OMC to BIII conversion mega thread

My current boat, a 1970-something Allmand Ticonderoga 24 is getting a Bravo 3 installed in place of the current OMC Cobra. The Cobra is fine, and no real reason to replace it other than I wanted a dual prop drive for like as long as I can remember and this B3 came along and was too good a deal to pass.
The engine on the Cobra is a Ford 302 that has about three hours on the rebuild. I did all kinds of stuff to it...made it fuel injected even. It was a pretty sweet setup. But, it has two strikes against it. It's OMC, for one and it's a single prop, for two. Anyway, even tho that engine is still brand new I'm gonna do this.
The Bravo 3 is from a something or other (searay, chapparal?) that was getting scrapped. I took everything...drive, engine, wiring, even the battery cables.
Engine is a 7.4 LX MPI. Raw water cooled. I'm OK with that since the boat lives on a trailer anyway.
So yesterday, I got the drive and the engine separated. Got the flywheel off the engine and bolted to an engine stand so now it's up where I can work on it. Let's say there are a few challenges.
First of all, the engine is seized. I know, I know, but hey it was really a gimme part of the deal so I'm into the engine side of this mess for zero money so far. The other thing is that the manifolds are rust-welded to the heads. The bolts are eroded away so no chance to get a tool on there to turn them.
So, chore #1 is to get those manis off the heads one way or another. Probably going to have to get in there with the air rasp and whiz the heads off. Not worrying about saving the manifolds, so I just need to get them free and then get the stumps of the bolts out of the heads. I am allocating an entire day for this.
With the manifolds off, I can finish removing all the external parts of the engine and get down to the block itself. I will have to determine if this should go out for machine shop or just buy another. There seems to be a lot of these out there, so maybe I can find another one for cheap and move the parts over to it. Dunno. That will be coming up in another installment.
Sorry for the lack of pics, I'll get some up soon.

But, it has two strikes against it. It's OMC, for one and it's a single prop, for two.

Click to expand...

Ayuh,..... 'n strike three,..... it's a Ford,.......

Welcome to the black drive side,........

Pics from yesterday. Got the port side manifold off after grinding the bolt heads off. Extensive rust damage.

Seems like the upload function is not Mac friendly

OK Had to resize these prior to uploading

Hoping to save this lump as I have been officially cut off from buying any more engines. It spins free. Lots of rust in there. Gonna fill it with rust dissolver and let it sit.

Well...if you wanted a DP you also could have simply converted the Cobra to a Volvo SX-DP by changing the Cobra pivot housing to the VP one and adding an engine driven impeller and kept your nice rebuilt engine!

Yeh, there's that. However, the b3 came along and, well, y'know....no replacement for displacement as they say. 5.0 or 7.4? hmmmmm.
The Volvo stuff I had been looking at was all pretty junky and for stupid money. Seems that people think that DuoProp drives are really super valuable.

They are a lot more expensive, but comparing re-built to rebult unit prices I think they are about the same, or even a bit less than a BIII. If you feel the Ford is underpowered in the boat you have then yep you are moving in the right direction. BTW, I have found that the OMC held up better in the salt water we have here (moored in salt 6 months every season, 15+ years) than most Merc drives and I have not had common problems seen on Alphas and Bravos in the salt (transom mount leaks and steering play, bad steering arm bolts, etc).

Boat gets the sweet life sitting under a roof all the time, on a trailer. When (if) I run it it gets a sweet water flush before it gets put away.
You know me, I don't buy new if I can get it used for cheap.

Ayuh,..... Alittle off topic, But,.......

I've got a L/R like the one in yer 1st picture,......
A '66, Ser.IIa, diesel powered,.....

Are you a Rover Enthusiast,..??
Mine needs a frame up resto, 'n I wouldn't mind seein' it go to somebody interested in such,........

Bondo asked about the 1966 2A. Here is a recent pic. Just completed frame up resto-mod. Turbo diesel, 5 speed, full time 4WD, disc brakes, etc etc....all Rover. Yes, I did all the work myself (except for the not-so-wonderful paint job).
OK now back to boatzzzzzz....

The Rover is truly a work of art! Great job!

Thank you!

Wow, yay! had a chance too get the cylinder heads off. What an ordeal! Three head bolts needed grinding off. Ugh. On the bright side, the engine seems to be pretty fresh. Not more than a hundred hours on it def. Need to clean up the rust damage but that's it. New bolts and gaskets and my "freebie" big block can go in.

Heads off! Next weekend I will flush out all the rust.

