Inboard outboard conversion to OB an donor boat?s

[thebrain]

Inboard outboard conversion to OB an donor boat?s

I’m planning a Inboard outboard conversion to OB (minimum 150HP max 250HP) on a 1977 Starcraft Chieftain it’s a 22’ aluimin cabin cruiser hull weight is 1650LBs using a Armstronge stainless steel transome bracket engine pod rated at 275HP simiairl to this swap attached image.

I believe the orginale SC transome (which is in good shape looking from the inside) only has one piece of ?” Plywood.
Can I glue two more ?” piece together making a 1 1/2'” then screw it to the orginale plywood and expect it to be stronge enought?

Step two of my plan would have a ?” square of a aluimin wider than the POD and same width as the stringers plan to weld angle braces to plate then bolt to stringer.


I was planning to trace out the stern drive hole and cut a piece of same thickness ?” Ply as the orginale transome glue it in then cover w/ a aluimin street sign screwed to outside of transome
Step two here would be to smear JB cold weld around sign to make water tight seal.

How’s the easiest way to locate to POD on the transome I’m thinking to attach pod to engine connect engine to cherry picker then have a straight edge on keel raise or lower Pod and engine until the cavatation plate is even w/ keel?

Attached images of a simiarl Starcaft of close to the same era white blue boat pod is even w/ keel.
Second newer black boat the pod is not even w/ keel.

I would prefer a XL shafted engine to keep the engine up out of water as much as possible will I have to use a 25” shafted engine ? like will a 20 be to short?

Any tips on this conversion is appreciated.

Donor boat
Will a bass boat (as a donor boat) controls/throttle cable and steering cable be to short to swap into the cabin cruiser? The helm on CC is located approximately halfway on hull.

The rear section of chieftain floor is removed to bach of helm station so instead of routeing controls to starboard side and mount to SB side I could reroute controls directly
To left side of helm station.
Any advice on this is appreciated
TB

 

[GA_Boater]

Before you get too adventurous. remove the complete existing Mercruiser set up, motor, outdrive and all transom hardware. Examine the existing transom plywood closely for signs of rot and other age damage. If it looks perfect, then take it out and throw it away after using it as a template for a brand new wood transom.

Why in the world do you want to cheap out when hanging 400+ pounds of outboard on the end of an 18-24 inch fulcrum? Scabbing new ply on top of old and making a plywood keyhole plug for is not the way to do this. The existing transom skin and plywood is not 3/4", but rather 2 to 2 1/4 inches thick in total.

You need to think this through. A solid foundation for the complete transom is needed before starting to add the pod. The transom must be rock solid to support the weight of the cantilevered motor. This is not a time for short cuts.

You will need new cables if it ever gets that far.

 

[Woodonglass]

Uhmmm, Yeah, I for one would definitely want to consider using knee braces tied into the stringers on this build

 

[HT32BSX115]

Before you get too adventurous. remove the complete existing Mercruiser set up

It might likely be cheaper and whole lot easier to just go craigslist or a (pickup) truck wrecking yard and get a 250cu-in L-6 to replace the 165.

 

[thebrain]

It might likely be cheaper and whole lot easier to just go craigslist or a (pickup) truck wrecking yard and get a 250cu-in L-6 to replace the 165.

1. what year model GM trucks L-6 engine can be swapped in? are there #s stamped on the usable blocks? and will this be a direct swap to connect to stern drive?

the pod is 29" long 15" high 15" wide can I mount a shorth shaft 20" engine or must it be a XL shaft?
Thanks

 

[HT32BSX115]

1. what year model GM trucks L-6 engine can be swapped in? are there #s stamped on the usable blocks? and will this be a direct swap to connect to stern drive?

the pod is 29" long 15" high 15" wide can I mount a shorth shaft 20" engine or must it be a XL shaft?
Thanks

It's going to be older trucks 60-80's I believe. You do need to pay particular attention to the mounting points on the block in the front of the engines. You can even use a 292 (L-6) block, as long as you use the original marine head and manifold. Certain blocks don't have the right engine mounting points on the block (to match the marine blocks) so you might have to fab a mount adapter etc.........

The other possible choice would be to find a rotted out boat with a complete 4.3L V-6 or 5.0/5.7L V-8 engine and associated drive.

Even if the donor boat has a freeze cracked engine block, the truck V-6/V-8 choices are plentiful.

If the boat you want to re-engine is in good enough shape, you could go to a much more modern engine and drive using a wrecking yard V-6/V-8 That would perform very well. The 4.3L V-6 and 5.0/5.7V-8's a currently still completely supported

 

[Woodonglass]

Before you consider that truck Engine you might wanna read this...http://forums.iboats.com/forum/boat-...-marine-engine

Can it be done...yeah...Is it easy...Nah...Should it be done...Prolly NOT!!!!

