Converting I/O engine to inboard?

[Dave B]

I'm in the process of building a boat and I've been watching for a used one with a good engine that I could part out. Of course the I/O's are a dime a dozen but so far I haven't found a good I/B.

I'm no mechanic, so what would it take to convert from I/O to I/B? Say for a Chev 350?

[PAR]

Given a choice between the two, I'd have the I/O every time for several reasons. They steer 100% better then any straight shaft inboard can dream of. The compact, self contained engine/drive have a smaller footprint inside the hull and it's located aft, where it's out of usual traffic flow within the boat. Finding someone to work on it is a simple affair, but inboards are harder to find good repair folks for. Parts will be available over the counter, rather then mail order or special order. Prop selection will be better and more available. In short, an I/O is a better way to go then an inboard, but maybe you have your reasons.

Certainly some boats need the inboard, if just to remain within the "style" of the vessel, but there's not much to redeem them in direct comparison. Don't get me wrong, I own both, but given a choice of which I'd prefer to operate, maintain and live with . . .

[StianM]

The chev 350 is a engine that I would pick since it's a easy engine anny mecanic can fix and it's cheap, maybe a 283(or whatever the volume was) witch is dirt cheap moust places since the custom guys think there is no replacement for displacement and you could get a new one every year with a low milage at a low cost.

[charmc]

PAR has some good points, but since you requested info on I/B, here are some thoughts:

No bellows to crack and cause major, even catastrophic, leak.

Steering an inboard in reverse is a skill requiring some training and practice, but once mastered, you can maneuver as adroitly as an I/O. (Key: keep the wheel hard over, "steer" with the shift lever.) The main reason for the popularity of I/O's, in my opinion, is the relative ease of steering in reverse. The mass market always goes for whatever is easiest, and I/Os allow folks with no boating experience to steer somewhat well without training.

There are fewer parts to worry about with an inboard, and they are easy to get. Whether I/O parts will be in stock locally depends on where you are. Everyone's trying to cut costs by limiting their stock of parts, so you might end up having to order regardless of which drive type. Gearbox is inside the hull, shaft needs only a packing gland and a strut, exhaust is the same setup, just with longer run to the transom (exhaust hose is inexpensive and easy to install).

Inboard gear boxes are inside the boat, not in the water at the air/water interface, where it is most corrosive. Inboard gearboxes will generally last 2 - 4 x longer than stern drive units.

Every engine location has advantages and disadvantages. I/B will be near the center of gravity, will free up space at the transom for fishing.

I'm not saying modern stern drive units are not good, just reinforcing the benefits of a straight inboard.

[charmc]

I'm no mechanic, so what would it take to convert from I/O to I/B? Say for a Chev 350?

To answer your particular question, you'd need a marine transmission, shaft coupling, shaft, packing gland assembly (also called a shaft log assembly), a strut (supports the shaft outside the hull; includes a bearing),and a rudder, with its own packing gland. You can sell/trade the sterndrive to help pay for the inboard gearbox; the other parts can be bought new for under $1,000., based on some recent prices.

[charmc]

Finding someone to work on it is a simple affair, but inboards are harder to find good repair folks for.

There I'd disagree. Engine repairs are identical, since all the engines are inboard. I/O sterndrives will need much more in the way of repair than inboard gearboxes, which is why there are more places that repair them. An inboard gearbox can go 3000 hours without repairs. For a recreational boater, that's 5 - 10 years.

[StianM]

An inboard gearbox can go 3000 hours without repairs. For a recreational boater, that's 5 - 10 years.

We had 6000 hours in less then a year on our main engines and gearboxes, but then that was a totaly different aplication. Only thing we did was changing oil.

Also lot of old gearboxes on smal fishingboats running 30 years and newer ben opened. Anny outboards you can say that about?

[Dave B]

I appreciate the discussion and apologize for not responding sooner, but I've been out of town and just got back.

I should have been more explicit. The boat I'm building is designed as an I/B and an I/O is not an option. My problem is not understanding if changing an engine installed as an I/O is as simple as unbolting the stern drive and bolting on the new I/B transmission (I understand about needing the stuffing box, shaft, etc.)? Are there special adapter plates or something similar that's needed? Is it even worth the hassle and potential conversion price? (Again, considering just the engine and not the tranny and other I/B parts.) The entire reason for asking is that there seems to be quite a few good used or recently rebuilt I/O engines out there. So can I just take one of those, unbolt the stern drive and bolt on the I/B tranny???

Sorry for being so dense.

[Jango]

So can I just take one of those, unbolt the stern drive and bolt on the I/B tranny???


Yes, Depending on what type of I/O you have, you may need to add a Raw water pump to the front of the Engine.

[Dave B]

Hhmm, does anyone know of any good books that describe the process and requirements?

[Jango]

Not aware of any literture specific to converting I/O TO I/B, but Glen-L,s book should answer most of your questions.

https://www.boatdesigns.com/prodinfo.asp?number=12%2D431

[cris craft dave]

Was there a definite answer to the question "Can/how to convert an I/O engine into an I/B engine? I'm new to this site, guess I'm rejuvinating an old question.

[PAR]

Each engine/drive installation tends to be application specific, but both setups are fairly straight forward. Weight distribution issues should be looked at, shaft and strut arrangements are pretty well covered, but ultimately, you have to be pretty mechanically comfortable with these systems, to consider making this type of change.

Last year I made a straight shaft boat an I/O propelled craft and the difference was astounding. The straight shaft boat couldn't back to starboard to save it's life, but the I/O had precise and hugely improved maneuverability in both forward and reverse.

Converting an I/O to straight shaft seems counter productive to me, but some folks just have to have it I guess.

If interested in making this type of conversion, consider getting familiar with the typical arrangements with this setup. You'll need to address engine beds, engine mounts, trans mounts, stringer stiffness and depth, weight redistribution, fuel storage, stuffing box, strut, a whole new steering arrangement (rudder, etc.), possibly the need for a skeg, etc., etc., etc. Once these basics are covered, you can look into other stuff like cooling and exhaust concerns.

[pistnbroke]

From the amount of knowledge you demonstrate I would take out the I/O block up the hole and put an outboard on it ...EPLS ...KISS .... and then enjoy.

[PAR]

Agreed, an outboard would be a simpler solution, though if he's having difficulty with the maintenance on an I/O, the outboard will likely cause him to scratch himself bald. Most I/O transoms aren't setup for an outboard, so you'll have to reinforce things a bit and build a splash well too.