You might want to get the heads checked out. There is a member over at iboats (Tpenfield) who had the same engine in a Formula. He did a top end over haul on it and if I recall right the machinist said something about the possiblity of a water leak due to corrosion near the valve guides. Salt water used engine. Well after all that work, it rusted through and hydrolocked the engine. So that might be a good thing to check out before bolting it all back together. Was the engine/drive used in the salt? Looks that way. I was able to take apart my OMC rigged 4.3 used in salt 15+ years and luckily it all came apart, did not break one bolt. OMC used plated studs and nuts to hold the manifolds on, I changed the manifolds 2x in the years I had it before the top end overhaul and never ever had a problem getting them off. One of their better ideas! I had 2 blown head gaskets due to an overheat a few years before this (2016). Wound up replacing the heads with a pair of re-man heads, and Fel Pro marine gaskets.

here's the finished product, 2 re-man heads, all new gaskets, new center riser exhaust conversion and rebuilt Quadrajet. Not too bad of a project. Got all the bolts out with my De Walt electric impact gun. Replaced the head bolts with ARP bolts because the originals were corroded.

back up and running:
https://www.dropbox.com/s/evphffy24u0cywm/IMG_0480.MOV?dl=0

https://www.dropbox.com/s/otc4vr4081vulhy/IMG_0481.MOV?dl=0

Uh, I'm actually getting rid of the OMC in favor of a 7.4MPI and Bravo 3. Cheers to you tho. As I write this, the heads are pickling in rust dissolver. Should be pretty clean when I get back to them on Friday.

Chesapeake is not very salty, in my area. I'm in the choptank river area and we have low salinity. Not that there isn't salt in the water...it's killing the trees in the marshlands....but it's nothing like seawater. A flush after use is plenty to keep it happy for the foreseeable future

Got everything cleaned up. Pretty much all the rust came out so the water jacket is open and free of crud. Heads back on.

TBH, there was a LOT of rust chipping. I had about every possible chisel, scraper, and whatever thing I could think of tinkering away at the rust. It was particularly bad where water had pooled in the gap between the manifold and the head. This is where the head bolts on both sides had rotted away so that I couldn't possible get a wrench on them. The scale was about an eighth to 3/16 thick. I had to wear a face shield as I chipped away at it. As you can see from the before and after pics it was quite a job to get rid of all the scale. I didn't use a dremel or any power tools cz I wanted to keep the level of dust and contamination to a minimum. Even so I spent a lot of time cleaning the particles out of the insides where the oil would carry it into the bearings and make trouble.
Maybe I should have taken it down to the block and had it all hot tanked. Meh.

Just off chance, does anyone know the thread size of the steering ram pivot pins for the transom shield? Converting to the Compact Hydraulic steering ram, and I didn't get the bolt kit with it. I wanna say it's like 3/4-16...does that sound right?

Took about a pickup-bed worth of jank out of the barn so that I could wheel the trailer outside. Ford lump up and out. It will go to the local VFD charity auction along with some of the other "extra" stuff I have laying around.

Typical before and after pics of the rust treatment using evapo-rust. Yeh OK, not the same bracket but you get the idea. After treatment they get POR-15 paint then topcoat with POR-15 2-part urethane. Haven't done the top coating yet...

Happy barn....

Oh and for you Evinrude fans, That's a 1957 18 hp Fastwin with electric start. Has maybe 50 hours on it. Yes, dual line hose and Cruise-a-day tank. Remote is Evinrude Simplex.

Thought that was a old dual hose. I've got a 1956 5.5 myself, need a new tank though... looks good !!

couple pics from yesterday coming up. In the meantime, a tech question. I have one of these Compact Hydraulic Steering rams. Very cool bit of kit. I am trying to fit it to my transom assembly but I've come up short regarding hardware. I need the pivot kit, which was not included when I bought the thing off ebay. It's item 12 in the diagram here.
This appears to consist of two bolts, two spacers/shims the bolts pass thru (these are NOT shown in the parts diagram) two nylon bushings, and a special locking tab washer.
I am pretty sure I can source everything but the locking tab washer. Does anyone have any experience with this steering?

Test fit drive in the hole and its OK.

Engine painted and ready for assembly. Does the painting ever end?

Need to replace the trim senders...wires rotten. Ugh.

Sorry no pics today. I determined that I need to raise the transom cut out a whopping 3 inches! O gawd. I will have to fill in the current hole with ply and epoxy and get it all faired and smoothed on the outside and then cut a whole new hole. However I was smart enough to score a Mercruiser transom drilling fixture for $120. This will probably kill and entire weekend at least.
In the process of taking the gimbal ring off, I busted the bellows which was probably rotten anyway. In for a penny, in for a pound (or many hundreds of dollars with the current exchange rate)