Author Topic: OMC Stringer Drive to Mercruiser Conversion (Read 73855 times)

Rich_V174SS · « **on:** October 28, 2013, 06:14:47 PM »

As some of you know I've started a new project on a non-Glastron boat that was given to me for FREE so I've created this thread to document converting it from a 1985 OMC Stringer drive package to Mercruiser stern drive. The boat is a 21 foot cuddy cruiser with a hard top over the cockpit and the engine is a GM 3.0 liter 140hp 4 cylinder and Stringer 400 drive package that I'll be pulling out to be parted out and/or sold complete. In will be going a Mercruiser 4.3 liter Vortec V6 and Alpha drive. This is just the start so I'll be updating the thread as I progress through it over the next few months.

Today was just a survey to see what I'll be dealing with on the original engine/drive. The engine had not been run in about a year but was winterized by the previous owner. After charging up the batteries it was time to see if the engine was any good. First crank revealed the starter was shot. I had a starter from an older Mercruiser 120 engine that came out of my Glastron V174 and I bolted that up to the OMC and got it turn over. After checking the condition of the fuel in the tank and priming up the carburetor a little from a fuel can the engine fired and ran surprisingly well. It didn't seem to be circulating a whole lot of water, I think the exhaust elbow is plugged up or the water pump needs replacing. I was able to run it about 10 minutes before the exhaust manifold and elbow started getting a bit on the warm side. I did find one water leak coming from the flywheel housing which leads me to think one of the rear freeze-out plugs might be corroded and leaking a little. But there was no water in the oil and the engine ran super smooth and accelerated nicely when given the gas. Forward and reverse shifting was also very good. I re-winterized the engine by fogging it out, drained the block and manifold, and refilled them with RV antifreeze. Next step is to start tearing it all out in preparation to rebuild the transom for Mercruiser.

Engine run video:

MikeB · « **Reply #1 on:** October 28, 2013, 07:22:02 PM »

Good luck Rich! I've always wondered how much work it would have been to convert the old CVX-16SS from a Stringer to Mercruiser. I'll be keeping an eye on this thread.

Rich_V174SS · « **Reply #2 on:** October 28, 2013, 07:26:53 PM »

Thanks! I'm kinda going into this blind and making it up as I go, so it's gonna be a lot of improvising.

Jerry · « **Reply #3 on:** October 28, 2013, 07:44:25 PM »

ever thought of an OMC 3.8 or V8 with an 800 Stringer? I'm going to put one in my Glasspar SeaFair (after all the other stuff is done)

Rich_V174SS · « **Reply #4 on:** October 28, 2013, 07:49:11 PM »

Quote from: Jerry on October 28, 2013, 07:44:25 PM

ever thought of an OMC 3.8 or V8 with an 800 Stringer?

Nope.

The whole point is to get away from the OMC Stringer, no matter how good it runs. The stringer drives are a pain to work on, always a potential for the drive boot to leak, parts are expensive, not to mention the re-sell value of the boat will be much better with a Mercruiser. Mercruiser parts are very abundant and there's a bonus having a real trim system and available power steering.

Jerry · « **Reply #5 on:** October 28, 2013, 08:12:29 PM »

I took out a Buick V6 and Muncy Gear Works outdrive. The Stringer is an upgrade, and I don't have to totally rebuild the transom. My 800 has power steering.

Rich_V174SS · « **Reply #6 on:** October 28, 2013, 08:23:04 PM »

In any case you still can't trim the drive like a Mercruiser. The OMC Stringer trim system (if equipped) allows you to trim the whole engine and drive as a unit, but how far? The Stringer 400 that's in my boat has no trim system to begin with, the drive is either up or down. For a boat made in the 80's where tilt & trim was standard on every Mercruiser produced since the early 70's OMC was late getting on the bandwagon.

CVX Fever · « **Reply #7 on:** October 28, 2013, 08:35:01 PM »

Plus that thing had to be a pooch with a little 4 cylinder.

Rich_V174SS · « **Reply #8 on:** October 28, 2013, 08:40:00 PM »

Exactly! Hence the reason for going with a GM Vortec V6. The guy I got the boat from has another boat identical to this one but with a Volvo Penta package running a GM 305 (5.0 liter) V8 rated around 200 hp. The Mercruiser Vortec V6 will put out around the same power. I'd be happy with that.

wexrocks · « **Reply #9 on:** October 28, 2013, 09:02:41 PM »

Quote from: Rich_V174SS on October 28, 2013, 08:23:04 PM

In any case you still can't trim the drive like a Mercruiser. The OMC Stringer trim system (if equipped) allows you to trim the whole engine and drive as a unit, but how far? The Stringer 400 that's in my boat has no trim system to begin with, the drive is either up or down. For a boat made in the 80's where tilt & trim was standard on every Mercruiser produced since the early 70's OMC was late getting on the bandwagon.

Ditto. I can't imagine a scenario where Mercruiser wasn't an upgrade. Leave it to B-liner to put a four banger in a 21' cruiser. Yah sure, you can get on plane... with a 10 pitch prop, no friends, no gear, no beer, and no fuel on board... with a tail wind. Jeez.

Quote from: Jerry on October 28, 2013, 08:12:29 PM

I took out a Buick V6 and Muncy Gear Works outdrive. The Stringer is an upgrade, and I don't have to totally rebuild the transom. My 800 has power steering.

Hmm... The Stringer is an upgrade... you don't hear that every day!

And just an observation (no response necessary) if you haven't already totally rebuilt the transom in that '63 boat... you should.

