Re: [OMC-Boats] Sportsman 155 Engine Replacement

From: BC Howk <bchowk@...>
Date: Wed, 17 Feb 2010 11:29:38 -0600 (CST)
Thanks for the question Don, and thanks Lee for the history..interesting!
So if I understand correctly all the type II's and III's should be the same at the FLOOR, so theoretically you'd just need to change out the engine mounting brackets depending on the engine going in (off the shelf OMC of course), right? This would make sense from a manufacturing stand point, no need to change how the basic boat is built depending on how many orders for inline 4's, 6's or V8's
Along those lines....What about those intermediate housings? I assume that the Buick V8 and the V6 would share the bolt pattern where outdrive meets engine, but what about the inline chevy's or later fords.....OMC must have had several different intermediate housings, depending on the engine going in, right? or are they all the same with adpter plates?
B.C. Howk
69 Sportsman 155
Portland, OR

Feb 17, 2010 08:48:52 AM, wrote:
Great question, Don.  It gets to the reason the 1st-gen OMC sterndrives got nicknamed "Stringers."

I'll try to provide an an uncomplicated answer.

Over the life of the electric-Stringer (1962-1977) OMC used three (or four)  types of engine mounting systems on all their electric-shift sterndrives.

First, as you recall the intermediate housing (the part that connects the engine to the sterndrive leg) is freely suspended or physically isolated inside the transom opening.

Unlike other sterndrives the transom is not used to provide structural support for the engine nor does it transmit or resist thrust-vector forces.

As in most successful designs there were evolutionary improvements. I'll attempt to describe the historic evolution without pictures so bear with me:

Type I  Mount (Rear Overhead Frame): 
The OMC Sterndrive was initially introduced in 1961-1962 using the V-4 90 cu in 2-stroke powerhead, borrowed from the 1960-61 75 hp outboard. As this powerhead was relatively light (~ 160 lbs) OMC engineers engineered a sturdy steel mounting frame which permitted hanging the powerhead and intermediate section using circular rubber isolation donuts. (An alternative floor-mount was provided to OEM boat builders). All OMC boats that used the V-4, initially the 1962-63 17-Deluxe, followed by the 1964 Evinrude 16, followed by the 1965 14 Caprice-Playboy used this simple but effective frame mount system. At first glance the steel frames, look like they are supported by the transom, but they actually tie into the floor and it's supporting (below floor) stringers.

Type II Mount (Rear Over Head Frame and Single-Point Floor Mount):
OMC realized they need to add four-stroke automotive engines to expand the power range. In 1964 a range of GM-supllied engines were added. This included the first V6, (the  150-hp Buick 225 V6 and the Chevy II inline-4 153 which offered 110 or 120 hp depending on single or dual carbs. In 1966 the Buick 300 cu in V8 (200 hp) was added in the new 19-foot range. These early GM engines all used the 4-bolt top cap sterndrive. The rear mounting continued to use the steel frame. You can easily spot the mounting isolation donuts near the electrical solenoids for the tilt motor. A single-point (central) front engine mount supported the additional engine weight and 
secured the engine to the floor. Essentially this is a three-point mounting system, two rear, one front.  As far as I can tell it did not provide much isolation. (I'm describing what I'm familiar with in OMC boats -- I'm not sure what they sold to OEM boat builders). 

Type III Mounts (Dual Wide Floor Mounts - Front/Rear):
Sometime in 1967 (might have been an ongoing change during the model year?)  OMC introduced the 5-bolt top cap sterndrives with many internal changes. They also moved to an improved ALL-FLOOR, 4-point, mounting system, which became the standard for both OMC-Built and OEM-built Stringer-powered boats. The advantage of the all-floor mount system is that has a wider stance for lateral stability and permits all for mounts to feature isolation and minor trim adjustment.  The mounts are elegantly engineering castings.  You can see how I adapted my 66 Sportsman (which originally had Type II mounts to the Type III mounts, which came with my 1971 Small Block Chevy 307.   ( see: )  In my opinion, this is the preferred system to use. The modifications to your (pre-67-1/2 OMC boat are NOT particularly difficult, if you take the time to "measure twice and cut once."   These mounts were provided for the inline GM engines, 4 and 6, as well as the GM V-series including Buick and Chevy.

Type IV Mounts (Dual Wide, Fixed Rear, Adjustable Front):
After OMC ceased boat production, the introduced the last variation of engine mounts. On the 70's OMC Inline GM engines and Ford V-8's OMC engineers introduced an adjustable front engine mount with the idea of permitting adjustable propellor thrust angles. (Remember, the Ball Gear UP-DOWN TILT is NOT TO EVER BE OPERATED as a THRUST TRIM. It's only there for beaching, trailering or LIMITED shallow water navigation). THRUST TRIMMING  was accomplished by "rocking" or lifting/lowering the entire engine and intermediate housing a few degrees. It also relied on the fact that the transom aperture was sealed by a rubber boot, but it did cause extra stress on the boot and gave the Stringer a bad reputation. These were available in both manual and hydraulic assist versions. The power-assist versions were called SelectTrim.  For several reasons, they aren't very practical for use in our OMC-built boats. It is far easier and less complicated to install trasom-mounted trim tabs. My advice is steer clear of these Walter Mitty nightmares.

