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Gray Marine Sea Scout vs Phantom Four

Old Marine Engine » Gray Marine Gas Engines - 4, 6, and 8 cylinder » Gray Marine Sea Scout vs Phantom Four « Previous Next »

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Colin Mac
New member
Username: surlacraque

Post Number: 1
Registered: 02-2019
Posted on Thursday, February 28, 2019 - 10:37 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only)

Hi guys, I'm trying to find out some more information about GM 4 cyclinder engines, I've searched but have only found partial answers.

I understand that the Sea Scout is built on the Continental Y91 block and generates 25HP at 2000 rpm.
Does anyone know what transmission typically comes with this engine and what gear ratio it is?

So I canít find as much detail on the Phantom Four 45. Iíve read that Gray took the Continental Y91 (91 c.i.) and made engines of 25, 45 & 50 HP. The 25 HP would be the Sea Scout, is the Phantom Four 45 basically the same engine as the Sea Scout just rated at 45 HP at a higher rpm like 3600 or whatever? 2000rpm for the Scout is relatively low for a gasoline engine, so that makes some sense. Can you convert the Sea Scout to a 45 HP engine by changing the compression or removing a limiter or something?
Iíve read that people have found Y400A stamped on their Phantom Four 45 engines, but that doesnít seem to be a Continental motor code, but maybe a gasket or piston part number?

TIA for any clarity you can provide.
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Colin Mac
New member
Username: surlacraque

Post Number: 2
Registered: 02-2019
Posted on Friday, March 01, 2019 - 12:25 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only)

Ok I found a copy of a Gray Marine manual online, and yes there's a Gray Marine Four-45 (maybe not a "Phantom") that has the same 91 c.i. block and the same bore x stroke as the Sea Scout and it's rated at 45 HP at 3600 rpm. The only difference in the specifications shown in that manual between the two engines are what seems to me minor differences in adjustment of the carburetor. What else could be different between them? The camshaft? Piston heads? Or are they really the same engine? It seems possible that the same engine could make 25HP at 2000rpm and 45HP at 3600rpm. No power curves were provided in the manual.
In fact I've seen the Sea Scout called the "lugger" Sea Scout which sounds about right, a gasoline engine is lugging at only 2000rpm. I think the Sea Scout was installed in heavy keelboats as an auxiliary and the Four-45 in small runabouts.
I note in some older Gray Marine engines there were "lugger" and "express" models of the same engine; the express generated more horsepower at higher max rpms. So the Sea Scout and the Four-45 fit that mold.
Basic question: can I easily convert a lugger (Sea Scout) to an Express (Four-45)?

TIA
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Jim Staib
Senior Member
Username: drrot

Post Number: 259
Registered: 09-2008


Posted on Friday, March 01, 2019 - 08:52 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only)

Can you convert? Yes. Easily? Probably not. Easier to find the 4-45. From my failing memory the cam, carburetor, and flywheel are different.
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Colin Mac
New member
Username: surlacraque

Post Number: 3
Registered: 02-2019
Posted on Friday, March 01, 2019 - 02:08 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only)

Ok thanks Jim. I can pick up a Sea Scout for a reasonable price is why I ask. If itís going to get rebuilt anyways could put those 4-45 parts in if I found a wrecked one. But yeah just find a 4-45 I see your point. I also see that there was a Fireball 50 HP based on the same engine, making its max power at 4000 rpm, so taking the concept further. Maybe those engines were a little over cooked...

I was guessing the Sea Scout comes with a 1:1 gearbox since 2000 rpm max isnít that high but do you know? I guess for spinning a large prop pushing a keelboat they could have targeted a lower prop shaft speed.

Similarly, did the 4-45 or 50 typically come with reduction gearbox or were they intended to spin their runabout props at 3600 or 4000 rpm direct drive?

TIA
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Jim Staib
Senior Member
Username: drrot

Post Number: 260
Registered: 09-2008


Posted on Saturday, March 02, 2019 - 09:05 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Moderator/Admin Only)

According to the 1956 manual the Sea-Scout 91 was available direct drive or with a 2-1 reduction. The 4-45 was direct drive only. The Fireball 4-50 was direct drive only also.
Problem is the 4-45 parts are probably not on a shelf and you would have to buy a complete engine to rob them out of.

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