Fabricating new engine mount platforms for a 4.3L

I know some of you have done the 3.0 to 4.3 swap so I was wondering if anyone with a capri or a trophy can help me out by giving me some info on how tall you made your new mount towers?

I never really did figure out what my "stringers" consist of in my Capri, but what I did is use heavy steel C channel and I welded them to another flat steel plate to form a T shape so I could lag them into the top of the "stringer" and to the inboard side of the "stringer". I put stringer in quotes because I don't think it's one solid piece of lumber in my Capri, but the lags went into tightly to wood and nothing has ever moved since. Here's a drawing I did for another thread once:
lag bolts are blue, steel is red and mount is grey

now that I look at that dwg., I don't think the mount is right - I turned it 90 degrees... but that's the general idea.

you can see the top of the starboard side steel plate - (actually painted black, not red), and 1 lag bolt in this pic

Ayuh,.... What I do is,.....(what hull is irrelevant)

Hang the motor on a crane, 'n mount it up to the rear motor mounts,...
Slip in the alignment bar, 'n adjust to alignment,...
Then measure, 'n build up the hull to meet the motor mounted motor mounts....

What you build with is up to you,...
Use metal, as above, or glass, 'n wood blockin',...

yer choice...

Either would work, but I prefer actually building up a fiberglass encapsulted wood engine mount tower structure.
I've used plywood on edge vertically before, and it has worked well.
Dimensional Fir lumber also works, but I think that plywood fairs better.

.

you don't want anyone else's measurements. Hang the engine as bondo suggested, insert the alignment bar and build the mounts to suit.

Ayuh,... Disagree all ya want,... You asked How it's done, 'n have been told....

Yer askin' for 3 dimensional dimensions, with no available center axis to measure from...

I've only done this, oh, 'bout a dozen times, 'n measurin' where it came outa, Don't help with where it's goin' too...

I did mine in my driveway. I actually think Bayliner does build the bilge area differently for a boat with a 3.0 than one intended to have a 4.3 (not sure on all models, but that appears to be the case in my 1851 - it is very 3.0 specific in there, and my model also came with a 4.3 that year).
That's why I used steel, the engine mounts now sit about even with the "stringers", so building anything "up" with plywood would not have worked (cannot build off my bilge floor, it isn't designed to support the engine). Building sideways with plywood off existing stringers and then setting a 600 pound engine on it - no thanks.
i.e. there's no way a 4.3 equipped 1851 has the same "stringers"... but I haven't seen one up close. Mine is a 1992 so maybe that all changed from 88 to 92.

I put the alignment bar in, set the threaded adjusters on the mounts at the middle of their range and made the mounts to suit.

If you made something on spec., off of measurements, I doubt you'd ever get the setup aligned. Alignment is so touchy. Unless you have the other boat sitting beside yours, I wouldn't trust the measurements. You could end up ripping everything out that you made and making a big mess.

What is the point of trying to make these mounts beforehand anyway? To save an hour? You have to lift the engine in, so it's going to be hanging there at some point. Just let it hang and build what you need to build.
Or crib the oil pan even and let it sit a couple inches higher than aligned position and build the mounts to within that 2 inches. Then jack it a bit, remove cribbing, let it down onto what you made. With the exh. manifolds off, and mounts off the V6, you won't have the engine in your way.

hystat said:

........... so building anything "up" with plywood would not have worked (cannot build off my bilge floor, it isn't designed to support the engine). Building sideways with plywood off existing stringers and then setting a 600 pound engine on it - no thanks.

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FYI and FWIW, two of my twin engine OEM engine mount towers sit off to the sides of each stringer and two are more or less sandwiched to the stringers.
They are fully fiberglass bedded and encapsulated, and they do contact the hull.

These are the new replacements that I did during my restoration.
Finish is actual gel coat.




I've done work on many boats that were set up in a very similar fashion, if not almost identically.
There are no issues with this that I can see.



.

bondo said:

Ayuh,... Disagree all ya want,... You asked How it's done, 'n have been told....

Yer askin' for 3 dimensional dimensions, with no available center axis to measure from...

I've only done this, oh, 'bout a dozen times, 'n measurin' where it came outa, Don't help with where it's goin' too...

Click to expand...

I didn’t ask how it was done in this thread, I asked for measurements.

You’re telling me that all boat manufacturers drop the motor in every boat, line it up and measure before they build the mount towers?

My boat came with a V-8 option so anyone with my boat (probably a few thousand of them still out there) and a V-8 should be able to provide accurate tower height.