 

[HT32BSX115]

Here's another thread to have a look at concerning the 250 cu-in 6.

http://forums.iboats.com/forum/engi...s/8190268-rebuilding-mercruiser-165-gm-250-i6

Also, the guys at Inliners International (inliners.org) have a lot of into on all the 6's

 

[HT32BSX115]

Before you consider that truck Engine you might wanna read this...http://forums.iboats.com/forum/boat-...-marine-engine

Can it be done...yeah...Is it easy...Nah...Should it be done...Prolly NOT!!!!

There are literally thousands of wrecking-yard "truck" engines running in boats. And many right here on iBoats that have done it successfully.

 

[Woodonglass]

I'm about as FAR from being a MEK-A-NEK as you can get. But...I do read and research such things quite a bit. Here's some things others have stated about these conversions...

Yeah, it ends up you can use the block (if you change the freeze plugs), the cylinders, the crank (usually), most of the head, lifters/rods, but not a whole lot else. Many boat engines started out as truck engines but the unique environment needs a lot of changes:

Shielding: Truck engines drop gas fumes out the bottom of the engine compartment, which is just outside air. The heavy fumes can't drop out the bottom of a boat, so it collects in the bilge in a cloud. Even when using the blowers, there might be some fumes around puffing out from time to time. That means everything electrical -- starter, alternator, various pumps, etc -- has to be shielded, usually with a fine metal screen, to keep sparks from escaping. The air intake above the carb is also shielded to prevent a potential backfire from igniting these fumes.

Pitch and Roll: Trucks may climb hills, but not like the sides of waves that boats take. The oil pan and pump have to be deeper so that the oil pump head is always submerged even if the boat is temporarily mostly sideways.

Power: Trucks and cars tend to like to run around 2000ish RPM -- transmissions can ease the truck up to speed, then drop into a lower RPM for cruising. Inboards like it around 3000ish RPM. The camshaft has to be different so that power/torque and fuel efficiency are geared toward the higher RPMs.

Cooling: The water pump on a truck is on the block. On an I/O it's on the outdrive, and the block holds a circulator. The exhaust system is cooled with water-jackets. Brass plugs aren't entirely necessary with a fresh-water cooled engine, but an engine compartment is a hostile environment, and if I operated in salt water, I'd be worried about paint eventually knicking off the plug and salt air corroding the steel.

It's cheaper and much less of a hassle to go with the marine engine, but I've read about a few people doing a conversion just for the fun of it. I've seen a few doing a Google search when I was looking for auto vs marine parts when I was overhauling my 3.0L.

 

[ondarvr]

This isn't an insult, but almost everything in your original post is a result of misunderstanding what needs to be done to successfully complete a project like this.

I don't think adding a bracket with an O/B is a bad idea, but there is far more involved than what you think at this point.

The low cost method is to repair or replace the current setup.

 

[thebrain]

the pod is 29" long 15" high 15" wide can I mount a shorth shaft 20" engine or must it be a XL shaft? Thanks

 

[ondarvr]

Either one would work, but that's the least of your problems. if you're doing all the work go XL

It's an anti ventilation plate, and depending of the set back the AV plate will be mounted several inches higher than than the bottom of the transom.

You will need to do significantly more work to strengthen the transom than what you have mentioned so far.

 

[Woodonglass]

I totally agree!! Fixing up what's there would be the BEST way to go!!!

 

[HT32BSX115]

I'm about as FAR from being a MEK-A-NEK as you can get. ......................................I've seen a few doing a Google search when I was looking for auto vs marine parts when I was overhauling my 3.0L.

And you probably discovered that you cannot find "automotive" parts for a 3.0L engine. (there isn't. The engine was NEVER installed in a car or truck.......but WAS installed in forklifts, generators, and other equipment))

I apologize for not making myself very clear in this.............


I of course am not talking about taking a complete truck engine and bolting it into a marine environment.

NO ONE here has suggested this ......... I am suggesting using a bare truck long block and bolt on the associated marine components from the marine engine that he already has (starter, carb, dist, manifolds etc) . There is essentially no difference (as long as one does change the core plugs and maybe the circulating pump) A truck/RV camshaft so closely approximates a marine cam, that it makes the differences negligible.

The "marine" camshaft in a 230/250/292 L-6 is so close to a truck engine that I wouldn't hesitate to use it IN a truck.

If the OP were to find a damaged/rotted out boat with a 4.3L V-6 or a 5.0L/5.7L V-8 PLUS the correct(for those engines) drive, and those engines were unusable due to freeze damage (pretty common this time of year) The boat could probably be had for very little money!

This is where you can easily replace the engine with a "TRUCK ENGINE" [that means a truck long block using the marine "stuff" from the cracked block engine you pulled out of the boat you got CHEEP!)

It's done all the time and people who do it save thousands of dollars and the boat runs for many years.

I'll also apologize to the OP for the hijack. His question WAS about changing the boat from an I/O to an outboard. Aside from changing the center of gravity (CG) and weight distribution and the work involved to make the swap if it needs a complete transom replacement, it might not be worth it.

Regards,


Rick