OMC 3.0 engine with a Merc Alpha 1 I/O

[MWatts9728]

Hello Ladies and Gentlemen,
. Well I just got this old tri hull from my GF's father who has no need for it anymore. I'm about to place the first parts order to resuscitate this old girl. But I'm curious/confused on a few issues. This Engine is 990245S1 which is a OMC part# and its bolted to a mercury Alpha 1. Is it common to see this? He had this old bolt for 15 years without a hitch other than loud lifter he just tolerated which I'd happily adjust or replace. I just wanna hear the noise and track it first and to do that I gotta get the motor started. I'll flush & replace old fluids, filters and a few soft parts like belt, hoses and impeller then finally a fresh optima.
. My next source of confusion is the prop was lost. So I gotta choose a prop blindly without a existing prop or performance data to rely on. Any suggestions would be great otherwise I'm gonna get a used 13.75- 14" X 19 pitch to get a benchmark.
. Next question: I've had old boats before and always love them mostly because there paid for. I had a cathedral hull and did some Inshore fishing in So-cal it before it was a pleasant experience. But at that time it was my 3rd boat and had to go. My only dislike about these old boats is that I always wish I could achieve the shine of a newer boat. Can gelcoat be color sanded and polished? I've never done more than wash and wax on my 71 crestliner buccaneer.

The boat is a:
1976 sea sprite
17' seahawk
tri hull/ cathedral hill open hull/ walk through runabout
12 gallon fuel tank
OMC 140hp 3.0
merc-cruiser Alpha 1

 

[Bondo]

This Engine is 990245S1 which is a OMC part# and its bolted to a mercury Alpha 1. Is it common to see this?

Ayuh,..... Welcome Aboard,..... It wasn't that way originally,.....

Somebody, somehow used the OMC motor to replace the original motor, no doubt with some, or many of the original Merc accessories on the long blocks,....

Got any pictures,..??

 

[Alumarine]

That prop or a 21p would be a good start for that boat.
The OMC 3.0 and Mercruiser 3.0's were the same block with different components put on them.
As Bondo says hopefully to make life easier they went with all the mercruiser parts.

 

[MWatts9728]

Thank you both for the quick responses. I ordered a 14" X 21P mercury black diamond prop already. No pictures of the Engine or stern drive as a whole just. I figured it was swapped out for the extra horsepower over the 120hp. Version originally available in the boat when it was new. I did photograph a few numbers and such mostly because I needed part#'s. I knew they would come in handy while I'm on the road, I'm an OTR truck driver. So my time with family and the boat are very limited.
. My newest problem is the starter is acting very strange. At first I thought the engine could be siezed because with a brand new fully charged Optima D31M the starter just clicked. Sa I suspected the bendix gear engaged the flywheel but couldn't turn it. Here fear set in but I was able to turn the engine over with significant trouble by leveraging the harmonic dampener. Next I removed the starterand tested it. This is where it gets weird, the bendix drive engages but the starter dosen't turn. WTF??? How does that happen? Isn't it centric centrifugal force that causes the Bendix drive to turn? Being that the shaft is not turning how is the Bendix drive engaging and sliding To engage the flywheel. Am I missing something obvious or is this alien technology?
I wanted to get a rebuild kit for it because I have faith in OEM. I havent disassembled the starter yet. Searching for a rebuild kit has proven difficult while at work. The Starter part# 108391 is obsolete as are the replacement part #'s I've cross reference. Will the rebuild kit for any starter meant for the GM 3.0 of other year mercruiser motors work?

 

[Bondo]

Ayuh,..... Welcome Aboard,..... The solenoid slams out the bendix,......

Don't waste yer time, 'n money, buy a new p/m motor starter, smaller, lighter, more powerful,.....

 

[MWatts9728]

What exactly is a P/M starter?

 

[MWatts9728]

Permanent magnet.... got it. Thx

 

[fishrdan]

I used to have a 16' Seaswirl tri-hull and a 140HP(3.0L) Mercruiser, 19P prop was a good match, but it had soaked foam and rotted decks.... Once you get the 21P prop installed (and all the gremlins sorted out) take the boat out for a WOT run and see the engine is reaching it's WOT RPM 4200-4600RPM. I'd want it towards 4600.

I have a permanent magnet starter on my current 140HP/3.0L, MUCH better than the old Delco starter, half the weight and spins the engine faster. It's a China knock-off from DB electric, but been in use for 7 years and still working fine. $50-60.

Bellows?

 

[MWatts9728]

Thanks for the good tip about the starter. I'll order a Sierra tonight when I get time to track down a 9 tooth.
. I thought 21" pitch would be a good place to start. Figuring it's better to have a little too much pitch than not enough to go wide open. I later plan to get a 4 blade so if the 21" works I'll be stepping down anyways. But for experimentation purposes I thought I'd save $$$. Either way no loss the 21" is a good spare.