What are you talking about when you say no center line to go from? Of course there’s a center line. Although I did ask; I can determine the width and front spacing on my own and whether or not the stringers will be lined up or if I need to offset. The mount towers will be built long enough and wide enough to compensate for any minor side adjustment. If I build too short I can shim the mounts and if it’s too tall I’ll cut them down and re-glass.

Fish-a-Palooza said:

You’re telling me that all boat manufacturers drop the motor in every boat, line it up and measure before they build the mount towers?

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I don't believe that's what he's suggesting, Wayne.

I will suggest that if a person was to aim for perfection, you'd need to somehow triangulate dimensions from a known-to-be-correct 4.3L OMC inner transom plate, to the known-to-be-correct engine mount towers.
You'd then need to transfer these triangulated dimensions accurately to your hull, and build the new tower height accordingly.

However, there's probably no need to aim for this type of accuracy. Perhaps build your new towers short, rather than tall, and shim if need be.

Here's what I think Bill is suggesting regarding this and a center axis;
Install the inner/outer transom unit, set the engine in on a "dry run" basis leaving it hang.
Use the alignment tool to gain your correct center axis (aka engine drive coupler alignment).
Set the engine mount stud nuts near the center of their adjustment range.
Now take your measurements from the side engine mount bottoms to the stringer tops.
Pull the engine back out of your way, and build the new towers to accommodate this elevation.

Snowflake said:

RicardoMarine aka 2850Bounty, That's NOT your pic !!!. :rolleyes:

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Wayne (aka Wayne's World, and a number of alias's), I see that you made it in under the guise of yet one more failed attempt at anonymity.
Does it not stop with you?
Sad.............. very sad!



And yes, that is indeed a photograph of my engine bay. Why would it not be?



.

Here's what I think Bill is suggesting regarding this and a center axis;
Install the inner/outer transom unit, set the engine in on a "dry run" basis leaving it hang.
Use the alignment tool to gain your correct center axis (aka engine drive coupler alignment).
Set the engine mount stud nuts near the center of their adjustment range.
Now take your measurements from the side engine mount bottoms to the stringer tops.
Pull the engine back out of your way, and build the new towers to accommodate this elevation.

Click to expand...

Ayuh,.... Yes Rick,... That's exactly what I'm tryin' to point out...

Cuttin' the tops off overly high mounts,... Ain't that easy.....

Wow, 3 posts and all 3 of them trolls...very subtle. Do me a favor Wayne, please stay out of my threads.

Well I don't know what happened to my post, it was here the last time I logged in. Either the 70's were harder on me than I thought or it was deleted? I would have assumed I would have received a PM is that was the case so, I'll try this again.

The answer to building the mount towers, at least for me was 2 inches. I dropped the motor in and it was obviously tipped down in front. I lifted the motor, stuck 2x4's under each mount and all was good. Your mileage may vary depending on the type of engine mounts you're using.

So two things here;

One: my hope was Bayliner would have built the boat so it would accomodate either motor it came with, the 3.0L or the 5.0L. Obviously they did not, and some modification to the stringers is necessary for the bigger engine.

Two: I went back and re-read my responses and some of them were a liitle crass. Sorry to Bondo if I offended you. In the end you were correct.

Last edited by Fish-a-Palooza; 10-15-2014 at 04:35 AM.

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Ayuh,.... I liked yer update much better, before ya deleted the Apology,....

Fish-a-Palooza said:

Well I don't know what happened to my post, it was here the last time I logged in. Either the 70's were harder on me than I thought or it was deleted? I would have assumed I would have received a PM is that was the case so, I'll try this again.

The answer to building the mount towers, at least for me was 2 inches. I dropped the motor in and it was obviously tipped down in front. I lifted the motor, stuck 2x4's under each mount and all was good. Your mileage may vary depending on the type of engine mounts you're using.

So two things here;

One: my hope was Bayliner would have built the boat so it would accomodate either motor it came with, the 3.0L or the 5.0L. Obviously they did not, and some modification to the stringers is necessary for the bigger engine.

Two: I went back and re-read my responses and some of them were a liitle crass. Sorry to Bondo if I offended you. In the end you were correct.

Click to expand...

bondo said:

Ayuh,.... I liked yer update much better, before ya deleted the Apology,....

Click to expand...

My last edit reads 01:35 but I guess maybe we see the time zone we are in? At any rate the apology was not deleted and is still there, unless you don't consider saying "Sorry to Bondo if I offended you" an apology.