Hope this long-winded, historical perspective is helpful.

Lee Shuster
Salt Lake City

On Feb 16, 2010, at 7:37 PM, Don Mandelas wrote:

I have a Question,
Does a 1967 GM-Buick V6 225 Engine mount to an 1967 Evinrude Sportsman boat floor at exactly the same locations on the floor as a GM-Chevy in line-4 153? or a GM-Chevy inline-6 230 ?   
Will an inline-4 or inline-6 use the same bolt holes on the floor as the V-6?
Or do modifications have to be made to a boat's floor in order to accept either of these 2 example engines and their floor mounting hardware?
I know of two older boats in my area that are currently not being used.  
One has the inline-4 153 with an OMC sterndrive.
the other has an inline-6 with an OMC sterndrive.
I would like to know for future planning.

From: Lee.Shuster@...
To: bchowk@...; omc-boats@...
Date: Tue, 16 Feb 2010 09:40:18 -0700
Subject: Re: [OMC-Boats] Sportsman 155 Engine Replacement

Actually if you want to stay with OMC sterndrives and OMC exhaust manifolds you have the following engine choices:
V6- 196-225-231-252  (the 231 was available in both even and odd-fire, the 252 is only even fire)
V8- 300 (it might be possible to use the 340/350)
Inline-4  153-194
Inline-6  230-250
V-8  265-283-307-327-350-400
British Ford Inline 4 (Kent)
V-8 289-302-351-W
Besides the issues that B.C. mentioned you also need to pay attention to sterndrive gear ratios when swapping engines.

From: [mailto:omc-boats-bounces@...] On Behalf Of BC Howk
Sent: Monday, February 15, 2010 9:10 PM
To: ohnoitsnexi@...
Cc: omc-boats@...
Subject: Re: [OMC-Boats] Sportsman 155 Engine Replacement

Hey Nexi,
Yep, I have some ideas about this...if you are looking for a straight up replacement you need a buick 225 odd fire, if you are talking about the 155 in NC then you SHOULD be able to reuse the manifols (exhaust and intake), hopefully rebuild the rochester 2G, the trick being finding a marine water pump...I understand that they are built with different impeller material that stand up to lake water better (I gather an automotive pump would work but would not last like the marine version) CAN get the manifolds still but they are not the cheapest items you'll ever find, just be aware....
OK, so the trick about looking for an odd fire BUICK V-6 is that they were NEVER put into BUICK's, LOL...they were put into JEEPS and OMC you are either looking for an OMC 155HP v-6 (again odd fire 225) or a "DAUNTLESS V-6" put in 60's era Jeeps (I know 69 jeepster FOR SURE as I used to own one :-) again the key is ODD FIRE 225
here is a site that has long blocks, I have never purchased from them myself but if I ever decided to replace my 225 here is where I would start...
OK so the next stop in the geneology is a 231 EVEN fire is some history to tell you what they would be in
SO......a 231 is a less striaght forward swap, you'll need to be sure your intake and exhaust manifolds still fit and you'll need a new destributor (good news is an HEI unit should be pretty easy to come by)...also if you REALLY wanted to step up you have more options for hot rod stuff (like the HEI, cams, edelbrock makes a 4bbl intake specifically for it, etc)....I hesitate to mention this option...I would like to do it myself but currently HAVE NOT so I cannot be sure if there are any hidden "gotchas" in there...however from what I underdand an early 70's even fire SHOULD bolt right in with your ODD fire manifolds and work just fine...I think there are a few people here on the list that have even fires, although am not aware of anyone who has done the swap personally..
AND of course if you really want to do the MAC DADDY swap (particularly down at sea level) you must stop by and take a look at Lee's site....he put in a good ol' fashioned chevy small block.....gotta say, if you gonna do it, go big and put in a V-8, 350 would be SOOOO sweet and forget about any kind of parts availability issues (at least as far as the engine is concerned) lot's of aftermarket upgrades too.
Hope this is helpful...

Heya BC...

Wondering if you know off hand what kind of engine I could drop into a sportsman 155. Don't know if I need to look for specific years or what not.

- Nexi

Hotmail: Trusted email with powerful SPAM protection. Sign up now. _______________________________________________
OMC-Boats mailing list

OMC-Boats mailing list
Received on Wednesday, 17 February 2010

This archive was generated by hypermail 2.2.0 : Tuesday, 29 July 2014 EDT