Jason · « **Reply #10 on:** October 28, 2013, 09:18:05 PM »

Quote from: wexrocks on October 28, 2013, 09:02:41 PM

Quote from: Rich_V174SS on October 28, 2013, 08:23:04 PM
In any case you still can't trim the drive like a Mercruiser. The OMC Stringer trim system (if equipped) allows you to trim the whole engine and drive as a unit, but how far? The Stringer 400 that's in my boat has no trim system to begin with, the drive is either up or down. For a boat made in the 80's where tilt & trim was standard on every Mercruiser produced since the early 70's OMC was late getting on the bandwagon.

Ditto. I can't imagine a scenario where Mercruiser wasn't an upgrade. Leave it to B-liner to put a four banger in a 21' cruiser. Yah sure, you can get on plane... with a 10 pitch prop, no friends, no gear, no beer, and no fuel on board... with a tail wind. Jeez.

Quote from: Jerry on October 28, 2013, 08:12:29 PM
I took out a Buick V6 and Muncy Gear Works outdrive. The Stringer is an upgrade, and I don't have to totally rebuild the transom. My 800 has power steering.

Hmm... The Stringer is an upgrade... you don't hear that every day! And just an observation (no response necessary) if you haven't already totally rebuilt the transom in that '63 boat... you should.

At least with the Stringer drive their shouldn't be much if any force on the transom. Are the stingers built any different in a boat with an OMC?

Jerry you sure that's not a Chevy 3.8? I had an 84 Centruy OMC that used a chevy 3.8. I am pretty sure the Buick 3.8 has the distributor in the front. The chevy 3.8 is a shortened 305 V8.

Sorry for the hijack Rich..

Rich_V174SS · « **Reply #11 on:** October 28, 2013, 09:29:17 PM »

Quote

At least with the Stringer drive their shouldn't be much if any force on the transom. Are the stingers built any different in a boat with an OMC?

With the Stringer drive there is no force on the transom, the drive is bolted directly to the engine so all drive forces are transferred to the stringers directly. I don't think the stringers in the boat are any different but the transom sure is not the same, there's only about an inch of wood lining the transom. Mercruiser requires a 2 to 2.25 inch thick transom to mount the drive assembly so in addition to closing up the hole and fiberglassing the outside flush I have to double the thickness from the inside and make sure that is supported behind the stringers somehow.

Jerry · « **Reply #12 on:** October 29, 2013, 02:12:41 AM »

The Muncy O/D uses a small hole, the OMC is just a cutout and the transom is good. The motor is the same as a BOP 3800 The Buick was a 63 V6 could hardly move the boat. I couldn't get shift dogs for the O/D and got the "almost new" motor for nothing. The 800 O/D cost a bunch, and needs gears, but should work OK in the Glasspar. It's the only SeaFair I ever saw with a O/D from the factory. I had to save it. Just a family fishin boat to replace the 63 Winner. Nothin fancy or fast. The Glasspar's a barge.

Hyperacme · « **Reply #13 on:** October 29, 2013, 11:49:08 AM »

How about an outboard transom mount and twin 250 HP Optimax's ?
OK ...Maybe not ...

Lookin' forward to your rebuild thread !

floater1 · « **Reply #14 on:** October 30, 2013, 06:50:33 PM »

I looked into doing this swap with my old cvx. You have more ambition, money, and time than I do. Good luck.

wiliermdb · « **Reply #15 on:** October 30, 2013, 08:31:37 PM »

Inboard to Outboard conversion has been done before with great success. I have a fishing buddy that found a 18' bowrider with a damaged outdrive and the motor had a cracked block. He pulled it all out, filled the keyhole, mounted a jack plate and a used 200 Merc and it performs better and was about $2k less than what it would have cost him to go the other route. (He bought it from his brother-n-law and he said it is quicker than before.)

Rich_V174SS · « **Reply #16 on:** October 30, 2013, 10:23:15 PM »

Quote from: floater1 on October 30, 2013, 06:50:33 PM

I looked into doing this swap with my old cvx. You have more ambition, money, and time than I do. Good luck.

Ambition - yes
Time - yes, over the winter
Money - not really. I've saved up some cash from a bunch of side jobs I did over the summer that should get me through most of what I want to do.

Quote

Inboard to Outboard conversion has been done before with great success.

Why would I want to do that?

Rich_V174SS · « **Reply #17 on:** November 02, 2013, 05:46:18 PM »

Got a little bit done today. Pulled off the drive which came off quite easily, but the shift cable wasn't cooperative so it had to be sacrificed. Disconnected everything from the engine, battery cables, fuel and harness lines, throttle and shift cables, and the steering. The biggest chore was getting the steering cable disconnected at the engine's intermediate housing. The whole steering system, helm and cable, have to come out because they will only work with the OMC stringer drive system. After a bit of a battle and getting a nice gash on one of my knuckles I was able to snake the steering cable out of the boat. It will be getting a whole new steering system to go with the Mercruiser, but that will be sometime down the road. Next the engine comes out which should be effortless.

Anyone want/need an OMC Stringer 400 drive or steering components?

Rosscoe · « **Reply #18 on:** November 04, 2013, 07:30:54 PM »

Maybe you should haven gotten your buddy, Brutus Beafcakes over there to help (hinder)?
LOL
Gashes go with the territory as you know. I have been wearing gloves a lot more lately and bleed a lot less often.

Rich_V174SS · « **Reply #19 on:** November 04, 2013, 07:36:53 PM »

Oh hell no! He wouldn't have been any help. Not only can he not do anything mechanical he's a germaphobe and wouldn't touch anything that could get his hands dirty. Plus I wouldn't want him around anyway. I'll live with the cuts on the hands. LOL!