX drive to AQ drive.

You mentioned that you now have a 280 stern drive. The 280 transom shield uses a particular exhaust Y-pipe and manifold/elbow system.
This Y-pipe will not interchange with a later SX or DP-S style...... or visa-versa.
Nor will the manifolds/elbows interchange.

The AQ style was continued up until around 1996 in the gasoline engines (diesel engines up to year 2000 or so), but changed in the SX DP-S style packages.
Don't let the differences throw you off.

BTW, the SX engine most likely uses the 168 tooth ring gear and the staggered bolt pattern starter motor.

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Some years ago a mechanic did an engine swap for me. 283 block with "log" exhaust manifold to a 350 block with a center rise manifold, the ultimate "does not fit". He cut off the ends of the Y-pipe at the vertical section, i.e, before the top turn. He connected the exhaust elbows to the Y-pipe with a section of exhaust duty hose to a 60 (??? but not 90 in my case) degree 3" dia cast elbow and then another section of exhaust hose to the Y-pipe. Double exhaust style band clamps on all 4 junctions on each side of the Y. Worked fine. You just need to be careful where you cut the Y-pipe, better a bit lower than too high. In my case since it originally was a log manifold, the cut was pretty far down. In your case, I'd trial fit the parts before cutting. If it won't work with straight hose, there are exhaust coupler hoses that are designed to deal with misalignment and can deal with a slight bend.
 
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Bob, if Roger is simply installing a later year model 4.3L, and is re-using his AQ series exhaust manifolds and 95mm elbows, along with his original AQ sereis 280 Y-pipe, he won't need to modify anything.


But I hear ya.
I've modified the upper section of the 95mm Y-pipes before, in order to adapt non-AQ series elbows.



.
 
Never thought about that but will they fit? The manifolds on the vp431 has 5 bolts but the new motor has 6 bolts...

One other idea. I spent the last hour googling and looking at drawings and I think that the Y-pipe for an aq200b or an aq225 might be the y pipe required. That way I wouldn't have to cut up the existing y pipe. Seems like these Y pipes are designed for older aq sterndrives to be used with center-rise manifolds.

Could maybe work....
 
Roger_70 said:
Never thought about that but will they fit? The manifolds on the vp431 has 5 bolts but the new motor has 6 bolts...

One other idea. I spent the last hour googling and looking at drawings and I think that the Y-pipe for an aq200b or an aq225 might be the y pipe required. That way I wouldn't have to cut up the existing y pipe. Seems like these Y pipes are designed for older aq sterndrives to be used with center-rise manifolds.

Could maybe work....
Click to expand...

Ayuh,.... You can use yer existin' exhaust, All of it,.... No worries 'bout changin' Anything,....

The only Must have is the 12" flywheel,...
 
My suggestions have been based on info from post #1.

Roger_70 said:
My old 431A connected to a 280 sterndrive
Click to expand...


Roger_70 said:
Never thought about that but will they fit? The manifolds on the vp431 has 5 bolts but the new motor has 6 bolts...
The 4.3L cylinder heads are threaded for 6 bolts.

images


Some Marine exhaust manifolds use all 6, some use only 5 of these.

Here's the AQ series style 4.3L exhaust manifold.
It's tough to see here......, but these use only 5 of the 6 threaded bolt holes.



images




Here's the 95mm OD exhaust elbow for the 4.3L engine.
images


Here's the V-8/V-6 280, 285, 275 double exhaust relief 95mm OD inlet Y-pipe.
(not same as 290, SP, SP-A, DP-A .... or any SX or DP-S etc.)

images



images




Here's the later manifold and 4" OD outlet elbow that you will not be able to use without modification.
images




One other idea. I spent the last hour googling and looking at drawings and I think that the Y-pipe for an aq200b or an aq225 might be the y pipe required.
The AQ200B and AQ225B Y-pipe has a 3" OD inlet.
Barr does offer a universal manifld with a 3" OD elbow outlet that will work with the AQ 200B Y-pipe. 3" coupling elbows would be required.
However, this Y -pipe is a single exhaust relief part.... and will not align with the 280/275 V-8/V-6 shield.

that way I wouldn't have to cut up the existing y pipe. Seems like these Y pipes are designed for older aq sterndrives to be used with center-rise manifolds.
Did your existing 4.3L not use center-rise manifolds similar to what I've shown you above?


Click to expand...

Here is a 431A schematic that shows the exhaust system.
This manifold happens to be machined for all 6 fasteners.

Here's the hyperlink to the main page that covers the 430A, 430B, 431A, 431B, 432A, 434A, 500B, 501B, 570A, 572A, 740B, DP-A, DP-A1, DP-A2, DP-C, DP-C1, DP-C1 1.95, DP-C1 2.30, DP-D, DP-D1, DP-D1 1.68, DP-D1 1.78, DP-D1 1.95, DP-D1 2.30, SP-A, SP-A1, SP-A2, SP-C, SP-C1. When you open this page, be sure that you're looking at the 431A.
I'm not seeing a 280 drive shown for this engine model.... of which may change what I've previously suggested to you.


Roger, I'm thinking that you do not have a 431A connected to a 280 stern drive.... unless this was done by a previous owner. Perhaps it's time for you to post a few images of your existing components. I'm certainly willing to help you with this, but let's meet half way. :D



.
 
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Hmmm... Maybe this is not as straight forward as I thought...

I am not close to the boat so I can take pictures but I can guarantee you that the engine is a vp431a and the outdrive is a 280. That was one of the findings I did already when I bought the boat 15 years ago that the sterndrive is likely original but the motor has been replaced.

It has the AQ style manifolds and risers. One of the faults on the current machine is that the manifolds are no longer usable, so I can't reuse them on a new motor. So I think that the options are to cut the existing y-pipe and puzzle with hoses and bends to get them fitted, or to purchase these aq style manifolds.
 
Ok..... if you are certain that it is a 280 Drive, then my suggestions stand!

So yes...... purchase the AQ series manifolds and 95mm elbows, along with two lengths of 95mm soft wall exhaust hose (2" longer than the OEM)...... and go boating!

Just an FYI: The 280 Y-pipe, w 95mm OD inlets, begins to taper up shortly after the 95mm area.
It also changes from circular to a more square shape, and I believe that it eventually exceeds 4" OD.

Point being........ a modification may involve TIG welding.

.
 
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